THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/
Edition: Model Aviation - 2008/08
Page Numbers: 29,30,31,32,33,34,35,36,37,38,39,40
THE BOEING COMPANY’S 727-100
made its maiden flight on February 9, 1963.
It is my favorite commercial jetliner, and an
Eastern Airlines 727-100 was my first jet
flight, with two round trips from Newark,
New Jersey, to Rochester, New York, within
10 days. I was in heaven.
I still think back to that first takeoff run
and feel all that thrust pushing me back in
the seat. The approach to landing was
fascinating. I watched the wing TE unfold to
a full flap extension, revealing all that
incredible engineering—neat stuff.
I started my initial drawing by trying to
keep the engine nacelles in scale, but that
generated a huge fuselage. So although the
GWS 50mm fans are out of scale, they are
minimized to provide the thrust they can
deliver. The weight-to-thrust ratio of
approximately 2:1, as noted on the plans, is
an initial static measurement using a fully
charged 2S Li-Poly battery.
The GWS EDF-40 and 30mm fans were
unavailable at the time of my engineering,
but the EDF-30 won’t deliver the thrust and
the EDF-40 might, but at much higher amps.
The EDF-50 will fit one of three rotors/
impellers: 2020 x 3, 2030 x 3, or 2030 x 5.
I chose the 2020 x 3 for maximum thrust
and minimum current drain.
August 2008 29
by David A. Ramsey
A semiscale RC model for 50mm electric ducted fans
The 727 will fly for five minutes on a seven-cell, 720 mAh NiMH or 15-20 minutes on a 1500 2S Li-Poly. Stock twin GWS EDF-50 fan
units are plenty of power and are managed with just one Castle Creations Pixie-7 ESC. Far right: The author prepares to gently toss
the 727-100 into a light headwind. Nobu Iwasawa photos.
30 MODEL AVIATION
Keeping with a pair of EDF-50 CN12-
RLC brushed motors, you can use a sevencell,
720 mAh NiMH battery pack, which
will give roughly five minutes of flying time,
or a two-cell (2S), 1500 mAh, 8C Li-Poly
battery, which will deliver better voltage and
a 15- to 20-minute flight at mostly half stick
power.
These motors’ maximum static amp draw
with the 2020 x 3 rotor is close to 6.8 amps,
and the tiny Castle Creations Pixie-7P ESC
works perfectly with this motor/battery
combination. Brushless motors would
certainly give this Boeing 727 some added
push, but that is beyond the scope of this
article. Do some testing to see if other power
options will work for you.
Battery weight is an important
consideration; 2.6-3.0 ounces is ideal. A
seven-cell, 720 mAh NiMH battery with JST
plug weighs 3.2 ounces, and its use may
require adding tail weight to balance the
model.
My older (2004) two-cell, 1500 mAh, 8C
Li-Poly with JST plug weighs 2.6 ounces
and balances the model with relative ease of
placement and removal on the battery tray.
Unfortunately this particular Kokam 1500
mAh battery is no longer available.
Because of weight increases caused by
higher “C” ratings and the addition of
balance connectors, a 1500 mAh Li-Poly has
gotten slightly heavy; however a two-cell,
900-1200 mAh Li-Poly will give excellent
flight times and fall within weight limits.
Choice of balsa is important. A firm 1/16 x
3 x 36-inch sheet weighs 0.6-0.7 ounce. I try
to use the lightest sheets for hard-balsa
stringers and spars. Lightening holes are
helpful at extreme ends of the balance point,
both for the fuselage and for the wing.
It’s important for you to know that the
holes indicated on wing ribs are to provide
heated air ventilation during covering, in
case additional lightening holes are not
added. I used thin and medium cyanoacrylate
adhesive for all wood construction.
There are many formers, but to speed
construction there are only two stringer
notches in F18 and the main assembly
notches. All former stringers are attached to
the former edges. I like this method because
it’s a pain to hand-cut perfect 1/16-inch
notches that align in all 27 formers.
If you notice a few stringers out of
alignment when sighting down the length of
the fuselage, you can easily break them free
The center and left nacelle side view shows that stringers are built
into the corners for covering adhesion points. So-Lite heat-shrink
film is recommended.
PTFE spaghetti tubing is used to house the 0.015-inch music wire
inside the 0.034-inch ID tube and actuate the top hinged aileron
controls.
The plug-in stabilizer control wire will start in an E/Z Connector
on the elevator servo arm and end in a single loop around a 3/32-
inch-OD x 3/32-inch-long aluminum tube.
The 50mm fan units are built into the nacelles, which are secured
with a small amount of silicone adhesive. The exhaust shroud has
been calculated for efficiency and scale shape.
August 2008 31
Photos by the author except as noted
and realign them. Plus, with the stringers
raised above the former, they’re easier to
sand and you can’t see the former after
covering. Although there is less glue surface
than with a notch, I can’t see a loss in the
strength that is required.
All my former halves are constructed from
two pieces of 1/16 balsa with the grain at 45°, as
shown on the former templates. The seam line
is at 90° to the former centerline, and a former
template lines up with the edge and seam.
It’s a bit more work, but I like to make
templates using 0.030-inch, high-impact
styrene plastic sheet. I spray the back of a
copied plans former with 3M Spray Mount
adhesive, let it dry, and press it on the sheet.
Since styrene has no grain, it can be scored at
the former lines rather than cut all the way
through. After I make all the cuts, I gently
flex the styrene at the scores and it breaks
away. Then I sand any rough edges smooth.
I cut out all balsa formers in pairs, using
small (1/16 x 3/8-inch) pieces of Intertape
double-stick masking tape to hold former
blanks and templates in alignment. I cut parts
with a No. 11 blade and sand them as
necessary. Then I transfer all stringer
centerline positions to the former edges and
gently separate the formers with a thin pallet
knife blade.
Two FS1 wing saddles and two delicate
N3 nacelle formers need to be reinforced
with 3/4-ounce fiberglass cloth. I very lightly
spray one side of the balsa sheet for these
parts with a coat of 3M Spray Mount
adhesive and let it dry for a few minutes.
Then I carefully lay the fiberglass smoothly
across the balsa and place a sheet of waxed
paper or polyethylene film over the fiberglass
to press it evenly to the sheet. I spread an
even film of thin cyanoacrylate to bond the
fiberglass to the sheet and follow that with a
light sanding.
I use an open-cell foam cradle to support
the fuselage during construction and flight
setup at the field.
CONSTRUCTION
Certain assembled parts will aid in other
part assemblies; following is the sequence I
followed.
Wing Center-Section: Glue 5, W1 ribs, LE
and TE, and main and 1/16 square spars. This
assembly will be used to set the distance
between former F11 and F17 during the
primary fuselage build.
Sheeting is used only where absolutely necessary. The two musicwire
pushrods lock into an E/Z Connector on the side-mounted
servo. Lightening holes serve as wire-chase locations.
Hardwire the motor leads to prevent the chance of a
disconnection. The former shapes are scale in shape but are
simplified so they don’t require intricate stringer notches.
The balsa-sheet platform will serve as the ESC, receiver, and
elevator-servo mounting point. Sheeting at the lower wing fairing
will act as a firm handhold.
Since the center wing section is built with the fuselage, the correct
fit is guaranteed. Be sure to select hard balsa for the stringers;
they will add the needed strength.
Type: Three-channel RC semiscale EDF
Scale: Approximately 0.368 inch = 1 foot
Skill level: Advanced building, intermediate flying
Wingspan: 45.125 inches
Flying weight: 13 ounces
Wing area: 1.76 square feet
Wing loading: 7.4 ounces/square foot
Length: 57 inches
Motor system: Two GWS EDF-50 fan units, CN12-
RLC brushed motors, 2020 x 3 rotors
Power system: 2S 950-1500 mAh, 8C Li-Poly
battery; Castle Creations Pixie-7P ESC
Construction: Balsa, basswood, plywood
Covering/finish: Solarfilm So-Lite
32 MODEL AVIATION
The builder could choose to go FF at this point since the ailerons
have yet to be cut away from the wing. Notice the provision of a
long battery platform.
Once the formers are shaped, construction starts with assembling
a fuselage half on a smooth, flat work surface. Thin cyanoacrylate
is the primary adhesive for construction.
A fuselage framing fixture greatly enhances the construction’s
speed and accuracy. It’s made from scrap material and should be
at least high enough to suspend the formers.
The primary material used in
construction is firm 1/16 balsa. Filler
areas and nose blocks should be soft
balsa, which is easier to shape.
Building a long, straight fuselage made
with half formers can be a challenge. I
constructed a fixture (see photo) from 3/4-inch
Medium Density Fiberboard (MDF). The
height of the sides and the notches cut in the
surface give clearance for all formers. A
removable front side allows the upside-down
half fuselage to be guided in place while
resting flat on the 1/16 x 1/8-inch center main
assembly stringer.
The fixture is a bit more work for the short
time it’s used, but it’s worth it for a straight
fuselage with formers at 90°.
Initial Fuselage Assembly: Using the primary
fuselage layout plan, pin down the 1/16 x 1/8-
inch medium balsa stringers. Dampen all
curved stringers with water to relieve bending
stress, and let them dry a bit after pinning.
Keep all formers at 90°, and use small
pieces of 1/16 balsa as spacers to maintain the
height of the former center edge above the
building surface. Use the wing center-section
to set distance between F11 and F17.
With all formers in place at 90°, glue the
top full-length (actually the 90° or 270°)
center 1/16-inch square stringer from F5
through F22. Glue full-length stringers on
each side of this center stringer from F5
through F22. The F11-F17 formers over the
wing are held together by former webs that
will be cut away after 1/16 balsa cross supports
are added later.
Attach the wing saddle—FS1—but don’t
wrap the TE fairing portion around F17.
Now I carefully remove the fuselage frame
from the building board, turn it over, and slide
it onto the fixture with the 1/16 x 1/8-inch
stringers resting on and taped to the fixture
surface. Attach the remaining half formers,
followed by the similar attachment of the 1/16-
inch square stringers and wing saddle.
The frame can be removed from the
fixture, and the previously attached stringers
can be drawn together, in pairs, and glued to
the formers. Water-dampen all bent stringers,
especially for the nose, to relieve bending
stress. Add all remaining straight-run stringers
in opposing pairs.
Stringers at the fin base and center
stringers along the bottom fuselage
contributing to the front and back wing fairing
will be completed later.
Flying Stabilizer: This assembly is next
because the vertical fin top—VF3—is needed
by itself to conveniently assemble and align
the swept symmetrical tapered stabilizer
halves. When the stabilizer halves are
assembled to the fin, the stabilizer top surface
is flat. So in effect, the stabilizer is built
upside down on the plans with main ribs S1
and S2 set at 90° to the building surface.
The 3/32-inch balsa cap rib is made from
sheet stock, drilled to match the tubing holes
in the S1 rib, and finish-sanded to match the
S1 profile. Accurately mark and drill 3/32-inch
holes in S1, and assemble the S1 and S2 ribs
to the tapered spar, LE, and TE.
Remove from the building surface and add
1/16-inch square stringer ribs in opposing pairs.
Add the 3/32-inch balsa cap rib with its 3/32-
inch drill holes aligned. The cap ribs need to
be relieved at the axel pivot hole to clear the
1/32-inch plywood reinforcement disc that is
attached to VF3.
Assemble the vertical fin top—VF3—
from three plies of 1/8 medium balsa, noting
the cutouts in the center plywood. Drill the
stabilizer axel bushing hole at 90°, and cut the
curved travel slot. Cut two 1/32 x 3/8-inchdiameter
plywood axel bushing reinforcement
discs, 3/32-inch center drilled, a length of 3/32-
inch-outside-diameter (OD) brass tubing to fit
the VF3 thickness, and 1/16 inch for the
thickness of the two plywood reinforcement
discs, but do not glue in place yet.
Do no further shaping now, other than
making sure the bottom surface is flat and
square.
Pin down VF3 right-side up, with the sides
at 90° to the building surface. Make lengths of
3/32-inch-OD aluminum tubing for each
stabilizer half.
One end of each tube butts to the LE or
tapered spar, and the other ends are flush with
the outside of the 3/32-inch cap rib. Plug the
angle-cut ends of these tubes with a small
piece of balsa or toothpick to prevent excess
glue from running inside the tube.
Cut two lengths of 1/16-inch-OD music
wire for stabilizer connectors. Make sure the
stabilizer halves are right-side up—they will
appear to have dihedral—and do a dry
assembly to confirm the fit of all parts.
With everything square, tack-glue the
tubes’ angled ends to the tapered spar and LE.
Tack-glue the tubing at the inside of the S1
ribs with a tiny drop of medium
cyanoacrylate. Don’t use thin cyanoacrylate; it
could wick its way along the tube and glue the
3/32-inch cap rib to VF3.
Slide the stabilizer halves approximately
1/4 inch away from VF3, confirm that the 3/32-
inch axel bushing is flush with the plywood
reinforcement discs, and place a tiny drop of
thin cyanoacrylate at the outside edge of both
reinforcement discs and VF3. Keep glue away
from the 1/16-inch wire axel and the brass
bushing. Slide the stabilizer halves back and
reconfirm alignment.
At this point the stabilizer halves can be
removed. Add the small gusset reinforcements
to the aluminum tubing, and form a small
fillet using medium cyanoacrylate around the
tubing at the S1 rib. Finish gluing the
plywood discs to VF3. Make sure the 3/32-inch
brass tube has received enough cyanoacrylate
to also be glued into VF3. VF3 is now free to
be finished and assembled to the fin.
Wing Assembly: Measure and cut the tapered
spars from 1/16 hard balsa. Make sure all spars,
including the 1/16 square hard balsa ones, are
fitted and glued flush with the rib-surface
edges. Each swept double-tapered wing panel
is built right-side up and in one piece with the
flat portion of the ribs resting on the building
surface at 90°.
The front tapered spar is not a straight run
from the root to the wingtip; it will run
straight from W1 to W5 and then change
direction to slightly forward as it runs straight
to W13. Rib W5 is the point where the main
tapered spars and the 1/16-inch square spars
make a compound change in direction.
Rather than cut these spars to make angle
changes, I carefully crack them at the W5 rib
until they are in alignment. Once thin
cyanoacrylate is applied at the joint, the spar
is much stronger than a butt joint.
The basswood LE and balsa TE are cut to
follow the angle change. When cutting rib
notches for the spars, it is initially easiest to
cut them at 90°. But because all spars cross
the ribs at an angle, open the notches
following the angle as necessary to avoid a
“crush-to-fit” assembly.
Align and pin the bottom front tapered
spar to the plans, loosely pin the rear tapered
spar in a couple places, and add the ribs. Add
the TE, top tapered spars, and LE.
When adding the top tapered spars and the
top 1/16-inch square spars, I don’t glue them
to the W1 rib until the wing panels are glued
to the center-section and the dihedral is set.
Install gussets at W5, W8, and ailerontube
exit supports. Gussets at W1 are added
after wing assembly to center-section.
Add top diagonal 1/16-inch-square, hardbalsa
rib/spar braces. It’s important that these
diagonal braces not be forced into position,
or the wing could end up warped. The top
braces attach to the top front and top rear
tapered spars at rib junctions and should be
positioned 1/32 inch below the spar/rib top
surface.
The wing panels can be removed from the
building board to add the bottom 1/16-inch
square spars and bottom diagonal braces.
Since the wing can’t be pinned flat when
adding the bottom diagonal braces, make
sure they are not forced to fit! After the
diagonal braces are in place, add the wingtip
and spar extensions.
Aileron separation is next, and the wing
panel should be pinned down right-side up.
The separation from the wing, while keeping
the ribs attached to the TE, is a bit tedious.
To make it easier, I’ll stabilize the TE ribs to
be cut by gluing 1/16 x 1/8-inch balsa
connector strips between the ribs, to be cut
away later.
Once the aileron is cut away, make new
aileron end ribs for W13 and W8 from 1/8
balsa. Stabilize these two additional ribs with
balsa strip connectors to allow for cutting and
sanding the necessary angle in the ribs when
adding the 3/32-inch balsa aileron LE. Once
assembled, I’ll remove the balsa stabilizing
strips by cutting them in the center with a
diagonal wire cutter and then flexing/twisting
the remainder off.
Sand the relief angle in the 1/8-inch balsa
end ribs for up-aileron clearance, and add the
aileron horn and rib reinforcement. Trim all
spars, LEs, and TEs flush to the outside of
the W1 ribs.
Start the wing assembly by pinning down
the center-section right-side up. Line up the
left and right panels against the centersection.
The dihedral is 9/16 inch under W13
at the forward main tapered spar. Trim LEs,
TEs, and top spars as dihedral is established
and the W1 ribs come together. Pin the outer
wing panels in place and use thin
cyanoacrylate to glue the assembly.
Add the W1, 1/16-inch balsa gussets, front
tapered spar webbing between wing W1 and
W2 and left and right outside center-section
W1 ribs. Add balsa filler sheeting at the
dihedral joint. Scrap 3/32 balsa works best for
the filler between the 1/16-inch square spars
because the excess can be sanded to follow
the curve of the ribs.
Fit the Wing to the Fuselage: Add 1/16-inch
balsa cross-supports to formers F11-F17. Cut
away the former extension webs also held
together by the 1/16 x 1/8-inch assembly
stringer.
Add the balsa triangular gussets at the
corners of F11 and the wing saddle. Add the
1/8-inch hard-balsa wing-hold-down
triangular gussets to wing saddle FS1 and
former F17. I set this gusset in place so that
there is a bit of free space between the wing
and saddle, to allow compression when the
wing is screwed down.
Confirm and drill 1/16-inch pilot holes in
the wing TE for 2-56, or 2mm, screws.
Prepare former F11A so that the top edge has
a 45° angle where it will meet the wing 45°
LE. Align the wing center-section in the
fuselage, and check the fit to the saddle and
the overall alignment to the fuselage.
The wing incidence should naturally be
set by the saddle. A bit less is okay, but not
more than 1.5°.
With the wing level and square, the
vertical centerline of the formers should be at
right angles to the wing, and the left- and
right-side center stringers should be at 90°
and 270°. This alignment needs to be correct
for placement of the fan nacelles and vertical
fin to be accurate.
Holding this alignment, center front winghold-
down F11A in position against F11 and
the wing LE (45° in F11A former butts
against, but not glued to, the 45° LE) and
tack-glue it in place along the edges away
from the wing. Former F11A also acts as a
finishing edge to the 1/16-inch stringers
ending at F11.
Drill the 1/16-inch pilot holes through the
TE into the hold-down gussets. Remove the
wing and open the TE holes for the screws.
Harden the area around the hole with thin
cyanoacrylate. Harden the gusset holes with
thin cyanoacrylate, and tap for the threads;
reharden with cyanoacrylate and tap again.
If you feel that the 1/8-inch gusset
thickness isn’t enough for your threads, you
can add another balsa thickness to the back of
the gusset. If you think your TE feels weak at
the screw head, you can add a small 1/64-inch
plywood disc under the screw head glued to
the TE.
Complete gluing F11A to F11. Reattach
the wing to the fuselage. Sand an angle in
F11B to match the wing, and attach F11B to
the wing, centered against F11A. I’ll slide a
piece of polyethylene film between F11A and
the wing to keep from gluing F11B to F11A.
Put a small drop of medium cyanoacrylate
in the center of the hole plug you removed
from F11B, and put the plug back in F11B so
that it is glued to F11A. Sand the outside
profile of F11B to match F11A. This
completes the front wing hold down and
alignment of the installed wing.
The fuselage wing saddle at the TE is
next. Remove the bottom section of F17 at
the wing TE line and from the bottom 1/16 x
1/8-inch stringer. Sand a 45° angle in the base
of F17B. It attaches to F17 at the TE and lays
back at a 45° angle. The notch needs to be
fitted to the center stringer, and the edges
need to be sanded to allow the free ends of
the FS1 wing saddle to wrap around.
The saddle is trimmed at the F17B
surface. Add the filler balsa pieces between
the saddle and the center stringer, and sand to
shape. The 1/16-inch sheet-balsa wing portion
of the saddle (there is no template) attaches
to the wing TE, mates to the completed
fuselage saddle, and is sanded to match the
contour of the fuselage portion.
Add the F12A-F17A formers to the
bottom wing center-section, and finish all
stringer attachments to complete the wing
and fuselage fairing. Add any remaining
fuselage stringers except for the fin. You can
see this completed arrangement better in the
photos than on the plans. Add and finishsand
the fuselage tail cone.
Vertical Fin Attachment: Two things aid
this initial alignment. First, the fuselage, with
wing attached, needs to be level and secured
to the building surface. Second, make two
standing right-angle fixtures. To prevent the fuselage from moving too much, you can
secure it to the building surface with long
strips of blue painter’s tape across the
formers.
The right-angle fixtures are two base
blocks of 3/4 x 3 x 4-inch MDF with two
pieces of 3/4 x 1 x 12-inch lengths of MDF,
one each, glued vertically to the surface of
the blocks and aligning with the center of the
3-inch edge. These fixtures will work
together against the top fin—VF3—to
achieve a vertical, centered alignment.
Shape VF3’s airfoil. Cut the 1/8-inch
square basswood LE and hard-balsa TE to
length and with matching angles. Glue the
LE and TE to the base of VF3 so they’re
parallel with its sides. Set this fragile
assembly in place on the fuselage. Use the
fixtures, one on each side of VF3, to hold the
fin vertical and in line with the fuselage
centerline, and glue the LE and TE to the
fuselage. Check this alignment a few dozen
times to confirm that the fin is placed
accurately.
Fit the forward fin spar VF1 in place,
followed by the rear VF2 spar. It will pass
through a reinforced sheeted area, supporting
a cutout in the center top 1/16 x 1/8-inch
assembly stringer between F25 and F26.
Confirm alignment again.
Add the left and right 1/16-inch square side
center stringers—in opposing pairs from
center engine former F20 to the fin TE. Add
the top two pairs, left and right, from the
vertical center of F20 to the fin TE.
Add the stringers for the fin-and-fuselage
junction. The line forming that intersection
has no stringer at this corner. The stringer
that runs along the base of the number-two
engine and fin is raised from the corner by
1/16 inch, and the stringer that runs on the
fuselage is offset by 1/16 inch so that the
corners of those stringers run together. This
is enough to provide definition and covering
attachment.
Add the remaining center engine and
vertical fin stringers in opposing pairs, and
finish shaping the LE and TE of VF3. For the
span between spars VF1 and VF2, there are
1/16-inch square blocking pieces to prevent
those stringers from flattening when covering
is applied and shrunk.
Complete the fuselage by adding the nose,
cockpit, and engine two’s fairing blocks and
intake ring, plus all filler pieces except the
fan nacelles. Once cut to fit, the battery tray
should have the surface prepared to accept
fuzzy loop-and-hook self-adhesive tape.
The useful area of this tray for battery
placement is from former F11 to F8. Seal the
tray in this area with thin cyanoacrylate, and
sand it smooth with 320-grit paper. Place two
5/16-inch-wide lengths of the hook tape on
each side of the tray or to suit your mounting
method. Don’t overdo the Velcro; too much
stress can be placed on the airframe during
battery removal. With Velcro attached, glue
the battery tray in position.
Fan-Nacelle Construction and Fuselage
Attachment: There are no fan-nacelle former
templates because it is more accurate to make
them with a compass directly on the template
material rather than copy from the plans. The
balsa grain arrangement is the same as with
the formers.
You could leave the EDF (electric ducted
fan) assembled or take it apart to keep the
motor free of sanding dust. To disassemble,
start by removing the rotor. In most cases,
holding the fan housing in one hand and
carefully grasping a three-blade rotor and
pulling will do the job.
These rotor blades are fragile. If one is
flexed so much that the orange or black color
turns whitish at the hub, it is no longer strong
enough to use.
If the rotor won’t pull off easily, drive a
No. 2 sheet-metal screw into its center hole
to provide a grasping point for removal.
Three things weaken the plastic rotor’s
hub’s grasp to the motor shaft: time, because
a tight fit will slowly relax; repeated removal
and replacement; and excessive motor heat,
which will expand the plastic.
Remove the motor’s two mounting
screws and withdraw it from the housing.
The heat sinks are important to use for
extended motor life; do not disgard them.
The fan duct will become a structural part
of the built-up nacelle; take care not to
deform it. The plastic (nylon, I think) needs
to be sanded where balsa is attached, which
includes the face and edge of the front and back rings and the duct’s outside surface.
With the duct sanded, cyanoacrylate will
work to hold it and the balsa in place.
Nacelle-ring formers N2 and N3 should be
a snug, easy fit to the duct rings and fit flush
to the outside surfaces. N4 is aligned and
glued to N3. Add N6 nacelle ribs at 90° to the
duct while noting the position of the duct
stators in relation to the mounting of a left
and right nacelle to the fuselage. (See the
small drawing on the plans for reference.)
Position and glue N5 to the N6 rib ends at
90° and check for centering. Add the N7 ribs.
Lightly tack-glue the N1 intake ring in place
and sand to shape with the inside of this ring
blending with the inside surface of the duct.
Once the intake rings are shaped, remove
them for sealing and finishing with a few
coats of silver enamel, as is done with the
smaller oval number-two engine intake ring. I
glue the painted intake rings in place, after
covering, with a bit of silicone adhesive
because silicone won’t attack the enamel
paint.
Make the N9 1/8-inch hard-balsa nacelle
mounting tongues, nacelle fuselage supports,
and four N8 1/16-inch balsa fuselage/nacelle
support covers. To aid alignment of the
fuselage nacelle supports, I set the front and
rear supports, centered, on top of the left and
right center fuselage 1/16-inch square stringers
and against formers F20 and F22.
Measure the distance between, which
should match the width of the nacelle
mounting tongue, and cut 1/8 x 1/4-inch balsa
spacers. Tack-glue these to the ends of the
supports, creating a one-piece square, flat
frame.
For a 1° support setting in the fuselage,
the rear support should be 1/16 inch above the
1/16-inch square stringer, and the front support
should be up just a tad under 1/8 inch, with
less being better than more.
Add 1/16-inch balsa fill between stringers,
per the plans, to box in the nacelle mounts.
Remove the temporary support spacers, and
add the N8 1/16-inch balsa covers and sand to
shape.
Check the fit of the nacelle mounting
tongues. They should go easily into the
mounting slot. It helps to score the wire chase
cut in the mounting tongues, but keep them in
one piece and attach above the appropriate
(remember there’s a left and a right) N6 rib of
the nacelle.
Tack-glue at the outside edges of the
tongue, remove the wire-chase portion, and
complete the gluing along with the balsa
reinforcements. The wire chase must accept
the passage of the motor wire and JST plug.
Sand the outside edges of the mounting slot to
match the nacelle.
Make the paper tail cones. Glossy-on-oneside,
black gift-wrap paper works best. Thin
acetate or 0.002 drafting Mylar will work, but
paper makes it easier to align the cone
overlap and adhere with Elmer’s white glue.
The exact sizing of this cone can be tricky.
When making the lineup at the overlap for
gluing, a slight change in either direction can
make quite a change in the final diameter.
Make a cone template and a couple copies
from copy paper to make a few samples.
The cone’s large end needs to fit inside
the N4 inside diameter (ID), and the
smaller diameter needs to fit the N5 ID.
The cone will be slightly longer for
trimming flush with the outside of N5.
Once you have noted the correct
placement of the overlap, make the cones
from the chosen material. It is inserted
through the N5 ID by carefully forming the
finished cone into a “U” shape without
creasing. Use cyanoacrylate to adhere the
front and rear of the cone to their formers.
Before installing the motor back inside
the fan housing, if it was disassembled the
motor wires need to be made longer. Cut
the motor wires 3/4 inch back from the JST
plug and add 41/2-5 inches of red and black
wire of the same gauge. Cut a small hole in
the paper duct at the wire-chase slot in the
mounting tongue.
You will need a tool to fit over the back
of the motor to install and add resistance
when pushing on the rotor, because the
completed balsa nacelle needs to be
handled carefully. The tool is made from a
10-inch length of 3/4-inch-diameter dowel,
1/2-inch center-drilled on one end to a depth
of 3/4 inch.
The drilled end of this dowel fits over
the back end of the motor and presses
against the heat sink. Cut a notch in the
drilled end to clear the motor wires. The
opposite end of the dowel is covered with a
thin, dense foam disc or the loop side of a
piece of Velcro to soften the pressure of
pushing against the motor’s capacitor.
I used a length of wire insulation forced
over the motor shaft to guide the motor
through the duct. The heat sink should be at
the back edge of the motor when the foamcovered
end of the dowel is used to push
the motor in place. The dowel’s notched
end is then used to seat the heat sink against
the stator.
Before inserting the motor, look at the
relationship of the plastic mounting tabs to
the motor screw holes; choose the motor
position that allows the motor wires to
easily pass through the wire-exit chase.
Also make sure the heat sink is a snug fit
on the motor case. Use a tiny bit of blue
thread locker on the motor screws, but do
not overtighten or the plastic mounting tabs
will collapse and break.
Use the notched end of the motor
mounting tool to offer resistance as you
press the rotor straight—no cocking—fully
on the motor shaft. The rotor can usually be
replaced two or three times and be tight
enough to stay on.
Aileron and Flying-Stabilizer Control
Setup: I like to use plastic tubing to house
the control wires. Du-Bro micro tubing will
work, but I prefer PTFE spaghetti tubing.
PTFE offers little resistance to clean music
wire running inside.
Cyanoacrylate will stick the tubing to
balsa if the tubing is sanded to make the
outside surface fuzzy; the tubing will stay
put if it’s tacked down in enough places.
GOOP adhesive works a bit better but is
messy in application.
Make sure the cut ends of music wire are
smooth before running through the tubing.
Before tacking the tubing in place, it should
have the control music wire inside; the
tubing will hold its shape and position better.
(PTFE tubing makes great cyanoacrylate
applicators. Trim off a new bottle tip just
enough to allow tight passage of the tube,
which is reusable and easy to remove for
recapping the bottle. Just snip off a clogged
tip. The 0.022-inch ID works nicely with thin
cyanoacrylate.)
The aileron wire is two lengths of 0.015-
inch music wire, and it runs in a 0.034-inch-
ID PTFE tube. Wire attachment to the aileron
horn is a 90° “L” bend, with a small ID piece
of PVC wire insulation as a keeper glued to
the wire with a dab of GOOP adhesive. Each
opposite end of this wire will cross and go
through a Du-Bro Mini E/Z Connector (item
845) in the wing center-section for attachment
to the aileron servo horn.
With the aileron servo mounted on its
side, you can just get a long, thin screwdriver
blade through the spars to tighten the E/Z
Connector screw. With thread locker this
screw will hold both 0.015 wires, but once
the ailerons’ final positions are set, I add a
drop of epoxy on each wire at the outside of
this connector.
The flying-stabilizer PTFE 0.038-inch-ID
control tubing and 0.025-inch music wire
needs to be supported on every other former
with a cross strip of 1/16 balsa as it makes its
way through the fuselage to the vertical-fin
rear spar and up to the forward-stabilizer 1/16-
inch connecting wire. The control wire will
start in an E/Z Connector on the elevator
control horn and end in a single loop around a
3/32-inch-OD x 3/32-inch-long aluminum tube.
The stabilizer forward 1/16-inch-musicwire
connecting rod will pass through the
control-wire aluminum tube to move the
stabilizer on the rear hinge connecting wire.
The 0.025-inch music-wire loop should be a
tight fit on the aluminum tube; add a bit of
epoxy as insurance.
Equipment Setup: Before covering, it helps
to set up the receiver on the elevator servo
tray, connect the receiver to the ESC, and
confirm ESC wiring to the fan motors and
battery. Servo and receiver-tray placement is
also a CG consideration.
For the ESC motor wires, I attached two
red and black wire pigtails with female JST
plugs and soldered them for a parallel
connection. The ESC is attached to a small
1/16-inch balsa strip glued between formers.
As a rule, you want the motor and battery
wires as short as possible without difficulty
making the connections. The receiver
antenna passes through the fuselage interior
and exits through the tail cone.
For aileron control movement, I set my
endpoints for as much down aileron as is
available and with an equal amount of up, to
a bit more. For the elevator, I use full
available up and down throw.
Finishing and Covering: Besides a general
finish-sanding with 320-grit paper, I’ll spend
some time rounding and shaping all the
basswood LEs except for the LE portion of
the wing center-section; its flat 45° is
necessary for the hold down to work.
All balsa, especially stringers, that has
cyanoacrylate hardened on the surface needs
to be sanded smooth. Any rough surface
areas will show up during covering.
A plastic kit model is helpful in locating
aircraft surface detail. I used a Hasegawa
1/200-scale Boeing 727-200 as the primary
source for scaling and detailing. There are
many liveries of the Boeing 727-100 and
numerous Web sites on which to view them.
I picked Trans World because I, ahh, love to
cut out windows. My second version will be
FedEx or maybe DHL.
I chose Solarfilm So-Lite for covering
and graphics. To learn about this material,
search for SoLite on RCGroups.com; you’ll
find some excellent information.
I used a GWS with the small flat shoe, set
to low, for initial covering attachment. For
shrinking I used a standard covering iron.
It works best to complete a part’s
covering job to be as wrinkle-free as possible
before attempting shrinking. It’s important to
do the shrinking “in the round,” slowly, to
avoid airframe warping.
I don’t recommend using a heat gun
because shrinking is too hard to control. Do
not underestimate So-Lite’s shrinking
power!
The fuselage is covered mostly in strips,
three stringers, or two open areas between
stringers at a time. Check the finished wing
and stabilizers for warping after shrinking
the covering. A small amount of equal wing
washout is okay.
The ailerons are hinged with 1/2-inchwide
x 3/4-inch-long pieces of So-Lite
between rib bays. Starting from the top, set
the aileron in place in the full down position
and iron on the five pieces, keeping the end
pieces close to the aileron ends.
Flip the aileron up until it rests on the
wing surface, and iron on five more pieces
in the same position as those already in
place. You may need to reheat the top hinge
strips until the aileron holds a neutral
position and is relatively easy to flex.
The cockpit window glazing is thin
acetate, with each of the six window panes
cut separately and glued with canopy
adhesive after covering.
Final Assembly: The battery weight and
location will determine the correct CG. A
placement closest to F11 will simplify
installation and removal.
To aid in battery placement and removal,
I’ll add a 3/8-inch-wide strip of fiberglass
filament tape wrapped around the battery so
I have a long overlapped strip on one end.
You can view the battery placement by
looking through the cockpit windows and
the viewing window in former F3.
To assemble the stabilizer halves to the
fin, mark the center point of each 1/16-inch
connecting wire. Apply a bit of clear
silicone sealant to one end of each wire, and
install them in one stabilizer half. The
halfway point marked on the 1/16-inch wire
should match up with the fin centerline.
Wipe off the excess and let cure. Once the
silicone has cured, install that stabilizer
half, capturing the elevator control-wire
tube, and slide into position.
Apply a minute bit of oil to the brass
bushing and to the aluminum push wire
tube. Put a bit of silicone on the 1/16-inch
wire ends, and slide the remaining stabilizer
half in place while keeping track of and
removing excess silicone. Keep a
minuscule amount of side-to-side play.
Check for free movement after this silicone
has cured. It takes only a small amount of
silicone to hold the wires in the tubing and
still allow stabilizer removal later, if
necessary.
Silicone also holds the fan nacelles in
place. Install the nacelle, allowing a 1/8-inch
space to remain. Apply a small amount of
silicone at each end corner of the nacelle
tongue and slide the nacelle home. Wipe off
any excess.
This is enough to hold the nacelle in
place and still allow removal. If you’re
worried, you could insert a couple of short
pins. But they alone should not be used if
the tongue is the least bit wobbly in the
mount.
The Scary Best Part: The plans’ CG
location is optimal for smooth, stable,
controllable flight. Moving the CG back
will cause the aircraft to become unstable in
pitch and basically feel uncomfortable to
fly.
Depending on the ready-to-fly weight,
cruise speed will be close to half
transmitter-throttle-stick position using a
two-cell Li-Poly battery. Prevailing winds
should be less than 5 mph.
At 13 ounces in flying weight, the 727 is
not fast or high powered, and the controls
will not act quickly to counter higher winds
or gusty conditions. The model will loop
with a full-power diving entry and roll with
a full-power, slightly climbing entry, downelevator
when inverted, and a bit of upelevator
to level. It will not maintain
inverted flight. The power-off glide is
lovely.
So with calm wind conditions, and after
you’ve repeatedly gone over your checklist,
it’s time to fly the Boeing 727-100. I find it
extremely easy to hold and balance, for a
hand launch, using my thumb and index
finger on each side of the rear wing fairing
and my middle finger lightly supporting the
wing center-section.
Bring the power up to half stick and
give the 727 a gentle, but firm, level toss. It
may lose a bit of altitude on the launch but
will recover quickly. Continue adding
power, as necessary, for the climbout.
During the first flight, you’ll find that
gentle aileron turns will require almost no
elevator input to keep the nose up.
Be prepared for a long glide on the
Boeing’s first landing. Once in ground
effect, keep adding up-elevator to hold a
slightly nose-up attitude until it settles in
for the touchdown.
My prototype showed no tendency to tip
stall with high bank and high elevator-input
turns using cruise power. In fact, when it
was up roughly 100 feet and I was trying to
induce a stall, I kept adding aileron, upelevator,
and power until I had nothing left.
It just stayed there, nose chasing the tail in
a tight, high-banked turn, and wouldn’t
stall.
A straight-ahead, power-off attempt to
stall will see the nose drop as airspeed runs
out, followed by an immediate recovery
with neutral elevator. Nothing like a light
wing loading!
I’d be happy to help with any questions; just
put “Boeing 727-100” in the subject line. MA
David A. Ramsey
[email protected]
Sources:
McMaster-Carr (polystyrene sheet plastic,
PTFE spaghetti tubing, double-stick masking
tape)
(630) 600-3600
www.mcmaster.com
GWS (electric power system)
(909) 594-4979
www.gwsus.com
Castle Creations (ESC, receiver)
(913) 390-6939
www.castlecreations.com
Du-Bro (hardware)
(800) 848-9411
www.dubro.com
Top Flite (trim-seal tool)
(800) 637-7660
www.monokote.com
Solarfilm (So-Lite)
(615) 373-1444
www.solarfilm.co.uk/