The author used long delta splices where angles were needed
and where long, square stringers needed to be spliced together.
18 M ODEL AVIATION
Pin the basic fuselage structure together, then check for
squareness before gluing. This is important!
Make a copy of your plans to use as cutting templates. Use 3M
artist’s spray mount to glue the templates to the wood.
Many of the wood pieces are doubled. Glue them together with
the 3M spray mount for cutting, then separate for final fitting.
Cut and “build” two sides of the fuselage over the plans and fit
(but don’t glue in) square-balsa uprights from F3 forward.
You can see the gussets glued in place. Notice how they contact
all of the pieces that are adjacent to them.
Cut, fit, and glue six gussets at the top of the fuselage stations
F4, F5, and F6. These add tremendous strength.
After the bottom stringers are fitted, capstrip formers F2 and F3.
Notice how clean and neat the structure looks.
Former F1 and the motor box are glued together at the same
time. Clamps are needed to keep everything straight.
Glue on the 1⁄4 balsa stringer formers BF1, BF2, BF3, BF4, and
BF5, centered over the 3⁄8-inch crosspieces.
January 2003 19
The fuselage behind F3 uses square balsa stock instead of
formers. Cut and fit the parallel pieces then the diagonals.
The landing gear is held in place with two aluminum angle
brackets that transfer landing forces to the motor-box plates.
The tail-wheel mounting plate and finished rear stringer area
shows the mounting details of the Haigh Style bracket.
35% Extra 300L Specifications
and Equipment
Wingspan: 106 inches
Length: 96 inches
Wing area: 2,060 square inches
Wing loading as tested: 30.75 ounces/square foot
Weight: 26-28 pounds
Engine: Desert Aircraft DA-100
Propeller:Mejzlik hollow carbon-fiber 28 x 10
Spinner: Tru-Turn 4.5-inch-diameter Ultimate
Canopy, cowl, cuffs, pants: Aeroglass Hurley 35% Extra
Radio: JR 10X
Receiver: JR 955 dual conversion
Servos (control surfaces): JR DS8411 digital
Servo (throttle): JR DS8231 digital
Servo matching: JR MatchBox
Switches: JR HD charge switches
Servo extensions: JR 22-gauge gold silicone twisted
Servo arms: SWB Manufacturing 1.25-inch aluminum
Linkages: Nelson linkages (formerly Rocket City), HD 1⁄4-inch
ball ends, K&S aluminum tube tapped with 4-40 ends
Control horns: Nelson (Rocket City) super swivel clevis
control horns
Rudder linkage: Nelson pull-pull system
Batteries: Three 6.0-volt Sanyo 2700 mAh NiMH
Covering:MonoKote
Fuel tank: Du-Bro 32-ounce with SWB aluminum stopper cap
Fuel line: Tygon 1⁄8-inch inside diameter
Wing tube: 0.049 inch 1.5- x 36-inch aluminum
Stabilizer tube: 0.035 inch 5⁄8- x 16-inch aluminum
Landing gear: TNT 33% Extra 300 aluminum
Axles: Du-Bro 3⁄16 inch
Wheels: 3.5-inch-diameter Sullivan Skylite
Tail wheel: Large Ohio Superstar Haigh Style
20 M ODEL AVIATION
24 M ODEL AVIATION
possible. The landing gear has been angled forward to
help change the twisting force from landing to a more
survivable compression force, and aluminum “L”
brackets transfer the load to the motor box, eliminating
the need for a heavy plywood plate.
The original prototype was built with a motor box
that captured the wing tube. With this design the
vibration from the engine was transferred more directly
to the wings, wreaking havoc on ailerons, hinges,
servos, and linkages. I noticed that designs that did not
capture the tube seemed to be much smoother, so in the
second design I stopped the motor box short of the wing
tube. It worked! The wingtips and ailerons vibrate much
less, and the hardware seems to incur less wear and tear.
One of this design’s unique qualities is the extensive
use of laminating balsa over long expanses of thin, light
plywood. The process creates a strength in shear that
outweighs the sum of the two materials and makes the
structure light while keeping it rigid.
Its shape is also different from other designs. The
full-scale Extra is slightly rounded at the front, but for
ease of construction and simplicity, most models are
designed in a wedge shape utilizing straight lines.
Viewed from the top, the fuselage sides form a long
triangle from the rear of the cowl to the tail, and the
transition to the cowl is often a sore spot. I wanted to do
something about that without creating any additional
complexity or weight, so slight angles were designed
into the airplane to fill it out slightly, getting rid of the
“starved horse” look and the strict delta shape. It’s not a
huge change, but it helps the overall appearance. It also
helps to smooth the transition from the cowl to the
fuselage.
In IMAC, percentage of full scale is calculated using
the wingspan. In this case the full-scale L has a
wingspan of 25 feet, 3 inches, giving a 35% span of 106
inches for this model. I kept the wing planform, the root
and tip chords, and the overall length at 35% scale but
made the width of the fuselage a bit smaller, at 33%. I
like the sleeker look of the slightly slimmed, but still
scale-shaped, fuselage. Keeping the fuselage smaller
may help keep the weight down, increase rigidity, and
slightly reduce drag (although in my opinion drag is not
a problem in SA models). I did it mostly because I like
the way it looks!
The number-two prototype—the finished one seen
here—came in at 27.5 pounds ready to fly. A huge wing
area of 2,060 square inches gives a very light loading of
30.75 ounces per square foot. Even at our mile-high
altitude here in Colorado, the Desert Aircraft DA-100
engine pulls this airplane out of sight with the ability to
accelerate out of a Torque Roll. At sea level this combo
would be ballistic! In normal flight the airplane floats on
the wing like a glider, and for 3-D it’s slow and agile.
Not being one to rest on success, this third rendition
strives for an even lighter weight. I opened up the
fuselage sides, eliminated the formers in the rear, and
made a more careful selection of wood, including some
contest-grade balsa sheeting for everything except the
main wings. I’m hoping to take a pound off the airplane
and get it down to 26.5, which would bring the wing
loading down into the 20s.
The Design: This airplane’s design is rather
conventional and compares to other SA aircraft
currently being produced. It was specifically designed
around Desert Aircraft’s twin-cylinder 100cc gas
engine. DA engines are light, powerful, and reliable, but
best of all the customer service from DA is second to
none.
Wings and stabilizers are each two-piece and
removable for storage and transport; they slide onto an
26 M ODEL AVIATION
aluminum tubing spar. The fuselage sides
are of 1⁄8 light plywood but are almost 70
inches long, so finding the wood will take
a little legwork. I found a 4 x 8-foot sheet
for roughly $16 from a local plywood
specialty distributor, and after a bit of
research I was able to find several sources
in my area.
The cowl, wheel pants, canopy, and
landing-gear cuffs are from Aeroglass.
Flying Foam.com offers high-quality
CNC-cut foam parts. However, if you want
to cut your own foam parts, the plans have
templates. The first two airplanes were
built with parts that we cut at home, but
this model uses foam parts from Flying
Foam.com.
The 1.5-inch-diameter x 36-inch .049
wing tube, 5⁄8-inch-diameter x 16-inch .035
stabilizer tube, and the landing gear are
from TnT Landing Gear Products. The
tubes come with the phenolic sockets you
will need for construction. (A complete list
of supplies and suppliers is included at the
end of the article.) I’ll discuss the
components that we chose as we install
them. The rest of the airplane is balsa and
light plywood with only three pieces of
aircraft plywood: the motor-box sides and
the landing-gear plate.
Erik Richard, an NOAA physicist, will
be constructing this airplane for our
demonstration purposes. Erik has spent his
lifetime building and designing model
aircraft and has been exposed to design
since early childhood. His father was an
aeronautical engineer with many famous
full-scale designs and was also an avid
model designer/builder. This design has
been an evolving process, and many good
changes have come from the results of
testing. We are building this third model in
as close to real time as possible for
conventional publishing.
In a model of this size and power, the
equipment and hardware you use needs to
be different from what you might use with
smaller glow-powered aircraft. We have
been very careful about our selections to
keep things simple yet strong enough to
handle the job. Pay careful attention to the
linkages and fasteners we use, and please
don’t risk off-brand or standard servos or
low-quality electronics. It’s not just your
airplane at risk; it’s you and everyone
around you. If you’re ready, let’s start
building!
CONSTRUCTION
I’d like to make a couple of notes about
the plans before we begin. You will notice
on sheet three that there are two different
hole sizes for the wing tube socket on the
fuselage side. This is because we measured
several different sockets, and there is
almost always a slight variation. The best
thing to do is measure your specific socket
with a caliper and cut the hole slightly
undersized. Gradually sand the opening to
obtain a snug fit on the socket. Remember
to do this with the two sides taped together
so the alignment is exact.
The plans also show the alignment
dowels at 90º to the wing root. That’s fine
for the wing hold-down bolt, but the
dowels need to be oriented parallel to the
wing tube so they slide into place when
installing the wing without binding.
Before you begin, make a copy of your
plans to use as a cutting template. With
scissors, cut from the plans the formers,
fuselage sides, fuselage floors, motor box,
LG (landing gear) plate, tail-wheel plate,
LG1, cowl formers, and stringer standoffs.
Tape two pieces of 1⁄8 x 70 x 8-inch
light plywood together for the fuselage
sides, and two pieces of 12 x 121⁄2-inch for
the cowl former and F1. Also tape two
pieces of approximately 20 x 91⁄8-inch
aircraft plywood together for the motorbox
sides. We used a light coat of
temporary spray glue (listed at the end of
the article) to keep the parts together and
aligned.
Parts that need to be cut out are: 1⁄8 light
plywood—formers F2, F3, fuselage sides,
fuselage floors (FL0, FL1, FL2, FL3),
cowl former and F1, and tail-wheel plate;
1⁄4 balsa—LG1 and BF1, 2, 3, 4, and 5, and
stringer standoffs; 1⁄8 aircraft plywood—
landing-gear plate and motor-box sides; 1⁄4
aircraft plywood—firewall.
January 2003 29
Use 3M artist’s spray mount 6065 to
glue the cut plans to your wood. On the
fuselage sides, remember to cut to the
outside edges. (The landing-gear plate glues
in between the motor-box sides.) Also cut
the lightening holes. We radiused the
lightening-hole corners to 5⁄8-inch diameter
and used an adjustable hole saw to get the
wing tube socket diameter just right. Cut
and sand the two pieces while still glued
together to ensure that they are identical.
As you cut the parts and before you
remove the paper template, it’s a good idea
to mark the centers from the plans onto the
edge of the part. After you remove the
paper, sand the parts lightly on a flat
surface to remove any glue residue, then
label the part with a pencil or fine marker
and mark the centerline.
The cowl former and F1 can initially be
cut and sanded together to the outside line.
We used the spray mount to temporarily
glue the two pieces of wood together so the
parts would be identical. After you’re
happy with the outline, scribe or draw an
alignment line at the top and bottom edges
and separate the two parts. Glue the second
template to the part without a drawing and
line it up on the cowl former using the line
you scribed earlier. Proceed with cutting the
inside lines on both parts. We’ll split the
cowl former later.
Fuselage: Splice together four pairs of 36 x
3⁄8-inch square balsa to form the longerons
that will be laminated to the inside of each
fuselage side. Use a long delta splice for the
bottom front part of the fuselage that angles
up. Glue on the longerons, and cut and glue
in the 3⁄8 square upright fuselage structure
from F3 back (the forward pieces will be
glued in later). Cut and fit the rest of the
forward 3⁄8 upright fuselage structure to be
used as former gussets, but don’t glue them
in at this time. Leave a little 3⁄8 overhang at
the front of the fuselage side, which will be
cut flush and sanded after the fuselage is
glued. Be sure to build a left and right
fuselage side.
Lay the plan out on a smooth, flat
surface and fold the front over the end of
the table at F1. Trial-fit motor-box sides,
F1, F2, F3, and fuselage sides over the plan,
and make any final adjustments so that the
parts fit properly. This is a good time to cut
the fuselage floors, FL0, FL1, FL2, and
FL3, and fit them to the fuselage. This is
also the time to cut and fit the aft-most
former from 3⁄8 balsa sheet.
Cut two lengths of 3⁄8 square balsa to fit
each former station. Mark a centerline on
one piece from each station. Trial-fit and
pin the whole assembly together including
the forward tank floor FL0, making sure
that the fuselage is straight along the
centerline. Use the wing tube socket center
phenolic and tube to check for square. Do
not glue the phenolic wing tube socket into
the fuselage at this time.
Note that former F1 is wider at the top
than at the bottom to fit the shape of the
cowl. The fuselage has a slight twist built in
to allow this fit. You can see in a picture
that the orange building square is flush at
F3 but not at F1. At F3, the fuselage sides
are 90° to the building surface and the
fuselage is built 90° from there to the rear.
Make sure to use some weight to hold the
fuselage flat on the building board.
F1 should fit the fuselage flush inside
the cutout between the upper and lower 3⁄8-
inch longerons. After you’re satisfied with
the fuselage alignment, glue the structure
together. At this time you can fit the precut
3⁄8-inch upright former gussets into position
next to their corresponding formers. Make
sure to glue these sticks into position only
after the rest of the structure has been
aligned and glued.
After the main part of the fuselage is
glued, you can unpin it from the table and
flip it over to finish fitting and gluing the
rest of the 3⁄8-inch stick structure and
upright gussets at formers F1, F3, and along
the rear of the motor box. We will laminate
some 3⁄8 square to the top inside surface of
the motor-box sides as a stiffener after the
firewall has been installed. This is also a
good time to finish gluing the floor (FL0) to
the motor-box sides.
Cut, fit, and glue six gussets at the top of
the fuselage at stations F4, F5, and F6.
Glue in fuselage floors FL1, FL2, and
FL3. (FL0 should already be in place.) Cut
and fit the top and bottom 1⁄4 square balsa
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Vision
Item #NFN101
Specifications:
Wing Span: 41 inches
Wing Area: 265 sq. inches
Fuselage Length: 28 inches
Flying Weight: 24 ounces
Engine Recommended: NORVEL .049-.061
Radio Recommended: 2-3 Channel
Classic
Item #NFN100
Specifications:
Wing Span: 41 inches
Wing Area: 265 sq. inches
Fuselage Length: 28 inches
Flying Weight: 24 ounces
Engine Recommended: NORVEL .049-.061
Radio Recommended: 2-3 Channel
Ucan-2
Item #NFN120
Specifications:
Wing Span: 41 inches
Wing Area: 265 sq. inches
Fuselage Length: 28 inches
Flying Weight: 24 ounces
Engine Recommended: NORVEL .049-.074
Radio Recommended: 4 Channel
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P. O. Box 520 • Montezuma, Iowa 50171-0520 • 641-623-5154
diagonal bracing from F6 to the rear. We
also glued in the top 3⁄8 diagonal braces
over the radio-compartment area, but for
convenience you can wait to do this after
the radio equipment is installed. Don’t glue
in the brace over FL1 until after the wing
tube socket is installed.
Glue on the 1⁄4 balsa stringer formers
BF1, 2, 3, 4, and 5, centered over the 3⁄8-
inch cross structures. Sand the rear of the
fuselage square, and glue on the tail-wheel
plate.
Bottom stringers: Delta splice a 12-inch
section onto a 48-inch length of 1⁄4 square
spruce for each 60-inch bottom stringer. Fit
the stringers to create a flat bottom. Adjust
the notches as necessary to keep the
stringers straight. The stringers should
follow the plan and bend at BF3 (see
photo). The stringers go from F2 rearward
to the tail-wheel plate. Sand them to fit
flush at the rear.
Add 1⁄16 x 1⁄4-inch capstrips to F2 and
F3. This gives a nice surface for sticking
down the covering. Center the capstrip on
F3, but fit F2’s capstrip to the rear of the
former.
Landing-Gear Plate: Using the plan, cut
the landing-gear plate from 1⁄8 aircraft
plywood and the doublers from 1⁄8 light
plywood. Scribe a line at a 1⁄8-inch depth
on the inside of the motor-box sides and
glue the doublers to the inside of the
motor-box sides, aligning them.
Referencing the plan, mark two points for
drilling bolt holes that will attach the
landing-gear “L” brackets. Cut two 41⁄2-
inch lengths from one-inch, .050-thick
extruded angled “L” aluminum, available
at most hardware stores.
Line up the brackets to match the top of
the doubler just shy of touching F2. Use
scrap blocks of wood and clamp them in
place to drill for the bolt holes. Drill all the
holes while clamped in place. Use 6-32 cap
screws with blind nuts on the outside, and
bolt it all together using Loctite. Glue the
landing-gear plate down flush inside the
motor-box sides. Erik decided that he
wanted the additional security of lock nuts
on the bracket bolts.
With your compass, mark a line 3⁄4 inch
inside each side of the motor box, and
mark the center of the landing-gear plate.
Line up your landing gear, and mark it
according to these lines. Drill four holes
for 8-32 bolts. Line up the gear on the
centerline of the LG plate, leaving a 3⁄32-
inch gap between the gear and F2 (note that
in the photo we used a 3⁄32 capstrip for a
spacer), and drill through the LG plate and
the “L” brackets.
Using 8-32 cap screws and lock nuts,
bolt the landing gear to the fuselage. Leave
a 3⁄32-inch gap between it and the gear, and
glue on the LG1 1⁄4 balsa former.
Tail-Wheel Plate: You can see in the
photo how the tail-wheel plate was
contoured at the edges. We also decided to
lighten this area and were able to do so
because our rudder servos will be mounted
in the hatch compartment. An additional
section of wood was removed from the
fuselage sides under the stabilizer. This
will also aid in later maintenance and
assembly. If you plan to use a heavier
engine, we suggest that you mount the
rudder servos in the fuselage sides under
the stabilizer.
We used an Ohio Superstar Haigh-type
tail wheel that requires an antirotation
block to be installed inside the fuselage.
The block was made from laminated scraps
of 1⁄8 light plywood. The result was light
and strong compared to hardwood. We
mounted the assembly with 2-56 cap
screws and blind nuts set into doublers
inside the tail-wheel plate. Do not use
wood screws to hold the tail-wheel
brackets.
Fitting the cowl: With a sanding block,
true the edges of the cowl so that the parts
have a good fit. We found that the
Aeroglass cowls are very good and require
only a light amount of sanding to make the
parts square and perfect. Tape the halves
together. With a compass, mark a line on
the cowl former approximately 1⁄32 inch
(.030) from the outside and carefully sand
January 2003 31
off material a little at a time, checking
cowl fit as you go. The idea is to get the
cowl to fit flush with the fuselage sides
and F1.
Once you’re satisfied with the fit, mark
the former to be cut at the cowl seam.
Place the marks approximately one inch
apart, centered on the 1/2-inch overlapping
seam. Do not cut at this time. Bolt the
cowl former in place with 4-40 cap screws
and blind nuts. Use four in the bottom half,
accessed from inside the cowl, and three
for the top half, accessed from inside the
hatch. We made small doublers from 1⁄8
light plywood for the blind nuts. Do a final
fit check and correct any imperfections
with the fit.
To prevent getting glue on F1, separate
the cowl former from F1 with waxed paper
and bolt the cowl former back onto F1.
Tape the cowl into place, and glue it to the
former with medium ZAP. Be careful not
to get any glue between the cut marks that
you just made. After the cowl is secure,
remove it from the fuselage and add a fine
fillet of Plexus Methacrylate or similar
adhesive over the ZAP.
With the cowl halves together, mark
and drill five holes on each side for the 4-
40 x 1⁄4-inch button-head screws. Back the
holes up with a small piece of 1⁄8 light
plywood and install small 4-40 blind nuts.
We used nylon washers on the outside of
the cowl to be a little kinder to the paint.
Cut the ring roughly 1⁄4 inch on either side
of the cowl half overlaps. We made our
marks a little too large, as seen in the
photo. Sand a nice beveled edge in the
cowl ring to finish it off, and add a bead of
Methacrylate to any part of the ring that is
not fully glued to the cowl.
Sheet the area between F1 and LG1
with 1⁄16 balsa. The sheeting will glue to
the inside of F1 and lay over the top of
LG1. First sand a bevel on LG1 to line up
with F1 (ensuring that the sheeting will lay
flat on LG1). We made a 1⁄4-inch-wide 1⁄8
balsa lip on the inside of F1 to give the
sheeting something to lay on while being
glued. Preglue the sheets together to do half
the area at a time. One stringer in the center
between LG1 and F1 will give you an area
to start from. Use a paper template to get
the shape just right, and trial-fit before
gluing. Perform this procedure with the
cowl in place to ensure proper alignment.
Odds and ends: Using 1⁄16-inch sheeting,
fill the open areas on each side of the
landing-gear mount. Follow what is shown
in the photo here, and put it in at an angle.
If you try to fill the gap, the gear’s flexing
action will break the balsa. The way we
have it positioned leaves room for the gear
to work.
Trace the top half of F1 onto a sheet of
medium-density 3⁄8 balsa. This will be used
as a stiffener for F1. Leave approximately
1⁄16 protruding past the top so that when the
hatch is installed all the parts can be blocksanded
to align perfectly. With a compass
set at roughly 1 inch, trace the outside line
to form the inside line. Drill three relief
holes for the cowl bolts with a piece of
sharpened 3⁄8-inch-diameter copper tubing.
We also glued in some 1⁄32 aircraft-plywood
washers to keep the softer light plywood
from crushing. Glue the stiffener in with
the cowl completely installed to keep the
former aligned and flat.
Glue a length of 3⁄8 square balsa into the
corners of the motor box and F1 from the
bottom of the motor box to the stiffener
you just installed.
At this point you have finished the wood
portion of the fuselage for your 35% Extra
300LX. The wing and stabilizer tube
sockets will be aligned and glued into
place after we have the wings and
stabilizers ready for alignment. Next
month we’ll sheet and trim all the foam
parts, looking at several different methods
to get the job done. MA
Mike Hurley
11542 Decatur Ct.
Westminster CO 80234
[email protected]
Manufacturers and suppliers:
Radio equipment:
JR
JR is distributed exclusively by Horizon
Hobby Inc.
(217) 355-9511
www.horizonhobby.com
Engine, mufflers, propeller, wing fasteners:
Desert Aircraft
140 S. Camino Seco, Suite 418
Tucson AZ 85710
(520) 722-0607
Fax: (520) 722-5622
www.desertaircraft.com
Cowl, wheel pants, gear cuffs, canopy:
Aeroglass
Box 185
Langton, ON
Canada, N0E 1G0
(519) 875-1533
Fax: (519) 875-1855
Landing gear, wing tube, stabilizer tube:
TnT Landing Gear Products, Ltd.
10530 Airport Hwy.
Swanton OH 43558
(419) 868-5408
www.tntlandinggear.com
4.5-inch Ultimate spinner:
Tru-Turn Precision Model Products
100 W. 1st St.
Deer Park TX 77536
(281) 479-9600
Fax: (281) 479-9090
www.tru-turn.com
CNC cut foam parts—foam wings,
stabilizers, hatch, turtledeck:
Flying Foam.com
1123 Doverwood St.
Corona CA 92880-1272
(909) 371-4913
Fax: (909) 739-0445
www.flyingfoam.com
Linkages, hardware:
Nelson Hobby Specialties
2900 S.W. Cornelius Rd.
Unit 762
Hillsboro OR 97123
(503) 259-8899
www.nelsonhobby.com
Plexus Methacrylate adhesive:
Aerotech Models, Inc.
2640 Minnehaha Ave. S.
Minneapolis MN 55406
(612) 721-1285
www.aerotechmodels.com
The following manufacturers carry a
similar-size Extra 300 that I recommend:
RadioCraft Industries Inc.
140 S. Camino Seco, Suite 419
Tucson AZ 85710
(520) 886-7272
Fax: (520) 886-4884
www.radiocraft.com
Aeroworks
401 Laredo St., Suite D
Aurora CO 80011
(303) 366-4205
Fax: (303) 366-4203
www.aero-works.net