designed and first flew the Talon
Zephyr in 1961 in collaboration with
my good friend Bob Baldwin, who has
since passed on. The original model
and several more like it were powered
by Cox Tee Dee .15 engines in
conformance with the then AMA Radio
Control Pylon Racing rules.
The model was controlled with elevator
and aileron only. There was no throttle
since the Tee Dee had no controllable
carburetor. A fixed pickup in the tank made
it possible to stop the engine by inverting
the airplane.
Those rules specified wing-area
requirements for .09, .15, and .19 engines.
The minimum wing area for a .15 was 576
square inches. Since I did not know how the
wing area would be measured, I designed
the wing, exclusive of control surfaces, to
576 square inches.
A later ruling clarified the intent of the
wing-area requirements to be that control
surfaces on a delta aircraft design could be
included in the wing area. Therefore, the
Talon Zephyr had more than the minimum
area required. That fact did not affect its
performance. It was the fastest airplane at
the 1962 Nationals, but an unfortunate
occurrence (pilot error) cost me first place.
With the best radio equipment available
in those days—reeds and Bonner Transmite
servos—the model weighed 40 ounces.
Today, with the small receivers, servos, and
radio batteries that are available, an airplane
powered by a light .15 could easily weigh
only 32 ounces. The Electric Zephyr weighs
42-48 ounces, depending on the engine and
power batteries used.
This weight “disadvantage” is not
apparent when the airplane is in the air,
except perhaps in vertical performance. The
Electric Zephyr will climb vertically, but
not forever. However, the advantages of
electric flight far outweigh the small
penalty of a slight amount of extra weight.
Electric models are clean and require
little support equipment. One can go to the
field dressed well, fly as many flights as
desired, and return home clean and
presentable to the family. I have built only
electric-powered models for more than 10
years, and I will continue to fly only
electric-powered airplanes.
If you are interested in further
information about early delta flying, refer to
the lead article in the March 1962 Model
Airplane News—“Hustler XD-7 Delta”—
the article “Flying Deltas” in the August
1962 issue of the same magazine, and the
construction article
about the Talon
Zephyr in the 1963
American Modeler
ElectricZephyr
18 MODEL AVIATION
The roots of this racy,
high-performance delta
design go back 42 years! I
In the early 1960s the author and Bob Baldwin designed the potent and famous Talon
Zephyr for RC Pylon Racing. This electric version is just as lively!
■ Weldon Smith
08sig1.QXD 5.23.03 3:22 pm Page 18
Annual. You can order copies of these
articles from the AMA library.
CONSTRUCTION
Make a fixture from straight 1 x 2-inch
wood using dimensions on plans. Buy an
extra piece of 1 x 2-inch wood; you will
need it later. Cut the trailing edge (TE) of
the fixture, measure the 45°, subtract it from
the leading edge (LE) pieces dimensioned
on the plans, and cut the LEs to that length.
Bevel the top of the TE to match the
upward curve of the ribs, then assemble.
Notch the LE pieces for the ribs. The
notches should be centered on each rib
position and approximately 3⁄16 inch to each
side. Wax the top of the fixture with
paraffin.
All sheet balsa is 3⁄32, 4- to 6-pounddensity
stock except where noted on the
plans. The LE spar looks like a boomerang
when assembled, so I will refer to it as such.
Make the boomerang, TE sheets, and LE
sheets, leaving some extra wood on all of
them at the ends. Be sure to add more sheet
behind the apex of the boomerang back to
the line indicated.
Double the front of the boomerang—the
top only—with 1⁄64 plywood back to the
same line. Pin it to the fixture at the extra
length of the ends. Cut the TE pieces to
shape, and pin the lower TE sheet to the
fixture at the excess
of the ends. Keep
the work in good
contact with the
fixture.
Cut out the ribs,
making provisions
for and mounting
the bellcranks on R-
3. Don’t forget that
you should end up
with a left and a
right! Drill holes for
the transverse
pushrod between
the bellcranks. If
you want to,
eliminate the
bellcranks and use
submicroservos in their place.
Install the ribs, gluing on each side to
the LE and TE with thin cyanoacrylate glue
(CyA). Keep the ribs square to the flat
surface under the fixture. If the ribs are too
long or too short, shift left or right slightly
so that the outboard side just touches the
LE and the rear is 1⁄8 inch ahead of the TE.
Lay a metal straightedge on top of one
wing in the spar position and score the ribs
with a razor blade. Place a 1⁄8 x 3⁄16-inch spar
in position and score the ribs on the other
side of the spar. Using a short piece of 1⁄8-
inch material as a
depth gauge, cut the
spar notches.
Repeat this process
for the other wing.
Install and
glue the spars,
joining them at the
center. Also join the
spars with a short
piece of spar
material spanwise
between the two R-
1s. Install the rear
spar in the same
manner. This spar is
only to keep the
false capstrips
following the airfoil
contour. The bottom is flat in this area so it
is unnecessary there, as are the false
capstrips.
The four LE sheets should extend at
least 1⁄4 inch beyond the LE. Each sheet can
be made from one sheet of 3 x 36-inch
balsa. Cut the sheet diagonally from one
corner to a point 3⁄4 inch ahead of the
opposite corner, then reverse ends on the
smaller piece and edge-glue the sheets
together. Trim the center end to 45°, and
trim the front portion to meet R-1.
Before installing a completed sheet, use
August 2003 19
Weldon shows off his handiwork and
gives us a feel for the size of the Zephyr.
It’s not a small model!
The fixture is on a flat surface. The “boomerang” (see text) and lower TE and ribs are installed. Notice the pushpins.
08sig1.QXD 5.23.03 3:22 pm Page 19
a long sanding block (with a length of at
least two rib spaces along the boomerang) to
brush the ribs from the spar forward until
the ribs are beveled full width. The LE of
the boomerang will also be beveled to match
the rib contour. (This is good because it
forms a gluing surface at the LE.)
I hope that when you bought material for
the fixture, you selected it to be straight;
you need that extra piece as long as the LE
now. Wax one edge of it or, if you are like
me and forget to use the waxed edge, wax
both edges. That way you won’t have a big,
ugly piece on the airplane when you fly it.
Have everything handy to do the following
because you are about to sheet one LE faster
than you have ever done before. Do a “dry
run” of what follows.
Put a bead of slow-setting glue (such as
Elmer’s) forward of the spar on each rib that
you are going to cover. Don’t put any glue
on the LE. Place the sheet in position
carefully, leaving a bit of the rear of the spar
exposed, and run thin CyA along the back of
the sheet, gluing it to the spar.
Press the sheet down to the ribs from the
spar forward by pressing with the straight
waxed piece at the spar and sliding it
forward until the piece is holding the sheet
tight to the LE of the boomerang.
Pick up the fixture and structure with
both hands, holding the waxed piece hard
against the LE, and position the whole thing
on the table vertically so you can continue to
hold it against the LE with one hand with
the fixture against your body.
Run thin CyA along the bottom of the
LE sheet where it joins the boomerang. It
takes less time to do this than it took me to
write it. Repeat for the other wing. Glue
filler blocks on the lower TE sheet for the
hinges, then use slow-setting glue (CyA if
you are daring) to install the top TE sheet.
Install capstrips and everything else on the
top except the zippered hatch, then remove
from the fixture. Whew!
Place the frame upside-down on a soft
pad and install the hardwood launching
hook, reinforcing it with 1⁄4 triangle stock. If
you will never launch with a bungee, install
a block to provide for a landing gear. (See
“Further Hints.”)
Install the bottom spar, and sheet the
bottom LE the same way you did the top,
first cutting and sanding the overhanging top
sheet and boomerang to match the contour
of the ribs. When you sand the overhang off
of the bottom sheet later, the LE will be
sharp. Leave it that way or round it slightly
if you are worried about stalling. I’ve never
been able to stall a delta unless the elevator
was adjusted to a ridiculously high limit that
no one would normally consider.
Install webbing between the top and
bottom spars with 1⁄16 sheet, or, if you would
like to have it on the front of the spars, do it
before adding the bottom LE sheet. Sheet
across the bottom of R-1s with an extra 1⁄4
inch on each side, and put a piece of 1⁄4
triangle stock there (on top of the bottom
sheet, outside R-1). Put a piece of 1⁄4 triangle
stock under the top R-1 capstrip also.
The plans call for 1⁄64 plywood in
addition on the bottom of the center-section,
but it can be left off if you will be flying on
grass fields or with a landing gear. Install
bottom capstrips on the ribs only, trim off
the ends of all sheeting at the tip ribs, and
install hollowed tips. If you made provisions
for the main aileron pushrod and installed
the bellcranks when you cut the ribs, finish
the servo and pushrod installation.
FMA Direct sells some smaller-thanmicro
servos that could be used in the
wings, flat with the arms extending out the
top, that would be more than enough power
to operate the ailerons individually. I
haven’t done that yet, but I will on my next
one. I will just build the servos into the wing
and not even use hatches for them. My
deltas don’t last very long anymore (age
brings wisdom but slower reflexes), and I’ve
only worn out a few servos throughout the
years.
Because of the large weight difference
between an electric motor and a light .15
engine, it is necessary to place the motor
farther aft, with an extension shaft to
achieve proper balance. Make the front
bearing mount for the extension shaft from
1⁄8 birch plywood. The bearing should be of
high quality. Buy one that is good for
10,000 rpm.
The bearing can be held to the mount
with three equally spaced pan-head machine
screws, drilled and tapped into the mount,
but you must drill the holes carefully so that
the screws just touch the bearing, with the
heads holding it against the mount.
If you have access to a lathe, you can
make a plastic cup to fit over the front of the
bearing, held with screws into the mount. If
you CyA the screw holes before and after
tapping the plywood, the machine screws
will hold fine. Make those provisions for
mounting the bearing before assembling the
mount.
After you are satisfied that the mount is
okay, cut roughly 1⁄4 to 1⁄2 inch off of the
delta’s nose to accept the front ring of the
nacelle, and glue the bearing mount in place
just far enough behind the nose to allow for
the face of the propeller driver to clear the
nacelle. Do this carefully. The amount you
cut from the front depends on your spinner
size. You won’t glue the front ring on yet
because you haven’t made it yet.
Now you can make the nacelle. Find a
bottle, a jar, or anything of a size that
closely matches the diameter of the spinner
you will use, minus 3⁄16 inch. Soak a piece of
3⁄32 balsa, wide enough to go around this “
mold,” in hot water spiked with ammonia.
How long you soak it depends on the
softness of the wood, but it must be pliable
enough to wrap around your form without
splitting.
When the balsa is ready, bend it around
the form and wrap it with masking tape. Let
it stay there at least overnight. Maybe it
would be better to do this before you make
the bearing mount; that way you can make
the mount instead of sitting and watching
the wet balsa dry.
Make a ring of light plywood; the outside
diameter (OD) should be your spinner’s
diameter minus 3⁄16 inch, and the inside
20 MODEL AVIATION
A view of the bottom of the model with all of the sheeting in
place. It builds into a durable and light aircraft.
This is the top of the sheeted wing assembly. Accuracy is a must
for best performance, so use the fixture!
08sig1.QXD 5.23.03 3:23 pm Page 20
22 MODEL AVIATION
ElectricZephyr
In this photo of the bottom of the Zephyr’s nose, you can clearly
see the air-intake holes. These are important!
This shows the inside of the completed hatch with the zipper
hold-downs glued on. Air outlets will be above batteries.
Photos courtesy the author Graphic Design by Lydia Whitehead
diameter (ID) should be large enough to clear
the propeller driver you will use
(approximately 1⁄2 inch less than OD). Make a
disc with a 5⁄32-inch hole in the center that fits
snug inside the ring. The ring is going to be
the front bulkhead of your nacelle, but before
you can mount it you must mount the motor.
You’re really going to do more before you
can mount the motor. The extension shaft has
to be on the motor too. You need some kind
of adapter to attach the shaft to the motor
shaft. I made mine from aluminum, with a
snug fit to the motor and a tight, undersize
hole at the front end, which required pressing
the shaft in place. These holes must be
reamed. The rear hole is reamed to fit the
motor shaft with no slop.
The assembly is held to the motor with
two diametrically opposed setscrews, so if
someone makes it for you, have that person
drill the tap holes. The shaft is 5⁄32-inch drill
rod, which is straight. Piano wire comes from
a coil that has been straightened and may not
be as straight as drill rod. Be sure to make the
shaft long enough to extend through the front
of the nacelle. You can trim it later, when you
attach your propeller adapter.
The bottom of the airfoil is at 1° to the
chord line. The thrustline is parallel to the
chord line. Therefore, you must make a
block, beveled 1° on the bottom, of a size
dependent on the motor you use, to get the
motor shaft up to the height of the position
shown on the plans, with the shaft parallel to
the chord line. Make the size so that you can
glue the bottom of a motor clamp of birch
plywood and balsa triangle stock above it and
have the shaft at the right height.
Now that the motor is mounted with the
shaft through the front bearing, slide the
plywood disc, with the plywood ring around
it, onto the shaft, back to the front of the
delta, and glue the ring in place—not the
disc. Do this carefully, and later the spinner
will match the front of the nacelle perfectly.
Shape the balsa cylinder—the nacelle—to
meet the LE sheeting, and glue it in place.
There is access to the front shaft bearing
through the nacelle opening. The new
Electric Zephyr is almost ready to cover now,
but I put the hatch on next because I still use
silk and dope, and it is easier for me to have
the airframe complete before covering. You
may want to do it differently, but I normally
cover with that good, old stuff.
Make the hatch from 3⁄32 sheet with the
grain spanwise. It should be 1 inch narrower
than the opening. I put some 1⁄64 plywood
“hooks” at the front and back to help keep it
in place after it is installed, and I put a pair of
1⁄64 plywood strips on the bottom edges to
stiffen it.
Obtain zippers (colored to match the
covering you will use) of a length that will
run from the rear forward beyond the hatch
and into the “pockets” in the front sheeting. If
you can’t find the proper length, get two that
are longer and put two or three thread stitches
around the teeth at the right length, and cut
off the excess.
Place the hatch on a flat surface, and with
the zipper closed, glue one zipper to the hatch
with the center of it 1⁄4 inch outside of the
hatch and the slide at the rear closed. Weight
the cloth until the glue sets, with the whole
thing on a flat surface. I use slow-setting glue
for this procedure. Repeat for the other side.
When it is all dry, place it in position to
Type: Electric RC Pylon Racing and sport
Wingspan: 40 inches
Power: AstroFlight FAI 25 with nine cells
Flying weight: 42-48 ounces
Construction: Balsa and plywood
Covering/finish: Silk and modeling dope
08sig1.QXD 5.23.03 3:23 pm Page 22
August 2003 25
check the fit, then glue to the framework. If
you did this correctly, all will be well and
opening the hatch to service the machine will
be as simple as opening two zippers. If the
zippers won’t open, you used too much glue;
don’t use so much that it squeezes into the
teeth.
The airplane is ready to be covered. I
suggest using silk and dope, but don’t look
for instructions on how to do that here. That is
a subject for another article.
Further Hints: Place the servos as far back
as the thickness of the airfoil allows. I do not
suggest using servos any bigger than the
largest microservos, which I have used in all
of my Talon Zephyrs for the last 11 years.
The servos are mounted on their sides. The
aileron servo is placed as far to the rear as the
rib height will allow and is offset to one side
so that it does not interfere with the elevator
pushrod.
The elevator servo is placed ahead of the
aileron pushrod so that the arm is in the center
of the wing, with a .047-inch-diameter musicwire
pushrod to the elevator horn through a
slot in the rear edge of the hatch cover. Or if
you want to be fancy, run it through a tube in
the TE. Put a slight bend in the wire if
necessary to have the rod move freely.
Good servo mounts can be made from 1⁄4 x
3⁄8 balsa. Treat the screw holes with thin CyA,
then tap 4-40. Use 4-40 socket-head nylon
screws with washers only. Cut or sand even
with the side of the servo, and glue to the
floor of the compartment while screwed to the
servo; it’s a perfect fit. A ball wrench makes
it easy to remove or set the screws.
The ailerons do not require a great deal of
throw. The bellcrank has one arm shortened,
and the pushrod between them can be
attached to the shortest hole on the servo arm.
Use .045 music wire for the pushrod from the
servo and the bellcrank-to-aileron rods. Du-
Bro makes a pushrod system (item number
113) with springs to solder onto .047 wire for
threads. The spring threads work fine on
nylon clevises.
Long, stainless 4-40 screws make good
hold-downs for the motor clamp mount. They
are nonmagnetic and, consequently, are easier
to guide into the blind nut in the bottom
plywood without being attracted to the motor
magnets.
If you want to make sure that the motor
does not twist in the mount, line the mount
with silicone rubber. Wrap thin polyethylene
film around the motor, apply silicone to the
insides of the mount, wrap it around the
motor, and squeeze it together with the
clamping screws. Let it sit for several days,
then remove the screws. The film will unroll
from the motor, and you can gently peel the
film from the silicone. Do this before
installing the clamp mount.
Cutting discs and rings from plywood is
easy on a drill press if you have a circle
cutter, which is obtainable at most hardware
stores. The cutting tool on one of these
gadgets is reversible for inside or outside
cuts.
To make a ring, cut the outside first
This is an overall view of the battery and radio compartment. There is plenty of room,
and nothing is too close to the battery.
Aft of the battery are the locations for the switch and servos. The Electronic Speed
Control is on the left rib; the receiver is on the right rib.
From the motor aft are two 30A fuses in parallel. The speed control is mounted on a rib
on the left side of the compartment.
08sig1.QXD 5.23.03 3:24 pm Page 25
26 MODEL AVIATION
Full-Size Plans Available—see page 191
08sig1.QXD 5.23.03 3:24 pm Page 26
then fasten the disc to a piece of 1-inch
pine with brads, reverse the tool bit, reset
the radius, and make the cut. All cuts
should only be slightly more than halfway,
then turn the work over and complete the
cut. This way the plywood doesn’t splinter
as the tool comes out the bottom side.
“Reversing” the tool bit means twisting
it so that the square edge of the work
comes out on the proper side. Use a
medium-slow speed on the drill press.
Watch out for the spinning tool when
you’re holding the plywood.
I used an AstroFlight FAI 25 motor on
the last Talon Zephyr, primarily because it
requires only 10 cells to provide great
power. I use nine cells in sticks of three,
Velcroed to the floor just behind the motor.
I have not tried 10 cells yet. Also, nine
cells divide up into a compact pack of
three in-line sticks of three cells.
The propeller is a 9 x 6 APC. The
receiver is Velcroed to the inside of one R-
1 rib, and the speed control is Velcroed to
the other. During the building process be
sure to apply a smooth finish to these areas
so that the Velcro will stick. The switch is
on the floor ahead of the servos.
The full antenna is in one wing in a
tube along one top spar and around into the
TE. Another option is to cut the antenna
close to the receiver and place a connector
at the break. Glue the long piece into the
wing, making a smooth bend at the tip.
The fins are made from 1⁄8 balsa, in
three pieces, with the center piece’s grain
vertical and the outer pieces’ grain more or
less parallel to the edge. If you use the
nylon angle brackets as shown on the
plans, it is easier to align the fin vertically
and apply a bead of Sig, Testors, or other
balsa glue along each side of the wing-fin
joint. You only use those glues on a doped
covering or bare wood. If you like film,
install a wider capstrip so you can remove
a strip of film where the fin attaches, then
glue it. If you’re in a hurry, use CyA!
I have used Easy Hinges fastened with
thin CyA, except that they are cut into
thirds. Two is enough for each aileron, and
four is enough for the elevator. Set the
elevator somewhat below an extension of
the bottom surface of the wing, but not as
low as “level.” Line up the ailerons with
the elevator. (You did check the elevator
for warps, didn’t you?)
Launching: There are two ways to use a
catapult launch, and either method requires
roughly 10 feet of 3⁄8-inch-diameter
surgical tubing tied to 10 feet of nylon cord
with a loop on the far end. Attach the
tubing to the ground with a sturdy stake; I
tightly tie the tubing to 18 inches of steel
rod.
If you have a helper, have him or her
grasp the leading edges outside the fins
from above and hold the delta out in front
of himself or herself while you attach the
loop (a key ring works fine). Guide your
assistant backward downwind 15 or 20
steps (or until he or she says that it is
getting too hard to step back any farther).
You should have turned on the radio
and made all checks before attaching the
ring. Hold approximately half up-elevator
and give him or her a prearranged signal to
release. Your helper merely has to raise his
or her hands, and the airplane is off and
flying.
The other launching method is to use a
pedal launcher. Hold half elevator again, or
the airplane will hit the ground near (or on)
the stake. Never open the throttle until the
line has fallen from the model. Regardless
of whether or not you think the launch is
weak, don’t help the speed with throttle.
The propeller will snarl the line, and you
will have a nasty repair to accomplish.
A streamer of silk tied near the
launching loop helps you know when the
line falls. When that happens, the airplane
should have enough speed to fly some
distance without power, so open the
throttle gently and fly it. The model has
flown well with a Speed 600 motor, so
what you use is up to you; it depends on
what sort of performance you want to
achieve: trainerlike or tiger-by-the-tail.
Landing Gear: If you must have a landing
gear, make it from 3⁄32-inch wire, including
the nose gear. Make that with two turns
around a 1⁄4-inch rod and of a length that
accommodates propeller clearance and
your takeoff surface. Place the rear gears
no farther back than 12 inches ahead of
the TE hinge line, with the strut at R-2 and
the torsion bar going to R-1. Make the
strut length so that the airplane will sit
level.
To mount the nose gear, drill a 3⁄32-inch
hole through the launch hook, 1⁄4 inch
behind where the front extension shaft
bearing plywood plate will be. Do this
before you install the hook (or block), and
keep the hole square and centered.
Later, extend that hole up through the
boomerang. Place an eyelet on top of the
coil, push the wire up through the launch
hook, and mark the wire 1⁄4 inch above the
boomerang. Remove the wire, cut where
marked, and thread 2-56.
That evening, put all of the wires in
your kitchen oven at the highest
temperature it will achieve. Leave them
alone for an hour, shut off the oven and
leave the door closed, and go to bed. In the
morning the wires will resist bending
much more than if they were not heattreated.
Install the gear using a nylon lock
nut to hold the nose gear in place (with the
extension shaft removed).
To steer the nose gear, solder a steering
arm to the eyelet, install another servo,
and make a pushrod from 1⁄32-inch wire
guided through small nylon tubing. If you
fly from a hard surface, Williams Bros.
makes nice, slim wheels that are adequate
without producing much drag.
Remember one thing on takeoff:
forcing the model off without flying speed
will result in a torque roll into the ground.
Similarly, adding a great deal of power to
go around when the aircraft is well slowed
on approach will give the same result.
You can direct any questions to me. Please
enclose a self-addressed, stamped
envelope for a reply. MA
Weldon Smith
311 Wooded Knoll Dr.
Cary IL 60010
August 2003 27
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