GEE BEE, LAIRD, CAUDRON,
Howard, and Wedell-Williams are
names that conjure up memories of
the colorful, exciting airplanes that
competed in the Thompson Trophy
races more than 50 years ago. Until
recently, most of us had to be content
with viewing old film clips or building
models of these fascinating aircraft.
Lately a fortunate few have been
able to create fullscale
replicas or
restorations of
these old race
airplanes. As a
result of a
groundswell of
such activity in
recent years, approximately 20 racing
replicas showed up at the 1995
Experimental Aircraft Association flyin
at Oshkosh, Wisconsin. And model
fliers, not to be outdone and ever on the
lookout for exciting, fun events, are
promoting various sorts of old-time race
airplane speed events in contest
schedules across the country.
The 1995 Society of Antique
Modelers old-time CL contest held at
Buder Park, Missouri, included an .049
Golden Age Speed event limited to pre-
World War II Thompson Trophy race
airplanes. The rules encouraged
participation and eliminated most
excuses one might have for not
participating. The first-time event drew
16 entries. As were the full-scale races
of old, it was exciting and was enjoyed
by spectators and participants.
The low-tech rules specified .049
reed-valve engines, allowed profile
fuselages, set a minimum wingspan of
18 inches, required authentic color-andmarkings,
and mandated a permanent
landing gear for takeoffs and landings.
Only one airplane at a time could fly,
and it was timed for six laps on sets of
control lines furnished by the club.
A rule that I considered particularly
significant permitted proxy fliers. This
allowed entrants who feared that they
couldn’t handle these fast little devils
on short lines because of lack of
experience or possible equilibrium
problems to participate.
Three-view drawings—enlarged to
the proper 18-inch wingspan—of
roughly 17 different racers were
58 MODEL AVIATION
444 4
Wittman D-12 Bonzo by Frank Beatty
Return to the age of air racing
with this legendary design
At left: A Cox
Black Widow .049
r e e d - v a l v e
engine nestles
neatly in the nose
of the model’s
profile fuselage.
07sig2.QXD 4/26/04 8:34 am Page 58
prepared from Lafayette Esquadrille club
members’ archives and were made available
for the asking.
Gus Vogele, a dedicated and talented
workhorse of the club, handcrafted a perpetual
trophy for the event—a Gee Bee Z banking
around a checkerboard pylon encased in a
protective plastic hood on a handsome base.
That was a real incentive for the trophy
hounds.
As time progressed, various members
exhibited their racers at club-meeting showand-
tells. Gus Vogele presented an
immaculately executed Folkerts SK-3 with
scratch-painted markings and an all-up weight
of 7 ounces. Ron Carr, a Speed flier of vast
experience, took great care to avoid
unnecessary or excessive weight and
produced a Pesco Special that weighed just
5.75 ounces.
Most designers adhered to the concept that
the model’s nose outline should be maintained
accurately in the profile view. To achieve that
goal, they mounted engines on aluminum
extrusions or metal brackets bolted to the
fuselage side. This offset the model-engine
centerline approximately 5⁄8 inch from the
fuselage centerline.
My first choice for a model was Tony
LeVier’s sleek Schoenfeldt Firecracker. When
I went shopping for materials and hardware
items, I learned that no commercial spinners
of the proper scale size were available and
that using largish spinners on these small
engines often caused operational headaches.
While flipping through my files I found
photographs of the 1939 version of Steve
Wittman’s D-12 Bonzo, which was flown
without a spinner. My choice was made on
that basis. I also noted that the Bonzo had a
sensible configuration. Self-imposed design
criteria were that I would keep the modelengine
centerline and the fuselage centerline
the same, install a fully enclosed control
system, and construct silk-covered wings with
scale rib spacing.
My first Bonzo, built in typical Scalebuilder’s
fashion, was “overengineered,” with
virtually every component oversized. Even
without paint, the Bonzo was much too heavy,
at more than 9 ounces. I could see that this
weight would escalate even more when I
added ballast to correct a tail-heavy condition.
I shelved that model.
The second Bonzo had components and
hardware items that were either eliminated or
reduced in size or weight. I also shifted the
wing back approximately an inch to correct
the tail-heavy situation so that no ballast
would be required. I rotated the engine 121⁄2°
to keep the engine and fuselage centerlines
identical.
The finished model weighed a tad less
than 8 ounces and balanced properly without
adding ballast. The wing area equaled 98
square inches, so the wing loading was
slightly less than 8 ounces per 100 square
inches of wing area. The scale was roughly 1
inch = 1 foot.
Contest day, August 6, 1995, was
beautiful with light winds. Equipment, judges,
and timers were on hand, and contestants
were lining up with their racers. The 16
entries included two Gee Bees, three Laird-
Turner racers, two Mr. Mulligans, three
Firecrackers, a Caudron, a Chester Goon, a
Marcoux Bromberg, a Miss Los Angeles, a
Folkerts, and a Bonzo.
Early on, Ron Carr’s Pesco Special set a
mark for all to shoot for, with a 60.40 mph
speed. Alan Arunski’s Firecracker took a bad
bounce, flew straight at him, changed its mind
at the last possible moment, turned tail, flew
into the proper orbit, and dutifully qualified
for its master.
Tim Pansic’s Firecracker made a serious
challenge with 58.06 mph. Tim’s model was
powered with a collectible Cox Space Hopper
(the oldie with the beam mounts), and many
marveled that Tim would put such an engine
at risk.
Bob Arata had chosen the Gee Bee R-1
because, as he put it, “When you think of the
Thompson Trophy races, you think of the Gee
Bee.” Of all the models entered, Bob’s made
the prettiest flight—a most graceful, long
rolling takeoff, followed by a smooth, rocksteady
flight; a long, graceful storybook
approach; and a two-point landing and
extended rollout. I was impressed.
Quite a few models tipped over on takeoff
attempts. Others charged on with propellers
thrashing the asphalt until they managed to
get airborne. This drilled into all observers the
relationships between wheel locations and
good ground handling. Scale wheel locations
don’t always hack it, especially when you’re
using small wheels on small models.
My Bonzo, which was proxy-flown by
July 2004 59
444 4
The 1⁄8 balsa profile fuselage core features weight-saving cutouts. The aircraft’s entire
control system is enclosed for less drag.
Designated proxy flier John Moll (left), Ron Carr (center), and the author prepare the
Bonzo for an official flight.
Photos courtesy the author
07sig2.QXD 4/26/04 8:35 am Page 59
sheet-balsa center-section bottom covering in
place. Make a rib cut-out template (see
drawings) and cut 42 ribs from 1⁄16 sheet balsa.
Fit and cement these ribs into place.
Cement the 1⁄16 x 1⁄2-inch plywood
bellcrank support in place, followed by the
four “A” ribs. When dry, lift the assembly
from the building board and add the 1⁄2-ounce
lead outboard tip weight. (Some club
members used a penny on their models.)
Fit the four basswood rigging wire locator
blocks between the ribs, and drill the 1⁄32-inchdiameter
holes as shown. Make the bellcrank
and leadout-wire assembly, slide the leadout
wires through the ribs, and bolt the bellcrank
to the plywood support.
Cover the top side of the center-section
with 1⁄16 sheet balsa. Cut the wingtips to
outline shape, and then carve and sand the
LEs, TEs, and wingtips to shape. Brush
several coats of clear dope over the
framework outline, sand lightly, cover with
silk, and set aside.
Tail Assembly: Notice on the plans that two
outlines are provided for the tail assembly.
The smaller of the two is the scale outline.
Although the model can be built and flown
successfully with the smaller tail assembly, I
recommend the enlarged unit. The model will
handle better, especially upwind on blustery
days.
The stabilizer and elevators are made from
1⁄8 sheet balsa. Fit the elevators with a
homemade elevator-horn assembly. (It can be
made lighter than commercially available
units.) Mate the elevators to the stabilizer with
nylon Klett RK-4 flex hinge points.
Cut the vertical fin and rudder from 1⁄8
sheet balsa. Coat with clear dope, sand lightly,
cover the fin, rudder, stabilizer, and elevators
with silk, and set aside.
Undercarriage: Bend the two 1⁄16-inchdiameter
music-wire landing-gear segments.
Bind their upper sections with fine, soft
copper wire and solder together. Drill a 5⁄32-
inch-diameter hole through the center of a 3⁄4-
inch length of 1⁄4 square basswood. Use needle
files to elongate the hole to an oval shape, slip
the undercarriage unit into it, epoxy, and set
aside.
Fuselage: Stack and tack-glue one piece of 1⁄8
x 4 x 20-inch sheet balsa, two pieces of 1⁄16 x 4
x 20-inch sheet balsa, and two pieces of 1⁄32 x
4 x 61⁄2-inch plywood, with the two plywood
pieces on top. Trace the fuselage outline with
the wing, stabilizer, engine, and firewall
cutouts included, and make these cuts on a
jigsaw. Check the wing and stabilizer cutouts
for fit.
Separate the plywood members from this
stack. Mark the undercarriage-support-block
locations, and make this cutout through all
60 MODEL AVIATION
1⁄2A Golden Age Speed Rules 1997
1. Any Cox .049 reed valve engine with
standard (low compression) glow head,
Cox tank only (except for
Spacehopper), may be used with 15%
Nitro Fuel (supplied). Cox prop,
unmodified except for balancing
(5D-3P) may be used.
2. Racers must be of full profile, builtup,
solid or combination structure of a
1929 through 1939 Thompson Trophy
Racer. (A photo and/or 3-view should
be available for proof.)
3. Minimum wing span is 18 inches.
(Bi-planes minimum top wingspan 12
inches, total span both upper and
lower wings 18 inches min.) Minimum
lead-out length is 12 inches.
4. Racer must look like the full scale
aircraft to include color, markings, and
wing struts, if used. No scale judging
nor scale points will be awarded.
5. Take-off and landing gear is
required, as all flights will be R.O.G.
(rise-off-ground).
6. Three attempts are allowed to make
two (2) official flights. Fastest time of
the two will be used for scoring.
7. Speed run will be time for six (6)
laps (1⁄4 mile) beginning one (1) lap
after a signal by the pilot.
8. Whipping, leading or towing is
prohibited.
9. 34-foot KevlarTM control lines will be
supplied by the contest committee.
10. Only one model per entrant is
allowed.
11. Proxy Fliers are allowed. A typical lineup of Golden Age racer
entries sits in front of a Bendix pylon that
Tim Pansic designed and built.
Wittman D-12 Bonzo
Type: 1⁄2A Golden Age racer
Wingspan: 18.125 inches
Engine: Cox Black Widow .049
Flying weight: 8 ounces
Construction: Balsa and plywood
Covering/finish: fiberglass cloth
and modeling dope
John Moll, had the engine sag on its first
attempt, and then an ill-advised propeller
change relegated the model to the middle of
the pack with a 49.18 mph speed.
Gus Vogele’s Folkerts SK-3 tipped over
on its nose, the engine went into reverse, and
the model tried to make like a canard. John
Moll saved the airplane with a one-hand catch
at the expense of a small nick on one finger.
The SK-3 dutifully qualified on a later
attempt.
An ailing Alan Van Artsalen had left the
contest site, but he recovered sufficiently to
return and make his last official attempt. Alan
fired up his Roscoe Turner 2 RT-1, and
anyone who heard its screaming engine knew
that he had a winner if the engine didn’t sag
out on him. It didn’t, and it clocked the
winning time of 62.50 mph. Way to go, Alan.
The old-time racing-airplane events we
read about in the modeling press are usually
the spectacular contests that require serious
commitment to research, engineering, labor,
time, and cost. Clubs can have good
participation and a great deal of fun by
including entry-level events such as the one I
just described. That contest attracted two
father-and-son teams and people we would
normally have thought of as Stunt, Speed,
sport, or Scale-oriented fliers. I’m looking
forward to future Golden Age Thompson
Trophy races at Buder Park.
CONSTRUCTION
Wing: Tape 20-inch lengths of 1⁄4 x 3⁄8-inch
balsa LE and 3⁄16 x 1-inch balsa TE stock
together so that you can cut the 1⁄16-inch
notches for the ribs at the same time in both
pieces with a razor saw or a modeling table
saw. Cover the plans with plastic or waxed
paper, and pin these members over the plans.
Fit the 3⁄8 x 3⁄4-inch tip blocks and the 1⁄16
444 4
07sig2.QXD 4/26/04 8:36 am Page 60
three balsa members. Separate the balsa
members. Take up the 1⁄8 sheet-balsa core
member, mark off the lightening-hole and
pushrod-tunnel cutouts, and make those cuts.
The rear of the fuselage is now floppy and
difficult to maintain in alignment, so cement
several 1⁄8 square balsa stiffeners to span
across these cutouts for now.
Final Assembly: Cut a slot in the wing
center-section sheet covering to allow
installation and passage for the elevator
pushrod. Slip the wing and stabilizer just
short of their true locations in the fuselage
while you eyeball the 1⁄32-inch-diameter
elevator pushrod wire and bend it to size.
Solder the bellcrank-to-pushrod connection,
and then locate and cement the wing to its
proper location in the fuselage core member.
Pass two hardwood guides onto the pushrod,
and cement them in their slots. Now you can
locate and cement the stabilizer. Solder the
elevator pushrod-to-horn connection, and
check the control system for freedom of
movement.
Cement into position the 1⁄16-inch
fuselage panel on the side opposite the
temporary stiffeners. Remove the stiffeners,
and cement the remaining panel into
position. Chamfer the rear edges of the 1⁄32
plywood fuselage stiffeners, and cement
them in place.
Cut out the 1⁄4 plywood engine mount.
You might be satisfied to use wood screws to
mount the Cox engine. I used blind mounting
nuts. It’s your call; either will work. Cement
the engine mount and balsa fairing blocks
into position.
Epoxy the undercarriage assembly into its
slot. Add the vertical fin, rudder,
undercarriage strut fairings, and tail skid. I
drilled 1⁄8-inch-diameter holes and filled them
with short lengths of 1⁄8-inch-diameter birch
dowels for the rear rigging wire locators in
the fuselage sides. I also bent and installed a
wire hoop in the fuselage top at the CG
location. You will suspend the model from
this point later to determine whether or not it
is balanced properly.
You can use a hand-tool burr to gouge
62 MODEL AVIATION
clearances for the engine cylinder head and
needle valve on the starboard side of the
fuselage nose. Also cut a hole in the fuselage
nose ahead of the engine cylinder to admit
additional cooling air to the engine. Mark and
drill all 1⁄32-inch-diameter rigging locating holes
in the fuselage, fin, and stabilizer.
Finish: I covered the fuselage with Sig .56-
ounce fiberglass using clear dope as an
adhesive. I brushed the entire model with four
coats of clear dope, sprayed on four coats of
filler-coat primer, and sprayed on six coats of
Stearman Red. I wet- or dry-sanded (400 grit)
these layers after I applied every second or third
coat.
I masked off the registration numbers and
canopy and sprayed them black, and I masked
off and sprayed the white racing numbers. I
applied the registration numbers on the fin
freehand using a No. 2 Alvin technical pen and
india ink, which I protected with a super-thin
coat of clear dope. I cemented silver-doped,
half-round dummy exhaust-stack headers to
the cowling.
I used a needle to sew black button thread
through the rigging locator holes. I drew these
taut and then fixed them with cyanoacrylate
glue.
If you haven’t already done so, bend the
loops in the leadout-wire ends. According to
the contest rules we were using, they must be a
minimum of 12 inches from the centerline of
the model. Solder the wheels on and bolt the
engine to the firewall.
Suspend the completed model from the CG
loop. If it does not hang in a slightly nosedown
attitude, the model is tail-heavy and will
be an unstable flier. Add weight to the nose if
this condition exists with your model. The
prototype Bonzo assumed roughly a 15° nosedown
attitude with no ballast added.
Flying: Select a calm day and a smooth paved
surface for the initial test flight. The prototype
takes off quickly with little tendency to nose
over. The flight pattern is smooth and steady,
with little or no fore and aft oscillation
patterns. The model gains a bit of altitude on
the upwind side of the circle (normal) and
loses a bit more altitude than it gained when it
enters the downwind side of the circle. That’s
something to keep in mind.
Landing approaches are long and graceful,
but the model does tend to bounce a few times
before it settles into its rollout. It is not prone
to nosing over or doing the cartwheel bit.
Using a 5 x 4 Tornado propeller, the Bonzo
has been clocked at slightly faster than 56
mph—not too bad for an overweight little
beastie that has quite a bit of scale detail built
into it.
If you like beautiful models, build the Bonzo
as I’ve described and have fun with it. If you
are a speedoholic, put this model on a diet and
experiment with fuels and propellers. Tweak
the Bonzo just right, and you might have the
best of both worlds: looks and speed. MA
Frank Beatty
2608 Pontoon Rd.
Granite City IL 62040
07sig2.QXD 4/26/04 8:36 am Page 62
Edition: Model Aviation - 2004/07
Page Numbers: 58,59,60,61,62
Edition: Model Aviation - 2004/07
Page Numbers: 58,59,60,61,62
GEE BEE, LAIRD, CAUDRON,
Howard, and Wedell-Williams are
names that conjure up memories of
the colorful, exciting airplanes that
competed in the Thompson Trophy
races more than 50 years ago. Until
recently, most of us had to be content
with viewing old film clips or building
models of these fascinating aircraft.
Lately a fortunate few have been
able to create fullscale
replicas or
restorations of
these old race
airplanes. As a
result of a
groundswell of
such activity in
recent years, approximately 20 racing
replicas showed up at the 1995
Experimental Aircraft Association flyin
at Oshkosh, Wisconsin. And model
fliers, not to be outdone and ever on the
lookout for exciting, fun events, are
promoting various sorts of old-time race
airplane speed events in contest
schedules across the country.
The 1995 Society of Antique
Modelers old-time CL contest held at
Buder Park, Missouri, included an .049
Golden Age Speed event limited to pre-
World War II Thompson Trophy race
airplanes. The rules encouraged
participation and eliminated most
excuses one might have for not
participating. The first-time event drew
16 entries. As were the full-scale races
of old, it was exciting and was enjoyed
by spectators and participants.
The low-tech rules specified .049
reed-valve engines, allowed profile
fuselages, set a minimum wingspan of
18 inches, required authentic color-andmarkings,
and mandated a permanent
landing gear for takeoffs and landings.
Only one airplane at a time could fly,
and it was timed for six laps on sets of
control lines furnished by the club.
A rule that I considered particularly
significant permitted proxy fliers. This
allowed entrants who feared that they
couldn’t handle these fast little devils
on short lines because of lack of
experience or possible equilibrium
problems to participate.
Three-view drawings—enlarged to
the proper 18-inch wingspan—of
roughly 17 different racers were
58 MODEL AVIATION
444 4
Wittman D-12 Bonzo by Frank Beatty
Return to the age of air racing
with this legendary design
At left: A Cox
Black Widow .049
r e e d - v a l v e
engine nestles
neatly in the nose
of the model’s
profile fuselage.
07sig2.QXD 4/26/04 8:34 am Page 58
prepared from Lafayette Esquadrille club
members’ archives and were made available
for the asking.
Gus Vogele, a dedicated and talented
workhorse of the club, handcrafted a perpetual
trophy for the event—a Gee Bee Z banking
around a checkerboard pylon encased in a
protective plastic hood on a handsome base.
That was a real incentive for the trophy
hounds.
As time progressed, various members
exhibited their racers at club-meeting showand-
tells. Gus Vogele presented an
immaculately executed Folkerts SK-3 with
scratch-painted markings and an all-up weight
of 7 ounces. Ron Carr, a Speed flier of vast
experience, took great care to avoid
unnecessary or excessive weight and
produced a Pesco Special that weighed just
5.75 ounces.
Most designers adhered to the concept that
the model’s nose outline should be maintained
accurately in the profile view. To achieve that
goal, they mounted engines on aluminum
extrusions or metal brackets bolted to the
fuselage side. This offset the model-engine
centerline approximately 5⁄8 inch from the
fuselage centerline.
My first choice for a model was Tony
LeVier’s sleek Schoenfeldt Firecracker. When
I went shopping for materials and hardware
items, I learned that no commercial spinners
of the proper scale size were available and
that using largish spinners on these small
engines often caused operational headaches.
While flipping through my files I found
photographs of the 1939 version of Steve
Wittman’s D-12 Bonzo, which was flown
without a spinner. My choice was made on
that basis. I also noted that the Bonzo had a
sensible configuration. Self-imposed design
criteria were that I would keep the modelengine
centerline and the fuselage centerline
the same, install a fully enclosed control
system, and construct silk-covered wings with
scale rib spacing.
My first Bonzo, built in typical Scalebuilder’s
fashion, was “overengineered,” with
virtually every component oversized. Even
without paint, the Bonzo was much too heavy,
at more than 9 ounces. I could see that this
weight would escalate even more when I
added ballast to correct a tail-heavy condition.
I shelved that model.
The second Bonzo had components and
hardware items that were either eliminated or
reduced in size or weight. I also shifted the
wing back approximately an inch to correct
the tail-heavy situation so that no ballast
would be required. I rotated the engine 121⁄2°
to keep the engine and fuselage centerlines
identical.
The finished model weighed a tad less
than 8 ounces and balanced properly without
adding ballast. The wing area equaled 98
square inches, so the wing loading was
slightly less than 8 ounces per 100 square
inches of wing area. The scale was roughly 1
inch = 1 foot.
Contest day, August 6, 1995, was
beautiful with light winds. Equipment, judges,
and timers were on hand, and contestants
were lining up with their racers. The 16
entries included two Gee Bees, three Laird-
Turner racers, two Mr. Mulligans, three
Firecrackers, a Caudron, a Chester Goon, a
Marcoux Bromberg, a Miss Los Angeles, a
Folkerts, and a Bonzo.
Early on, Ron Carr’s Pesco Special set a
mark for all to shoot for, with a 60.40 mph
speed. Alan Arunski’s Firecracker took a bad
bounce, flew straight at him, changed its mind
at the last possible moment, turned tail, flew
into the proper orbit, and dutifully qualified
for its master.
Tim Pansic’s Firecracker made a serious
challenge with 58.06 mph. Tim’s model was
powered with a collectible Cox Space Hopper
(the oldie with the beam mounts), and many
marveled that Tim would put such an engine
at risk.
Bob Arata had chosen the Gee Bee R-1
because, as he put it, “When you think of the
Thompson Trophy races, you think of the Gee
Bee.” Of all the models entered, Bob’s made
the prettiest flight—a most graceful, long
rolling takeoff, followed by a smooth, rocksteady
flight; a long, graceful storybook
approach; and a two-point landing and
extended rollout. I was impressed.
Quite a few models tipped over on takeoff
attempts. Others charged on with propellers
thrashing the asphalt until they managed to
get airborne. This drilled into all observers the
relationships between wheel locations and
good ground handling. Scale wheel locations
don’t always hack it, especially when you’re
using small wheels on small models.
My Bonzo, which was proxy-flown by
July 2004 59
444 4
The 1⁄8 balsa profile fuselage core features weight-saving cutouts. The aircraft’s entire
control system is enclosed for less drag.
Designated proxy flier John Moll (left), Ron Carr (center), and the author prepare the
Bonzo for an official flight.
Photos courtesy the author
07sig2.QXD 4/26/04 8:35 am Page 59
sheet-balsa center-section bottom covering in
place. Make a rib cut-out template (see
drawings) and cut 42 ribs from 1⁄16 sheet balsa.
Fit and cement these ribs into place.
Cement the 1⁄16 x 1⁄2-inch plywood
bellcrank support in place, followed by the
four “A” ribs. When dry, lift the assembly
from the building board and add the 1⁄2-ounce
lead outboard tip weight. (Some club
members used a penny on their models.)
Fit the four basswood rigging wire locator
blocks between the ribs, and drill the 1⁄32-inchdiameter
holes as shown. Make the bellcrank
and leadout-wire assembly, slide the leadout
wires through the ribs, and bolt the bellcrank
to the plywood support.
Cover the top side of the center-section
with 1⁄16 sheet balsa. Cut the wingtips to
outline shape, and then carve and sand the
LEs, TEs, and wingtips to shape. Brush
several coats of clear dope over the
framework outline, sand lightly, cover with
silk, and set aside.
Tail Assembly: Notice on the plans that two
outlines are provided for the tail assembly.
The smaller of the two is the scale outline.
Although the model can be built and flown
successfully with the smaller tail assembly, I
recommend the enlarged unit. The model will
handle better, especially upwind on blustery
days.
The stabilizer and elevators are made from
1⁄8 sheet balsa. Fit the elevators with a
homemade elevator-horn assembly. (It can be
made lighter than commercially available
units.) Mate the elevators to the stabilizer with
nylon Klett RK-4 flex hinge points.
Cut the vertical fin and rudder from 1⁄8
sheet balsa. Coat with clear dope, sand lightly,
cover the fin, rudder, stabilizer, and elevators
with silk, and set aside.
Undercarriage: Bend the two 1⁄16-inchdiameter
music-wire landing-gear segments.
Bind their upper sections with fine, soft
copper wire and solder together. Drill a 5⁄32-
inch-diameter hole through the center of a 3⁄4-
inch length of 1⁄4 square basswood. Use needle
files to elongate the hole to an oval shape, slip
the undercarriage unit into it, epoxy, and set
aside.
Fuselage: Stack and tack-glue one piece of 1⁄8
x 4 x 20-inch sheet balsa, two pieces of 1⁄16 x 4
x 20-inch sheet balsa, and two pieces of 1⁄32 x
4 x 61⁄2-inch plywood, with the two plywood
pieces on top. Trace the fuselage outline with
the wing, stabilizer, engine, and firewall
cutouts included, and make these cuts on a
jigsaw. Check the wing and stabilizer cutouts
for fit.
Separate the plywood members from this
stack. Mark the undercarriage-support-block
locations, and make this cutout through all
60 MODEL AVIATION
1⁄2A Golden Age Speed Rules 1997
1. Any Cox .049 reed valve engine with
standard (low compression) glow head,
Cox tank only (except for
Spacehopper), may be used with 15%
Nitro Fuel (supplied). Cox prop,
unmodified except for balancing
(5D-3P) may be used.
2. Racers must be of full profile, builtup,
solid or combination structure of a
1929 through 1939 Thompson Trophy
Racer. (A photo and/or 3-view should
be available for proof.)
3. Minimum wing span is 18 inches.
(Bi-planes minimum top wingspan 12
inches, total span both upper and
lower wings 18 inches min.) Minimum
lead-out length is 12 inches.
4. Racer must look like the full scale
aircraft to include color, markings, and
wing struts, if used. No scale judging
nor scale points will be awarded.
5. Take-off and landing gear is
required, as all flights will be R.O.G.
(rise-off-ground).
6. Three attempts are allowed to make
two (2) official flights. Fastest time of
the two will be used for scoring.
7. Speed run will be time for six (6)
laps (1⁄4 mile) beginning one (1) lap
after a signal by the pilot.
8. Whipping, leading or towing is
prohibited.
9. 34-foot KevlarTM control lines will be
supplied by the contest committee.
10. Only one model per entrant is
allowed.
11. Proxy Fliers are allowed. A typical lineup of Golden Age racer
entries sits in front of a Bendix pylon that
Tim Pansic designed and built.
Wittman D-12 Bonzo
Type: 1⁄2A Golden Age racer
Wingspan: 18.125 inches
Engine: Cox Black Widow .049
Flying weight: 8 ounces
Construction: Balsa and plywood
Covering/finish: fiberglass cloth
and modeling dope
John Moll, had the engine sag on its first
attempt, and then an ill-advised propeller
change relegated the model to the middle of
the pack with a 49.18 mph speed.
Gus Vogele’s Folkerts SK-3 tipped over
on its nose, the engine went into reverse, and
the model tried to make like a canard. John
Moll saved the airplane with a one-hand catch
at the expense of a small nick on one finger.
The SK-3 dutifully qualified on a later
attempt.
An ailing Alan Van Artsalen had left the
contest site, but he recovered sufficiently to
return and make his last official attempt. Alan
fired up his Roscoe Turner 2 RT-1, and
anyone who heard its screaming engine knew
that he had a winner if the engine didn’t sag
out on him. It didn’t, and it clocked the
winning time of 62.50 mph. Way to go, Alan.
The old-time racing-airplane events we
read about in the modeling press are usually
the spectacular contests that require serious
commitment to research, engineering, labor,
time, and cost. Clubs can have good
participation and a great deal of fun by
including entry-level events such as the one I
just described. That contest attracted two
father-and-son teams and people we would
normally have thought of as Stunt, Speed,
sport, or Scale-oriented fliers. I’m looking
forward to future Golden Age Thompson
Trophy races at Buder Park.
CONSTRUCTION
Wing: Tape 20-inch lengths of 1⁄4 x 3⁄8-inch
balsa LE and 3⁄16 x 1-inch balsa TE stock
together so that you can cut the 1⁄16-inch
notches for the ribs at the same time in both
pieces with a razor saw or a modeling table
saw. Cover the plans with plastic or waxed
paper, and pin these members over the plans.
Fit the 3⁄8 x 3⁄4-inch tip blocks and the 1⁄16
444 4
07sig2.QXD 4/26/04 8:36 am Page 60
three balsa members. Separate the balsa
members. Take up the 1⁄8 sheet-balsa core
member, mark off the lightening-hole and
pushrod-tunnel cutouts, and make those cuts.
The rear of the fuselage is now floppy and
difficult to maintain in alignment, so cement
several 1⁄8 square balsa stiffeners to span
across these cutouts for now.
Final Assembly: Cut a slot in the wing
center-section sheet covering to allow
installation and passage for the elevator
pushrod. Slip the wing and stabilizer just
short of their true locations in the fuselage
while you eyeball the 1⁄32-inch-diameter
elevator pushrod wire and bend it to size.
Solder the bellcrank-to-pushrod connection,
and then locate and cement the wing to its
proper location in the fuselage core member.
Pass two hardwood guides onto the pushrod,
and cement them in their slots. Now you can
locate and cement the stabilizer. Solder the
elevator pushrod-to-horn connection, and
check the control system for freedom of
movement.
Cement into position the 1⁄16-inch
fuselage panel on the side opposite the
temporary stiffeners. Remove the stiffeners,
and cement the remaining panel into
position. Chamfer the rear edges of the 1⁄32
plywood fuselage stiffeners, and cement
them in place.
Cut out the 1⁄4 plywood engine mount.
You might be satisfied to use wood screws to
mount the Cox engine. I used blind mounting
nuts. It’s your call; either will work. Cement
the engine mount and balsa fairing blocks
into position.
Epoxy the undercarriage assembly into its
slot. Add the vertical fin, rudder,
undercarriage strut fairings, and tail skid. I
drilled 1⁄8-inch-diameter holes and filled them
with short lengths of 1⁄8-inch-diameter birch
dowels for the rear rigging wire locators in
the fuselage sides. I also bent and installed a
wire hoop in the fuselage top at the CG
location. You will suspend the model from
this point later to determine whether or not it
is balanced properly.
You can use a hand-tool burr to gouge
62 MODEL AVIATION
clearances for the engine cylinder head and
needle valve on the starboard side of the
fuselage nose. Also cut a hole in the fuselage
nose ahead of the engine cylinder to admit
additional cooling air to the engine. Mark and
drill all 1⁄32-inch-diameter rigging locating holes
in the fuselage, fin, and stabilizer.
Finish: I covered the fuselage with Sig .56-
ounce fiberglass using clear dope as an
adhesive. I brushed the entire model with four
coats of clear dope, sprayed on four coats of
filler-coat primer, and sprayed on six coats of
Stearman Red. I wet- or dry-sanded (400 grit)
these layers after I applied every second or third
coat.
I masked off the registration numbers and
canopy and sprayed them black, and I masked
off and sprayed the white racing numbers. I
applied the registration numbers on the fin
freehand using a No. 2 Alvin technical pen and
india ink, which I protected with a super-thin
coat of clear dope. I cemented silver-doped,
half-round dummy exhaust-stack headers to
the cowling.
I used a needle to sew black button thread
through the rigging locator holes. I drew these
taut and then fixed them with cyanoacrylate
glue.
If you haven’t already done so, bend the
loops in the leadout-wire ends. According to
the contest rules we were using, they must be a
minimum of 12 inches from the centerline of
the model. Solder the wheels on and bolt the
engine to the firewall.
Suspend the completed model from the CG
loop. If it does not hang in a slightly nosedown
attitude, the model is tail-heavy and will
be an unstable flier. Add weight to the nose if
this condition exists with your model. The
prototype Bonzo assumed roughly a 15° nosedown
attitude with no ballast added.
Flying: Select a calm day and a smooth paved
surface for the initial test flight. The prototype
takes off quickly with little tendency to nose
over. The flight pattern is smooth and steady,
with little or no fore and aft oscillation
patterns. The model gains a bit of altitude on
the upwind side of the circle (normal) and
loses a bit more altitude than it gained when it
enters the downwind side of the circle. That’s
something to keep in mind.
Landing approaches are long and graceful,
but the model does tend to bounce a few times
before it settles into its rollout. It is not prone
to nosing over or doing the cartwheel bit.
Using a 5 x 4 Tornado propeller, the Bonzo
has been clocked at slightly faster than 56
mph—not too bad for an overweight little
beastie that has quite a bit of scale detail built
into it.
If you like beautiful models, build the Bonzo
as I’ve described and have fun with it. If you
are a speedoholic, put this model on a diet and
experiment with fuels and propellers. Tweak
the Bonzo just right, and you might have the
best of both worlds: looks and speed. MA
Frank Beatty
2608 Pontoon Rd.
Granite City IL 62040
07sig2.QXD 4/26/04 8:36 am Page 62
Edition: Model Aviation - 2004/07
Page Numbers: 58,59,60,61,62
GEE BEE, LAIRD, CAUDRON,
Howard, and Wedell-Williams are
names that conjure up memories of
the colorful, exciting airplanes that
competed in the Thompson Trophy
races more than 50 years ago. Until
recently, most of us had to be content
with viewing old film clips or building
models of these fascinating aircraft.
Lately a fortunate few have been
able to create fullscale
replicas or
restorations of
these old race
airplanes. As a
result of a
groundswell of
such activity in
recent years, approximately 20 racing
replicas showed up at the 1995
Experimental Aircraft Association flyin
at Oshkosh, Wisconsin. And model
fliers, not to be outdone and ever on the
lookout for exciting, fun events, are
promoting various sorts of old-time race
airplane speed events in contest
schedules across the country.
The 1995 Society of Antique
Modelers old-time CL contest held at
Buder Park, Missouri, included an .049
Golden Age Speed event limited to pre-
World War II Thompson Trophy race
airplanes. The rules encouraged
participation and eliminated most
excuses one might have for not
participating. The first-time event drew
16 entries. As were the full-scale races
of old, it was exciting and was enjoyed
by spectators and participants.
The low-tech rules specified .049
reed-valve engines, allowed profile
fuselages, set a minimum wingspan of
18 inches, required authentic color-andmarkings,
and mandated a permanent
landing gear for takeoffs and landings.
Only one airplane at a time could fly,
and it was timed for six laps on sets of
control lines furnished by the club.
A rule that I considered particularly
significant permitted proxy fliers. This
allowed entrants who feared that they
couldn’t handle these fast little devils
on short lines because of lack of
experience or possible equilibrium
problems to participate.
Three-view drawings—enlarged to
the proper 18-inch wingspan—of
roughly 17 different racers were
58 MODEL AVIATION
444 4
Wittman D-12 Bonzo by Frank Beatty
Return to the age of air racing
with this legendary design
At left: A Cox
Black Widow .049
r e e d - v a l v e
engine nestles
neatly in the nose
of the model’s
profile fuselage.
07sig2.QXD 4/26/04 8:34 am Page 58
prepared from Lafayette Esquadrille club
members’ archives and were made available
for the asking.
Gus Vogele, a dedicated and talented
workhorse of the club, handcrafted a perpetual
trophy for the event—a Gee Bee Z banking
around a checkerboard pylon encased in a
protective plastic hood on a handsome base.
That was a real incentive for the trophy
hounds.
As time progressed, various members
exhibited their racers at club-meeting showand-
tells. Gus Vogele presented an
immaculately executed Folkerts SK-3 with
scratch-painted markings and an all-up weight
of 7 ounces. Ron Carr, a Speed flier of vast
experience, took great care to avoid
unnecessary or excessive weight and
produced a Pesco Special that weighed just
5.75 ounces.
Most designers adhered to the concept that
the model’s nose outline should be maintained
accurately in the profile view. To achieve that
goal, they mounted engines on aluminum
extrusions or metal brackets bolted to the
fuselage side. This offset the model-engine
centerline approximately 5⁄8 inch from the
fuselage centerline.
My first choice for a model was Tony
LeVier’s sleek Schoenfeldt Firecracker. When
I went shopping for materials and hardware
items, I learned that no commercial spinners
of the proper scale size were available and
that using largish spinners on these small
engines often caused operational headaches.
While flipping through my files I found
photographs of the 1939 version of Steve
Wittman’s D-12 Bonzo, which was flown
without a spinner. My choice was made on
that basis. I also noted that the Bonzo had a
sensible configuration. Self-imposed design
criteria were that I would keep the modelengine
centerline and the fuselage centerline
the same, install a fully enclosed control
system, and construct silk-covered wings with
scale rib spacing.
My first Bonzo, built in typical Scalebuilder’s
fashion, was “overengineered,” with
virtually every component oversized. Even
without paint, the Bonzo was much too heavy,
at more than 9 ounces. I could see that this
weight would escalate even more when I
added ballast to correct a tail-heavy condition.
I shelved that model.
The second Bonzo had components and
hardware items that were either eliminated or
reduced in size or weight. I also shifted the
wing back approximately an inch to correct
the tail-heavy situation so that no ballast
would be required. I rotated the engine 121⁄2°
to keep the engine and fuselage centerlines
identical.
The finished model weighed a tad less
than 8 ounces and balanced properly without
adding ballast. The wing area equaled 98
square inches, so the wing loading was
slightly less than 8 ounces per 100 square
inches of wing area. The scale was roughly 1
inch = 1 foot.
Contest day, August 6, 1995, was
beautiful with light winds. Equipment, judges,
and timers were on hand, and contestants
were lining up with their racers. The 16
entries included two Gee Bees, three Laird-
Turner racers, two Mr. Mulligans, three
Firecrackers, a Caudron, a Chester Goon, a
Marcoux Bromberg, a Miss Los Angeles, a
Folkerts, and a Bonzo.
Early on, Ron Carr’s Pesco Special set a
mark for all to shoot for, with a 60.40 mph
speed. Alan Arunski’s Firecracker took a bad
bounce, flew straight at him, changed its mind
at the last possible moment, turned tail, flew
into the proper orbit, and dutifully qualified
for its master.
Tim Pansic’s Firecracker made a serious
challenge with 58.06 mph. Tim’s model was
powered with a collectible Cox Space Hopper
(the oldie with the beam mounts), and many
marveled that Tim would put such an engine
at risk.
Bob Arata had chosen the Gee Bee R-1
because, as he put it, “When you think of the
Thompson Trophy races, you think of the Gee
Bee.” Of all the models entered, Bob’s made
the prettiest flight—a most graceful, long
rolling takeoff, followed by a smooth, rocksteady
flight; a long, graceful storybook
approach; and a two-point landing and
extended rollout. I was impressed.
Quite a few models tipped over on takeoff
attempts. Others charged on with propellers
thrashing the asphalt until they managed to
get airborne. This drilled into all observers the
relationships between wheel locations and
good ground handling. Scale wheel locations
don’t always hack it, especially when you’re
using small wheels on small models.
My Bonzo, which was proxy-flown by
July 2004 59
444 4
The 1⁄8 balsa profile fuselage core features weight-saving cutouts. The aircraft’s entire
control system is enclosed for less drag.
Designated proxy flier John Moll (left), Ron Carr (center), and the author prepare the
Bonzo for an official flight.
Photos courtesy the author
07sig2.QXD 4/26/04 8:35 am Page 59
sheet-balsa center-section bottom covering in
place. Make a rib cut-out template (see
drawings) and cut 42 ribs from 1⁄16 sheet balsa.
Fit and cement these ribs into place.
Cement the 1⁄16 x 1⁄2-inch plywood
bellcrank support in place, followed by the
four “A” ribs. When dry, lift the assembly
from the building board and add the 1⁄2-ounce
lead outboard tip weight. (Some club
members used a penny on their models.)
Fit the four basswood rigging wire locator
blocks between the ribs, and drill the 1⁄32-inchdiameter
holes as shown. Make the bellcrank
and leadout-wire assembly, slide the leadout
wires through the ribs, and bolt the bellcrank
to the plywood support.
Cover the top side of the center-section
with 1⁄16 sheet balsa. Cut the wingtips to
outline shape, and then carve and sand the
LEs, TEs, and wingtips to shape. Brush
several coats of clear dope over the
framework outline, sand lightly, cover with
silk, and set aside.
Tail Assembly: Notice on the plans that two
outlines are provided for the tail assembly.
The smaller of the two is the scale outline.
Although the model can be built and flown
successfully with the smaller tail assembly, I
recommend the enlarged unit. The model will
handle better, especially upwind on blustery
days.
The stabilizer and elevators are made from
1⁄8 sheet balsa. Fit the elevators with a
homemade elevator-horn assembly. (It can be
made lighter than commercially available
units.) Mate the elevators to the stabilizer with
nylon Klett RK-4 flex hinge points.
Cut the vertical fin and rudder from 1⁄8
sheet balsa. Coat with clear dope, sand lightly,
cover the fin, rudder, stabilizer, and elevators
with silk, and set aside.
Undercarriage: Bend the two 1⁄16-inchdiameter
music-wire landing-gear segments.
Bind their upper sections with fine, soft
copper wire and solder together. Drill a 5⁄32-
inch-diameter hole through the center of a 3⁄4-
inch length of 1⁄4 square basswood. Use needle
files to elongate the hole to an oval shape, slip
the undercarriage unit into it, epoxy, and set
aside.
Fuselage: Stack and tack-glue one piece of 1⁄8
x 4 x 20-inch sheet balsa, two pieces of 1⁄16 x 4
x 20-inch sheet balsa, and two pieces of 1⁄32 x
4 x 61⁄2-inch plywood, with the two plywood
pieces on top. Trace the fuselage outline with
the wing, stabilizer, engine, and firewall
cutouts included, and make these cuts on a
jigsaw. Check the wing and stabilizer cutouts
for fit.
Separate the plywood members from this
stack. Mark the undercarriage-support-block
locations, and make this cutout through all
60 MODEL AVIATION
1⁄2A Golden Age Speed Rules 1997
1. Any Cox .049 reed valve engine with
standard (low compression) glow head,
Cox tank only (except for
Spacehopper), may be used with 15%
Nitro Fuel (supplied). Cox prop,
unmodified except for balancing
(5D-3P) may be used.
2. Racers must be of full profile, builtup,
solid or combination structure of a
1929 through 1939 Thompson Trophy
Racer. (A photo and/or 3-view should
be available for proof.)
3. Minimum wing span is 18 inches.
(Bi-planes minimum top wingspan 12
inches, total span both upper and
lower wings 18 inches min.) Minimum
lead-out length is 12 inches.
4. Racer must look like the full scale
aircraft to include color, markings, and
wing struts, if used. No scale judging
nor scale points will be awarded.
5. Take-off and landing gear is
required, as all flights will be R.O.G.
(rise-off-ground).
6. Three attempts are allowed to make
two (2) official flights. Fastest time of
the two will be used for scoring.
7. Speed run will be time for six (6)
laps (1⁄4 mile) beginning one (1) lap
after a signal by the pilot.
8. Whipping, leading or towing is
prohibited.
9. 34-foot KevlarTM control lines will be
supplied by the contest committee.
10. Only one model per entrant is
allowed.
11. Proxy Fliers are allowed. A typical lineup of Golden Age racer
entries sits in front of a Bendix pylon that
Tim Pansic designed and built.
Wittman D-12 Bonzo
Type: 1⁄2A Golden Age racer
Wingspan: 18.125 inches
Engine: Cox Black Widow .049
Flying weight: 8 ounces
Construction: Balsa and plywood
Covering/finish: fiberglass cloth
and modeling dope
John Moll, had the engine sag on its first
attempt, and then an ill-advised propeller
change relegated the model to the middle of
the pack with a 49.18 mph speed.
Gus Vogele’s Folkerts SK-3 tipped over
on its nose, the engine went into reverse, and
the model tried to make like a canard. John
Moll saved the airplane with a one-hand catch
at the expense of a small nick on one finger.
The SK-3 dutifully qualified on a later
attempt.
An ailing Alan Van Artsalen had left the
contest site, but he recovered sufficiently to
return and make his last official attempt. Alan
fired up his Roscoe Turner 2 RT-1, and
anyone who heard its screaming engine knew
that he had a winner if the engine didn’t sag
out on him. It didn’t, and it clocked the
winning time of 62.50 mph. Way to go, Alan.
The old-time racing-airplane events we
read about in the modeling press are usually
the spectacular contests that require serious
commitment to research, engineering, labor,
time, and cost. Clubs can have good
participation and a great deal of fun by
including entry-level events such as the one I
just described. That contest attracted two
father-and-son teams and people we would
normally have thought of as Stunt, Speed,
sport, or Scale-oriented fliers. I’m looking
forward to future Golden Age Thompson
Trophy races at Buder Park.
CONSTRUCTION
Wing: Tape 20-inch lengths of 1⁄4 x 3⁄8-inch
balsa LE and 3⁄16 x 1-inch balsa TE stock
together so that you can cut the 1⁄16-inch
notches for the ribs at the same time in both
pieces with a razor saw or a modeling table
saw. Cover the plans with plastic or waxed
paper, and pin these members over the plans.
Fit the 3⁄8 x 3⁄4-inch tip blocks and the 1⁄16
444 4
07sig2.QXD 4/26/04 8:36 am Page 60
three balsa members. Separate the balsa
members. Take up the 1⁄8 sheet-balsa core
member, mark off the lightening-hole and
pushrod-tunnel cutouts, and make those cuts.
The rear of the fuselage is now floppy and
difficult to maintain in alignment, so cement
several 1⁄8 square balsa stiffeners to span
across these cutouts for now.
Final Assembly: Cut a slot in the wing
center-section sheet covering to allow
installation and passage for the elevator
pushrod. Slip the wing and stabilizer just
short of their true locations in the fuselage
while you eyeball the 1⁄32-inch-diameter
elevator pushrod wire and bend it to size.
Solder the bellcrank-to-pushrod connection,
and then locate and cement the wing to its
proper location in the fuselage core member.
Pass two hardwood guides onto the pushrod,
and cement them in their slots. Now you can
locate and cement the stabilizer. Solder the
elevator pushrod-to-horn connection, and
check the control system for freedom of
movement.
Cement into position the 1⁄16-inch
fuselage panel on the side opposite the
temporary stiffeners. Remove the stiffeners,
and cement the remaining panel into
position. Chamfer the rear edges of the 1⁄32
plywood fuselage stiffeners, and cement
them in place.
Cut out the 1⁄4 plywood engine mount.
You might be satisfied to use wood screws to
mount the Cox engine. I used blind mounting
nuts. It’s your call; either will work. Cement
the engine mount and balsa fairing blocks
into position.
Epoxy the undercarriage assembly into its
slot. Add the vertical fin, rudder,
undercarriage strut fairings, and tail skid. I
drilled 1⁄8-inch-diameter holes and filled them
with short lengths of 1⁄8-inch-diameter birch
dowels for the rear rigging wire locators in
the fuselage sides. I also bent and installed a
wire hoop in the fuselage top at the CG
location. You will suspend the model from
this point later to determine whether or not it
is balanced properly.
You can use a hand-tool burr to gouge
62 MODEL AVIATION
clearances for the engine cylinder head and
needle valve on the starboard side of the
fuselage nose. Also cut a hole in the fuselage
nose ahead of the engine cylinder to admit
additional cooling air to the engine. Mark and
drill all 1⁄32-inch-diameter rigging locating holes
in the fuselage, fin, and stabilizer.
Finish: I covered the fuselage with Sig .56-
ounce fiberglass using clear dope as an
adhesive. I brushed the entire model with four
coats of clear dope, sprayed on four coats of
filler-coat primer, and sprayed on six coats of
Stearman Red. I wet- or dry-sanded (400 grit)
these layers after I applied every second or third
coat.
I masked off the registration numbers and
canopy and sprayed them black, and I masked
off and sprayed the white racing numbers. I
applied the registration numbers on the fin
freehand using a No. 2 Alvin technical pen and
india ink, which I protected with a super-thin
coat of clear dope. I cemented silver-doped,
half-round dummy exhaust-stack headers to
the cowling.
I used a needle to sew black button thread
through the rigging locator holes. I drew these
taut and then fixed them with cyanoacrylate
glue.
If you haven’t already done so, bend the
loops in the leadout-wire ends. According to
the contest rules we were using, they must be a
minimum of 12 inches from the centerline of
the model. Solder the wheels on and bolt the
engine to the firewall.
Suspend the completed model from the CG
loop. If it does not hang in a slightly nosedown
attitude, the model is tail-heavy and will
be an unstable flier. Add weight to the nose if
this condition exists with your model. The
prototype Bonzo assumed roughly a 15° nosedown
attitude with no ballast added.
Flying: Select a calm day and a smooth paved
surface for the initial test flight. The prototype
takes off quickly with little tendency to nose
over. The flight pattern is smooth and steady,
with little or no fore and aft oscillation
patterns. The model gains a bit of altitude on
the upwind side of the circle (normal) and
loses a bit more altitude than it gained when it
enters the downwind side of the circle. That’s
something to keep in mind.
Landing approaches are long and graceful,
but the model does tend to bounce a few times
before it settles into its rollout. It is not prone
to nosing over or doing the cartwheel bit.
Using a 5 x 4 Tornado propeller, the Bonzo
has been clocked at slightly faster than 56
mph—not too bad for an overweight little
beastie that has quite a bit of scale detail built
into it.
If you like beautiful models, build the Bonzo
as I’ve described and have fun with it. If you
are a speedoholic, put this model on a diet and
experiment with fuels and propellers. Tweak
the Bonzo just right, and you might have the
best of both worlds: looks and speed. MA
Frank Beatty
2608 Pontoon Rd.
Granite City IL 62040
07sig2.QXD 4/26/04 8:36 am Page 62
Edition: Model Aviation - 2004/07
Page Numbers: 58,59,60,61,62
GEE BEE, LAIRD, CAUDRON,
Howard, and Wedell-Williams are
names that conjure up memories of
the colorful, exciting airplanes that
competed in the Thompson Trophy
races more than 50 years ago. Until
recently, most of us had to be content
with viewing old film clips or building
models of these fascinating aircraft.
Lately a fortunate few have been
able to create fullscale
replicas or
restorations of
these old race
airplanes. As a
result of a
groundswell of
such activity in
recent years, approximately 20 racing
replicas showed up at the 1995
Experimental Aircraft Association flyin
at Oshkosh, Wisconsin. And model
fliers, not to be outdone and ever on the
lookout for exciting, fun events, are
promoting various sorts of old-time race
airplane speed events in contest
schedules across the country.
The 1995 Society of Antique
Modelers old-time CL contest held at
Buder Park, Missouri, included an .049
Golden Age Speed event limited to pre-
World War II Thompson Trophy race
airplanes. The rules encouraged
participation and eliminated most
excuses one might have for not
participating. The first-time event drew
16 entries. As were the full-scale races
of old, it was exciting and was enjoyed
by spectators and participants.
The low-tech rules specified .049
reed-valve engines, allowed profile
fuselages, set a minimum wingspan of
18 inches, required authentic color-andmarkings,
and mandated a permanent
landing gear for takeoffs and landings.
Only one airplane at a time could fly,
and it was timed for six laps on sets of
control lines furnished by the club.
A rule that I considered particularly
significant permitted proxy fliers. This
allowed entrants who feared that they
couldn’t handle these fast little devils
on short lines because of lack of
experience or possible equilibrium
problems to participate.
Three-view drawings—enlarged to
the proper 18-inch wingspan—of
roughly 17 different racers were
58 MODEL AVIATION
444 4
Wittman D-12 Bonzo by Frank Beatty
Return to the age of air racing
with this legendary design
At left: A Cox
Black Widow .049
r e e d - v a l v e
engine nestles
neatly in the nose
of the model’s
profile fuselage.
07sig2.QXD 4/26/04 8:34 am Page 58
prepared from Lafayette Esquadrille club
members’ archives and were made available
for the asking.
Gus Vogele, a dedicated and talented
workhorse of the club, handcrafted a perpetual
trophy for the event—a Gee Bee Z banking
around a checkerboard pylon encased in a
protective plastic hood on a handsome base.
That was a real incentive for the trophy
hounds.
As time progressed, various members
exhibited their racers at club-meeting showand-
tells. Gus Vogele presented an
immaculately executed Folkerts SK-3 with
scratch-painted markings and an all-up weight
of 7 ounces. Ron Carr, a Speed flier of vast
experience, took great care to avoid
unnecessary or excessive weight and
produced a Pesco Special that weighed just
5.75 ounces.
Most designers adhered to the concept that
the model’s nose outline should be maintained
accurately in the profile view. To achieve that
goal, they mounted engines on aluminum
extrusions or metal brackets bolted to the
fuselage side. This offset the model-engine
centerline approximately 5⁄8 inch from the
fuselage centerline.
My first choice for a model was Tony
LeVier’s sleek Schoenfeldt Firecracker. When
I went shopping for materials and hardware
items, I learned that no commercial spinners
of the proper scale size were available and
that using largish spinners on these small
engines often caused operational headaches.
While flipping through my files I found
photographs of the 1939 version of Steve
Wittman’s D-12 Bonzo, which was flown
without a spinner. My choice was made on
that basis. I also noted that the Bonzo had a
sensible configuration. Self-imposed design
criteria were that I would keep the modelengine
centerline and the fuselage centerline
the same, install a fully enclosed control
system, and construct silk-covered wings with
scale rib spacing.
My first Bonzo, built in typical Scalebuilder’s
fashion, was “overengineered,” with
virtually every component oversized. Even
without paint, the Bonzo was much too heavy,
at more than 9 ounces. I could see that this
weight would escalate even more when I
added ballast to correct a tail-heavy condition.
I shelved that model.
The second Bonzo had components and
hardware items that were either eliminated or
reduced in size or weight. I also shifted the
wing back approximately an inch to correct
the tail-heavy situation so that no ballast
would be required. I rotated the engine 121⁄2°
to keep the engine and fuselage centerlines
identical.
The finished model weighed a tad less
than 8 ounces and balanced properly without
adding ballast. The wing area equaled 98
square inches, so the wing loading was
slightly less than 8 ounces per 100 square
inches of wing area. The scale was roughly 1
inch = 1 foot.
Contest day, August 6, 1995, was
beautiful with light winds. Equipment, judges,
and timers were on hand, and contestants
were lining up with their racers. The 16
entries included two Gee Bees, three Laird-
Turner racers, two Mr. Mulligans, three
Firecrackers, a Caudron, a Chester Goon, a
Marcoux Bromberg, a Miss Los Angeles, a
Folkerts, and a Bonzo.
Early on, Ron Carr’s Pesco Special set a
mark for all to shoot for, with a 60.40 mph
speed. Alan Arunski’s Firecracker took a bad
bounce, flew straight at him, changed its mind
at the last possible moment, turned tail, flew
into the proper orbit, and dutifully qualified
for its master.
Tim Pansic’s Firecracker made a serious
challenge with 58.06 mph. Tim’s model was
powered with a collectible Cox Space Hopper
(the oldie with the beam mounts), and many
marveled that Tim would put such an engine
at risk.
Bob Arata had chosen the Gee Bee R-1
because, as he put it, “When you think of the
Thompson Trophy races, you think of the Gee
Bee.” Of all the models entered, Bob’s made
the prettiest flight—a most graceful, long
rolling takeoff, followed by a smooth, rocksteady
flight; a long, graceful storybook
approach; and a two-point landing and
extended rollout. I was impressed.
Quite a few models tipped over on takeoff
attempts. Others charged on with propellers
thrashing the asphalt until they managed to
get airborne. This drilled into all observers the
relationships between wheel locations and
good ground handling. Scale wheel locations
don’t always hack it, especially when you’re
using small wheels on small models.
My Bonzo, which was proxy-flown by
July 2004 59
444 4
The 1⁄8 balsa profile fuselage core features weight-saving cutouts. The aircraft’s entire
control system is enclosed for less drag.
Designated proxy flier John Moll (left), Ron Carr (center), and the author prepare the
Bonzo for an official flight.
Photos courtesy the author
07sig2.QXD 4/26/04 8:35 am Page 59
sheet-balsa center-section bottom covering in
place. Make a rib cut-out template (see
drawings) and cut 42 ribs from 1⁄16 sheet balsa.
Fit and cement these ribs into place.
Cement the 1⁄16 x 1⁄2-inch plywood
bellcrank support in place, followed by the
four “A” ribs. When dry, lift the assembly
from the building board and add the 1⁄2-ounce
lead outboard tip weight. (Some club
members used a penny on their models.)
Fit the four basswood rigging wire locator
blocks between the ribs, and drill the 1⁄32-inchdiameter
holes as shown. Make the bellcrank
and leadout-wire assembly, slide the leadout
wires through the ribs, and bolt the bellcrank
to the plywood support.
Cover the top side of the center-section
with 1⁄16 sheet balsa. Cut the wingtips to
outline shape, and then carve and sand the
LEs, TEs, and wingtips to shape. Brush
several coats of clear dope over the
framework outline, sand lightly, cover with
silk, and set aside.
Tail Assembly: Notice on the plans that two
outlines are provided for the tail assembly.
The smaller of the two is the scale outline.
Although the model can be built and flown
successfully with the smaller tail assembly, I
recommend the enlarged unit. The model will
handle better, especially upwind on blustery
days.
The stabilizer and elevators are made from
1⁄8 sheet balsa. Fit the elevators with a
homemade elevator-horn assembly. (It can be
made lighter than commercially available
units.) Mate the elevators to the stabilizer with
nylon Klett RK-4 flex hinge points.
Cut the vertical fin and rudder from 1⁄8
sheet balsa. Coat with clear dope, sand lightly,
cover the fin, rudder, stabilizer, and elevators
with silk, and set aside.
Undercarriage: Bend the two 1⁄16-inchdiameter
music-wire landing-gear segments.
Bind their upper sections with fine, soft
copper wire and solder together. Drill a 5⁄32-
inch-diameter hole through the center of a 3⁄4-
inch length of 1⁄4 square basswood. Use needle
files to elongate the hole to an oval shape, slip
the undercarriage unit into it, epoxy, and set
aside.
Fuselage: Stack and tack-glue one piece of 1⁄8
x 4 x 20-inch sheet balsa, two pieces of 1⁄16 x 4
x 20-inch sheet balsa, and two pieces of 1⁄32 x
4 x 61⁄2-inch plywood, with the two plywood
pieces on top. Trace the fuselage outline with
the wing, stabilizer, engine, and firewall
cutouts included, and make these cuts on a
jigsaw. Check the wing and stabilizer cutouts
for fit.
Separate the plywood members from this
stack. Mark the undercarriage-support-block
locations, and make this cutout through all
60 MODEL AVIATION
1⁄2A Golden Age Speed Rules 1997
1. Any Cox .049 reed valve engine with
standard (low compression) glow head,
Cox tank only (except for
Spacehopper), may be used with 15%
Nitro Fuel (supplied). Cox prop,
unmodified except for balancing
(5D-3P) may be used.
2. Racers must be of full profile, builtup,
solid or combination structure of a
1929 through 1939 Thompson Trophy
Racer. (A photo and/or 3-view should
be available for proof.)
3. Minimum wing span is 18 inches.
(Bi-planes minimum top wingspan 12
inches, total span both upper and
lower wings 18 inches min.) Minimum
lead-out length is 12 inches.
4. Racer must look like the full scale
aircraft to include color, markings, and
wing struts, if used. No scale judging
nor scale points will be awarded.
5. Take-off and landing gear is
required, as all flights will be R.O.G.
(rise-off-ground).
6. Three attempts are allowed to make
two (2) official flights. Fastest time of
the two will be used for scoring.
7. Speed run will be time for six (6)
laps (1⁄4 mile) beginning one (1) lap
after a signal by the pilot.
8. Whipping, leading or towing is
prohibited.
9. 34-foot KevlarTM control lines will be
supplied by the contest committee.
10. Only one model per entrant is
allowed.
11. Proxy Fliers are allowed. A typical lineup of Golden Age racer
entries sits in front of a Bendix pylon that
Tim Pansic designed and built.
Wittman D-12 Bonzo
Type: 1⁄2A Golden Age racer
Wingspan: 18.125 inches
Engine: Cox Black Widow .049
Flying weight: 8 ounces
Construction: Balsa and plywood
Covering/finish: fiberglass cloth
and modeling dope
John Moll, had the engine sag on its first
attempt, and then an ill-advised propeller
change relegated the model to the middle of
the pack with a 49.18 mph speed.
Gus Vogele’s Folkerts SK-3 tipped over
on its nose, the engine went into reverse, and
the model tried to make like a canard. John
Moll saved the airplane with a one-hand catch
at the expense of a small nick on one finger.
The SK-3 dutifully qualified on a later
attempt.
An ailing Alan Van Artsalen had left the
contest site, but he recovered sufficiently to
return and make his last official attempt. Alan
fired up his Roscoe Turner 2 RT-1, and
anyone who heard its screaming engine knew
that he had a winner if the engine didn’t sag
out on him. It didn’t, and it clocked the
winning time of 62.50 mph. Way to go, Alan.
The old-time racing-airplane events we
read about in the modeling press are usually
the spectacular contests that require serious
commitment to research, engineering, labor,
time, and cost. Clubs can have good
participation and a great deal of fun by
including entry-level events such as the one I
just described. That contest attracted two
father-and-son teams and people we would
normally have thought of as Stunt, Speed,
sport, or Scale-oriented fliers. I’m looking
forward to future Golden Age Thompson
Trophy races at Buder Park.
CONSTRUCTION
Wing: Tape 20-inch lengths of 1⁄4 x 3⁄8-inch
balsa LE and 3⁄16 x 1-inch balsa TE stock
together so that you can cut the 1⁄16-inch
notches for the ribs at the same time in both
pieces with a razor saw or a modeling table
saw. Cover the plans with plastic or waxed
paper, and pin these members over the plans.
Fit the 3⁄8 x 3⁄4-inch tip blocks and the 1⁄16
444 4
07sig2.QXD 4/26/04 8:36 am Page 60
three balsa members. Separate the balsa
members. Take up the 1⁄8 sheet-balsa core
member, mark off the lightening-hole and
pushrod-tunnel cutouts, and make those cuts.
The rear of the fuselage is now floppy and
difficult to maintain in alignment, so cement
several 1⁄8 square balsa stiffeners to span
across these cutouts for now.
Final Assembly: Cut a slot in the wing
center-section sheet covering to allow
installation and passage for the elevator
pushrod. Slip the wing and stabilizer just
short of their true locations in the fuselage
while you eyeball the 1⁄32-inch-diameter
elevator pushrod wire and bend it to size.
Solder the bellcrank-to-pushrod connection,
and then locate and cement the wing to its
proper location in the fuselage core member.
Pass two hardwood guides onto the pushrod,
and cement them in their slots. Now you can
locate and cement the stabilizer. Solder the
elevator pushrod-to-horn connection, and
check the control system for freedom of
movement.
Cement into position the 1⁄16-inch
fuselage panel on the side opposite the
temporary stiffeners. Remove the stiffeners,
and cement the remaining panel into
position. Chamfer the rear edges of the 1⁄32
plywood fuselage stiffeners, and cement
them in place.
Cut out the 1⁄4 plywood engine mount.
You might be satisfied to use wood screws to
mount the Cox engine. I used blind mounting
nuts. It’s your call; either will work. Cement
the engine mount and balsa fairing blocks
into position.
Epoxy the undercarriage assembly into its
slot. Add the vertical fin, rudder,
undercarriage strut fairings, and tail skid. I
drilled 1⁄8-inch-diameter holes and filled them
with short lengths of 1⁄8-inch-diameter birch
dowels for the rear rigging wire locators in
the fuselage sides. I also bent and installed a
wire hoop in the fuselage top at the CG
location. You will suspend the model from
this point later to determine whether or not it
is balanced properly.
You can use a hand-tool burr to gouge
62 MODEL AVIATION
clearances for the engine cylinder head and
needle valve on the starboard side of the
fuselage nose. Also cut a hole in the fuselage
nose ahead of the engine cylinder to admit
additional cooling air to the engine. Mark and
drill all 1⁄32-inch-diameter rigging locating holes
in the fuselage, fin, and stabilizer.
Finish: I covered the fuselage with Sig .56-
ounce fiberglass using clear dope as an
adhesive. I brushed the entire model with four
coats of clear dope, sprayed on four coats of
filler-coat primer, and sprayed on six coats of
Stearman Red. I wet- or dry-sanded (400 grit)
these layers after I applied every second or third
coat.
I masked off the registration numbers and
canopy and sprayed them black, and I masked
off and sprayed the white racing numbers. I
applied the registration numbers on the fin
freehand using a No. 2 Alvin technical pen and
india ink, which I protected with a super-thin
coat of clear dope. I cemented silver-doped,
half-round dummy exhaust-stack headers to
the cowling.
I used a needle to sew black button thread
through the rigging locator holes. I drew these
taut and then fixed them with cyanoacrylate
glue.
If you haven’t already done so, bend the
loops in the leadout-wire ends. According to
the contest rules we were using, they must be a
minimum of 12 inches from the centerline of
the model. Solder the wheels on and bolt the
engine to the firewall.
Suspend the completed model from the CG
loop. If it does not hang in a slightly nosedown
attitude, the model is tail-heavy and will
be an unstable flier. Add weight to the nose if
this condition exists with your model. The
prototype Bonzo assumed roughly a 15° nosedown
attitude with no ballast added.
Flying: Select a calm day and a smooth paved
surface for the initial test flight. The prototype
takes off quickly with little tendency to nose
over. The flight pattern is smooth and steady,
with little or no fore and aft oscillation
patterns. The model gains a bit of altitude on
the upwind side of the circle (normal) and
loses a bit more altitude than it gained when it
enters the downwind side of the circle. That’s
something to keep in mind.
Landing approaches are long and graceful,
but the model does tend to bounce a few times
before it settles into its rollout. It is not prone
to nosing over or doing the cartwheel bit.
Using a 5 x 4 Tornado propeller, the Bonzo
has been clocked at slightly faster than 56
mph—not too bad for an overweight little
beastie that has quite a bit of scale detail built
into it.
If you like beautiful models, build the Bonzo
as I’ve described and have fun with it. If you
are a speedoholic, put this model on a diet and
experiment with fuels and propellers. Tweak
the Bonzo just right, and you might have the
best of both worlds: looks and speed. MA
Frank Beatty
2608 Pontoon Rd.
Granite City IL 62040
07sig2.QXD 4/26/04 8:36 am Page 62
Edition: Model Aviation - 2004/07
Page Numbers: 58,59,60,61,62
GEE BEE, LAIRD, CAUDRON,
Howard, and Wedell-Williams are
names that conjure up memories of
the colorful, exciting airplanes that
competed in the Thompson Trophy
races more than 50 years ago. Until
recently, most of us had to be content
with viewing old film clips or building
models of these fascinating aircraft.
Lately a fortunate few have been
able to create fullscale
replicas or
restorations of
these old race
airplanes. As a
result of a
groundswell of
such activity in
recent years, approximately 20 racing
replicas showed up at the 1995
Experimental Aircraft Association flyin
at Oshkosh, Wisconsin. And model
fliers, not to be outdone and ever on the
lookout for exciting, fun events, are
promoting various sorts of old-time race
airplane speed events in contest
schedules across the country.
The 1995 Society of Antique
Modelers old-time CL contest held at
Buder Park, Missouri, included an .049
Golden Age Speed event limited to pre-
World War II Thompson Trophy race
airplanes. The rules encouraged
participation and eliminated most
excuses one might have for not
participating. The first-time event drew
16 entries. As were the full-scale races
of old, it was exciting and was enjoyed
by spectators and participants.
The low-tech rules specified .049
reed-valve engines, allowed profile
fuselages, set a minimum wingspan of
18 inches, required authentic color-andmarkings,
and mandated a permanent
landing gear for takeoffs and landings.
Only one airplane at a time could fly,
and it was timed for six laps on sets of
control lines furnished by the club.
A rule that I considered particularly
significant permitted proxy fliers. This
allowed entrants who feared that they
couldn’t handle these fast little devils
on short lines because of lack of
experience or possible equilibrium
problems to participate.
Three-view drawings—enlarged to
the proper 18-inch wingspan—of
roughly 17 different racers were
58 MODEL AVIATION
444 4
Wittman D-12 Bonzo by Frank Beatty
Return to the age of air racing
with this legendary design
At left: A Cox
Black Widow .049
r e e d - v a l v e
engine nestles
neatly in the nose
of the model’s
profile fuselage.
07sig2.QXD 4/26/04 8:34 am Page 58
prepared from Lafayette Esquadrille club
members’ archives and were made available
for the asking.
Gus Vogele, a dedicated and talented
workhorse of the club, handcrafted a perpetual
trophy for the event—a Gee Bee Z banking
around a checkerboard pylon encased in a
protective plastic hood on a handsome base.
That was a real incentive for the trophy
hounds.
As time progressed, various members
exhibited their racers at club-meeting showand-
tells. Gus Vogele presented an
immaculately executed Folkerts SK-3 with
scratch-painted markings and an all-up weight
of 7 ounces. Ron Carr, a Speed flier of vast
experience, took great care to avoid
unnecessary or excessive weight and
produced a Pesco Special that weighed just
5.75 ounces.
Most designers adhered to the concept that
the model’s nose outline should be maintained
accurately in the profile view. To achieve that
goal, they mounted engines on aluminum
extrusions or metal brackets bolted to the
fuselage side. This offset the model-engine
centerline approximately 5⁄8 inch from the
fuselage centerline.
My first choice for a model was Tony
LeVier’s sleek Schoenfeldt Firecracker. When
I went shopping for materials and hardware
items, I learned that no commercial spinners
of the proper scale size were available and
that using largish spinners on these small
engines often caused operational headaches.
While flipping through my files I found
photographs of the 1939 version of Steve
Wittman’s D-12 Bonzo, which was flown
without a spinner. My choice was made on
that basis. I also noted that the Bonzo had a
sensible configuration. Self-imposed design
criteria were that I would keep the modelengine
centerline and the fuselage centerline
the same, install a fully enclosed control
system, and construct silk-covered wings with
scale rib spacing.
My first Bonzo, built in typical Scalebuilder’s
fashion, was “overengineered,” with
virtually every component oversized. Even
without paint, the Bonzo was much too heavy,
at more than 9 ounces. I could see that this
weight would escalate even more when I
added ballast to correct a tail-heavy condition.
I shelved that model.
The second Bonzo had components and
hardware items that were either eliminated or
reduced in size or weight. I also shifted the
wing back approximately an inch to correct
the tail-heavy situation so that no ballast
would be required. I rotated the engine 121⁄2°
to keep the engine and fuselage centerlines
identical.
The finished model weighed a tad less
than 8 ounces and balanced properly without
adding ballast. The wing area equaled 98
square inches, so the wing loading was
slightly less than 8 ounces per 100 square
inches of wing area. The scale was roughly 1
inch = 1 foot.
Contest day, August 6, 1995, was
beautiful with light winds. Equipment, judges,
and timers were on hand, and contestants
were lining up with their racers. The 16
entries included two Gee Bees, three Laird-
Turner racers, two Mr. Mulligans, three
Firecrackers, a Caudron, a Chester Goon, a
Marcoux Bromberg, a Miss Los Angeles, a
Folkerts, and a Bonzo.
Early on, Ron Carr’s Pesco Special set a
mark for all to shoot for, with a 60.40 mph
speed. Alan Arunski’s Firecracker took a bad
bounce, flew straight at him, changed its mind
at the last possible moment, turned tail, flew
into the proper orbit, and dutifully qualified
for its master.
Tim Pansic’s Firecracker made a serious
challenge with 58.06 mph. Tim’s model was
powered with a collectible Cox Space Hopper
(the oldie with the beam mounts), and many
marveled that Tim would put such an engine
at risk.
Bob Arata had chosen the Gee Bee R-1
because, as he put it, “When you think of the
Thompson Trophy races, you think of the Gee
Bee.” Of all the models entered, Bob’s made
the prettiest flight—a most graceful, long
rolling takeoff, followed by a smooth, rocksteady
flight; a long, graceful storybook
approach; and a two-point landing and
extended rollout. I was impressed.
Quite a few models tipped over on takeoff
attempts. Others charged on with propellers
thrashing the asphalt until they managed to
get airborne. This drilled into all observers the
relationships between wheel locations and
good ground handling. Scale wheel locations
don’t always hack it, especially when you’re
using small wheels on small models.
My Bonzo, which was proxy-flown by
July 2004 59
444 4
The 1⁄8 balsa profile fuselage core features weight-saving cutouts. The aircraft’s entire
control system is enclosed for less drag.
Designated proxy flier John Moll (left), Ron Carr (center), and the author prepare the
Bonzo for an official flight.
Photos courtesy the author
07sig2.QXD 4/26/04 8:35 am Page 59
sheet-balsa center-section bottom covering in
place. Make a rib cut-out template (see
drawings) and cut 42 ribs from 1⁄16 sheet balsa.
Fit and cement these ribs into place.
Cement the 1⁄16 x 1⁄2-inch plywood
bellcrank support in place, followed by the
four “A” ribs. When dry, lift the assembly
from the building board and add the 1⁄2-ounce
lead outboard tip weight. (Some club
members used a penny on their models.)
Fit the four basswood rigging wire locator
blocks between the ribs, and drill the 1⁄32-inchdiameter
holes as shown. Make the bellcrank
and leadout-wire assembly, slide the leadout
wires through the ribs, and bolt the bellcrank
to the plywood support.
Cover the top side of the center-section
with 1⁄16 sheet balsa. Cut the wingtips to
outline shape, and then carve and sand the
LEs, TEs, and wingtips to shape. Brush
several coats of clear dope over the
framework outline, sand lightly, cover with
silk, and set aside.
Tail Assembly: Notice on the plans that two
outlines are provided for the tail assembly.
The smaller of the two is the scale outline.
Although the model can be built and flown
successfully with the smaller tail assembly, I
recommend the enlarged unit. The model will
handle better, especially upwind on blustery
days.
The stabilizer and elevators are made from
1⁄8 sheet balsa. Fit the elevators with a
homemade elevator-horn assembly. (It can be
made lighter than commercially available
units.) Mate the elevators to the stabilizer with
nylon Klett RK-4 flex hinge points.
Cut the vertical fin and rudder from 1⁄8
sheet balsa. Coat with clear dope, sand lightly,
cover the fin, rudder, stabilizer, and elevators
with silk, and set aside.
Undercarriage: Bend the two 1⁄16-inchdiameter
music-wire landing-gear segments.
Bind their upper sections with fine, soft
copper wire and solder together. Drill a 5⁄32-
inch-diameter hole through the center of a 3⁄4-
inch length of 1⁄4 square basswood. Use needle
files to elongate the hole to an oval shape, slip
the undercarriage unit into it, epoxy, and set
aside.
Fuselage: Stack and tack-glue one piece of 1⁄8
x 4 x 20-inch sheet balsa, two pieces of 1⁄16 x 4
x 20-inch sheet balsa, and two pieces of 1⁄32 x
4 x 61⁄2-inch plywood, with the two plywood
pieces on top. Trace the fuselage outline with
the wing, stabilizer, engine, and firewall
cutouts included, and make these cuts on a
jigsaw. Check the wing and stabilizer cutouts
for fit.
Separate the plywood members from this
stack. Mark the undercarriage-support-block
locations, and make this cutout through all
60 MODEL AVIATION
1⁄2A Golden Age Speed Rules 1997
1. Any Cox .049 reed valve engine with
standard (low compression) glow head,
Cox tank only (except for
Spacehopper), may be used with 15%
Nitro Fuel (supplied). Cox prop,
unmodified except for balancing
(5D-3P) may be used.
2. Racers must be of full profile, builtup,
solid or combination structure of a
1929 through 1939 Thompson Trophy
Racer. (A photo and/or 3-view should
be available for proof.)
3. Minimum wing span is 18 inches.
(Bi-planes minimum top wingspan 12
inches, total span both upper and
lower wings 18 inches min.) Minimum
lead-out length is 12 inches.
4. Racer must look like the full scale
aircraft to include color, markings, and
wing struts, if used. No scale judging
nor scale points will be awarded.
5. Take-off and landing gear is
required, as all flights will be R.O.G.
(rise-off-ground).
6. Three attempts are allowed to make
two (2) official flights. Fastest time of
the two will be used for scoring.
7. Speed run will be time for six (6)
laps (1⁄4 mile) beginning one (1) lap
after a signal by the pilot.
8. Whipping, leading or towing is
prohibited.
9. 34-foot KevlarTM control lines will be
supplied by the contest committee.
10. Only one model per entrant is
allowed.
11. Proxy Fliers are allowed. A typical lineup of Golden Age racer
entries sits in front of a Bendix pylon that
Tim Pansic designed and built.
Wittman D-12 Bonzo
Type: 1⁄2A Golden Age racer
Wingspan: 18.125 inches
Engine: Cox Black Widow .049
Flying weight: 8 ounces
Construction: Balsa and plywood
Covering/finish: fiberglass cloth
and modeling dope
John Moll, had the engine sag on its first
attempt, and then an ill-advised propeller
change relegated the model to the middle of
the pack with a 49.18 mph speed.
Gus Vogele’s Folkerts SK-3 tipped over
on its nose, the engine went into reverse, and
the model tried to make like a canard. John
Moll saved the airplane with a one-hand catch
at the expense of a small nick on one finger.
The SK-3 dutifully qualified on a later
attempt.
An ailing Alan Van Artsalen had left the
contest site, but he recovered sufficiently to
return and make his last official attempt. Alan
fired up his Roscoe Turner 2 RT-1, and
anyone who heard its screaming engine knew
that he had a winner if the engine didn’t sag
out on him. It didn’t, and it clocked the
winning time of 62.50 mph. Way to go, Alan.
The old-time racing-airplane events we
read about in the modeling press are usually
the spectacular contests that require serious
commitment to research, engineering, labor,
time, and cost. Clubs can have good
participation and a great deal of fun by
including entry-level events such as the one I
just described. That contest attracted two
father-and-son teams and people we would
normally have thought of as Stunt, Speed,
sport, or Scale-oriented fliers. I’m looking
forward to future Golden Age Thompson
Trophy races at Buder Park.
CONSTRUCTION
Wing: Tape 20-inch lengths of 1⁄4 x 3⁄8-inch
balsa LE and 3⁄16 x 1-inch balsa TE stock
together so that you can cut the 1⁄16-inch
notches for the ribs at the same time in both
pieces with a razor saw or a modeling table
saw. Cover the plans with plastic or waxed
paper, and pin these members over the plans.
Fit the 3⁄8 x 3⁄4-inch tip blocks and the 1⁄16
444 4
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three balsa members. Separate the balsa
members. Take up the 1⁄8 sheet-balsa core
member, mark off the lightening-hole and
pushrod-tunnel cutouts, and make those cuts.
The rear of the fuselage is now floppy and
difficult to maintain in alignment, so cement
several 1⁄8 square balsa stiffeners to span
across these cutouts for now.
Final Assembly: Cut a slot in the wing
center-section sheet covering to allow
installation and passage for the elevator
pushrod. Slip the wing and stabilizer just
short of their true locations in the fuselage
while you eyeball the 1⁄32-inch-diameter
elevator pushrod wire and bend it to size.
Solder the bellcrank-to-pushrod connection,
and then locate and cement the wing to its
proper location in the fuselage core member.
Pass two hardwood guides onto the pushrod,
and cement them in their slots. Now you can
locate and cement the stabilizer. Solder the
elevator pushrod-to-horn connection, and
check the control system for freedom of
movement.
Cement into position the 1⁄16-inch
fuselage panel on the side opposite the
temporary stiffeners. Remove the stiffeners,
and cement the remaining panel into
position. Chamfer the rear edges of the 1⁄32
plywood fuselage stiffeners, and cement
them in place.
Cut out the 1⁄4 plywood engine mount.
You might be satisfied to use wood screws to
mount the Cox engine. I used blind mounting
nuts. It’s your call; either will work. Cement
the engine mount and balsa fairing blocks
into position.
Epoxy the undercarriage assembly into its
slot. Add the vertical fin, rudder,
undercarriage strut fairings, and tail skid. I
drilled 1⁄8-inch-diameter holes and filled them
with short lengths of 1⁄8-inch-diameter birch
dowels for the rear rigging wire locators in
the fuselage sides. I also bent and installed a
wire hoop in the fuselage top at the CG
location. You will suspend the model from
this point later to determine whether or not it
is balanced properly.
You can use a hand-tool burr to gouge
62 MODEL AVIATION
clearances for the engine cylinder head and
needle valve on the starboard side of the
fuselage nose. Also cut a hole in the fuselage
nose ahead of the engine cylinder to admit
additional cooling air to the engine. Mark and
drill all 1⁄32-inch-diameter rigging locating holes
in the fuselage, fin, and stabilizer.
Finish: I covered the fuselage with Sig .56-
ounce fiberglass using clear dope as an
adhesive. I brushed the entire model with four
coats of clear dope, sprayed on four coats of
filler-coat primer, and sprayed on six coats of
Stearman Red. I wet- or dry-sanded (400 grit)
these layers after I applied every second or third
coat.
I masked off the registration numbers and
canopy and sprayed them black, and I masked
off and sprayed the white racing numbers. I
applied the registration numbers on the fin
freehand using a No. 2 Alvin technical pen and
india ink, which I protected with a super-thin
coat of clear dope. I cemented silver-doped,
half-round dummy exhaust-stack headers to
the cowling.
I used a needle to sew black button thread
through the rigging locator holes. I drew these
taut and then fixed them with cyanoacrylate
glue.
If you haven’t already done so, bend the
loops in the leadout-wire ends. According to
the contest rules we were using, they must be a
minimum of 12 inches from the centerline of
the model. Solder the wheels on and bolt the
engine to the firewall.
Suspend the completed model from the CG
loop. If it does not hang in a slightly nosedown
attitude, the model is tail-heavy and will
be an unstable flier. Add weight to the nose if
this condition exists with your model. The
prototype Bonzo assumed roughly a 15° nosedown
attitude with no ballast added.
Flying: Select a calm day and a smooth paved
surface for the initial test flight. The prototype
takes off quickly with little tendency to nose
over. The flight pattern is smooth and steady,
with little or no fore and aft oscillation
patterns. The model gains a bit of altitude on
the upwind side of the circle (normal) and
loses a bit more altitude than it gained when it
enters the downwind side of the circle. That’s
something to keep in mind.
Landing approaches are long and graceful,
but the model does tend to bounce a few times
before it settles into its rollout. It is not prone
to nosing over or doing the cartwheel bit.
Using a 5 x 4 Tornado propeller, the Bonzo
has been clocked at slightly faster than 56
mph—not too bad for an overweight little
beastie that has quite a bit of scale detail built
into it.
If you like beautiful models, build the Bonzo
as I’ve described and have fun with it. If you
are a speedoholic, put this model on a diet and
experiment with fuels and propellers. Tweak
the Bonzo just right, and you might have the
best of both worlds: looks and speed. MA
Frank Beatty
2608 Pontoon Rd.
Granite City IL 62040
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