Small-Field Flying-2011/08

94 MODEL AVIATION
learning what you find hiding inside some of
the other RTF foamie models either on the
market or coming in the future.
The Fly Baby is a small-field flyer based on a
classic home-built aircraft. Home-built aircraft
are great subjects for scale model airplanes.
Some home-builts look as if they could be
scaled-up model airplanes. One that comes to
mind is Peter Bowers’ Fly Baby designed in
1962.
The design started out as a low-wing
monoplane. As is the case with model builders,
biplanes are also popular within the full-scale,
home-built community. As a result, a biplane
version of the popular Fly Baby was
developed.
When it comes to small-field models,
biplanes really excel, especially when built
light. This is certainly not lost on our friend,
Pat Tritle. He has developed a number of
lovely lightweight biplanes that are favorites
within the small-field flying community.
Pat has reached into the catalog of
appealing full-scale biplanes and selected the
Fly Baby biplane for his latest offering to the
small-field flying community. With a 33-inch
wingspan and a flying weight of slightly less
than 15 ounces, you have a perfect scale smallfield
flyer.
YOU MAY have heard a quote by
Michelangelo that goes something like this:
“Every block of stone has a statue inside it
and it is the task of the sculptor to discover
it.” I think Ron Sims of St. Joseph, Missouri,
has a similar feeling about what’s lurking
inside RTF foamie model airplanes.
You may recall that in the August 2010
edition of this column, I shared what Ron, a
Hughes Racer model owner, discovered
inside his ParkZone Sukhoi. Guess what? He
acquired a ParkZone P-51D Mustang and
discovered there was a Bell P-39 Airacobra
hiding inside the foam.
Ron has performed another of his
masterful conversions of an existing model
from one format to another. I want to share
with you his transformation of the ParkZone
Micro P-51 to a P-39.
Most of the effort was reworking the
fuselage from the classic P-51 shape to that
of the slim-nosed P-39. This involved
cutting away the belly air scoop and then
reshaping things with some judicious
sanding, and adding pink foam. Ron found
he could not fit the P-51 motor/gear drive
power unit in the nose because of the slim
profile of the P-39, so he elected to use an
AP05 brushless motor.
The wings required a little work, which
included tip reshaping and removing the
dogleg at the LE root. The wing saddle was
moved ¼ inch on the fuselage to maintain
the scale geometry.
The tail surfaces were made from foam
sheet obtained from take-out box lids. The
texture of the take-out box foam is a close
match to the original P-51’s tail surfaces.
One neat thing Ron did for the fin and
rudder, is to make the unit from two
laminations of the foam. Tucked in the
middle of the foam laminations is a 1/64-inch
plywood strip along the hinge line. The
plywood holds a 3M Blenderm tape hinge.
The overall finish is olive-drab and gray
paint. The star roundels were made from the
P-51 decals with the bars cut off. When the
decals were in place, a final top coat of
Testors Dullcote was applied.
A few notes about the power setup of the
P-39 need to be included as well. The
aforementioned AP05 motor is powered by
two ParkZone-compatible Li-Poly cells in
series. This required Ron to use an ESC. The
motor, ESC, and two cell adapters were
obtained from Bob Selman Designs.
To maintain the scale look of the P-39,
Ron wanted a three-blade propeller. He used
a GWS 5030 cut down to a diameter of 4½
inches. The propeller blades were also
narrowed, which created a more scale look
and also helped keep the load on the motor
in the proper range.
The final flying weight is 50 grams. Ron
reports that the model performs nicely.
Great effort, Ron. I look forward to
Paul Bradley | bradleyp@Small-Field Flying ix.netcom.com
There is a P-39 lurking inside that ParkZone Micro P-51
Also included in this column:
• The Fly Baby biplane as
rendered by Pat Tritle
• Keeping the vintage look
when using current-day
components
• New location for
Diels Engineering
Left: With a little foam
bashing by Ron, a ParkZone
P-51 was converted to a Bell
P-39.
Ron Sims’ completed
P-51-to-P-39 conversion
uses a brushless AP05
for power.
Power for the model comes from an E-flite
Park 370 brushless outrunner motor driven by
two 1320mAh Li-Poly cells which swings the
9 x 5 propeller. All control functions are
included with dual servos used for the ailerons.
Pat offered some comments regarding
flying its qualities.
“The Fly Baby flies a lot differently than I
expected it would. I thought it would be a bit of
a floater, similar to the Tiger Moth, but turned
out to be a far more solid flyer. Control input is
crisp, very positive, and the model grooves
really well. Surprisingly, there was no adverse
yaw from aileron input so no rudder is needed
in the turn, though it turns equally as well on
either rudder or ailerons, and the Fly Baby will
sideslip nicely.
“On takeoff, ground handling is no
problem. The rudder is effective, but not overly
aggressive, so tracking a straight line is easy.
Landings are easy too, in that the model floats
a little in ground effect, and touches down and
sticks to the runway at a perfect three-point
attitude with no tendency to bounce.”
Pat is offering short kits for the Fly Baby
biplane.
Sleight-of-Hand Illusions to Keep a Vintage
Model Looking Vintage: A popular source of
small-field flyers is the world of Vintage
model aircraft. Often, these subjects are scaled
down because many Vintage model airplanes
were quite large. Some, such as the old Sterling
Mambo, work well in the original size.
The Mambo has a 48-inch wingspan and is
well suited for flying in smaller venues. This
particular model was designed to be a singlechannel
RC trainer when it first appeared in the
mid 1950s.
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August 2011 95
My brother, Ralph, acquired a partially-built Mambo. The original
model was flown on glow engine power. Ralph wanted to use electric
power but also wanted to keep the look of the model as close to the
original as possible.
Keeping the original look involved two areas of challenge: the glow
engine and the fact that the original used an escapement for rudder
control. The latter meant the use of a torque rod rather than a pushrod for
moving the control surface.
In case there are others who like the older models and the original
look, I want to share Ralph’s approaches to achieving a vintage look with
current-day components.
Other modelers have created the illusion of a fuel-engine-powered
model by fabricating a dummy engine. Ralph and I still have our engines
from the early days and he decided one could be used—namely a Fox
Manufacturing .15 model engine. The task was to not make any changes
to the engine that would prevent it from returning to service using glow
fuel. His solution was simply to remove the piston, crankshaft, and
backplate.
A bearing was placed in the forward end of the crankcase, and
Loctite Removable Threadlocker was used to secure the bearing. A 4mm
drill rod was used to make a propeller shaft extension for the electric
motor. The electric motor was then mounted behind the Fox .15 with a
homemade shaft coupler. The result was a complete Fox .15 mounted in
the proper place looking like the power source for turning the propeller.
The setup runs smoothly. The only external giveaway is the lack of
engine compression.
To simulate the use of an escapement-driven torque rod for the
rudder control, Ralph built the rig shown in the photos. This involves an
actual torque rod but it is driven by a servo as shown. You end up with
the control surface being actuated as it was back in the beginning of RC
models, but have the full benefits of proportional control.
Great work, Ralph. I hope this gives others some ideas for small-field
flyers based on models from the early days of RC flying.
Diels Engineering has moved. Some of us like to convert rubber-
Pat Tritle’s latest offering is a 33-inch model
of the home-built Fly Baby biplane.
Pat’s Fly Baby biplane in flight.
The Fox Manufacturing .15 engine in the
nose of Ralph Bradley’s Sterling Mambo
is hiding a secret.
The secret behind Ralph’s Fox .15
is a PJS 800 brushless electric
motor.
To help maintain the vintage
look of the original 1950s
Mambo, Ralph is using a
torque rod driven by a servo.
powered FF models to small-field RC aircraft. One great source for
such kits is Diels Engineering. Please see the “Sources” listing for the
new contact information.
As always, let me know what you are up to in the wonderful world of
small-field flying. MA
Sources:
BSD Micro RC
(417) 358-9521
www.bsdmicrorc.com
Fly Baby by Peter Bowers
www.bowersflybaby.com
Pat’s Custom Models
(505) 296-4511
www.patscustom-models.com
Diels Engineering, Inc.
[email protected]
www.dielsengineeringinc.com
Paul Bradley
10201 Scarletoak Dr.
Independence KY 41051
www.parmodels.com
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