108 MODEL AVIATION
conversion steps were not as convenient.
Ivo shared a photo of his model as it waits for conversion and a
little refurbishing. Having built a Comet 54-inch Taylorcraft many
years ago, I can understand Ivo’s desire to take advantage of the
existing airframe. The big airplane is an excellent conversion subject
when building the model initially, but I do not know the best way to
handle the conversion.
Several things come to mind. The landing gear will need some
beefing up and provisions will need to be
made for mounting the motor and other RCrelated
equipment. Since Ivo wants his
Taylorcraft to be electric powered, a provision
for accessing the flight battery pack will be
necessary. The layout of the model’s structure
makes some of these “adjustments” slightly
challenging with an existing airframe, but
certainly not out of reason.
Stripping off the tissue covering, a step
already deemed necessary for renewing this
nice model, will provide great access to the
large, spacious airframe. That should make it
easy to add structure to strengthen the landing
gear.
Since the Taylorcraft is a high-wing
airplane with wing struts, making the struts
load bearing should allow the existing wing
structure and fuselage attachment points to
carry the flight loads of the heavier RC model.
Using something such as spruce or basswood
Small-Field Flying Paul Bradley | [email protected]
Also included in this column:
• Another new design from
Pat Tritle
• Solar-powered micro model
• New battery and charger
offerings from FMA Direct
Converting an existing rubber-powered FF model to an electric-powered RC aircraft
A new Pat Tritle offering is a 54-inch-span Aeronca Chief—a nice companion to Ivo’s 54-
inch Comet Taylorcraft.
Pat’s Aeronca Chief is designed for electric power and radio control and retains the
wonderful look of a covered, built-up structure.
Ivo Lucchitta wants to convert this already
built 54-inch-span FF Comet Taylorcraft to an
electric-powered RC model.
CONVERTING RUBBER-powered FF
models to small-field RC models is a common
practice within the small-field-flying
community. I have mentioned doing this on
more than one occasion and I’ve had the
privilege of highlighting the conversion projects of
some fine modelers in these pages.
Reader Ivo Lucchitta sent me a note on this
subject and suggested that the steps to perform such
conversions may not always be obvious to the builder.
Rubber-powered FF aircraft are generally built with
lightweight structures that go along with their relatively low
wing loadings. When we add things such as a motor, batteries,
radio gear, and movable control surfaces, some adjustment to the
original model structure is in order.
When contemplating such a conversion using a kit or set of plans,
you have a number of options. You can add a little structure for the
landing gear (if the model has landing gear), add some structure for a
motor, perhaps add some structure to the wing to allow for a higher
flying weight, and modify the flying surfaces to allow for the intended
movable surfaces.
What happens if you have an already built model in your inventory
that you would like to convert to motor-powered RC? That was the
situation for Ivo. He had a Comet 54-inch rubber-powered
Taylorcraft that seemed to be a perfect candidate for conversion.
Since the model was already built, some of the “normal”
06sig4.QXD 4/20/07 2:22 PM Page 108
for the struts and adding some load-distribution structure at the attach
points should be all that is necessary.
The biggest challenge I see would be modifying the nose structure
to make it easy to access the motor and flight battery. The Taylorcraft
uses a nice layout of shaped sticks to generate the form of the cowl. In
a rubber-powered model the cowl does not have to be removable
because the motor is wound by pulling it out through the nose plug.
For RC conversion it would be best if the
nose of the fuselage represented by the cowl
area could be easily removed. That would
give good access to the motor, the
corresponding mount, and the speed control.
I would be inclined to cut off the nose at
the cowl line and add some structure to allow
the cowl to be a removable unit. I would
retain the covered framework of the cowl
structure to keep the classic look of the stickand-
tissue model. Several rare-earth magnets
would be ideal for retaining the cowl.
I think the rest of the conversion—things
such as control surfaces and mounting the
RC gear—would be straightforward,
especially with the room available in the
Taylorcraft.
I’m sure Ivo has some good ideas for
how he will handle the conversion. I look
forward to seeing his completed project. I
will keep after him for pictures so we can all
June 2007 109
Ralph Bradley’s 8-inch-span smallfield
flyer is strictly solar powered
and contains no onboard buffer
battery.
The equipment side of Ralph’s solar
micro model includes a homemade
7.1:1 gear drive that uses watch
gears.
FMA Direct has linked up with WorleyParsons of Australia to bring the world of electric
power new offerings under the name of Cellpro Revolution.
enjoy his challenge and the results. Thanks for the teaser Ivo.
Before leaving the subject, a source for laser-cut reproduction kits
of the excellent Comet 54-inch rubber-powered models is Tom Martin
Radio Control. Please see the source listing at the end of this column
for contact information.
It is interesting how things go in this world. At roughly the same time
I received the note from Ivo regarding his Taylorcraft, Pat Tritle sent
word that he had just completed a 54-inch Aeronca Chief for electric
power. That’s a coincidence since Comet has a 54-inch Aeronca Chief
as a stablemate to the Taylorcraft.
For those of us who don’t want to make the conversion decisions,
Pat’s model provides a great alternative. It is designed from the ground
up for electric power and radio control. Pat’s model retains that
wonderful look of a covered, built-up structure and has the structural
design details already worked out.
I have included inviting pictures of Pat’s Chief. This gets my juices
flowing, as do all of Pat’s models. It’s lovely. He wrote:
“The first step out of the norm was to fatten up the typical 12%
thick airfoil to 14%. Because this type of airplane often requires upelevator
trim for cruise power settings, I set up the horizontal stabilizer
at 1° negative.
“The stabilizer incidence was against my better judgment at the
time because of the fatter airfoil, but it proved to work well since the
model trims completely neutral at cruise power. With the downthrust
set up as it is, a click or two of power can be added to climb or power
reduced slightly to descend—exactly what I was after! The whole idea
behind the change was to set the model up to fly at scale speeds, which
in that scale are slow!
“The model spans 53.8 inches with a flying weight of 14.9 ounces.
Power is a Himax 2812-850 outrunner motor with a Thunderbird-18
ESC, an APC 9 x 6 slow-fly propeller, and energy from a Thunder
Power 1320 two-cell Li-Poly battery pack. The four-channel control
operates four servos.”
Watch for a construction article in Model Airplane News. When it is
published, Pat indicated that laser-cut kits will be made available.
Let the sun shine, let the sun shine in ... well, maybe not in but on in
the case of a small model developed by Ralph Bradley. Awhile back I
had the opportunity to show you a nice solar-powered small-field flyer
that Ralph developed called the Sol Mite.
That model has a 30-inch wingspan and is relatively small by solarpower
standards. When developed, Ralph had hoped he could one day
build a solar-powered small-field flyer that was more in his preferred
size range: tiny.
As luck would have it, Spectrolab, the company that developed the
solar cells he used, has come up with cells that are even more efficient.
The cells Ralph received are improved triple-junction gallium arsenide
with efficiencies of approximately 31% under terrestrial conditions.
06sig4.QXD 4/20/07 2:00 PM Page 109
With only two of the new cells in hand, Ralph
developed a solar-powered model with an 8-
inch wingspan that weighs 9.5 grams. I’ve
included a couple photos of it for your review.
As was the case with his other solar-power
effort, this new model is directly solar with no
onboard buffer battery. If the sun does not
shine, this little aircraft does not run.
Equipment for the airplane includes a 900
MHz Plantraco .38-gram receiver, magnetic
actuators from Nick Leichty, a 4mm pager
motor, a Plantraco Carbon Butterfly propeller,
and a homemade 7.1:1 gear drive that uses
watch gears.
To fly the model you orient the wings to
the sun and plug the receiver into the solar
cells connector. With the motor running,
launch and you are off. The model has nice
power overhead with the two solar cells and
the 4mm geared motor.
The only issue Ralph has run into so far
with the model is making sure the sun is high
enough in the sky when flying (on a calm day
only). If the sun is too low, the power can
brown out when the model turns away from
the sun. That causes the receiver to reset and
the motor shuts off. As long as the sun angle
is adequate to keep the solar cells delivering
power, all is well.
I have the feeling that as the demand for
alternate power sources continues to climb,
we are likely to see some nice solar-cell
developments. Perhaps one day they will be
good enough to allow solar-powered indoor
flying. When that day arrives, Ralph notes
with a big smile, we’ll need someone on the
building dimmer switch to control altitude!
FMA Direct was an early player in the world
of Li-Poly battery technology as it applied to
the model-aviation industry. Along with
offering quality Li-Poly cells, the company
has been a source for related products such as
innovative chargers and battery-care
equipment.
In the interest of continuing to be a valued
source of products for people who fly electricpowered
models, FMA Direct has announced
a new working arrangement with
WorleyParsons Advanced Energy Solutions
of Australia. The Advanced Energy Solutions
group, based in Singapore, has focused on
portable energy systems since 1997 with
micro turbines, renewables, fuel cells, and
advanced batteries as part of its scope of
work.
The companies’ combined engineering
resources will help ensure that the latest
developments in Li-Poly battery and charger
technology are made available to the RC
modeling community. The products will be
marketed and sold under the brand Cellpro
Revolution.
It is nice to see FMA Direct continue to
work toward advancing the state of the art in
electric power. We all benefit when the
manufacturers make such efforts to deliver
better products to help us fly our models.
Here we are once again at the end. As
always, don’t be bashful about sending me
a picture or two of your latest project. In
addition to the E-mail address in the
column header, you can reach me via
regular mail at 32238 Spinnaker Run,
Magnolia TX 77354. MA
Sources:
Reproduction kits for the 54-inch Comet
series:
Tom Martin Radio Control
20808 S. Prospect Ave.
Belton MO 64012
(816) 331-8807
[email protected]
www.tmrcsailplanes.com
Solar cells:
Spectrolab
12500 Gladstone Ave.
Sylmar CA 91342
(818) 365-4611
Fax: (818) 361-5102
[email protected]
www.spectrolab.com
Li-Poly cells and chargers:
FMA Direct
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com