IT SEEMS THAT there is always something
new and different to challenge us in this hobby
and to stimulate a deeper interest. Such was
the case when I had the opportunity to join a
group of university engineering students in an
international design/fly competition for Radio
Control (RC) models: Aero Design East, held
April 12-14 at Titusville, Florida.
I had seen articles in the modeling press
regarding the Aero Design competition
sponsored by the Society of Automotive
Engineers (SAE), and I knew it was a contest
for college engineering students to build RC
models with the greatest payload capacity.
Aeronautical engineering students at the
University of Cincinnati (UC) contacted our
club—the Greater Cincinnati Radio Control
Club (GCRCC)—through our Web site. The
students had minimal experience with RC and
were looking for advice and information. Our
webmaster forwarded the request and
suggested that some of the engineers in the
club might want to get involved. Fred Murrell
and I quickly volunteered; he is a mechanical
engineer and had built an Aero Design entry
when he attended UC, and I’m a chemical
engineer.
Fred and I attended one of the students’
meetings. We were introduced to the team and
their faculty advisors, and we told them about
our club. We hit it off immediately and began
a rewarding relationship. I learned the
contest’s general rules and the aircraft-design
constraints.
Each airplane is limited to a maximum of
1,200 square inches of total projected area.
Only stock K&B or O.S. Max .61 engines are
allowed. The aircraft must be airborne within a
200-foot takeoff zone and land with all wheels
on the ground in 400 feet. Rollout beyond that
is permitted. A 300-cubic-inch cargo hold is
specified, and the propeller must turn at the
same rpm as the crankshaft; i.e., no reduction
units.
Direct participation is limited to SAE
members, but any AMA member can serve as
pilot. Competition includes a formal written
report, an oral presentation with questioning,
and flying the model.
We invited the Aerocats (the team name is a
February 2003 59
Aerocats
Aero Design East
and The Aerocats’ entry utilized vacuumbagged
foam wing with plywood spar,
riveted aluminum fuselage, carbon
tailboom.
■ Chuck Snyder
The UC Aerocats (front L-R): Tyler Frost, Steve Holman, Aaron Bricker, Alfonso
Capetillo; (back L-R) Curtis Aldrich, Slava Garb, Chuck Snyder, Liz Wiesehan, Nick
Elchert.
This is a successful flight. Models flew
several rounds with increasing loads until
they failed to become airborne.
02sig2.QXD 11.21.02 2:24 pm Page 59
60 MODEL AVIATION
play on the UC Bearcat mascot) to attend our
club meetings and offered a demonstration at
our field that weekend. They accepted
enthusiastically! The demonstration was a
success, and the Aerocats and GCRCC
members quickly became friends. We flew
many different types of aircraft, and several of
the Aerocats tried flight on buddy boxes. This
made believers out of them regarding our
advice that they find an experienced pilot.
Our club president, Mike Bluestein, had
brought an old Craftair Butterfly with a
SuperTigre .15 engine. I suggested to the
Aerocats that their airplane might resemble
this model, which is essentially a powered
glider. Then we started teasing Mike about
trying to see how much the Butterfly could
lift. Eventually he gave in, and somebody
found a softball-size stone that we rubberbanded
on top of the wing center-section.
It took several attempts, primarily because
of ground-handling difficulties presented by
the tail-wheel configuration, but Mike coaxed
the Butterfly aloft, flew a circuit, and landed
to a round of applause. The Aerocats decided
that they would build a tricycle-gear model!
Later Mike was besieged with chants of
“More rocks, more rocks!” He took the bait
again, and another rock was somehow
strapped on top of the first one. The landing
gear on the poor little Butterfly was splayed
U. of Missouri at Rolla team with Unlimited model, ready for
attempt after all-night repair session. It was unsuccessful.
This beautifully carved winglet on one of the University of
Warsaw (Poland) models would make any modeler envious.
Several teams had the capability to conduct all-night repair
sessions. Unfortunately this was needed often!
Most models in competition were of “normal” configuration, but
there were unusual approaches such as this pusher design.
This Unlimited Class entry from the University of Missouri at Rolla used two Jett .95
engines for power. Imagination abounded at this event!
Photos courtesy the author Graphic Design by Lydia Whitehead
almost to the point of letting the belly drag,
and the engine could barely move the model.
It took several attempts and the assistance of
the downhill portion of our runway, but Mike
got both rocks airborne. After wallowing
around the pattern, he landed and announced
that there would be “Absolutely no more
rocks!”
During the winter Fred and I attended
Aerocats meetings, and they brought progress
reports and aircraft components to our
meetings. In addition to a great deal of
unsolicited advice from the general
membership (surprise, surprise), the Aerocats
received a trainer kit and an old radio from
Ernie Jones that they could build to get some
modeling experience. At some point during
this time period they asked me to be their
pilot.
The modelers tended to look at this project
as if it was just a model-airplane contest; in
reality, it was the Aerocats’ senior
engineering design project in which they were
charged with integrating everything they had
studied into a logical project yielding a
02sig2.QXD 11.21.02 2:25 pm Page 60
“product” that would achieve certain goals.
Being able to predict the aircraft’s
performance was a major portion of the
project. Every aspect of the design had to be
evaluated and appropriate calculations
completed. The team had access to computeraided
design and drawing programs and plenty
of computing power. Later we’ll see how well
they did with the forecasts.
Several of the Aerocats had had summer
jobs or co-op experience at full-scale-aircraft
manufacturers, so it was not surprising that
their airplane resembled a “miniature” fullscale
aircraft rather than a big model. The
fuselage was aluminum with a carbon-fiber
tailboom, and the wings were vacuum-bagged
fiberglass and carbon over foam.
The team decided that maximizing lift
would be its top priority, and other major
considerations would be engine thrust,
structural integrity, and weight reduction.
After reviewing the video of a previous
competition, they decided on a conventional
high-wing aircraft.
The airfoil would have to provide high lift
at low airspeeds, but it would never have to fly
at “high speed.” Consequently, they selected a
Selig S1223 airfoil that I understand was
developed specifically for this competition. It
is a highly undercambered section of
approximately 15% maximum thickness. It
achieves a lift coefficient greater than 2.0 (by
comparison, the classic Clark Y has a
maximum coefficient of 1.6).
The Aerocats evaluated the tradeoffs
between wingspan, taper ratios, area, aspect
ratio, induced drag, strength, and weight. The
result was a wing with a span of 110 inches,
an aspect ratio of 12.5, and an area of 968
square inches. With the stabilizer and fuselage,
the total planform area would be 1,194 square
inches.
This airfoil has pitching characteristics that
require a great deal of down force to be
generated by the stabilizer to control the
aircraft. The Aerocats selected a low-drag,
lifting airfoil for the stabilizer, but they
mounted it inverted to get all of the down
force required. I saw several other airplanes at
the contest that used the same airfoil and had
their stabilizers on “upside down.”
The second priority was structural
integrity, and the airplane was designed for 2.5
grams with a 1.5 safety factor. The fuselage
and tailboom were designed to withstand
simultaneous maximum deflection of the
elevator and rudder. The wing was analyzed as
if it was an I-beam with a birch plywood shear
web and carbon-fiber caps.
The calculations showed that the shear web
could be 3⁄32-inch thick at the root and taper to
1⁄32 inch at the tip. For ease of construction the
team used a web of constant thickness. The
carbon-fiber caps were designed as two layers
of cloth with a constant thickness of 0.018
inch. The width could vary from 3⁄4 inch at the
root to 1⁄16 inch at the tip. The model used
some extra material “just in case.”
There was excellent data available for the
preceding parts of the design, but engine thrust
was another story. The Aerocats selected the
O.S. .61 FX, but did not have horsepower or
torque curves for the engine. I found several
magazine engine-review articles with curves
for similar engines; these provided the basis
for design estimates.
The computerized calculations confirmed
what experienced modelers intuitively know:
the propeller should have a large diameter and
low pitch. Unfortunately there are no
commercially available propellers with the
optimum diameter and pitch.
The design went forward with an
optimistic assumption of the thrust that could
be developed. This decision was rationalized
by budget constraints that didn’t allow for the
purchase of a dynamometer. When I learned
that they “couldn’t get” any actual thrust data,
I invited the team members to meet me at the
field and asked that they bring their collection
of propellers, a short length of rope, and a fish
scale. I brought one of my airplanes with an
older O.S. .61 and a tachometer.
We set the model on a picnic table and tied
the scale to the tail. This looked like a
reasonable approximation of a dynamometer
to me! Within an hour we had data on several
propellers. Propellers in the 12 x 6 to 14 x 4
range produced similar thrust readings, but no
usable propeller let the engine come close
to the horsepower peak at 16,000 rpm.
This information was included in the
project report with the comment that
“tested props were never able to obtain
[the calculated performance].”
made the oral presentation. The old wing was
also put back in service.
The father of one of the Aerocats was able
to attend the contest. Steve Frost is a corporate
pilot who knows how an airplane ought to
look. He and I walked into the motel room
where the first group was having a lively
discussion about the wing and stabilizer
incidence. Clearly there wasn’t a consensus,
and the Aerocats were about to vote.
“If you are going to vote,” I announced,
“Steve and I get to vote too, and we are going
to age weight the voting!” There wasn’t a
vote, but the stabilizer was installed properly.
Ours was not the only crash. Takeoff and
departure stalls were common, and I saw a
couple of airframes break up in midair. The
Unlimited airplane with the Nelson .40s
managed a few feet of straight-ahead flight,
and one of the other Unlimiteds crashed in
front of us. Neither of them looked
controllable to me.
The oral presentations were made at the
local community college, and I intended to
listen to several in hopes of learning some of
the other teams’ secrets. Wrong! Only team
members and associates were permitted to
hear the presentations. The Aerocats did a
great job and tied for the highest oralpresentation
score.
Surprisingly the questioning was not
focused on the technical aspects, but was
directed at the project-management side of the
experience. This made sense after I talked to
the event organizer who told me that most of
the teams do not actually complete their
airplanes!
The next morning brought the beginning of
official competition. The Aerocats were
excited because they were in fifth place based
on the written and oral presentations. Their
only shortfall turned out to have been in the
area of stability. Although my engineering
background didn’t provide experience with
these calculations, as a modeler I was
painfully aware that they deserved the low
score.
When our turn to fly came, guess what
happened? Another short roll, pitch up, stall,
and crash. By the way, we had moved the
center of gravity farther back than it was in
Cincinnati. Fortunately the damage was
reparable. The Aerocats did a great job of
effecting repairs again with the aid of power
tools lent to them by another team.
We were ready to fly again by late
afternoon. Hooray! It flew! But the flight
didn’t count because the takeoff roll exceeded
the 200-foot limit. Even though we had a
trimmed and flyable airplane, my self-image
as a pilot was low.
For the next attempt I decided to stand at
the 200-foot marker so I could better judge
when to rotate. Maybe that would help me
make an official flight. I had been checking
scores and knew we could make a good
showing if we could duplicate the weight we
lifted in Cincinnati, but competition was over
for the day.
Sunday was another beautiful day, but Lady
Luck was still leaving large teeth marks in our
collective rear ends. This time a
propeller/spinner combination did not allow
the propeller nut to tighten properly. They
don’t give points for shaft runs, and we were
running out of scheduled rounds to get on the
board. The spinner was discarded, and the
propeller was attached with a plain, old hex
nut.
Then the discussion revolved around
picking a payload we knew we could lift or
“going for broke” with what the calculations
said the airplane could lift. I don’t recall
the decision method, but they loaded the
model with a “little more” than we lifted
back home.
We finally had a successful takeoff and
circuit of the field. I flew a second circuit
of the pattern to settle down, then I landed
the model to the cheers of the Aerocats and
the other teams. I think the payload was
roughly 18.0 pounds. That got the team on
the board, in 12th or 14th place, and I
began to feel like a human being again.
There was time for one more round, and
the Aerocats put 20.3 pounds in the cargo
bay. What a flight! Video cameras
recorded a couple of snaps right after
takeoff with the right wingtip almost
dragging the ground. The big,
counterbalanced rudder overcame the
snaps, and after a long, slow climb I gently
turned crosswind for a really big pattern.
The airplane flew fine as the speed built
and landed to the applause of everyone on
the flightline.
The contest ended with the Aerocats
being one of only five teams to lift more
than 20.0 pounds. The winners from the
University of Warsaw lifted 25.0 pounds.
The scoring is not directly related to the
amount lifted, but rather to the ratio of
actual to forecast. As a result, the Aerocats
finished in 10th place because they had
predicted a maximum of 28.0 pounds.
How did the other predictions come
out? The team was right on the estimate of
11.5 pounds for the model’s empty weight.
The airplane survived, so it must have been
strong enough, but we’ll never know how
overbuilt it was. I had overheard claims of
airplanes that weighed 6.0 pounds.
And what about the “real world”
propeller thrust we had measured?
Theoretically the airplane should not have
been able to fly on that last flight. I guess it
is a good thing they didn’t tell me that
ahead of time!
This was a fantastic performance for a
first-time team, and the students were
rightfully proud of their accomplishment.
The association between the Aerocats
and the GCRCC was fun and rewarding for
everybody involved. All of the Aerocats
were seniors, and they started their careers
in aeronautical and aerospace engineering
after graduation. I’m sure that the overall
modeling experience was positive for
them, and several will probably take up our
hobby when they have time. If you get a
chance to participate in a similar
opportunity, jump on it!
P.S.: None of the Unlimited airplanes had
successful flights. It made me wish I had
brought my Moki 1.8; we could have stuck it
on the front of the Aerocats airplane and won
that event. MA
Chuck Snyder
10759 Moss Hill Ln.
Cincinnati OH 45249
