156 MODEL AVIATION
The difference between a system and a setup for a Stunt model
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Control Line Aerobatics P.T. Granderson
VSC party time at Keith Trostle’s. Ken Ribardo’s 1959 Ares gets fine adjustments with an
incidence meter. L-R: Charlie Reeves, Warren Tiahrt, Bob Hunt, Ken, Keith. Randy
Smith photo.
Ray Firkins puts his beautiful Phoenician through its paces. This
model is a Clair Sieverling design.
Ace pilot Michael Duffy won the 2006 Vintage Stunt
Championships’ Spirit of 64 competition with his Nobler.
Also included in this column:
• More thoughts about finishing
• Meet Mike Duffy
• The author signs off
SYSTEMS AND SETUPS: What is the
difference? A system comprises
components with a range of performance
that can be adjusted and tuned for changing
conditions. A setup comprises specific
components that are supposed to work
together consistently. Setups can be
problematic if we have little or no
knowledge of the system on which they are
based.
After deciding to write about this topic,
my first thought was to ask some wellknown
experts for their setups and publish
the information as a sort of reference guide.
When I talked to a few pilots (and judging
from my experience), it was apparent that
no matter how precise the setup is, there
will always be changes and compromises
depending on the desired result.
What’s your setup? I hear this question
with some regularity. That inquiry covers
the entire spectrum of CL Aerobatics
(Stunt), from power to airframe and even
control lines to line clips.
In our quest for the ultimate flying
machine, we often look for the most direct
and quickest method of success. Use
certain engines, head shims, propellers,
fuels, plugs, etc., and everything will work
perfectly. Use this airfoil, flap-to-elevator
ratio, wing area, tail moment, thrustline,
etc. Through the years much of the setup
information has taken various forms and
compilations, including charts, graphs, and
diagrams.
If you give five experts the same
equipment, each will set it up differently.
07sig5.QXD 5/23/07 10:09 AM Page 156
What mysterious, secret knowledge does
each possess that causes them to be
different?
They understand the systems that
support the setups and apply that
knowledge in an effort to reach success at
a specific time and place. The more
knowledge you have of the systems, the
easier it is to make the setup work.
At a contest last year my good friend
Phil Juarez was flying his beautiful Stiletto
and having problems with power output.
He had purchased the entire O.S. .40 VF
setup used, but it was in perfect condition
with the pipe header installed and adjusted
for the propeller that was included in the
setup from one of the local cache of
National Champions and world-class fliers.
During flight the engine seemed weak
and was noisier than usual, slowing and
stalling in maneuvers. After Phil landed
the model he complained about the lack of
power and turned the needle valve in a
little more to get additional power.
The next flight was worse, with the
problems becoming more exaggerated.
Watching Phil’s flight I suggested that the
engine was not running on the pipe and
began looking for the problem.
When the cowl was removed the issue
was immediately identified. The rubber
hose connecting the header and pipe had
ruptured. After replacing the hose, the
power returned instantly. After landing the
aircraft Phil made an interesting comment.
“The guys I fly with don’t use pipes
and we just don’t know what to look for if
something goes wrong,” he said.
Given a reasonable understanding of
how the pipe system works, the diagnosis
and fix was easy.
In the past year of writing this column I
have tried to provide straightforward
information that can be easily understood
and applied to achieve good results.
Although the information is not intended
for or directed toward the experts, many
have commented that they have found it
informative.
In this age of TMI (too much
information), it is often difficult to digest
and understand what works and how it
works. The Internet is bursting with
information, good and bad, about almost
any subject imaginable, model aviation
included.
In general, if you read or hear
something and it sounds too complicated,
it probably is. So let’s go back to the
basics.
When it comes to internal-combustion
engines, the one thing to avoid is any kind
of leak. There should be no leaks in the
fuel tubing, tank, exhaust, head, backplate,
etc. Avoiding leaks is simple, yet it is the
cause of 90% of all the problems I’ve seen
throughout the years.
The next thing to avoid is anything
being loose. There should be no loose
mounting bolts, engine mounts, propellers,
spinners, etc.
If you have been considering using a
tuned pipe but are not sure how it works,
the pipe regulates and controls the speed of
the engine in flight. It has at least one
baffle internally, and the distance of the
first baffle (in the case of multiple baffles)
from the engine exhaust determines how
fast the engine will run.
Moving the baffle closer to the engine
exhaust will cause the engine to run faster.
Moving it farther away will cause the
engine to run slower. To determine the
distance we measure a straight line from
the center of the combustion chamber—
usually the glow plug to the first baffle.
Although that was an oversimplification
of how a pipe works, that is how it is used
in practice. It is only part of a power
system that includes the fuel, fuel mixture,
fuel tank, glow plug, engine timing,
cooling, seal, and a host of subcomponents
to these primary parts, but the setup gives
you a good starting point for these.
Another common problem is your
airplane hunting or climbing and diving
during level flight. Let’s say you built it
straight, balanced it properly, and set up
everything exactly as the designer
specified. You tried adding nose weight
and tail weight, changing the handle
spacing, taping the hinge lines, etc., and
nothing seemed to work.
You did everything right, but you
missed one basic thing. The controls are
stiff and don’t move freely. You got some
paint or glue in the hinges. A drop of oil or
cleaning with alcohol frees up your
controls, and your airplane settles into a
perfect groove in level flight.
The setup was correct, but the problem
was in understanding the system and its
basics. A setup is a good starting place.
The goal is to find a combination that
works best for you and not for someone
else.
So what is the best way to learn about
the various systems? The answer is closer
than you think.
Our airplanes talk to us all the time. By
making sure things are straight, tight, and
leak free, you will force your model and its
systems to tell you the truth.
Have you ever noticed that most experts
who fly classic airplanes don’t use a
tachometer to set the engine? They can
seldom tell you what the rpm is at launch.
Have you ever seen someone start the
engine, remove the battery, hear a change
in engine speed, and diagnose the problem
as a faulty glow plug? They listen to what
the engine is telling them.
In every case the common link is
practical experience. These fliers have run
many engines and made many flights. They
know the fundamentals.
Enough of the boring but necessary
fundamentals. The flying season is here.
Most people think it’s never rainy,
windy, or cold in California, so let’s go
with that. We just don’t fly much in the
winter months because airplanes have to
be built. I hope you have at least one new
model for the spring coming-out party.
If you’re a contest flier, I hope to see
you at an event somewhere. If you’re a
sport flier who likes to do tricks, maybe
you have some super-fun stuff that makes
you smile and even laugh.
I have a new design ready for paint,
but I have painter’s block. I can’t figure
out the exact paint to use and where to put
it!
Past columns about paint preparation
and finishing have brought quite a few
questions and revealed some products and
sources that are now extinct. My
apologies for recommending out-ofproduction
items.
When I find something that works, I
usually stockpile it and sometimes lose
track of where I got it. Since I have a 50-
pound bag of talc I bought at Tap Plastics,
it never occurred to me that the company
would no longer carry the stuff, but it
doesn’t.
There are other sources for pure talc
that contains no asbestos, oils, or
perfume. If you have Internet access, you
can find a variety of fitness- and billiardsupply
sources that sell the pure stuff.
On the subject of talc, many have
asked why I prefer it as a filler when other
materials are marginally lighter and stay
suspended in clear modeling dope. The
fact that it does not stay suspended in
paint is exactly why I prefer talc.
The object of filler is to fill the low
spots on our models. Talc settles into the
low spots, and after sanding it is held in
place with a thin layer of paint. By having
less paint that shrinks and more filler in
the low spots, you greatly reduce the
event of grain and low spots reappearing
as the paint ages and shrinks.
Others have asked whether they should
cover open bays on wings, stabilizers, and
elevators before or after the carbon veil.
These are covered with silkspan or tissue
over the carbon veil.
The photo in the previous column
shows a model with open bays on the
wing where the carbon veil has been cut
out between the ribs. Covering with tissue
and subsequent painting add tremendous
integral and tensile strength to the
airframe.
There have also been many questions
about using full-strength dope brushed on
and no sanding between coats. The reason
for this is that thinner is a solvent.
Solvents mix with the dope and slow the
evaporative process of drying.
Thinned dope sinks deeper into the
grain and low spots. It will require more
coats, while softening and trapping the
previous coats deep in the pores and low
foundation on which to apply the final
finish.
The reason for not sanding or removing
sanding dust between coats is that balsa dust
is the perfect filler and adds absolutely no
weight while retaining its inert stability. It
might seem crazy, but it works!
The PPG Global Performance System
D893 clear automotive coat has not been
readily available since 2004. My apologies
again, but I bought a gallon in 1999.
Because it flows out so well and takes
little liquid to cover, I have enough left to
finish at least another seven or eight models.
So far I have used that same gallon for 14
airplanes. Although the purchase price
seemed extremely high, this product has
proven to be extremely economical.
In March at the Vintage Stunt
Championships in Tucson, Arizona, there
were many opportunities to smile and laugh
and just have some fun. My most
memorable smile was prompted when I had
the good fortune of watching a skilled and
determined young pilot give an impromptu
flying lesson.
Many people may not recognize the
name Michael Duffy, but I hope you have
the good fortune of meeting him as I did. At
the age of 13, he is bright, articulate, flying
very well, and having almost too much fun!
“At times I get very competitive and at
others I will lay back and just fly for the fun
of it,” he said.
Thanks, Michael, for reminding us all
why we do this!
This month’s column is the final
installment of a commitment I made to MA a
year ago. I sincerely hope you have found
food for thought, stimulation of ideas, and a
bit of useful information.
For me this has been yet another chapter
of the adventure that began 52 years ago. I
thank you, the reader, and MA for sharing
and allowing me this opportunity. The
adventure continues as I focus on a
commitment I made to myself 10 years ago.
Alas, I am much more of a builder, flier,
and competitor than writer. By the time you
read this I will be in Muncie, Indiana, at the
Nats, flying, waiting for the rain to let up,
and trying to pick the best placement of
maneuvers in crazy wind conditions.
One thing is certain: although I have
equipment and setups that work consistently
in a variety of conditions, there are sure to
be some surprises. If problems result from
changing conditions, the systems that
support the setups will be critical in the
solutions.
My good friend Bob Hunt will be your
new columnist, and I’m sure you’ll be
entertained, enlightened, and get a charge
from this column as he shares his vast
knowledge and enthusiasm with you.
Get out and fly, have some fun, and
