by Dave Scott
Optimum setup rules-of-thumb for the way you fly
Note: The following information might upset a career
aerodynamicist, because it does not include explanations of mean
aerodynamic center, decalage, neutral point, etc. when describing
optimum CG location and wing incidence.
The objective of this article is not to teach in-depth
aerodynamics, but to condense flight dynamics into simple, foolproof
rules of thumb that the average pilot can wrap his or her head
around and thereby achieve an optimized airplane setup that
ensures the greatest opportunity for success.
For those who wish to study in more detail the formulas that are
the stock and trade of professional aerodynamicists, there are plenty
of sites online, such as Wikipedia. See the link in “Sources.”
There is probably no other subject with more varied opinions than how to best set up an airplane. Yet, if you could rank all of the different setup methodologies
based on the results obtained within four or five days, you
would quickly discover that certain setups promote faster
rates of learning and better results than others.
This article features the setup rules of thumb that have
proven to produce the best overall results in the shortest
amount of time during 1st U.S. R/C Flight School’s solo and
RC pilots are regularly trying new setups that promise to
improve their flying, but if they could objectively evaluate
their performances, they would realize that in some cases
they actually flew better before the new setup. However,
instead of returning to what worked best, they hope to
overcome the new challenges with more practice.
The tricky part of airplane setup is knowing what really
helps, what sounds good in theory but isn’t, and what may
be applicable to some forms of extreme flying, but would be
detrimental to most or all of your flying.
Where you chose to balance your model will have a huge
impact on how it handles in the air and how well you fly it.
When an airplane pitches up or down, it pivots around a
point on or near the wing’s thickest point (Figure 1). When
CG in-line with pitch axis = “Neutral”
CG (Aft of pitch axis)
the CG is located
at this pivot point,
the airplane tends
to be “neutral,”
or prone to doing
only what you tell
it to do.
When the CG
is aft of the pivot
will tend to be
to shooting an
arrow backward, a
would be inclined
to swap ends in
flight if it were not
for the tail and the
at the extreme
ends of the flight
envelope, but as a consequence the airplane requires much
more effort to fly the rest of the time, especially at slower
speeds when the tail forces are less firm. A nose-heavy
airplane tends to be less stable and less maneuverable, and
will behave differently depending on the speed.
A neutral CG location at the wing’s thickest point provides
the best overall handling without restricting maneuverability.
Wing’s thickest point
As a rule, airplanes in flight pivot around a point on or near the
wing’s thickest point.
When the CG is neither forward nor aft of the wing’s thickest
point, the airplane neither resists nor exaggerates what it is
told to do and behaves basically the same at any speed.
When the CG is aft of the
wing’s thickest point, the
airplane will be unstable at
all speeds and require more
effort to fly.
Setting up your airplane with engine right- and downthrust
will cause it to fly more true.
As the propeller turns, it produces a spiraling slipstream or
AUGUST 2013 www.ModelAviation.com