propwash that strikes the left side of the vertical tail and tries
to yaw the airplane to the left.
Propwash is generally held in check at higher speeds by the
faster airflow over the tail. However, at lower airspeeds with
high power, such as during takeoff or approaching the top of
a loop, the pilot has to correct the propwash. Building in a
couple of degrees of engine right-thrust helps to counter the
effects of propwash, therefore reducing the demands on the
pilot (Figure 2).
Ya w Axis a w Axis
Building in a couple
of degrees of right
thrust helps to reduce
by the propeller
P-Factor is a left-turning tendency
when the airplane is at a positive angle of attack, because
the propeller blade on the right side of the airplane is biting
more air and producing more thrust than the blade on the left
Building in a couple of degrees of downthrust places the
propeller at slightly less of an angle to the relative wind to
achieve a more equal bite on both blades during inside (
up-elevator) maneuvers, reducing P-factor and demands on the
Another benefit of downthrust is providing a down force
to counter excess wing lift when an airplane is flying at higher
speeds. This is especially important with flat-bottom-wing
Control Surface Travel Rules of Thumb
As a rule, how an airplane responds to control inputs is a
function of how fast and how far the control surfaces deflect,
regardless of the airplane’s size or strength of performance.
Seldom can you go wrong by initially setting up your control
surface deflections/travels according to the manufacturers’
However, don’t make the mistake of thinking that those
recommendations are what the manufacturer intends you to
stay with. To fly your best, you must adjust the control surface
travels to suit your immediate skill level.
Perfectly good airplanes are often faulted or retired because
the pilot did not like how it handled, tried unsuccessfully to
become accustomed to it, and finally went looking for another
airplane. By simply changing the travels to suit your comfort
level, you’ll immediately start flying with more confidence and
begin building on that success, instead of continuing to try to
get used to the airplane.
When setting travels using a computer radio, it is vital that
you triple-check the physical deflections of all the control
surfaces in all directions. For a variety of reasons, it is often
necessary to program different percentages to achieve the same
physical travel of a surface in both directions.
AUGUST 2013 www.ModelAviation.com
Thousands of airplanes are faulted because their owners
make certain assumptions based on the “numbers” they read
off of the transmitter, but leave out the step of confirming all
of the physical deflections. They either end up unhappy with
the way their airplanes handle, or assume that having to make
numerous and/or large adjustments later is an indication of a
poor design when, other than more left aileron than right for
example, the airplane is fine.
Another vital component of good flying is achieving
balanced control responses. “Balanced controls” describes
the ideal condition in which all of the controls are equally
sensitive. Other than a lack of control-stick tension, possibly
nothing inhibits progress more than when one of the controls
is noticeably more or less sensitive than the others, forcing
At positive angles of attack, the propeller blade on the right side of the
airplane bites more air and produces more thrust than the blade on the
left. Building in a couple of degrees of downthrust places the propeller
at slightly less of an angle to the relative wind to achieve more equal bite
on both blades during inside maneuvers.
(Asymmetric propeller thrust)
Left-side blade bite
Right-side blade bite
Left-side blade bite
Right-side blade bite
the pilot to remember to use two different control pressures
depending on the input.
Even a novice pilot can tell when the ailerons are more
sensitive than the elevator, for example, so why would you
accept one control that is more or less sensitive that the others
when a simple control surface travel adjustment is all that’s
needed to start feeling more comfortable?
Aileron Rudder Mixing Adverse Yaw
Adverse yaw is an inherent opposite yaw or skid that occurs
with aileron deflections.
A positive angle of attack is generally required to produce