the wing lift needed to keep an airplane in the air. When the
ailerons are deflected at a positive angle of attack, the down
aileron presents a wider frontal cross-section, thus creating
= Left yaw
In flight, the down aileron presents a wider cross-section, increasing
drag and causing adverse yaw (a yaw in the opposite direction that the
ailerons are applied).
more drag and causing the airplane to yaw in the opposite
direction in which the ailerons are applied (Figure 4).
When two aileron servos and the flaperon function are used,
adverse yaw can be lessened by programming a small amount
of differential aileron travel (for example, approximately 5°
less down aileron than up), consequently improving control
and producing cleaner axial rolls.
The exception is when the airplane has a flat-bottom
wing. Drag on the side of the down aileron and adverse yaw
is so much more pronounced with a flat-bottom wing that
differential aileron travel has little effect.
To eliminate adverse yaw, rudder must be coordinated
or mixed in the same direction as the aileron. As a rule, a
symmetrical-wing airplane may require only a 3% to 5%
rudder mix with the aileron to eliminate adverse yaw, whereas
a flat-bottom-wing airplane requires nearly as much rudder
deflection (in degrees) as aileron (Figure 5).
Not only does eliminating adverse yaw improve control,
pilots who initially
learn to fly with
mixing are also
able to more easily
You must coordinate
or mix rudder with
the aileron in the
same direction to
yaw when flying a
transition into higher-performance, symmetrical-wing airplanes
because they are already accustomed to flying with minimal
Contrast that to those who learn to fly with adverse yaw
then have to retrain their flying habits when they switch to a
symmetrical-wing airplane with little adverse yaw.
Advanced Dual Rate and Exponential Rules of Thumb
Expert pilots are often asked about their favorite aerobatic
airplane. After a person graduates to flying Edges, Extras,
Sukhois, and similar models, he or she will find that these
aircraft are equally capable. Any differences that are not setup
related are barely noticeable to all but the most expert of fliers.
The real question is whether your airplane will be set up to
promote maximum success.
Although not necessary for Precision Aerobatic flying, a
computer radio with dual rates and exponential is required for
3-D flying. That’s because the large control-surface deflections
required for 3-D maneuvers would cause an airplane to be too
responsive during normal flight.
Dual rates allow a pilot to achieve optimal control response
modes of flight.
Figure 6 Figure 6
“high” rates allow
for 3-D flying,
LINEAR HIGH RATE
flying, takeoff, and
landing (Figure 6).
To help you stay
focused on flying
and not on flipping switches, it’s recommended that you put
all of your dual rate and exponential settings on one switch.
On high 3-D rates, an airplane will be too sensitive and hard
to control between maneuvers, so 30% to 50% exponential is
used to reduce control sensitivity through the first third or half
of stick deflection. Exponential will allow you to fly with the
“feel” of normal rates when the stick inputs are less than half,
but then rapidly ramp up beyond that.
Because of the current dominance of extreme 3-D flying,
airplane manufacturers more frequently recommend low rates
that are low relative to high 3-D rates, but are still too much
for Precision Aerobatics flying, takeoff, and landing. That is
why manufacturers recommend exponential even on low rates.
To develop the precise timing required to fly aerobatics well,
it’s important to maintain a close correlation between your
inputs and the response of the airplane. The ideal low/normal
rate settings should provide a comfortable control response
with minimal use of exponential (Figure 7). If the airplane is
touchy on low rates, before you start adding exponential, first
try reducing the low-rate percentages.
LINEAR LO W RATE
50% 25% 75%
S TICK DEFLEC TION
Mixing Rules of Thumb
For many reasons, every airplane exhibits some unwanted
AUGUST 2013 www.ModelAviation.com