Aileron-Rudder Mixing Explained - rcflightschool.com

Aileron-Rudder Mixing Explained

“Building Good Habits for a Better Future”

By Dave Scott. Instructor, 1st U.S. R/C Flight School
Illustrations by Dave Scott

Drag

Adverse Yaw Dave Scott is a champion full-scale
aerobatic competitor and airshow pilot. He
1ST U.S. R/C FLIGHT SCHOOL founded 1st U.S. R/C Flight School and has
1ST U.S. R/C FLIGHT SCHOOL professionally training more than 1500 R/C
pilots of all skill levels. His groundbreaking
training manuals and articles feature the
accelerated teaching techniques developed
during his 14,000 hours of instruction and
experience setting up and test flying over
1000 airplanes at his school. More
information about his books and school can
be found at www.rcflightschool.com

The following article details the use of pre-flight preparation. As a result, Adverse yaw is most pronounced on
programmable Aileron-Rudder mixing most pilots learn to fly by “reacting" to high lift flat-bottom wing aircraft and
to eliminate “adverse yaw”. While what the plane does. Consequently, gets worse at slower airspeeds and/or
primary aimed at eliminating adverse many pilots naturally think that when making larger aileron inputs.
yaw on a primary trainer, the getting better at making corrections, (Adverse yaw is so severe on a scale
descriptions and explanations should good reflexes, and more stick-time are Piper Cub for example, that when flown
help cement your grasp of a subject the keys to becoming a better flyer. near stall speed it will actually turn left
that few in the sport understand, even Thus, rarely does adverse yaw or the when right aileron is applied, and vice-
through all pilots experience the effects advantages of A/R mixing when versa.) Also, since the principle effect
of adverse yaw every time they fly. learning to fly ever come up. However, of wind is exaggerating deviations that
if you where to objectively compare the would otherwise be minor on calmer
Introduction results achieved training with A/R days, adverse yaw creates a whole slew
mixing versus without, you would of problems when trying to fly a trainer
Nearly 100% of computer radios discover an immediate improvement in in windy conditions.
today feature Aileron-Rudder (A/R) consistency and therefore the rate of
mixing to reduce adverse yaw, i.e., the learning. In fact, as you will soon see, Some common approaches to reduce
inherent opposite yaw or skid that is learning to fly with A/R mixing can be the effects of adverse yaw in R/C have
especially pronounced during aileron credited for helping to instill proper been: Flying at higher speeds; making
deflections on flat-bottomed wing control habits that actually accelerate the trainer less stable and more
aircraft, such as those used for primary future progress. maneuverable by lessening wing
flight training. dihedral; differential aileron travel
Adverse Yaw (more up aileron travel than down);
As the name implies, adverse yaw is an avoiding wind; accepting it as how
adverse or unfavorable condition that, Space does not permit going into all trainers fly; and continued reassurance
among other things, inhibits progress. the aerodynamics involved during from club members that the student will
Traditionally, struggling and aileron deflections, so put simply; eventually get it with more practice -- all
committing to many hours of practice adverse yaw is caused by the wing with of which only help to small and varying
before soling has been the assumed the down aileron generating more lift degrees.
normal burden of the novice pilot until and therefore more drag than the wing
his or her skills improve. However, with the raised aileron (figure 1). The Aileron-Rudder (A/R) Mixing
they have unknowingly been fighting drag differential causes the airplane to
the additional challenge of flying with yaw/skid in the opposite direction that The logical solution to counter
adverse yaw as well. Indeed, pilots the ailerons are applied while banking adverse yaw is with the surface that
have always assumed that the lack of into turns, making course corrections, controls yaw, i.e., the rudder (figure 2).
correlation between their control exiting turns, etc.. Pilots therefore have Coordinated rudder deflections along
inputs/intentions and the response of to hold in the aileron longer to overcome with and in the same direction as the
the plane to be strictly the need for more the adverse skid, thus increasing the ailerons prevent the plane from
practice, and sometimes wind, when in potential for over-controlling, as well as skidding in the opposite direction while
fact adverse yaw has been a big reason! deal with a lack of consistency caused banking into and out of turns, making
by the out-of-sync relationship between course corrections, rolling, etc.. Most
It’s probably safe to say that most of the their control inputs and the response of importantly, with adverse yaw
people reading this learned to fly by the plane. eliminated, the airplane response more
trial-and-error or at the side of a closely matches the inputs and
recreational flyer/instructor with little intentions of the pilot!

Adverse yaw: An inherent A coordinated rudder deflection in the same direction
opposite yaw or skid during as the aileron prevents the nose from yawing in the
aileron deflections that is opposite direction during aileron deflections, thereby
especially pronounced on keeping banks and rolls axial.
flat-bottom wing airplanes.
Original flight path Coordinated
Right Bank
Axial

Right Bank

Increased drag on Rudder deflecting in the
the lifting wing drags same direction with the
the wing rearward, ailerons prevents the nose
causing the nose to from skidding to the left.
yaw left as the plane
is banking right.

Lift

Be clear, the function of the rudder here going to learn proper control earlier. rudder control on the left stick for left-
is not to turn the airplane. Rather, the However, as a bonus, A/R mixing also hand ground steering and maneuvers
purpose of the rudder is strictly to expands the aerobatic capabilities of a requiring independent rudder. In fact,
prevent adverse yaw in order to achieve primary trainer airplane by helping learning to use independent rudder on
a precise “axial” bank and roll aileron rolls remain axial and on the left stick proves easier after
response. heading throughout. Furthermore, the learning to fly with A/R mixing because
improved control achieved with A/R much of the right stick control will have
1st U.S. R/C Flight School trains its mixing permits flying in winds that become routine or automatic thanks to
students on planes setup to would normally ground most trainers. the consistency achieved with the mix.
automatically coordinate the rudder E.g., The main challenge of flying in
with the aileron through the A/R wind is that it tends to exaggerate Aileron-Rudder Mixing
mixing function in the radio. Radio deviations, however, the positive Setup Rules-of-Thumb
manufacturers have in fact been control achieved with A/R mixing
providing A/R mixing for the purpose of makes it possible to more precisely and Upon activating A/R mixing, you
countering adverse yaw since the promptly correct deviations before the need to confirm that the rudder moves
1980’s, but since most people are wind has a chance to exploit them. in the same direction as the aileron
inclined to keep passing down the way Thus, even experienced sport flyers (rudder moves toward the up aileron).
they were taught, it is still not widely have good reasons to utilize this setup The rule-of-thumb on a flat-bottom
used or even understood in R/C. on their flat-bottom wing planes. wing airplane is to adjust the A/R
mixing percentage so that the degree of
Those who learn to fly an honest trainer Of course, when A/R mixing is being rudder deflection matches the degree of
set up to more accurately reflect the used, pilots still have independent aileron deflection 1-to-1 (figure 3). At
control inputs they make are obviously 1st U.S. R/C Flight School we simply

gauge the degree (angle) of aileron Full deflection
deflection visually, and visually match
an equal degree (angle) of rudder. If for Rear view
some reason we are unable to set a
1-to-1 relationship, we’ll get it as close Fin Right wing
as we can, knowing from experience top 1-to-1 equal degree aileron-rudder
that a few degrees more or less is not view
going to make any appreciable deflection
difference. We then check the setup by On a flat-bottom wing airplane,
flying the airplane directly at or away adjust the A/R mix percentage so Semi-symmetrical
from us while banking left and right to that the degree of rudder 2-to-1 aileron-rudder deflection
confirm that the banks are axial and deflection matches the aileron
the fuselage stays pointed in the same deflection 1-to-1. On a semi- Fully-symmetrical
direction throughout. symmetrical wing plane, setup Minimal aileron-rudder mix
the A/R mix so that the rudder
Of course, if you are hesitant to use A/R deflects half as far as the
mixing, you can always start with less, ailerons. Using A/R mixing on a
and then keep increasing it until the fully-symmetrical wing plane is
bank and roll response is finally axial. optional, and typically no more
Although, you can be confident that than a degree or two when
after applying the 1-to-1 rule-of-thumb activated.
to a flat-bottom wing airplane adverse
yaw will be virtually undetectable: Axial Symmetrical wing airplanes exhibit
Banks, corrections, and rolls will be minimal adverse yaw and remain almost
smooth and axial, and you will feel Symmetrical perfectly axial while banking and rolling
more connected to the plane when you (except when the airspeed is low), and thus
fly. By comparison, adverse yaw is Axial there is little or no need for A/R mixing with
minimal during aileron deflections on this type.
fully-symmetrical wing airplanes Flat-bottom
(except during slow flight), and Flat-bottom wing airplanes exhibit
therefore fully-symmetrical wing significant adverse yaw and thus require
airplanes require little or no A/R mix. significant A/R mixing to achieve an axial
That means that a semi-symmetrical bank/roll response.
wing (in-between flat-bottom and fully-
symmetrical) requires approx. half as In short, learning to fly a flat-bottom wing
much rudder deflection as aileron to trainer utilizing A/R mixing leads to learning
eliminate adverse yaw. the same control habits used to fly a
symmetrical wing aircraft, thus making the
Differential Aileron transition easier because pilots are flying
without adverse yaw in both cases.
If your airplane utilizes 2 aileron
servos, you can program a small Once again, symmetrical wing without adverse yaw and maintaining a
amount of differential aileron travel airplanes require little or no A/R direct correlation between their inputs
(more up aileron deflection than down) mixing because adverse yaw is and the response of the plane (figure 4).
to help further reduce the chances of negligible with this type (until slowed). Conversely, those who learn to fly with
adverse yaw occurring, particularly at adverse yaw (un-mixed) will have to re-
slower airspeeds. Those who learn to fly a flat-bottom train their habits when flying an
wing trainer with A/R mixing will aerobatic model without much adverse
While differential aileron travel is a actually find the transition into yaw. Thus, the aim of A/R mixing a
common practice used to reduce symmetrical wing models easier than primary trainer is not only to facilitate
adverse yaw, its effect is slight, and the most. That’s because the control learning to fly, but ultimately to
only way to fully eliminate adverse yaw habits learned flying an A/R mixed compliment the transition into higher
is with simultaneous rudder. Note that basic trainer are the same techniques performance airplanes that require
if you did attempt to reduce adverse used to fly symmetrical wing airplanes, little or no A/R mixing.
exclusively with differential, you would since in both instances pilots are flying
end up with so much up aileron travel
that the airplane would be unduly
prone to dropping at the start of turns
and rolls. Thus, a little differential is
good, just don’t get carried away.

A/R Mixing for the Future

Many new flyers eventually go on to
enjoying the “flying on rails” handling
and increased capabilities of
symmetrical wing aerobatic models.

It’s important to note that if you’re but remember that technique only corrections may not even exist. That’s
inclined at some point to switch off the applies to flat-bottom wing airplanes when a pilot becomes free to think
A/R mixing on a flat-bottom wing and would not be appropriate when ahead of the airplane and more
airplane, expect to need a lot more flying symmetrical wing airplanes. efficiently take on new challenges.
control inputs to overcome the sloppier Thus, by removing the obstacle of
responses (something that you do not Conclusion adverse yaw, A/R mixing proves to be
want to make a habit of if you also plan As stated, maintaining a direct one of the most effective tools to ensure
to fly less encumbered aerobatic that pilots learn proper control from the
models). Of course, you could correlation between control inputs and start and therefore continue to enjoy
physically coordinate the aileron and the response of the plane is steady advancement and a more
rudder control sticks using 1-to-1 instrumental to developing optimum successful future. Happy flying!
movements to eliminate adverse yaw, control habits. Consider that when
the initial control inputs are applied
correctly, the need for additional