Model Forum / Radio Controlled / Air Models / July 2006

 Adverse yaw doesn't make the airplane turn the wrong way, it just
makes the airplane slip in the turn and requires more rudder to
coordinate things. Airplanes with enough differential, and with the
Frise-type aileron that sticks its lower leading edge into the
slipstream when it's raised, can reduce adverse yaw to nothing and no
rudder input is necessary most of the time. The Cessna light singles
are like that. Makes the airplane easy to fly and makes for pilots who
get into trouble when they fly something less refined.
    The downgoing aileron in a non-differential system can stall that
wing, since aileron movement changes the wing's angle of attack. Maybe
that's what some are seeing on takeoff when speed is low and the
modeler applies aileron one way and the airplane turns (banks) in the
other.

     Dan

Hi Ken,
Boy. my brain is turning to mush ;-) The problem is I can't use my hands!
Have you ever seen a pilot who could explain *anything* pertaining to flight
without using the hands <VBG>.

Yaw is movement about the bird's vertical axis. Adverse = Moving in an
opposite or opposing direction.  I'm not splitting hairs when I say I have
never seen a model *turn* because of Adverse Yaw.  When you say "...the
wrong way" I assume you mean opposite the bank direction. Adverse Yaw causes
a bird to *yaw* left while it banks right in response to right aileron.
Adverse Yaw is directly proportional to the AOA.  Higher AOA = increased
Adverse Yaw. Therefore, the model on final to which you refer could have
appeared to "turn" left when the pilot applied right aileron. But remember
that Adverse Yaw is momentary.  As soon as the ailerons are neutralized it's
gone. The opposite turn you saw could have been caused by conditions other
than Adverse Yaw.  One of which could have been dumb thumbs and another is
over-the-top snap. When an aircraft turning in one direction stalls and snap
rolls in the opposite direction. (opposite wing stalls before the turn
direction wing).

Dan,
I still believe we are saying essentially the same thing.  Your references
are impressive in number but not necessarily totally accurate. Statements
like "...but if one wing stalls before the
other, that wing will drop, the plane falls out of the air." and "...But the
deflected aileron gives it a lower incidence," raise the issue of the
authors' qualifications. We both know that no individual versed in
aerodynamics would say "..the plane fall out of the air," or indicate that
ailerons could possibly affect incidence. Incidence is fixed, riveted,
welded, bolted, etc., into the aircraft. Unless the surfaces involved are
variable incidence surfaces. (Gasp, nothing is simple!). Internet
information/references should never be relied upon unless made by a
qualified source. BTW, John Denker's site is pretty good.  I use the parts
with which I agree to reinforce my arguments ;-))

I believe that our major area of disagreement lies in your use of the term
"lift" I think you are probably using the term to refer to the lift as
defined in Bernoulli's famous theory. As with drag there are different forms
of lift. Among which are Bernoulli's lift and Newton's lift. I am most
concerned with Newton's lift explained by his Third Law of Motion, i.e. "For
every action there is an equal and opposite reaction."

When the ailerons move up or down, the deflected airflow creates an equal
and opposing force.  In the down aileron that force moves the wing up while
the up aileron does the opposite. You contend that the down aileron
increases the AOA thereby increasing lift and drag. I say that the down
aileron increases the camber thereby increasing lift and drag.  Seemingly a
nitpicking difference.   BUT I also contend that the lift caused by the
increased camber is minimal compared to the comparatively large up force
(lift) caused by the deflection of the air downward and the resultant
opposing up force (Newton's lift).

Stick you hand out of a car window so the it is horizontal and palm down.
Now tilt it upward slightly and you can feel.see the effect of Newton's
lift.  The increase in AOA does not increase the lift vector it increases
the down flow or air which increases the opposite opposing force (lift).

Dan, the more I think about it the more I'm convinced we are saying
essentially the same thing. The major cause of our differences is your use
of "angle of attack."  In the case of leading edge flaps (dropping the
leading edge of the wing) the AOA is decreased.  By yoir definition the lift
would be decreased.  Insead it is increased by virtue of the increased
camber which, in turn, increases the down flow of air and the resultant
opposing reaction.

Newton's Third Law explains the action caused by rudder, elevator, and
aileron movements. AOA doesn't, at least not without becoming confusing to
mere mortals. <BG>.

I think I've muddied the waters enough so this time I'm definitely - OUT!

On planes that used wing warping instead of ailerons, do they have
adverse yaw?