Check out "chapter 8" at this web site:
http://www.monmouth.com/~jsd/fly/how/htm/airfoils.html
This site has an interesting explanation for roll/adverse yaw effect
using a pitcheron/wingeron setup to explain it.
A summary of the info related to roll/yaw:
There are two types of yaw associated with aileron/pitcheron/wingeron
usage. The initial roll acceleration phase, (initiate the roll and
accelerate it), and the constant roll phase (maintaining the roll
rate). The initial phase involves more overall drag.
On a typical aerobatic glider, there's little roll "resistance" (momentum),
and the initial roll acceleration phase is fairly small. The roll rate
will very quickly follow aileron throw, and the adverse yaw during the
roll acceleration stage can be ignored, so it's the constant roll phase
that's important in these cases (it would be different on a glider/plane
with a lot of mass in the wings, for example a twin engine plane, or
a glider with really long wings).
A pitcheron/wingeron without differential example was used to explain
what happens during the constant roll phase. Once a roll rate is
established, it's similar to having a cylindrically spiralling airflow
across each of the pitcheron's wings. Since the roll rate is now constant,
each wing's lifting force must be in balance, or else the roll rate would be
changing.
Using a clockwise or "right" roll (viewed from behind the plane),
for this example, note that the right wing is pitched downwards relative
to the fuselage, and the left wing is pitched upwards. JSD states
that the lifting forces are perpendicular to each wing, and the vertical
components of these lifting forces (relative to the fuselage) must equal
since the roll rate is constant. What's left is a forwards component of
lift on the right wing, and a backwards component on the left wing. These
remaining forwards/backwards components of lift result in an adverse yawing
torque.
My guess is that with a pitcheron setup (only the wings move, and the tail
is fixed), and with no differential, you could press forwards on the right
stick (logical "down elevator"), and reduce the lift of the pitcheron wings
to zero. If each wing is at it's relative "no angle of attack" (no lift)
state, then there are no lifting and therefore no yawing forces generated
by the wings. Similarly, if an aileron/wingeron differential was setup so
that there was no lift generated while rolling, then you'd also eliminate
the constant roll rate adverse yaw component, but a fixed differential would
only work for a specific roll rate. Applying (or mixing in) just enough
down elevator to set the overall lift to zero should also get rid of the
adverse yaw due to constant roll rate.
At higher speeds, (or slower roll rates), "weather vane" effect probably
reduces the adverse yaw to a point that it doesn't need to be corrected
for, which is why powered rudderless aileron/elevator kits fly reasonably
well.
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