Dudley Henriques wrote in
:

Paul kgyy wrote:
On a 3 hour cross country today I was amusing myself by flying with
rudder pedals only (all right, OK, a little yoke usage to maintain
altitude). But then I got to wondering why applying rudder pressure
causes the plane to bank. All I could think of was that rudder usage
produces asymmetric lift because one wing is somewhat blanked by the
sideways motion induced by the rudder? Also, the rudder surface is
above the plane's center of lift but I don't know how much of a
factor
that is.

It's called a yaw/roll couple. As you create yaw you acellerate the
outside wing which then has more lift. It raises coupling with roll
and
you have turn.


Gotta disagree there Dudley. While it is true, and that's what happening
to some degree initially, the majority of the yaw roll couple in
lightplanes comes from the dihedral. the wing opposite the direction of
yaw has a higher angle of attack and generates more lift then the
opposite, which now has a lower alpha. Airplanes with no dihedral will
still roll slightly in the direction of yaw but it's nearly zilch.
can prove the first statement for yourself by introducing the yaw so
slowly as to make the diffrence in speeds insignificant. The airplane
will still roll in the direction of the yaw.
The V1 cruise missile had no dihedral and no ailerons and was easily
upset for this reason. Once it was off a wings level flight path it's
gyros had no chance of getting it back into straight and level.
Swept wing airplanes can have a huge yaw roll couple because as you yaw,
the forward moving wing's aspect ratio becomes massive just as the aft
moving's wing shrinks.(transonic ones have a reverse effect couple at
altitude, but that's another story)


Bertie