Pete,

Unfortunately, you are wrong on this one. You can, in fact, use rudder
to change direction, much to the aerodynamicist's chagrin. It is very
inefficient, but by holding wings level and ruddering (a skid) you
create an inward pointing force caused by the fuselage (along with a
rearward componenet -- drag). It is this force that allows you to slip
by counteracting the turning force of the wing with an opposite force
from the fuselage. (Again, much to the chagrin of the aerodynamicist.)

You need rethink your model. Remember, things only go straight if in
equilibrium. An aircraft flying sideways through the air wings level
won't be in equilibrium, therefore either speed or direction must
change.

Pete Zeugma wrote in message ...
If you have zero bank, and apply rudder you will begin
a
flat turn.

Wrong! UTTERLY WRONG!!!! A rudder yaws the airframe,
it does not 'turn' or 'steer' the aircraft.

Your whole problem seems to be in compairing a glider
with a boat. They may both have rudders, but they both
do totally different things.

Next time you fly in your glider, line yourself up
with a straight feature. Apply some rudder to yaw the
glider, but keep the wings level. All you will do is
continue in a straight line, sideways on. (commonly
known as a side slip)

However, the rudder does has a secondary control effect,
which introduces a roll moment due to differences in
lift between the wings. (which is why the first thing
you do is apply full opposite rudder to counteract
the rotation in a spin)

It is the ailerons that instigate a turn, the rudder
is used in a coordinated manner to 1) check the adverse
yaw (secondary effect of ailerons), and 2) to align
the airframe correctly into the airflow.

Please stop using language which inforces a belief
that the rudder is used to turn a glider in flight.
Your very action in doing so may well end up enforcing
that belief into a low airtime pilot reading these
posts and KILLING THEM!