Matt Whiting wrote:


Not true. The vertical fin can only provide a weather-vane affect when
a slip or skid has been induced.

You have no clue what you are talking about. The skid and slip are the
result of the airplane NOT weather vaning into the wind. There are
a number of reasons for this. The primary one in turns is the "adverse
yaw" due to the differing drag caused by the displaced ailerons. Many
designs do a lot of things to mitigate this. Still it takes a lot of
aileron displacement to overcome the natural desire for the airplane
to track into the wind (due to the vertical stab).

In coordinated flight there is no slip
or skid and hence the fin provides no lateral force.

This is the definition of coordinated flight, not cause and affect.

The rudder isn't there to help the vertical stab do its job, it is there
to do a job that the vertical stab can't do.

Sorry. The incorrect. You need the vertical stab to even fly
coordinated when you are not turning. If it is two small the
airplane will tend to yaw on it's own (the more bulbous your
fuselage, the more this is a probelm...there was a design Piper
tried that used an almost helicopter like bubble on the front...
without the slab sides to help the vertical stab, the plane
just would as well fly slipping as nromal).

The vertical stab is nearly always set up to get the aircraft
to fly coordinated in normal cruise level flight. It is frequently
slightly offset to correct for other aerodynamic unbalances.

The rudder is just at trim to handle other flight regimes.
It's mostly there for the high AOA regimes of Take-off and
landing.