Coordinated turns without rudder, and autopilots

Ron Natalie wrote:
Matt Whiting wrote:

A vertical stabilizer does not provide any lateral force unless there
is some degree of slip or skid.

Precisely! Now you are beginning to understand. As soon
as uncoordinated flight occurs (skid or slip) the vertical stab
deflects the aircraft back into the coordinated flight.

It does sounds like you are beginning to understand! With use of the
rudder, you can enter and exit a turn and maintain coordination at all
times. Without rudder and depending on the fin alone, you will be in
and out of coordinated flight as you enter and exit the turn. The
degree of departure from coordinated flight maybe be large or small
depending on the specific airplane and the rate at which you enter and
halt the turn, but without using the rudder, you will NOT be coordinated
at all times.



That's it's job! It is the primary job to provide the primary
aerodynamic forces to keep the airplane coordinated.

In coordinated flight, it is just along for the ride.

Yep, and as soon as something deflects the aircraft from coordinate
flight, it generates a force to correct it.

Yes, which is precisely what I said at the start. You have to enter
uncoordinated flight for the fin to work. With proper rudder use, you
can remain coordinated at all times (if you are good enough).


Many airplanes will oscillate slight in the yaw axis for this reason.

And they oscillate in pitch, and they oscillate in roll. This is
one of the fundamental modes of stability.

Yes, and that is one reason you have control surfaces, to stop these
oscillations or prevent them.


It takes a very large vertical stab to keep the excursions small
enough to not be detectable, especially in a longer fuselage
airplane. The rudder can provide a side force in anticipation of a
slip or skid and thus maintain coordinated flight and never allow the
slip or skid to develop in the first place.

Are you trying to tell me that you sit there and tweak the rudders
during flight continually to damp yaw oscillations? Don't think
anybody finds that fun. The few airplanes where it is a persistant
problem have autopilots that do that, but for most it's unnecessary
in normal flight regimes.

No, that is what yaw dampers are for. But, yes, I use the rudder and
ailerons and elevator to damp oscillations caused by turbulence when
they exceed a certain threshold. No sense in waiting through several
oscillations when you have the controls to stop it now.