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Old May 29th 07, 12:35 PM posted to rec.aviation.piloting
Ron Natalie
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Posts: 1,175
Default Coordinated turns without rudder, and autopilots

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.

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.

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.

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.