Thread: CFI oral intel
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Old June 5th 08, 08:19 PM posted to rec.aviation.piloting,rec.aviation.student
Michael[_1_]
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Posts: 185
Default CFI oral intel

On Jun 4, 10:42*am, Dudley Henriques wrote:
Below is a very well done white paper on stability by Russel Williams
that addresses much of what we have been discussing.


The link does not work, and I can't find it through google. Do you
have another link?

The long and short of it in my opinion is that positive lateral
stability is present in GA airplanes


As lond as you mean static stability, then yes - weak positive lateral
stability is present in most non-aerobatic (and a few aerobatic) GA
airplanes as long as the displacement from wings-level is small.

and they will tend to recover from
the sideslip coupling.


Again, as long as the displacement is small and the lateral trim is
near-perfect.

Your key point addresses potential disturbances
that can indeed exceed this recovery tendency.
I agree totally with you that such a disturbance can exceed positive
stability tendencies if strong enough.


And I guess my point is that in most cases, these disturbances will be
strong enough, especially in an airplane that can cruise 110 kt. I
think this is something easy enough to prove in most cases. For those
playing along on the home game, try this next time you fly. Do this on
the smoothest possible day you can get.

Set up the plane in cruise at 110 kt. Trim it out as well as you can,
both in pitch, and, if aileron and/or rudder trim is available, in
roll as well. My guess is that most airplanes that can cruise 110 kt
will have aileron or rudder trim available - I can't off the top of my
head think of any certificated exceptions to this (I am sure there is
one).

Let go of the controls. All of them - hands off the yoke/stick and
feet off the rudders - and just sit there. Note how long it takes to
exceed 25 degrees of bank or change heading by 90 degrees.

If in 15 minutes that doesn't happen, smoothly bring the throttle to
idle to simulate fuel exhaustion. Let the plane descend 2000 ft or so
(use carb heat if appropriate). Now see if you are still within 25
degrees of wings level. The reason this matters - generally the
engine is offset just enough that at cruise, you should need no
rudder. On takeoff the left-turning (for CW engines) tendencies are
increased, so you need some right rudder. On a power-off descent, you
need some left rudder. Yaw and roll are coupled. So even if you were
in perfect lateral trim before you went to idle, you're not anymore.

Now I'm willing to bet that at least 9 out of 10 people who try this
will find that the plane won't fly level for 15 minutes without pilot
input, and of the few that do, the engine coming back to idle will
change the yaw enough that more than half the rest will enter a
spiral.

Michael