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Re: Definitions



At 09:49 10/28/00 -0500, Glen Carlson wrote:

... When someone talks about "static equilibrium", but cannot
distinguish static equilibrium from non-static (dynamic?) equilibrium.
...
Glenn A. Carlson, P.E.


Not quite on topic, but this reminds me of the need for testing
airplane flight performance.
Departures in pitch being the fastest way to say hello to the
ground, longitudinal static and dynamic stability tests are topics
of perennial interest.

It seems odd at first to consider pitch static stability testing
when the airplane has to keep moving, or else.

(This is how it goes: check the stick position at stabilized
air speeds, faster should be further stick forward - the slope of
the position with speed describing the property in question.
Or increase and decrease 10 kts from a trim speed.
The slope of these three points on a speed - deflection graph if
modestly positive can compensate for a flattish slope established
in the first test.)

I think you'd agree that pitch dynamic stability seems more
intuitive.
(Recipe: attempt to excite a short period oscillation
- these things are less damped with speed, so you start slow.
Input a pitch doublet - a push and pull for one cycle at about
1 Hertz - and let go. The oscillation should damp quickly, and
continue in this mode at higher speeds.)

There are of course, numerous more elaborate measures....






brian whatcott <inet@intellisys.net> Altus OK
Eureka!