Re: Physics of Flight

[brian whatcott <inet@INTELLISYS.NET>]

Engineers involved with evaluation and performance testing use
the word 'stability' in a technical sense - so that a plane
may be flying straight and level, stable in your sense, while the poor
pilot is stirring the pot in high gain-bandwidth to keep the attitude
level.
 By contrast, an engineer may call for various static and dynamic stability
tests, where for example a test engineer-pilot trims to a given airspeed
straight and level,  then pulls back on the stick for a 10 kt reduction and
releases the stick.
   This is one measure of a particular stability margin - that the plane
describes a convergent oscillation onto the former airspeed.

 I expect that you will not be surprised to find there are twenty stability
derivatives involved in the longitudinal stability of an airplane, using
various simplifying assumptions of a perturbed steady state model.

Brian Whatcott

At 11:27 8/18/99 -0500, you wrote:
> Bryan
>
> I seem to have missed the distinction between "stable" and "steady".
> Please elucidate.
>
> poj
>
> brian whatcott wrote:
>
> > At 16:28 8/17/99 -0500, P.O Johnson wrote:
> > > ... If the shape and attack angle of the foil are vital, how can
> > > an airplane remain stable while flying upside down?
> > >
> > > poj
> > > Collin County College
> >
> > By 'stable' I expect Paul referred to 'in steady inverted flight'.
> >
> >  One sees occasional flypast photos of inverted light planes with
> > asymmetrical foils at airshows. It is often noticeable that their
> >  tail is 'hanging down' quite noticeably.

/snipped/
brian whatcott <inet@intellisys.net>
Altus OK