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Path: utzoo!linus!philabs!cmcl2!seismo!hao!noao!terak!doug
From: doug@terak.UUCP (Doug Pardee)
Newsgroups: net.aviation
Subject: Re: Conditions for stall
Message-ID: <737@terak.UUCP>
Date: Fri, 27-Sep-85 12:24:47 EDT
Article-I.D.: terak.737
Posted: Fri Sep 27 12:24:47 1985
Date-Received: Tue, 1-Oct-85 11:24:05 EDT
References: <763@infopro.UUCP> <2900005@hpcvrd.UUCP> <2717@hplabsc.UUCP>
Organization: Calcomp Display Products Division, Scottsdale, AZ, USA
Lines: 48

> > When you take your written test, one of the questions the FAA seems to always
> > ask is under what conditions an airplane can stall.  The correct answer is at 
> > any attitude and any airspeed, and they mean it.
> 
> This answer may be correct, but is pretty nebulous.  Isn't it better
> to say "when the angle of attack is too great"?

Even this strikes me as useless, unless you have an AOA indicator (the
best of all possible worlds).  I find it more practical to consider the
stalling condition to be a combination of three somewhat determinable
factors:
  a) airspeed
  b) gross weight
  c) G-force

At "Max Gross" and 1.0G, the stall speed is (it says here) as specified
in the Flight Manual.  Well, 'twould be in your best interest to
determine empirically what the airspeed indicator reads at stall in the
specific plane in question.

Stall speed is proportional to the square root of the gross weight.  If
the plane is currently at 90% of max gross (allowing for fuel burned,
etc.) the stall speed will be 5% lower than at max gross.

Stall speed is proportional to the square root of the G force.  If the
plane is held at 2G in a steep bank, the stall speed will be 41% higher
than at 1G.

So: making steep turns at low airspeed will not induce a stall provided
that you allow the nose to drop sufficiently that you stay at 1G.  This
will, of course, cause you to lose altitude.  If the altitude loss
becomes intolerable, the "way out" is to roll out of the turn, *not* to
pull back on the wheel/stick.

Caveat: If the ball is out of center, nobody knows what the stall speed
is (nor what the Angle of Attack is).  The airflow to the wings is not
consistent across the entire wingspan.

Another Caveat:  Knowing that your stall speed under current weight and
G-loads is X knots is only somewhat useful, since you don't know for
sure what the airspeed indicator will read when you get to X knots.

...  What is this nonsense the FAA (and others) say about being able to
stall a plane in any attitude at any airspeed?  Try to stall a plane
at Vne.  It won't stall.  (You'd have to pull maybe 15 G's, and the
plane will come apart instead :-)
-- 
Doug Pardee -- CalComp -- {calcom1,savax,seismo,decvax,ihnp4}!terak!doug


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