At 23:09 02 January 2011, Bruce Hoult wrote:
On Jan 3, 12:01=A0am, Derek C wrote:
Actually the only totally reliable sysmptom of being stalled is that
the elevator will no longer raise the nose.

But that is neither necessary nor sufficient!

If you put enough weight in the front cockpit then there are plenty of
gliders where you reach the back stop while they are still flying just
fine.

Conversely, there are also plenty of gliders with sufficiently
powerful elevators that the wing can be stalled and you're mushing at
500+ fpm but you still have perfect control over the attitude of the
nose and can raise or lower it at will. Not to mention other aircraft
such as the F/A-18 which can be flown in perfect control with the wing
stalled at huge angles of attack.

I see in another post the definition:

Admittedly that is still a stall according to FAR23/25 definitions "a
sta=
ll is produced, as shown by either:
(1) An uncontrollable downward pitching motion of the airplane;
(2) A downward pitching motion of the airplane that results from the
acti=
vation of a stall avoidance device (for example, stick pusher); or
(3) The control reaching the stop."

Without having that document in front of me I will hazard a guess that
this is not a definition of a stall, but rather a definition of the
standards for what a pilot should do in order to pass a practical
flight examination. They're not going to fail him when the aircraft
fails to actually stall because the elevator reaches its stop first,
so they explicitly allow that as a signal that the pilot is allowed to
terminate the "stall" attempt and commence the stall recovery
procedure.

The only true definition of a stall is when the wing is at an angle of
attack such that a further increase of AoA produces a decrease of
lift.

*Usually* this will be accompanied by a large increase in drag such
that the combination of lift and drag is easily capable of supporting
the aircraft against gravity at a low speed and steep nose up descent
angle, but that may not necessarily always be the case and some
aircraft might speed up while stalled (perhaps at high altitude?).


Exactly - FAA 'legal' definitions of stall are aimed at defining speeds
for certification purposes. Most recently, more use has been made of the
'1g stall speed', which is the slowest speed you can fly and still
maintain level flight (obviously a bit tricky for a glider!) - which
corresponds to your definition of teh AoA at which a further increase
produces a decrease of lift (= maximum lift). The problem for the
regulators is that some (many?) aircraft become uncontrollable one way or
another before you get to this point - which is why stall such a bl*^dy
difficult thing to define precisely