Martin Gregorie wrote:

This is the usual result of a stall, and is what occurs in the typical
training situation, but it isn't the definition of a stall. Generally, a
stall begins when the airflow starts to separate from the wing at
increasing AOA. It is this separation that keeps the lift from
increasing and sets the maximum lift coefficient.


Usually major airflow separation coincides with a stall and the drag
increase ensures that a stall will happen because of the associated
loss of airspeed. However, flow separation is not the same as a stall.

Perhaps we are not discussing the same thing. It sounds like you are
talking about "a stall", meaning the aircraft's behavior from the pilots
viewpoint (buffeting, loss of lift, poor control, etc), and I am talking
about the aerodynamic situation during "a stall" (high AOA leading to
flow separation and constant or diminishing lift coefficient).

Many aircraft have quite a high degree of flow separation during low
speed flight. In the model world we assume separation always occurs at
about 60% chord at min.sink and this would appear to be close to the
mark for sailplanes judging by Will Schumann's experiments.

I think our modern airfoils have very little separation at minimum sink,
and certainly far aft of the 60% point. Instead of "separation", perhaps
you mean the transition from laminar flow to turbulent flow? That does
occur somewhere around the 60% point (maybe 70% or so) on modern airfoils.


A wing can be stalled and still produce plenty of lift; for example, in
a high speed pull up done with too much elevator can stall the wing, but
the stalled wing will still have more lift than the weight of the
aircraft because of the high speed.


I would normally call that a high drag flight regime rather than a
stall.

I agree it is not "a stall", but I think is sometimes referred to as
"stalled flight", and the wing is considered "stalled". For some
aircraft, like fighters with their powerful engines, it is a useful
situation. For gliders, I think any time the AOA is high enough to stall
the wing, the glider will suffer "a stall", regardless of the load on it!


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Eric Greenwell
Washington State
USA