DENIS SMITH wrote:

Sometimes we bury ourselves with numbers.  In the
regime most of us fly a stall is defined by a
situation where the angle of attack of a lifting (read
wing) surface exceeds a point where smooth airflow is
possible and separation of the airflow over the top of
the wing causes loss of lift and that sinking
sensation most of us have experienced.  The reason
canard type aircraft claim to be stall proof is that
the mechanism they use for pitch control has
insufficient authority to put the wing at a high
enough angle of attack to cause the wing to stall
during normal (whatever that means) operations.
Typically, angle of attack required to stall an
airfoil is the same regardless of airspeed.  Your spam
can will stall at 45, 100, or 150mph if that angle of
attack is exceeded.  Whether it is caused by control
input, wind shear, updraft, or whatever, it is angle
of attack that is critical.  Paul is right that any
airfoil can be stalled.  Usually the "Stall Proof"
folks are just saying that whatever pitch mechanism
they are using has insufficient authority to put the
main airfoil at an angle of attack where a stall will
occur.

 
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