On Sat, 06 Aug 2005 15:10:05 +0100, W.J. (Bill) Dean (U.K.). wrote:

In all normal flight the maximum lift, i.e. stalling, AoA is constant.
However, at the very low speeds met with in light winds at the start of
take-off and the end of landings, the stalling AoA is very much less.

Whereas in all normal flight conditions, from 1G "stalling speed" to Vne,
the stalling AoA remains constant at a figure probably between 16 and 19
degrees, at 5 or 10 mph it is around 10 degrees.

This is interesting, it explains a lot. I would like to read up some
more. Do you know of any references (perhaps on the net, or Reichman) that
describe this effect?

Also is there any "hysteresis" in this effect. In other words, if an
airfoil is "flying" at say 12 degrees angle of attack, and you reduce the
airspeed, to say 20 km/h, until it "stalls", not in the conventional
sense - in that it is not producing lift to support the aircraft mass at
1G, but because the airflow separates and the co-efficient of lift
deteriorates.

Will the same airfoil, at the same angle of attack "unstall" if the speed
is increased above 20 km/h, or will it require a higher speed, say 25
km/h before the airflow normalises and the expected co-efficient of lift
returns?

In my experience, in a glider with marginal aileron (or rudder) control,
in a hot & high cross wind take off, it is better to keep the controls
neutral until the glider has some airspeed before correcting for a wing
drop (or yaw). If you immediately apply full control deflection then wait
for the speed to build up, it seems to take longer before the controls
"unstall" and become effective enough to correct the situation. (Either
way the left hand is never far from the release...)

Thanks

Ian