"Ken Kochanski (KK)" wrote in message
oups.com...
An 800 pound sailplane flying at a steady 50 knots has all forces
balanced. Lift ~ offsets weight ... i.e. the lift vector is tilted a
bit forward to generate a thrust resultant to offset drag ... let's say
it is ~ 20 pounds.

If you fly into a sharp edged 10 knot thermal at 50 knots ... the wing
'sees' a change in the relative wind equivalent to an AOA increase of ~
11 degrees.

I don't know how much lift the wing would develop ... but lets say the
lift doubles .. and doubles the thrust resultant to 40 pounds. Since
the drag is 20 ... the ship would accelerate ... but 20 pounds of extra
'thrust' on an 800 pound ship would seem to take some time to
translate into velocity. If you made the lift resultant 40 pounds ...
I still don't think you would see the speed increase we all experience.
So is something else also happening ... I think the lift vector also
tilts forward as AOA increases ... so the thrust resultant might be be
much higher. Udo ... where are you when we need you? :-)

There are more qualified theoreticians then I.
I will try to rise to this challenge and give some observations.

From a practical view point, watching radio controlled gliders, I was able
to take advantage of that. It would tell me when I entered a thermal, the
fuselage boom would tilt up and when I fell out of one, it would go down.
I noticed that the model glider would stay in an accelerate state after is
stabilized in the thermal In a stick fixed position,
The model would have to be set up similar to a free flight model, so as not
to crash if no control input is given. To take full advantage of the thermal
I would have to use up elevator to maximize the climb and the speed would
be reduced of course, not unlike in the full size gliders.
That would indicate that the relative plane relative to the horizon has
shifted
due to the thermal. The glider wants to fly "more down hill" if no other
input is
given.

The same indicators are use when encountering sink but in reverse.
That is how I see it.
Anybody wants to put some numbers to that.
Udo