At 13:23 04 January 2011, wrote:
OK..........how about this for (simple) explaination?

"Climbing in descending air" (that's what I get from all of the
complicated explainations of down wash, vortex etc.)

I think that if we compared a motor glider climbing at say 50 MPH and
500 FPM to the same glider on tow at the same climb angle and rate,
and if we assume the air behind the tow plane is moving
downward..........

Then the glider on tow would have a larger AoA.....???


Cookie


For the same lift (see previous!) and the same indicated airspeed the AoA
should be the same, because the angle of attack is measured relative to
your motion through the air.

The AoA for a given lift at a given airspeed could only change if
something significant happens to part of the airflow around the glider
wing (for example putting the flaps down, opening the airbrakes, icing up,
hitting the propwash, or flying into a tip vortex*)

The pitch angle relative to the ground on the other hand will be larger
for two reasons - (a) you are climbing and (b) the airmass you are in is
moving downwards.

It's really difficult to explain without something to draw on ... oh for
a whiteboard or at the very least the back of an envelope!

*not necessarily a bad thing: birds use the upwash outboard of a tip
vortex to increase range by flying in a v-formation - so perhaps what we
should be doing is towing two gliders at a time ...