"wladkummer76" wrote in message
...
On Dec 31, 9:40 am, "Doug" wrote:
As an aerodynamicist/flight dynamicist recently re-soloed after 25 years
off, people keep asking me hard questions. One that has come up recently
is
why a heavy glider on tow feels horrible, but thermalling in the same
glider
at lower speeds is fine? (see also Mike Fox's article on aerotowing in the
October issue of S&G).

I did some calculations, and I reckon it's probably due to the tug wing
wake
(tip vortices generating a downwash inboard, upwash outboard) changing the
lift distribution on the glider wing - with an increased angle of attack
out
at the tips reducing aileron effectiveness. There's possibly an
interesting
academic research project here, but it's always best to get a reality
check
first ...

Is poor handling at low speed on tow a common experience? I'd appreciate
any thoughts/comments/war stories ... particularly bad tug/glider/speed
combinations, incidents of wing drop during a tow etc etc?

Doug Greenwell

Sure, even more with flaps equipped ships! But yaw control seems to be
more affected than roll. Can we explain that?
Just a little faster please is what doctor ordered here...usually 5
mph more is enough to a more pleasant tow.

Good question ... the only thing I can think of at the moment is that the
tug tip vortices would also generate an inwards 'sidewash' flow above the
wake, which would be stronger the heavier and slower the tug was. If you
are then for some reason off to one side of the tug the sidewash at the fin
from the nearer vortex would tend to yaw you 'nose-out', in the wrong
direction.

Doug