On Mar 16, 9:33*am, The Real Doctor wrote:
On 16 Mar, 13:00, Derek Copeland wrote:

... but the K13 definitely starts 'wallowing' below
about 52knots, whereas its normal free flight stalling speed is about
36knots.

OK, here's my latest theory. Gliders have bigger wingspans than tugs.
Therefore the outer bit of each glider wing is in the upwards moving
bit of the tug's tip vortices, and the centre bit is in the downwards
going bit. Effective result: much higher angle of attack at the tips,
particularly since the nose has to come up to maintain AoA at the
centre. Hence wash-in, tips near stall, downgoing aileron actually
stalling, reduced control effectiveness, wallowing.

Questions: does it happen as much out to one side hen boxing the wake?
Does it happen when the tug - a motorglider - has the same span as the
tug?

Ian

I fly a 20 meter glider that sometimes is loaded with 60 gallons of
water and I have to say that I've not noticed this effect when towing
behind either a Pawnee or a Cub. Aileron control on tow is no worse
than in free flight. The slower Cub is easier to follow if anything.
Over the years, I've been towed by everything from a 85HP 7AC champ to
a 400HP Pawnee Brave. It's all pretty much the same - just follow the
tug.

What I have noticed is that a glider in high tow will tend to drift
laterally toward the center which is generally a good thing. I
haven't noticed any of the pitch related stuff people are talking
about.

On one occasion a pilot was complaining that his glider needed more
than 80 knots on tow to feel "right". I flew the glider and radioed
the tow pilot to reduce towing speed until he started complaining
about control authority but I saw no problems with this glider. The
only thing I could point to was the pilots tendency to over control
his glider and to use positive flap "to see the tow plane better". I
suspect the excess flap was limiting aileron authority. He would have
been better off with some cushions.