This theory certainly explains the poor aileron control or wallowing at
slow towing speeds, even though it seems the wing, (on average) is no
where near the stall angle of attack.

I have seen guys try to fly model planes with wash in instead of wash out
in the wings. Doesn't work too well!


Cookie





At 15:33 16 March 2009, 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