The Discus 2 exhibits the same behavior. It's a problem mostly seen in newer unflapped racing ships because of the angle of incidence of the wing. This results in a nose-up attitude at low speeds and on aerotow this results in a downward pull on the nose from the towrope. This down-pull has to be counteracted by up elevator. With ballast, I run out of up elevator around 60 knots or so, and I have had my glider sink into low tow a couple of times with a slow tug and have had to release a couple more. In free flight, the glider will stall at its placarded speed and handles fine. Tows below 60 knots have very poor aileron and elevator control.

There may be other things going on, but I suspect the relative angle of the towrope to the fuselage on tow is responsible. Flapped ships alter their pitch and hardly suffer from this effect.

Mike

Discus 2b