On Sat, 14 Mar 2009 18:08:23 -0700, The Real Doctor wrote:

The behaviour of the Pirat on aerotow is rather different, by the way.
At low speeds it handles very nicely, but if the tuggy is a bit
enthusiastic the ailerons get horribly heavy and ineffective. Quite the
opposite of wallowing, really. At the same speed off tow they are light
and responsive. I'm guessing that the tug downwash affects the centre of
the wing more, effectively increasing the washout. Meanwhile, I just
cajole tuggies into flying with the CHT just below the red ...

How does the downwash angle vary with position along the wing span? Since
the lift distribution varies across the span its unlikely that the
downwash angle is constant. As an additional factor, even a single seat
glider's span is larger than the tugs span, so the glider's tips (and
ailerons) will be in a somewhat different airflow to the inboard sections
of its wing.

If the downwash angle behind the tug reduces as you move outboard along
its wing then that's effectively washin at the glider's tips, i.e. an
increased AOA, so during slow tow the glider may be nearly tip stalling,
which would account for the symptoms people have mentioned: poor aileron
response and apparent loss of lift. However, it doesn't explain the
behavior of Ian's Pirat, so I must have missed something obvious.


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martin@ | Martin Gregorie
gregorie. | Essex, UK
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