At 10:00 08 February 2004, Ir. K.P. Termaat wrote:
Did some simple calculations to get an idea of what
caused the spin of
the DG500.
If the glider flew initially with an IAS of 100km/h
and had a headwind
of say 25 km/h then its speed relative to the ground
is 75km/h. If
after making the 180° turn back to the airfield the
glider flew again
with an IAS of 100km/h but now with a tailwind of 25km/h,
then its
speed relative to the ground is 125km/h. This means
that during the
180° turn the glider had to be accellerated from 75km/h
to 125km/h
relative to the ground.

That old red herring again!

The glider is flying in an airmass which is moving
over the ground at a constant rate. No additional
acceleration is required apart from that normally needed
in a turn to supply the turning force.

There may be some effect caused by descending/putting
the lower wing down through any wind gradient but this
actually improves the situation as the air is moving
'away' from the path of the glider more slowly and
will consequently cause some increase in airspeed.
(You can try the opposite of that effect by pulling
up from a downwind racing finish through a strong wind
gradient; watch the airspeed decay at an alarming rate).

The biggest problem is that the apparent speed over
the ground in say a 15kt wind jumps by 30kts and results
in people trying to reduce the ground rush by raising
the nose with no reference to the ASI.