Spin

Looking at the windsock I'd say there was also a considerable wind gradient.
The aircraft had one wingtip within 1 span of the ground and the other a
good 15 to 20 m above that.

This little clip really is a classic, so many things wrong in one 10 second
period!

Ian




"ir. K.P. Termaat" wrote in message
om...
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.

For a banking angle of 45° and an IAS of 100km/h one finds from simple
mathematics that a 180° turn takes 8.9 secs when properly flown. The
forward accellaration of the glider during the 180° turn must then be
(125-75)/(3.6)/8.9=1.56m/s2 to come out at the same speed of 100km/h.
Suppose the mass of the glider (including the pilot) is 650kg, then
the force needed to accelarate the glider with 1.56m/s2 is 650x1.56 =
1014kgm/s2 or 1014N.

Where does this force come from. Indeed, from gravity. The glider must
pitch down to keep its IAS up. With a glider mass of 650kg, its weight
is 650x9.8=6370N. The pitch down angle must then be
arc(sin)1014/6370=9.2°. Add to this a normal glide angle of 1.4° (for
a glide ratio of 40), then the total pitch down angle during the 180°
turn of the DG500 should have been over 10°.

If the pilot does not move his stick quite a bit forward to achieve
this relative large pitch angle, the glider will loose its IAS, then
stall and spin. This looks to me what happened unfortunately with the
DG500 at Magdenburg.

Karel, NL