Hello Everybody, and many thanks for your most useful answers!

Let me tell you the strange story behind my strange request:

The aviation accident investigation establishment of an "old" european
country is preparing to present the result of their investigation
regarding a glider accident with a sailplane having Discus-like
performance (the pilot is a good friend of mine, and got away
unscathed).

The investigators of this establishment have observed that some metal
parts of the air brakes were bent in the wreck. Bench testing of these
parts indicate that an abrubt extension of the airbrakes at 460 km/h
(250 kts) or above can indeed cause the observed bending. For your
information, the Vne of the concerned glider is less than 270 km/h.
Surprisingly enough, this accident investigation establishment is now
using this fact as a proof that the pilot did indeed fully extend the
airbrakes at 460 km/h (250 kts).

I am now trying to help my friend present another proof, which is to
show that a speed of 460 km/h simply was unreachable the given day,
considering weak thermals and fairly low cloud base. However, to
prepare this proof I need some high speed polar data for the Discus,
which has a performance similar to the given glider type.

Best regards

Karl

PS: I would be very interested in having your opinon about the
probability a standard class glider has to survive an abrubt airbrake
extension at 460 km/h (250 kts).