I'm taking a wild guess here, a hypothesis only...

If you exceed VNE can you divide the failure causes into two families?
Structural and Flutter?

Ok, discount Flutter for the moment and consider only a structural failure.

If you are in moderate dive, the wings still have to support the weight
of the glider and therefore you have higher drag because the wing is at
some positive angle of attack.
However, if you are in a near zero G pushover, the wings are unloaded
vertically and therefore you are at a minimum drag condition from an AoA
standpoint. Then, if there is no flutter, you might get well beyond VNE
before something goes bang..

pondering out loud...



Eric Greenwell wrote:
wrote:

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).


Have investigators given an opinion about how the pilot was able to
achieve 460 km/h and still had any wings attached before opening the
spoilers? And why he would wait until then to open the spoilers?


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).


I think most of us are still trying to imagine how a standard class
glider can even get to 460 km/h and be in only one piece.