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#11
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Discus polar curve at high speeds
If "something goes bang" it is either because of a) flutter or b)
extreme drag forces when extending airbrakes at extreme speeds. Which are the known incidents of gliders fluttering to bits? (apparently Dirks parachuted from the DG-600 prototype after wing loss, also almost loosing his eyeballs in the process...) Karl |
#12
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Discus polar curve at high speeds
Gary Emerson wrote:
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.. To go from level flight at 125 knots to 250 knots would require losing over 2000 feet in this zero lift flight, much of which would vertical. I have to wonder how a pilot could resist pulling back on the stick or opening the spoilers for such a long distance! And how carefully he'd have to fly to avoid G forces that would remove the wings; after all, this maneuver isn't in the usual glider training syllabus. -- Change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#13
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Discus polar curve at high speeds
In article , Eric Greenwell wrote:
Gary Emerson wrote: To go from level flight at 125 knots to 250 knots would require losing over 2000 feet in this zero lift flight, much of which would vertical. I have to wonder how a pilot could resist pulling back on the stick or opening the spoilers for such a long distance! And how carefully he'd have to fly to avoid G forces that would remove the wings; after all, this maneuver isn't in the usual glider training syllabus. You might also want to consider the twist in the wings. Ever looked along your wing at high speed and noticed the tips bending down? At really high speed you can twist your wings off. A blanik did that in NZ a few years ago. One wing twisted off leading edge up, the other went leading edge down. -- Philip Plane _____ | ---------------( )--------------- Glider pilots have no visible means of support |
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