Originally Posted by
Mark1234
Genghis: My immediate reaction is to say you're wrong, but I think I know something of your background, which suggests you know a lot more than me. Therefore, I'm going to ask why.
Just to make sure we're on the same page, I'm not talking about abrupt, full scale deflections, nor deflecting multiple controls - I entirely understand how they may cause bits to fall off. However, according to my understanding the Vn/Vg/whatever you call it diagram gives an envelope within which you can fly, in terms of G loading, and speed (confined to the pitch plane, but rolling gliders is kinda tedious anyway
). Anywhere in there you should be fairly sure bits will not drop off?
It's known as the V-N diagram, and looks like this...
This diagram's quite a good one, because it shows two different diagrams - the manoeuvre envelope (what you can do in still air), and the gust envelope (what turbulence can potentially do to the aeroplane).
The tapering in the top right, and bottom right, corners, when you combine these two flight envelopes, covers the risks of gust induced overload at high speeds. It's not to do with combined high speed / high g manoeuvring.
In flight, the main loads in the wing are in most designs taken in what's called the "D-box", comprising the leading edge and the mainspar. Manoeuvering loads (g force if you like) mostly bends this, so everthing's trying to bed tip-upwards. Flight loads - those related to airspeed - tend primarily to twist the whole wing, normally in the sense nose-up at the tip (one of the design parameters not often talked about in flying circles is the torsional divergence speed - where the whole wing twists off at high speed), although include bending and also drag loads.
So, at high speed and high g, there will be bits of the wing - most likely somewhere on the leading edge, which is taking simultaneously loads due to g, loads due to speed related drag, and loads due to torsion. These may all add up in the same bit of structure, and cause it to fail.
Now, if the design and certification team did their jobs right, at Vne and N1, it shouldn't, because that combination should have been accounted for, as the loads have at Vdf and 1g. But, I doubt that at Vdf and N1 + safety factors, the same will be true and I'd reckon on a significant risk of structural failure.
Safety factors incidentally do vary a bit, but they should never be less than 40% on structural limits, and 10% on speed limits - they may often be rather more, particularly with composite aeroplanes.
Many years ago, I won a sweatshirt in the Flyer's "that worst day" competition with pretty much this explanation!
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