On 15 Jul 2004 18:17:04 GMT, Derrick Steed
wrote:

Eric Greenwell wrote
Andy Durbin wrote:


I couldn't find the photos last night so I can't attempt any
measurements of wing deflection. The scenario I imagine is this. The
pilot makes an agressive contest finish pull up. The pull up starts
at over 100kts, the pilot continues to pull as the speed decays to say
60kts where the wing experiences an accelerated stall.

If he waits to 60 knots, he is well into a loop. Based on my contest
finishes, I'd guess he'd be back at 1 G before the speed decreases to
85-90 knots. The high G part of the pull-up is very short - just long
enough to get the glider aimed upward.

I've read most of these posts and now I'm thoroughly confused:
1. isn't it true that unless the pilot aggressively pushes over, the wings will unflex too slowly to cause a large AOA increase? And even then, the increase is relatively small - at most about 1 degree for realistic speeds of travel and rates of unflexure?

2. isn't it more likely that the pilot tried to initiate a low speed, initially low G turn, then as the load factor increased due to the increasing angle of bank the wing AOA went past the stalling angle and so the (then inevitable) spin became a fact?

3. everything I've ever read and learned about wing theory states that a stall results when the AOA is greater than the stalling angle - it doesn't matter what the G loading is or what the speed is.


I'm not certain any of us know enough detail about the accident to
make a sensible guess about its cause.

FWIW, on Tuesday evening I decided to investigate turning stall/spin
behaviour in my '20 at a sensible altitude. It was calm and with
little air movement under a high overcast. With the aircraft clean and
flaps at zero (setting 3) I flew some moderately steep turns - about
45 degrees of bank and at speeds ranging down to about 43 kts. This
was completely uneventful - no buffeting, burble or hints of
departure. In short, it flew like a pussycat. I'll try this again by
myself in a turbulent thermal next time because all that series of
turns told me was that in nearly still air my '20 can fly uneventful
turns at stupidly slow airspeeds. By comparison I typically fly at
48-50 kts for that steep a turn in zero flap during normal thermalling
turns.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :