ASW 20 SPIN CHARACTERISTICS

In article ,
Andreas Maurer wrote:

On 13 Jul 2004 14:33:53 -0700, (Andy Durbin)
wrote:

Just catching up with this thread and no-one seems to have mentioned
the effect of the flexible wings. I don't have experience in the 20
but I do have a series of photos of a fatal accident that started
with a contest finish pull-up and quickly ended up in a spinning
impact with the ground. I believe that the increased angle attack
caused by the wings returning to normal deflection contributed to the
accident.

Flexible wings do NOT change their AoA while they are bending -
otherwise flutter would start immediately.

It's not the amount of bend, it's the change in the bend.

Anything that makes the wings move vertically changes the angle of
attack to generate a lift force that opposes the movement. That's why
gliders roll so slowly, for example.

The exception to the above is if the extra angle of attack is sufficient
to cause the wing to stall, in which case the lift becomes less and
rolling/bending becomes anti-stable.

That's what the original poster is talking about, not about twisting of
the wing or some such thing.


I'd be very surprised though if that was a big enough effect to *cause*
the accident. Especially given that things are normally designed so
that the wing roots stall considerably before the tips.

-- Bruce