Long wing twisting

At 12:30 27 June 2005, John Sinclair wrote:

My thought was that wing twisting (digging in) might
have gotten them (Ivens & Engen) into the spiral dive
in the first place. Once you get a big ship pointed
down with the speed near red-line and increasing, you
might very well have already had the snitz.

We probably can't say definitively one way or the other.
Many big ships have a tendency to digging in at the
stall even without any aeroelastic (twisting) effect.
This can be exacerbated by a pilot trying to pick the
wing up through use of aileron rather than rudder.
As you say, once the nose gets pointed down in a big
ship you can have very little time to get things straightened
out before you're past some limit or other.

Generally you need pretty high Q before the aileron
can produce enough moment to twist the wing. This could
happen once the spiral is established and speed has
built up, but the root cause of the spiral is likely
related to a more common stall/wing drop sequence.
In the Minden accident there wasn't any asymmetric
wing bending reported, but there was quite pronounced
symmetric bending observed leading to structural failure.
It's not clear to me that you can un-twist a wing
without slowing down, so I'd be hard pressed to come
up with the sequence of events that would have the
glider go directly from an asymmetric wing bending
to symmetric bending/failure.

Notwithstanding the specifics of that accident, the
general warning about aeroelastic effect - particularly
in sailplanes over 20m in span - is noteworthy.

9B