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

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

Not meaning to be glib about this serious subject, but it reminds me of
a video I once saw. They were clearing out the flight research lab at
the university, and I came across a short film of flight testing on the
Goodyear Inflatoplane. For the unitiated, this was (as the name
implies) an inflatable aircraft designed to provide a platform for
forward recon to the army and potentially recovery to downed aviators.


There's an air-to-air sequence during stability tests that showcases
bending and twisting moments like nothing else I've ever seen. It
ought to be required viewing. The inflatoplane had a VNE somewhere in
the 60-70 mph range if I recall, and these tests were done near that
range. In one shot, the left wing (I think) tucks briefly like a
folded napkin. In this wing, however, the structure was elastic
enough that it basically "sproinged" back into shape. I spoke with a
guy who was a test pilot on the project, and he seemed to be of the
opinion that springy wings weren't such a great idea after all :-))

P3