"Mike Ash" wrote

Makes sense to me. Seems like there are several potential explanations:
sudden flexing of the wings like I said, sudden pitch up like you said,
or simply CG changes causing increased load on the wing. Lots of ways
for this failure to occur given a weakened wing, but the idea of the
wings failing under constant load with more Gs due to less weight
doesn't seem to make sense.

It does seem counter-intuitive. I had problems with the concept when it
came to explaining max maneuvering speed.

I had it explained to me, something like this: You are cruising along at
low weight, and hit a strong upward air column, suddenly. With a light wing
loading, the strength of the updraft will make the machine move upward
rapidly, which will cause a G to register on your G meter.

Now, you take the same plane, loaded to max weight and going the same speed
as before. You hit the same updraft, but the plane has a higher wing
loading, and higher mass, but the same wing area, so it will accelerate
upwards more slowly. That will register a lower G on your meter. Same
force applied to the higher mass is equal to less acceleration, as shown in
F=MA.

In thinking about max maneuvering speed, the more gradually you move into an
updraft, the less force will suddenly be applied, and I think another factor
comes into play in this. The same wing with a higher wing loading will not
be as efficient at creating more lift. It will slip, or "mush" through the
air more at higher wing loading.

I believe the same factor took place in the fire fighting airplane that
pulled the wing off. With the lighter load, the wing slipped less, and
created more lift at the lighter weight. It changed direction much more
quickly, which converts to higher G's, which broke it's wing.

I don't know. I hope to always (usually?) explain things in the least
technical way possible. That is the teacher side of me trying to make
things make sense to people who are not experts in the subject that I am
attempting to explain. It makes sense to me, but maybe I'm all wet.
Something must make it true, because that is what people say who know how to
make fancy math work as related to aeroplanes.
--
Jim in NC