"
I think that people proposing utrasonic quality checks don't have an exact
idea how a wing is constructed. Utrasonic QC basically detects interfaces,
and a composite glider wing is made up from interfaces all over the place.
I'd say that the error rate in an utrasonic QC would be completely through
the roof.

I think it would be more easy (and straightforward) to do just a structural
load test up to 1.5 times max rated load :-)
Bert Willing
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I understand your point about ultrasonic testing. The sound wave
would have to go through the outer skin, foam, inner skin, carbon
fibre rovings spar cap, bonding paste, shear web of differing
compositions. I guess there could be too many interfaces although I
would think that one could find an ultrasonic frequency which didn't
reflect off of the interfaces but did reflect off of voids. Or
reflects different frequencies and giving a picture.
Any idea how composite structures are inspected on large airplanes? I
assume x-ray wouldn't be very sensitive on nonmetallic structures.
How about neutron radiation? Acoustic emission transducers? Ballistic
Recovery Chutes?

Also, if the cotton fibres carry the load, is the repair done with an
epoxy/cotton mixture? How do they get it into a blind air bubble?