First of all, it is not the epoxy which bears the load but the cotton
threads. Epoxy is just the matrix, and the rated load of cotton/epoxy is
around 7N/mm.

Microballons are much heavier and the composite formed of balloons/epoxy
doesn't hold the same load as cotton threads/balloons (balloons are spheres
so in this case it's the epoxy which finally bears the load). Microballoons
are rather used for surface cosmetics.

Seperated glass rovings would be ideal - but the beasts don't bend easily
into small radii if threaded and a paste made up of them would leave many
mm-sized voids. so it just doesn't work.

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

ASW20 "TW"


"Martin Gregorie" a écrit dans le message de
...

Does anybody on here know what advantage cotton threads would have
over, say, microballoons or separated glass rovings?
--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :