[donarb]

That was my thought as well, especially since the carbon fiber wings flex so much more. That flex might induce more stress on the wing mounts which in turn deform the cylinder. The good thing is that these test fixtures are fitted with lots of sensors that record all of the stress.

[rolph]

In my experience there are strain guages installed all over the air frame for testing and for operation, so the strain history of the frame can be reviewed.

The thing to keep in mind, is the different goals in testing engineered products like this.

there is a thing called Mean Time Before Failure [MTBF] that usually involves sampling of a number of units to arrive at a maintenance and replacement interval.

there is also a need to find the maximim service limits of a product, for example the swash plates and rotor linkage of a helicopter has a threshhold requiring at instance replacement. so for example, if you shook the yoke of a heli quickly left and right beyond a point you will probably knock yourself out of the air, but you will also induce damage requireing immediate replacement.

and then, there is what happened with the airframe of topic. immediate catastrophe during testing. I suspect this wasnt the immediate goal, as the engineers projected it would hold up, and were suprised, luckily not injured.

then the last thing that is usually a pre-production test, is an intentional induction of failure. you have a good idea when its going to break, and you take it there and beyond to gawp at the failure mode and the pieces, and re- engineer it until catastrophe is far beyond extreme duty conditions.[ideally]