Many manufacturers claim to support amazing overload situations but I would say it makes the plane too heavy. All parts should be build to support a defined load and then break. This way the plane ends up as light as possible and in flight strength from some parts does not help much if not all structural parts support the load.
Exactly. Plenty of impressive videos on the web of static tests to destruction where you can see wings bend upwards to crazy angles where you start wondering what margins we are using. But of course fatigue is a different issue. But then these static tests often show a failure at just one point of the wing. A perfectly designed wing would fracture at various different points or ideally disintegrate all over. If not, all portions that did not break were simply too strong and thus too heavy. I guess we’l get there one day.
aart wrote:
A perfectly designed wing would fracture at various different points or ideally disintegrate all over. If not, all portions that did not break were simply too strong and thus too heavy. I guess we’l get there one day.
Perhaps for Experimental Category structures. Otherwise see Page 23 of AC 23-13A.
In fail-safe design, the failure of the primary load path is due to crack growth (from fatigue initiation of material/manufacturing defect). And the remaining structure is only good to withstand limit load.
So in an ultimate load test, both the primary and secondary load path might fail together. Or even if it is not a waiting failsafe configuration the secondary load path might fail first.
I’m familiar with a structure that is actually stronger after it fails. In that case strength is not the primary requirement because the application requires stiffness to combat a magnetic load that increases with displacement.
For an aircraft structure, I think the chance of designing two parallel load paths with stiffness, elongation and strength identical to the point that they fail simultaneously under a static load test is zero. I also think it’s safer that one of the load paths fails first under static loading, as well as providing redundancy if one fails due to long term fatigue and crack growth. A great big bang followed by flying home is better than the wing falling off. An aircraft structure that is not fault tolerant for any one of its loading conditions is not ideal IMO.
