Originally Posted by old,not bold
I always thought that the fuselage structure is supposed to withstand quite severe unexpected and unusual forces. And this one didn't.
Among other things, an airframe also has to be lightweight. This is not only achieved by using lightweight, strong materials, such as aluminium, composite materials, and, in highly stressed places, even titanium alloys.
It is also achieved by designing it for a very precisely defined type of loads and forces, so it is in fact made to withstand only expected forces. It is the designers' and engineers' job to think of all the forces to which the structure could reasonably be expected to be exposed. Scaling a concrete wall is most likely not on their list.
The design must clearly state what types of loads and at what magnitude are expected, and how these maximum loads were derived, and must be demonstrated to break no earlier (in the case of the wings, at least) than at 150% of that load. For the wing this means, an actual production model must be bent until it breaks. This
Youtube-Video shows what it looks like.
The certification authorities must agree with the calculations for the maximum design load and certify that the structure has met the test for the aircraft to receive airworthiness.
Bernd