Thanks fellows,
I posted this thread before realizing, in another one, that acceleration was measured on TOC models up to 30g.
In this case what appeared to me as a waste of strength now can be called security factor and is about 3.
I was thinking of structural buildings calculation (it's my job), where this factor is a a bit more than 2 (2.400 kg/cm2 working stress, 5.000 kg/cm2 breaking stress) and mostly for linearity of stress to strain ratio.
In aerodyinamics, where wheight is an issue more then in static buildings, it appeared all natural applying some engineering.
OK, next week I'll call my brain surgeon.
Greetings.
Enrico