Local perforation of structures

Parts of an impacting aircraft, especially the engines, cause local effects such as perforation and missUe generation in the rear side of an impacted wall. 

Many formulae exist for the evaluation of these effects, not all of them applicable in the range of 

This formula is valid for impact velocities ranging from 150 and 300 m s and has been verified by experimental tests. 

The protection against spalling is obtained by empirically increasing by 25 per cent the thickness calculated by the formula. 

An increase of thickness up to 1.8 m guarantees an absence of damage due to the simultaneous explosion of the normal weapons carried by a fighter aircraft (missiles), but not of the possibly carried bombs (which is justified on a probabilistic basis if the bombs are not triggered to explode). This thickness also offers protection against other types of impacts, such as an obhque one due to the separation of an engine and that of a missile due to the explosion of a nuclear plant turbine (for which in general 80 cm are sufficient). 

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