The System Approach to Crashworthiness for the NH90

Like for most new military helicopters the ‘Weapon System Development Specification’ of the NH90 includes - among others - also requirements concerning crashworthiness. This paper will concentrate on the development of fuselage crashworthiness. Nevertheless the characteristics and properties of other crash related components like landing gears and seats are considered too or even checked in the complete helicopter environment. Furthermore also other crash related features like upper-deck mass and cargo retention, provisions for a protective shell and post-crash fire hazards are considered during the development but not covered directly in this paper. As crashworthiness is at the most of equal importance than the other requirements the objective of this development is to achieve the best compromise among them and not the ultimate crash resistance. It will be shown how the hybrid program KRASH85 was used in the very early design phase to determine first basic characteristics of the fuselage that are necessary to fulfil tough crash requirements. During the further development KRASH85 and lateron DRI/KRASH-PC were employed to verify these results and to check first designs of components. In the meantime DRI/KRASH-PC is integrated in a closed loop of testing and simulation. On one side the required characteristics of energy absorbing elements are determined by simulations and on the other side test results of those elements are checked again for their applicability and if necessary modifications of the structure are initiated. The final objective of this system approach is to demonstrate, that simulations (in this case with DRI/KRASH-PC) are adequate to substantiate the complete crash envelope of the NH90 provided they are supported by tests. For that purpose the correct representation of the whole helicopter by a numerical model has to be assured by further comparisons and adjustments between tests and simulations. These advanced test articles range from frames to a complete center structure including equipment and heavy mass dummies. This paper deals with activities that are already completed, describes current efforts, and gives an outlook to work that will be done in the future.