VARIABLE DESIGN CRITERIA FOR ROTARY WING AIRCRAFT CRASH RESISTANCE

The current MIL-STD-1290 provides one set of crash resistance design criteria for military helicopters. It is recognized that for small helicopters it is more difficult to meet the seat stroke and high mass component retention than for a medium and large size helicopter and to meet current design criteria, the percentage of weight empty dedicated to crash-worthiness can become unacceptably high. In addition, how a helicopter crashes must be taken into account. Accident data shows that low inertia main rotor blade helicopters with high disc loadings crash at higher impact velocities than the same weight aircraft with high inertia rotor blade systems and lower disc loadings. In addition, indications are that the helicopter type (i.e., attack, air assault, utility, cargo) also affects aircraft crash modes. Suggested different levels of design criteria for crash resistance are presented with supporting rationale for variable design criteria.