Effects of Variations in Crashworthiness Criteria on Sikorsky S-75 ACAP Landing Gear Weights

Army helicopter landing gear design requirements (MIL-STD-1290) have become more stringent in recent years to provide for improved aircraft crashworthiness as demonstrated in the utility helicopter (UTTAS) and attack helicopter (AAH) programs and, currently, in the Advanced Composite Airframe Program (ACAP). Reported in this paper are the results of a study to evaluate the effects of variations in crashworthiness design criteria on the weight of landing gear and backup structure using the Sikorsky S-75 ACAP as a baseline. Critical design parameters such as aircraft sink speed, roll and pitch angles were separately varied to individually assess their effects on landing gear system loads and weights. Parametric studies of the various combinations of maximum sink speed, roll, and pitch crash conditions indicated 24 to 32% increases in landing gear system weights. Sink speeds were varied from 9.1 to 12.8 m/sec (30 to 42 ft/sec), while roll and pitch angles were varied from 0 to 20 degrees. Results quantify significant aspects of the Army's latest crashworthiness criteria and provide a basis for future design decisions.