Evaluation of a Retrofit OH-58 Pilot's Seat to Prevent Back Injury.

Abstract : This report documents the development of pilot and copilot retrofit seats, flight tests and evaluation of the seats based on crash tests, flight tests, and a 5-year usage test in the USAARL OH-58, serial no. 71-207781. The Bell Helicopter Textron (BHT) designed seat consists of a new seat pan, hinged at the forward edge, and attached to "load-limit" devices at the rear edge. The seat will rotate about its forward edge mount and move downward approximately 5 inches at the rear edge when the impact sink speed of the helicopter is excessive. The 5-inch stroke of the seat occurs while sustaining approximately 12 G on a 50th percentile pilot (1500-lb maximum in the lower lumbar spine). The seats, mounted in a standard OH-58 fuselage, were subjected to simulated "sink" speeds of 26.5, 29.6, and 32.2 fps. The seats easily prevented "injury" to the dummy pilots at 26.5 fps, but the seats "bottomed" against the cyclic control yoke at greater sink speed.