Abstract: A holdback bar for restraining an aircraft temporarily prior to catapult isted launch which utilizes a ball and piston unloader valve to insure rapid, positive release of a pressurized hydraulic fluid. Compensator chambers each having a resilient piston cushion against release shock caused by rapid release of stored strain energy in the hydraulic fluid and provide hydraulic fluid make-up to allow for expansion and contraction and slight leakage losses.

Abstract: A holdback bar for temporarily restraining an aircraft against the combined orces of engine thrust and catapult force prior to a catapult assisted launch of the aircraft which utilizes strain of a mechanical component to measure the level of combined forces. Housing stretch beyond a pre-determined amount actuates a floating trigger rod to lift a valve from its seat and permit escape of hydraulic fluid from a pressure chamber. The holdback bar includes a compensator for absorbing fluid volume changes caused by thermal expansion or contraction of the hydraulic fluid, and a rupture disk for limiting the pressure obtainable within the hydraulic fluid pressure chamber.