Remedial Measure To Avoid Repetitive Failure Of Actuator In Brake Parachute Release Mechanism

Abstract: ABSTRACT Brake parachute release mechanism assembly of Hawk aircraft, Pt No KB959K0139-026 is failing at large numbers at air force field units. It was revealed that the failure is due to excess load on the actuator and subsequent burning of armature, Pt NoN162492. It is observed that friction load between the cam arm and the catch, of the release unit is overloading the actuator. So, the prime concern is to reduce friction load to ensure stress free operation of the actuator. The normal torque developed by the actuator is 3.39 NM (as. per the OEM data sheet). The existing length of the cam arm from the centre is 21.2 mm. if the length of the three arms of cam is reduced by 2.0 mm and catch thickness is increased by 2.0 mm, i.e the point of contact of catch and cam arm is made 2.0 mm nearer to the centre of the cam than the original item. Now, the force exerted by the actuator to move from " lock" (stream) to "unlock"Qettison) position is more with the reduction of cam arm length with rated current and rated torque. Brake parachute release mechanism is assembled with modified cam arm and catch. Bench checks were carried out. The results are found satisfactory. High speed taxi trials and flight trials were carried out with modified unit in coordination with regulatory agencies and performance was found satisfactory. Based on the flight trial performance, the modified brake parachute release mechanism assembly is ratified for use on the aircraft.

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