FM 1-506 Fundamentals of Aircraft Power Plants ... - Survival Books

WWW.SURVIVALEBOOKS.COMFM 1-506Fail-safe to high power. By placing theschedule high, the torque motor is designed toreduce the schedule to the desired level when itis energized. Because loss of torque motor currentcauses the schedule to return to thehighest level, this provides failure protection toa high power. A schedule that is biased high dueto electrical failure does not cause power limiting.In the event of an electrical system failure,it can be manually retarded to a more desirablelevel using the PAS. With all engine protectionfunctions in the HMU, no engine damage orstall can occur during or following any loss ofelectrical signal to the torque motor.Power available with one engine out. Theschedule is placed high enough that, in the eventof failure of one engine, the remaining engine’sgas generator can increase power enough (automaticcontingency power) to carry the load atthe given LDS (collective pitch) setting.Without this arrangement of schedules, a singleenginefailure could not be compensated for bythe remaining engine and would result in a significantloss of available power.Electrical Control Unit OperationThe ECU, powered from an engine-mounted alternator(Figures 4-21, 4-22)—4-20