Investigation of Coordinated Free Turbine Engine Control Systems for Multiengine Helicopters

摘要

Various multiengine helicopter control concepts were analyzed and evaluated to determine an optimum system design to relieve engine monitoring during critical flight maneuvers. Power turbine governing mode evaluations showed that a proportional power turbine governor with a lagged gain reset (feedback) is desirable. Governing stability was based on a linearized representation of the engine-controls-rotor system and included both Bode diagram analysis and analog simulation. Power transient response was evaluated by using a nonlinearized digital computer simulation of the different modes and the engine and rotor system, with collective load transients imposed. The gas producer control requirements found necessary were automatic start sequencing, closed-loop steady-state turbine temperature limiting, emergency power operation capability with both manual and automatic selection, and governing action using a gas producer control fuel metering valve. Isochronous control of power turbine speed was evaluated and found to be a feasible alternative to collective pitch lever coordination of the power turbine governors. The isochronous speed control also was found to cause potentially undesirable speed excursions during collective induced power transients. The multiengine governing-load sharing concept selected utilized individual governors for each engine, with closed-loop load sharing control and an automatic engine malfunction detector. A digital computer simulation of promising control schemes and a multiengine-helicopter power system was developed and utilized in steady-state and transient analyses. (Author)