Exhaust Gas Reingestion Measurements

Results of flight tests to measure the magnitude and effects of engine exhaust gas reingestion and inlet pressure distortion are presented. The tandem rotor CH-47 and single rotor YUH-61A helicopters were flown with instrumented engine inlets using fast-response probes. A wide range of flight maneuvers were evaluated, including operating in and out of ground effect, flares, hovering turns, lateral and rearward flight. The dynamic inlet air temperature and pressure patterns, time histories, and variation of basic engine parameters during exhaust reingestion are provided. The effect of instrumentation time constant on the maximum inlet temperature rise is discussed. Also shown is the effect of an inlet screen on pressure distortion. Conclusions are drawn as to the use of this data to establish turbine engine compressor stall margin requirements needed to avoid experiencing problems with the engine/ helicopter integration.