Engine/Airframe Response Evaluation of the HH-60A Helicopter Equipped with the T700-GE-701 Transient Droop Improvement Electronic Control Unit.

The enginedrive train response was stable for all speedpower turbine speed droop recovery characteristics, and power turbine speed governing characteristics was the HH-60A with the T700-GE-401 engines equipped with the -401 transient droop improvement engine control unit. The HH-60A with the T700-GE-401 engine equipped with the -701 transient droop improvement engine control unit with and without the collective potentiometer input exhibited larger rotor speed droop, noticeable drive train oscillation during droop recovery, and less desirable power turbine speed governing characteristics. The undesirable engineairframe characteristics of the HH-60A with the -701 transient droop improvement engine control unit is a shortcoming. The UH-60A with the T700-GE-700 engine demonstrated the largest main rotor speed droop but residual drive train oscillations were small, droop recovery characteristics were more predictable and power turbine speed governing was noticeably more stable than demonstrated by the T700-GE0-401 engines equipped with the -701 transient droop improvement engine control unit. The undesirable engineairframe response large main rotor speed droop of the UH-60A with the T700-GE-700 engines is a previously identified shortcoming. Future designs for the UH-60 engine control units should include all the transient droop improvements of the -401 transient droop improvement engine control unit. Additionally, future designs of engine control units should have dynamics tailored to the particular helicopter in which the engines are to be installed.