Pre-test Analysis on Slowed Mach-scaled Thrust Compounding Rotorcraft

This paper details the propeller analysis in forward flight to finalize the wind tunnel test matrix of the thrust compounding rotorcraft model. First, the University of Maryland Advanced Rotorcraft Code (UMARC) is validated with main rotor hover test data at the tip Mach number of 0.2 and 0.5. It is further validated with slowed rotor (tip Mach number 0.2) wind tunnel test data up to a high advance ratio of 0.7. Next, the lifting-line-based propeller analysis is integrated into UMARC and validated with the propeller hover test data at various RPMs and propeller pitch settings. This analysis examines the isolated propeller performance in forward flight followed by a combined main rotor and propeller analysis using Maryland Freewake in the time domain. The wind tunnel test will be carried out at the propeller pitch of 30, and 35 and RPM will be varied between 1400 to 3500 up to a wind speed of 100 knots. A rotorcraft system-level comparison study is conducted using previous Mach-scaled wind tunnel test data at different shaft tilts and the propeller analysis at the corresponding speeds. Based on this coupled main rotor-propeller analysis, it is found that the thrust compound does not have much impact on rotorcraft efficiency, L/D. However, it helps extend the speed by using the propeller for propulsive force and the main rotor shaft tilted backward for efficient lift.