Wind Tunnel Testing of a Slowed Mach-scaled Hingeless Rotor with Lift and Thrust Compounding

The present study investigates a lift and thrust compounded helicopter model equipped with a slowed Mach-scaled main rotor, a retreating side wing, and a pusher propeller through testing in the Glenn L. Martin Wind Tunnel. The main rotor rig included four NACA0012 uniform blades attached to a hingeless hub, a tapered symmetric retreating side wing, and a ROBIN fuselage. The propeller rig consisted of a four-bladed Sensenich L26H propeller. Tests were conducted with a parametric sweep of advance ratio (µ), lift trim target (CL/σ), propeller RPM (Ωprop), wing incidence angle (θw), and rotor shaft tilt (αs). Vehicle performance, blade loads, hub vibratory loads, and component interactions were measured under various flight conditions and vehicle configuration modifications - which were used to validate the modified University of Maryland Advanced Rotorcraft Code (UMARC). The rearward shaft tilt (αs = -4 ◦ ) and positive wing incidence angle case (θw = 8 ◦ ) was the best for vehicle performance as it increases L/D by 44% at µ = 0.5. At a wing incidence angle of 4◦ , increasing the advance ratio from 0.3 to 0.7 increases vehicle L/D by 58% due to the wing generating a significant portion of total lift. In-plane hub vibratory loads decreased by 20% when wing incidence increased from 4° to 8° for the same shaft tilt case at µ = 0.5. The presence of a wing (at 8° incidence) causes the propeller's propulsive efficiency to decrease by 26% due to the wing wake. At low speeds, rotor-wing interactions result in the wing's L/D decreasing by 2 for every 0.04 increase in CL/σ, with this decrease diminishing notably at higher speeds.