Aerodynamic Scaling of Rotorcraft Blades in Hyperbaric Conditions*

Novel multirotor aircraft have been developed for applications ranging from urban transportation to military use. Techniques for modelling the performance of aircraft rotors continue to improve, but they still fall short of perfectly replicating the full highly complex flow physics, including unsteady aerodynamics, scale effects, and wake dynamics. Blade element momentum and vortex wake methods are commonly used to analyze rotorcraft performance but resort to simplified models based on assumptions about the flow physics, such as prescribed inflow or wake geometries, or quasi-steady conditions. Experimental testing provides higher fidelity data, but the cost of fabricating and testing models in a suitably large wind tunnel can be prohibitively expensive due to the sheer scale of rotor blades. Testing with scale models has been done, but small models fail to replicate full-scale performance. The compressible nature of the flow means Reynolds number (Re) and Mach number (Ma) cannot both be matched. Conducting experiments on scaled rotors in compressed air allows density to be tuned to match Re and Ma across a range of scales. Data from single rotors in hover will be presented to examine the dependence of performance, such as thrust and power coefficients on Re, as density varies.