Aerodynamic Interaction Effects Between Propellers in Typical eVTOL Vehicle Configurations

Many electric vertical takeoff and landing concepts are characterized by nontraditional vehicle layouts with distributed propellers. Two propeller interaction types were distinguished in this Paper, which investigates how propeller interaction in side-by-side and one-after-another configuration affects performance, in terms of thrust, power, in-plane forces, and out-of-plane moments, and how those performance effects depend on axial and lateral propeller spacing. A wind-tunnel experiment was performed with two propeller units, one instrumented with a force/torque sensor and the other introducing the aerodynamic interaction. Total pressure and planar particle-image velocimetry measurements were taken to investigate slipstream characteristics. A strong dependency of interaction effects on the geometric layout was found. For side-by-side interaction characteristic of vertical takeoff and transition, interaction effects varied from weak at small angle of attack to strong at larger angles. A drop in rear propeller thrust of up to 30% was found at constant advance ratio. Keeping thrust constant resulted in power penalties up to 13% for the two propellers combined. For one-after-another interaction, characteristic of cruise, a maximum reduction of thrust of up to 80% was observed. Thrust compensation led to power penalties up to 30% for the rear propeller alone. An extended blade element momentum model captured most interaction effects with sufficient accuracy.