Impact of Detailed SFC on Hybrid-Electric VTOL Sizing

Data from a 3.43 kW piston engine-generator is integrated with rotorcraft sizing analysis to assess its impact. First, the measured SFC map of the powerplant is modeled. Second, the sizing is validated with XV-15 flight test aircraft and NASA conceptual reference quadrotor. The power and platform models are then integrated to size a hypothetical quadrotor bi-plane unmanned air vehicle of 5 lb payload. Several cases for how the engine can be operated to meet the vehicle torque and speed are detailed. The key conculsion is that a detailed SFC model is as important as the aircraft model. Without it, errors in tip speed reduction, gross weight, and range would be quite dramatic from 50-100%. A tip speed reduction to 65% hover in cruise was found to strike the best balance between rotor performance and engine performance of the hypothetical aircraft, resulting in a gross weight of 50 lb and range of 120 nm at 60 kts cruise speed.