Hybrid-Electric Rotorcraft Sizing with Detailed Engine Specific Fuel Consumption

Data from a 4.5 hp piston engine generator is integrated with rotorcraft sizing to assess its impact. First, the specific fuel consumption (SFC) map of the powerplant is measured and modeled. Second, a sizing loop is developed for vertical take-off and landing (VTOL) aircraft and calibrated with XV-15 flight test aircraft and a NASA conceptual electric-VTOL aircraft. The power and platform models are then integrated to size a quadrotor biplane unmanned air vehicle of 5 lb payload. Several cases on how the engine speed can be controlled to meet the vehicle torque and speed are detailed. The key conclusion is that a detailed SFC model is as important as the rotor aeromechanics model. Without a detailed SFC model, errors in gross weight and range can be as high as 100%, due to incorrect tip speed reduction. With a detailed SFC model, a tip speed reduction of 30–40% is optimal to maximize the range of a 50 lb aircraft. The resulting aircraft has a minimum gross weight of 50 lb and a maximum range of 37 nm at 60 kt cruise speed.