Endurance Optimization of a Tandem Helicopter with Variable Speed Rotors and a Spark-Ignition Engine

Rotary unmanned aerial vehicles (R-UAV) are becoming commonplace as a solution for maritime surveillance activities due to their vertical take-off and landing (VTOL) capability. Extending flight duration is thus crucial; one approach is to slow down the rotors in flight, which improves their efficiency. An in-house tandem rotorcraft performance model is used to evaluate the benefits of slowed rotors in endurance flight when used in conjunction with a spark-ignition engine. The performance model is validated using experimental data from flight tests in hover and lowspeed flight. A surrogate-based optimization approach determines the flight and engine speeds required for minimal fuel consumption throughout a typical endurance mission. Payload-Endurance and Payload-Range curves for flights at various payload and fuel capacities show overall benefits. Gains up to 25% and 15% in endurance are possible for f lights at standard and maximum fuel capacity. Range is not impacted negatively and sees gains at maximum fuel capacity. The spark-ignition engine plays a beneficial role as it contributes up to 38% of fuel burn reduction.