Design, Analysis and Flight Testing of a High Altitude Synchropter UAV

This paper describes the architecture and performance of a 36 kg to 56 kg synchropter (intermeshing rotors) with 3.3 m rotor diameter that was specifically designed for high altitudes. The design mission of this prototype is to climb from 5000 m to 9000 m above mean sea level, descend back to 5000 m with autorotation, and cruise back to the departure point. The design is intended to be a compromise between controllability in gusty winds and low overall system power consumption through low disc loading and tip speed. The prototype features variable tip speeds from 100 m/s to 135 m/s and is able to hover with an overall system power of 80 W/kg. This paper presents flight test data of this prototype at low altitude with a special focus on rotor performance and rotor blade root flap moments in hover, forward flight, and vertical climb. The flight test data is compared to a lower order aeromechanics model using the comprehensive helicopter analysis CAMRAD II that was previously used to design the rotorcraft. The couplings between the control inputs and their corresponding axis motion are discussed. Finally, the design mission was simulated by the performance validated model to bridge the design and the real prototype.