Investigation Into Lift-Offset Coaxial Rotorcraft Rotor-Fuselage-Pusher Interference

Conventional helicopters are limited flight speed and combat range compared to fixed- wing aircraft. Nowadays, the high speed and long-range VTOL(Vertical takeoff and landing) rotorcrafts are required. To overcome weaknesses of convention helicopter, various rotor systems (tilt rotor, tractor propeller, coaxial rotor, etc.) are being adopting. Lift-offset coaxial rotorcraft has excellent hovering performance and maneuverability, and can fly at high speeds using a pusher prop. But, complex main rotor system and the rear-positioned pusher design can cause interference. This study was conducted to investigate the effects of this interference. The CAD geometry was generated through reverse engineering of a coaxial rotor helicopter design obtained from public data. Maneuvering conditions for high-speed, long-range flight were extracted using helicopter simulation software (FLIHGHTLAB). The pusher propeller, located at the rear of the fuselage, can experience thrust loss due to wake interference from the fuselage, and may also be affected by buffeting vibrations. This fuselage–rotor–pusher interference was analyzed using high-fidelity CFD software (STAR-CCM+). The results showed that by adjusting the crossover angle to a non-parallel orientation with the fuselage, vertical drag could be reduced by up to 1.5 times at low speeds. Furthermore, analysis of pusher buffeting indicates that the downwash from the coaxial main rotor has a substantial impact on the pusher propeller. This study analyzed the pressure distribution on the fuselage surface based on the crossover position of the upper and lower blades of the coaxial rotor. Fuselage and Pusher Interaction: Analysis of fuselage-pusher interference revealed that the wake generated by the fuselage increases the effective angle of attack on the pusher, enhancing its performance. However, this also led to an increase in fuselage drag.