Ground test and numerical investigation on aerodynamic performance of a quad tilt-rotor aircraft in ground and water effects

Abstract

Ground and water interferences significantly affect the safety of takeoff and landing for Quad Tilt-Rotor (QTR) aircraft. However, the mechanism is extremely complex. An unsteady numerical simulation method suitable for amphibious QTR aircraft is established and verified through ground tests. This study explores the distinct aerodynamic characteristics of the QTR aircraft in water and ground effects (IWE and IGE) and compares them to those out of ground effect (OGE). Results indicate that the wing, ground or water surface strongly affects the QTR's aerodynamic performance by influencing the downwash flow form the rotors. The lift and torque coefficients exhibit irregular fluctuations during IGE compared with OGE. However the distribution of lift and torque coefficients become more periodic and regular during IWE due to the flexible water surface, which serves as a flow rectifier accelerating the dissipation of ground vortices and rotor tip vortices. The soft water surface is impacted to form a “drainage area”, which increases the distance between the rotor and the water. Therefore, the water effect is not as strong as the ground effect. The higher the height of rotors above the surface, the weaker the interference effects. The water effect vanishes when the vehicle is at least 0.9 times the rotor diameter above the water surface while the ground effect vanishes when the vehicle is at least one rotor diameter above the ground.