Abstract: The propulsion system of the large amphibian aircraft AG600 includes four turboprop engines rotating in the same direction. Targeting the unstable interference of propeller slipstream to the yawing moment appeared in the wind tunnel test of a 1:15 model take-off and landing configuration under crosswind, a large scale parallel unsteady numerical simulation is conducted for the powered wind tunnel model. The numerical simulation re-produced the wind tunnel observations, showing that the outboard wing separation and the dorsal-fin vortex breach are the major causes, which are verified by a later wind tunnel test. Considering the lower Reynolds number and the higher propeller rotating speed due to the limited size of the wind tunnel model, an unsteady numerical analysis and an yawing stability estimation are continued for the full size aircraft under real flight take-off and landing condition with crosswind, ensuring flight safety. The results of the computation show that, under flight Reynolds number and propeller rotating speed, the flow separations at wind tunnel condition disappear under the same yawing angle, and the acceptable crosswind range for yawing stability has significantly increased. The present investigation realizes the unsteady analysis of the slipstream interference on the lateral aerodynamic characteristics of four propeller aircraft take-off and landing configurations, establishing the Reynolds number correlation of wind tunnel test and full size flight via computational fluid dynamics. The study also assesses the virtual flight test. The research results are verified by the first flight and the following flight test of AG600.

Key words: amphibian aircraft, propeller slipstream, yawing stability, computational fluid dynamics, unsteady flow, wind tunnel test, Reynolds number effect