The Research On Aerodynamic And Take-off Performance Of WIG Graft In The Influence Of Front Propeller

The take-off phase in water is related to the power reserve,structural strength and take-off stability of the WIG craft,so the WIG craft is often required to shorten the take-off distance as much as possible to achieve rapid take off from water.In order to achieve this goal,a feasible method is to install a propeller on the front of the wing of the WIG craft.At present,there are few numerical simulations focus on the aerodynamic performance of the wing in ground effect in the influence of front propeller,so it is necessary to concentrate on this research.At the same time,there is currently no quick and convenient engineering method for estimating the take-off performance of a WIG-craft,so it is meaningful to put forward a method to preliminary analyze the take-off performance of WIG-craft.Using a CFD commercial software,the Glenn Martin 21 airfoil body is used to be calculated and analyze the change law of aerodynamic coefficient when flight height and pitch angle changing in ground effect.It is found that the upper surface lift of the wing is the main component of the lift in ground effect.However,as the flying height drops,lift on the upper surface decreases slightly.And the lift gain caused by the flying height drops is mainly the result of the increase in the lower surface pressure.As the pitch angle increases,the lift of the airfoil body will first increase and then decrease.The reason for the drop in lift is the stall phenomenon,and the existence of the ground effect makes the stall angle smaller than when there is no ground effect,that is,the ground-effect wing is more likely to stall.The longitudinal static stability condition can be used to determine the longitudinal static stability of the wing in ground effect,and adjust the position of the center of gravity to the direction required by the design.Based on the study of the Glenn Martin 21 airfoil body in ground effect,a virtual disk model is added to simulate the influence of the front propeller.First,the design parameters of the front propeller under the cruising state of the wing in ground are optimized,and the relative horizontal distanceLp=1,relative height hp=0.875,the front propeller inclination angle β=0 are the best design parameters.As the relative flying height decreases,if the inclination angle of the front propeller is kept at zero,the lift coefficient gain is smaller than that without the front propeller,so the front propeller inclination angle should keep increasing to keep highest lift coefficient.Keeping the best design parameters unchanged and under the influence of the front propeller,the stall angle of the wing is smaller in the ground-effect area then that in the non-ground-effect area.In same height,the stall angle of the wing under the influence of the front propeller is smaller than that without front propeller.In other words,the wings are more likely to stall under the influence of the front propeller.Based on the resistance estimation method of the planning craft,an improved method suitable for the take-off estimation of the WIG-craft is obtained.This method can be used to quickly estimate the take-off performance of the WIG-craft and analyze the main design parameters of the WIG-craft.Using this method to estimate the take-off performance of the WIG-craft,it is found that the further the center of gravity is,the smaller the maximum resistance peak the WIG-craft suffering when take-off,the lower the take-off speed,and greater the angle of inclination.The improvement of the front propeller on the take-off performance of the WIG-craft is mainly due to the increase of the lift coefficient of the main wing,which significantly reduces the drag peak during the take-off phase and reduces the take-off speed.In addition,the front propeller can also weaken the influence of the position change of the center of gravity on takeoff speed.