Abstract:To investigate the flow field characteristics of largesize plant protection unmanned helicopter hedgehopping,the numerical simulations were conducted,and the fullsize physical model of the largesize helicopter was established. The threedimensional flow field of largesize unmanned helicopter hedgehopping was simulated by SST kω turbulent flow model. The results show that the downwash flow field is relatively disorder under the fuselage because of the obstruction of fuselage.The distribution characteristics of downwash are generally consistent at the same nozzle location of different height,however the distribution characteristics of downwash are quite different for the same flight altitude at different nozzle location. The vertical velocity is increased with latter decreasing along the direction of rotor at the spray boom location,and the maximum velocity is obtained near the x/R value of 0.8. The width of plant canopy velocity is increased with the decreasing of flying height,and the better fly height of H is 4 m. The boom of UAV should be installed in the area with z from -1.50 to -2.00 m and x from -0.50 to 0.50 m.