sentences:  The VGs are placed on the airfoil to enhance the lift if they are placed on the lower (flatter) surface or limit the maximum lift if placed on the upper (higher camber) surface.Furling works by decreasing the angle of attack, which reduces the induced drag from the lift of the rotor, as well as the cross-section.One major problem in designing wind turbines is getting the blades to stall or furl quickly enough should a gust of wind cause sudden acceleration.