Rotorcraft Flying Menu >General Aerodynamics >Lift > Newton’s Third Law of Motion

Additional lift is provided by the rotor blade’s lower surface as air striking the underside is deflected down- ward. According to Newton’s Third Law of Motion, “for every action there is an equal and opposite reac-tion,” the air that is deflected downward also produces an upward (lifting) reaction.

Since air is much like water, the explanation for this source of lift may be compared to the planing effect of skis on water. The lift which supports the water skis (and the skier) is the force caused by the impact pres-sure and the deflection of water from the lower surfaces of the skis.

Under most flying conditions, the impact pressure and the deflection of air from the lower surface of the rotor blade provides a comparatively small percentage of the total lift. The majority of lift is the result of decreased pressure above the blade, rather than the increased pressure below it.