Lateral Flapping in Fbrward Flight

Steady lateral flapping, like steady longitudinal flapping, is caused by asymmetric airloads. In this case, the asymmetry of airloads is on the blades at \f = 0° and |f = 180° and is caused by coning. In forward flight, the coning causes the blade over the nose to be affected by a velocity component of forward speed that is more up with respect to the blade than for the blade over the tail. This asymmetry of vertical velocity at the blades at j/ = 0° and |/ = 180° produces a corresponding asymmetrical angle of attack and airload distribution that causes maximum response 90° later and thus lateral flapping that is upward on the retreating side. The magnitude of this flapping is a function of the coning and tip speed ratio. Because of it, the pilot must move his stick toward the retreating blade as well as forward in order to keep the helicopter in trim as he increases speed.

Cyclic Pitch Change in Forward Flight

Just as in hover, flapping is produced in forward flight by changes in cyclic pitch. For a rotor with no hinge offset, the flapping occurs 90° after. the cyclic pitch input. Because of the distribution of the aerodynamics, a 1° change in lateral cyclic pitch, Av will cause the rotor to flap down to the right by exactly 1э, but a 1° change in the longitudinal pitch, Bu will cause the rotor to flap down in front by slightly more than 1°. Thus the response to longitudinal control is somewhat more sensitive in forward flight than in hover, but the response to lateral control remains the same. If the rotor has hinge offset, the maximum response is less than 90° after the input and the magnitude of the response is a function of the offset, as will be shown by the flapping equations.