5 – Flight dynamics and control

Publisher Summary Degrees of freedom and fuselage of blade make flight dynamics and control look complicated. Before dealing with flight dynamics and dynamic stability problems analytically, it is important to consider the physical effects of velocity and angular rate disturbances on the helicopter. This chapter highlights all the disturbances affecting a helicopter: forward speed disturbance, vertical speed (incidence) disturbance, pitching angular velocity disturbance, sideslip disturbance, and Yawing disturbance. A helicopter is unstable both laterally and longitudinally in hovering flight, and the longitudinal instability becomes worse with increase of forward speed, particularly when the rotor has hinge-less blades. Tail plane is effective only in the upper half of the speed range. The unstable characteristics of the rotor deteriorate with speed and the tail plane becomes incapable of making the machine stable. Although adequate control power is available to correct disturbances, an unstable aircraft requires continuous correction and it is tiring to fly for long periods, even in calm weather. The stabilization devices fall into two categories: a mechanical/gyro device and automatic flight control systems.