21 - Flight Dynamics

Summary

Handling qualities are defined as “those qualities or characteristics of an aircraft that govern the ease and precision with which a pilot is able to perform the tasks required in support of an aircraft role” (Cooper and Harper (1969)). Generally the terms “flying qualities” and “handling qualities” are interchangeable, although the titles of specifications more often refer to flying qualities. Handling qualities involve the aircraft, the pilot, the tasks, and the environment (Padfield (1998)). Most of this chapter deals only with the aircraft flight dynamics or stability and control characteristics: the equations and fundamental behavior of the rotorcraft rigid-body motion. Simplifications and approximations are made to focus on the fundamental behavior of the aircraft. A more rigorous approach is needed to obtain models sufficient for rotorcraft flight control system design. Padfield (2007) covers rotorcraft flight dynamics and handling qualities in depth.

Control

Rotorcraft control requires the ability to produce moments and forces on the vehicle to establish equilibrium and thereby hold the aircraft in a desired trim state, and to produce accelerations and thereby change the aircraft velocity, position, and orientation. Like airplane control, rotorcraft control is accomplished primarily by producing moments about all three aircraft axes: pitch, roll, and yaw. The helicopter has in addition direct control over the vertical force on the aircraft, corresponding to its VTOL capability. This additional control variable is part of the versatility of the helicopter, but also makes the piloting task more difficult. The control task is eased by the use of a rotor speed governor to automatically manage the power.