Concept of helicopter flight regimes. The helicopter flight regime can be either steady state or nonsteady state. Rectilinear flight at constant velocity is termed a steady state regime. The steady-state regimes can be subdivided as follows.

1. Vertical flight regimes: hovering;

vertical climb; vertical descent.

There are two varieties of vertical descent: descent with engine

operating and descent in the main rotor autorotation regime.

2. Horizontal flight regime.

3. Climb regime along inclined trajectory.

4. Descent regime along inclined trajectory (can be performed with engine operating or with main rotor autorotating).

The unsteady flight regime is one in which the velocity vector changes in magnitude or direction. The unsteady regimes include takeoff, landing, maneuvering (horizontal turns, heading changes, spiral, snaking, and so on) and transition from one flight regime to another.

In accordance with the law of inertia, a body travels uniformly and rectilinearly or is in a state of rest if no external forces act on it. The steady-state flight regime is uniform, rectilinear motion of the helicopter. Consequently, for the realization of this regime it is necessary that the geometric sum of the forces acting on the helicopter in flight be equal to zero. Moreover, the sum of the force moments acting on the helicopter relative to the center of gravity must also he equal to zero. These will then be the conditions for complete equilibrium of the helicopter.

Unsteady flight can occur only if some unbalanced force acts on the helicopter and imparts an acceleration to it, i. e.,

EF ^ 0 and EM ^ 0. eg eg

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