Autorotation (helicopter)

Auto-rotation is driven by the wind turning the main rotor of a helicopter or a gyroplane. The air flows diagonally from the bottom toward the main rotor which is driven by a similar wind turbine. The rapid movement of the blades created by the air through a dynamic lift force, which acts counter to the force of gravity.

If the auto-rotation is strong enough, this buoyancy is sufficient to hold the device in the air. When gyroplane this is the normal flight condition. To permanently provide sufficient wind, they are driven by a motor-driven propeller. When the helicopter autorotation is an emergency measure that prevents unrestrained he falls to the ground in case of failure of the engine. The main rotor key must be brought by the pilot into a suitable angle to the wind. During the autorotation, the helicopter falls rapidly. But he can still be controlled, so that a forced landing is possible.

Autorotation in rotorcraft

Gyroplane

In a gyroplane, unpowered rotor serves instead of fixed wings of the generation of lift. The propulsion is provided by a motor and propeller, or by towing. This is the gyroplane - in contrast to the helicopter - permanent in autorotation.

Helicopter

The auto-rotation allows a helicopter to land without driven main rotor. It is based on the emergency maneuver after the drive fails or necessary throttling of the drive after the failure of the tail rotor. It is comparable to the sliding of an aircraft without ( working) engine and is divided into two phases:

In the first phase, height and speed of the aircraft in controlled, but relatively steep glide in speed of the rotor is converted, the air flow from below ( " wind " ) causes the driving of the rotor. For this purpose, the angle of attack of the rotor with the collective lever (pitch) is set very low. Thus, the rotor has a low resistance, but produced very little buoyancy. The principle of generating lift is similar to the autogyro in this flight condition. In this phase, as much rotational energy to be included in the rotor with controllable speed and rate of descent. Considered to be optimal, depending on the type of the aircraft, a speed of 110 to 130 km / h with a sink rate 5-10 m / s The rotor speed is kept at 100 % in the area - it is controlled with the collective. To achieve a " stretching " of the flight path, the rotor speed can be reduced, depending on the pattern to up to 85 percent of the speed of rotation while increasing the speed. This allows a somewhat more distant emergency landing can be achieved.

In the second stage immediately above the bottom is again generated more lift by strong pitching of the rotor ( flare ), the stored kinetic energy of the rotating rotor is converted into a short time and thus a greater lifting relatively soft fitting is made possible.

The autorotation landing places high demands on the pilot and requires regular exercise, as the right level and timing of pitch change must be made precise. This is mainly due to the fact that the kinetic energy of the rotor only once for the increase in lift is ( necessary to brake the rapid descent during the descent phase ) is available. If the angle of attack increases too early, the helicopter is already slowed down in to a great height and then can " sag " with decreasing rotational speed of the main rotor. If the angle of attack increases too late, the remaining altitude is no longer sufficient to decelerate the helicopter sufficient.

For the feasibility of an autorotation landing, the flight altitude is crucial: only with adequate height above the ground, a record (due about a motor failure ) to a slowly rotating rotor in the first phase of the autorotation landing again sufficiently ride.