Translated automatically from the French version of Kelclinic. Contact us for remarks, questions or help.
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hover mode and hovering helicopter mode
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hover mode and hover

hover mode and hover

 

 

Hover (or man) is called a flight mode, in which there is not any movement of the center of gravity of the helicopter with respect to the air and there is no rotation of the helicopter around the center of gravity.

This definition implies, in particular, that for a hover in the presence of wind is necessary to move the helicopter hanging in the wind direction at a speed equal to the speed of the wind. Sometimes called a hover flight at which the helicopter is hanging motionless over a given point of the earth's surface. However, this mission can be called only when hovering calm. Saving a fixed position relative to the ground in the presence of wind can be performed only by a flight at a speed equal in magnitude but opposite in direction to the speed of the wind.

When hovering in calm in the single-rotor helicopter the force of weight lift helicopter, which coincides with the direction of the complete wind power rotor on the Y axis, the reactive torque from the main rotor and tail rotor thrust.

Determine which relationships must support the pilot operating forces and moments to satisfy the above conditions six steady state.

For this purpose it is necessary to balance the force of a force equal in magnitude but opposite in direction.

To create this force is equal in magnitude to the thrust of the tail rotor and called lateral force, pilot rejects the rotor in the opposite direction of tail rotor thrust.

However, in order not to distract the attention of the need to balance the power of the pilot, the designer usually attached to the screw axis of the helicopter a certain inclination in the direction opposite to the direction of the force TVB. Then balance the forces on the operating condition is achieved automatically.

If the leg (the vertical distance) from the center of gravity force and shoulder lateral force caused by the mounting angle of the rotor were of different sizes, then it would appear the additional moment about the longitudinal axis X. To avoid this, the steering axis of the screw is placed at one level with the rotor hub, tail rotor to which rises above the horizon due to its installation on the end beam.

Let us examine the first condition of hovering. Hover almost the entire thrust of the rotor is used to generate lift, as directed close to the axis of the screw (other than a minor Zawa that to balance the thrust of the tail rotor) and hence can be calculated from the formula. E. For hovering helicopters at specified our environment requires that the engine has an output of 300 l. from.

It should be noted that the engine power, the need to hover depends on the density of the air, or, in other words, the height of hovering above the sea level and the height of hovering above the ground (earth impact airbags). In our calculations, the air density p was considered a choice factor, and the value of which depends on the density of air

This density in accordance with the international standard atmosphere corresponds to the height in meters 4300.

The higher the altitude, or, in other words, the more rarefied air, the more power the engine has to develop to a helicopter could hang. Meanwhile, with increasing altitude decreases also the engine power. Because of this, limit the height at which helicopters can hang out, is usually low.

Each helicopter has some limit the height of hovering above which, despite the use of full throttle and the big collective pitch rotor lifting force can not balance the weight of the helicopter.

Maximum altitude at which the helicopter can hang out, is called static ceiling of the helicopter.

Static ceiling modern helicopters is 2-4 km.

The second condition is hovering to reactive torque balanced by the moment of the tail rotor.

In the map, it is seen that for a given direction of rotation of the rotor tail rotor should be pushing instead of pulling.

On rotation of the tail rotor when hovering spent average 10% engine power, and in forward flight the power requirement is reduced to 5%, since the airflow propeller plane of rotation leads to an increase in thrust at an expense of the same capacity or a decrease in the required power for the creation of the same thrust.

 

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