Tail rotor

The tail rotor is a common design configuration for helicopters. So that the main rotor can produce lift, it must be rotated by a motor or turbine to a rapid rotation. This is attached to the hull generates a drive torque in the opposite direction due to the conservation of angular momentum. The tail rotor to compensate this torque by a counter- thrust. The idea of ​​using horizontal thrust against the rotor movement to stabilize the aircraft, originally by Étienne Öhmichen and was a result of intensive observations of nature.

The tail rotor configuration was developed by Igor Sikorski ready for deployment and first demonstrated successfully at the Sikorsky VS -300 in 1939. Because of the lower development, construction and maintenance costs compared with double rotors ( coaxial rotor or tandem configuration), this construction is still used today for the majority of the helicopter.

Functions of the tail rotor

The drive of the main rotor, produces in dependence on the angle of attack of the rotor blades a acting against the direction of rotation of the main rotor torque to the fuselage of a helicopter. Attached to one of the tail boom beyond the rotor circuit, a horizontal tail rotor thrust is generated about the vertical axis (yaw axis) to counteract the rotation of the body ( see schematic diagram of the left). This thrust is not constant but must be entered by the pilot at each change of torque ( other angle of attack of the rotor blades, modified engine power) to be adjusted. 56

Rear rotors, depending on the power requirement from two to six blades, which partly also an X-shaped arrangement is used (eg, Mil Mi -28). More than 60% the noise level of a helicopter produced by the tail rotor. In order to reduce this and to reduce the risk of injury from the rotating tail rotor blades, are also enclosed tail rotors, called Fenestron used. Here is the up to 18 leaves are sometimes arranged asymmetrically, to reduce noise spikes on.

The horizontal thrust acting against the torque of the main rotor, irrespective of the design of the tail rotor produces a laterally acting force to the hull, which is called drift. This drift is compensated by a reversed roll movement at the start and landing, but especially in hover, the pilot (see schematic diagram right). 57 In some helicopter models with automatic hover stabilization system ( Hover Mode) like the Russian Mil Mi- 26, this is done automatically.

In addition to the torque balance of the tail rotor is also used to control the helicopter around the vertical axis, ie, the right / left rotation. The pilot operates the tail rotor on the pedals on the cockpit floor. The control commands are transmitted in the control of the pedal via a linkage to a sliding sleeve or sliding rod, which changes the collective pitch of the rotor blades. According to the same principle, the collective control of the main rotor by means of the swash plate is done. The tail rotor take up to 20% of the engine power of a helicopter.

Assist or take over many helicopter models aerodynamic control surfaces in forward flight - about one fin to the tail boom - at an increasing rate to stabilize around the vertical axis. In some helicopters, the tail rotor is again slightly downward to counteract the weight of the tail boom by the air flow directed obliquely downward; the Sikorsky UH -60, this angle is about 20 degrees.