Tail rotor configuration

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Tail rotor of a helicopter, the blade adjustment linkage in the middle

The tail rotor configuration is a common type of construction in helicopters . So that the main rotor can generate a lift, it must be set into rapid rotation by a motor or a turbine . This drive, which is attached to the fuselage, generates a torque in the opposite direction due to the conservation of the angular momentum . The tail rotor should compensate for this torque with a counter-thrust. The idea of ​​using horizontal thrust against the rotor movement to stabilize the aircraft originally came from Étienne Œhmichen and was the result of intensive observations of nature. However, the brothers Fritz and Wilhelm Achenbach designed the principle with main and tail rotor as early as 1874.

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

Functions of the tail rotor

Functional principle of the tail rotor
Compensation for drift by rolling

Depending on the angle of attack of the rotor blades, the drive of the main rotor generates a torque acting against the direction of rotation of the main rotor on the fuselage of a helicopter. A horizontal thrust is generated by the tail rotor attached to a tail boom outside the rotor circle in order to counteract the rotation of the fuselage around the vertical axis ( yaw axis ) (see schematic diagram on the left). This thrust is not constant, but must be adjusted by the pilot with every change in torque (different angle of attack of the rotor blades, changed drive power).

Tail rotors have two to six rotor blades, depending on the power requirement, whereby an X-shaped arrangement is sometimes used (e.g. Mil Mi-28 ). More than 60% of the noise produced by a helicopter is generated by the tail rotor. Encapsulated tail rotors, so-called fenestrons , are also used to reduce these and the risk of injury from the rotating tail rotor blades . Here the up to 18 blades are partly arranged asymmetrically to further reduce noise peaks.

The horizontal thrust, which acts against the torque of the main rotor, generates a force that acts laterally on the fuselage, regardless of the type of tail rotor, which is called drift . This drift is the launch and landing, but especially in the hover , the pilot through a reversed roll offset movement (see schematic diagram on the right). In some helicopter models with an automatic hover stabilization system ( automatic hover ), such as the Russian Mil Mi-26 , this is done automatically.

In addition to torque compensation, the tail rotor also serves to control the helicopter around the vertical axis , i.e. the right / left rotation. The pilot operates the tail rotor using the pedals on the cockpit floor. The control commands are usually passed on from the pedals via a linkage to a sliding sleeve or push rod, which changes the collective setting angle of the rotor blades. The collective control of the main rotor via the swash plate is based on the same principle . The tail rotor uses up to 20% of the engine power of a helicopter.

Assist in forward flight or take on many helicopter models aerodynamic control surfaces - such as a vertical stabilizer on the tail boom - at an increasing rate stabilization around the vertical axis. On some helicopters, the tail rotor is again directed slightly downwards in order to counteract the weight of the tail boom through the airflow directed downwards; on the Sikorsky UH-60, for example, this angle is 20 degrees.

See also

Other concepts for balancing the torque:

literature

  • Walter Bittner: Flight mechanics of the helicopter. Technology, the flight dynamics system helicopters, flight stability, controllability. 3rd, updated edition. Springer, Berlin et al. 2009, ISBN 978-3-540-88971-7 .
  • Ernst Götsch: Aircraft technology. Introduction, basics, aircraft science. Motorbuchverlag, Stuttgart 2009, ISBN 978-3-613-02912-5 .
  • Niels Klußmann, Arnim Malik: Aviation Lexicon. 3rd, updated edition. Springer, Berlin et al. 2012, ISBN 978-3-642-22499-7 .
  • Jens Rosenow: Bell's innovative approach: electric tail rotors. In: Rotorblatt , No. 2/2020, pp. 40–41

Individual evidence

  1. ↑ Achenbach Brothers: 1874 , accessed on November 17, 2016
  2. ↑ Timeline. In: Kyrill von Gersdorff, Kurt Knobling: helicopter and gyrocopter . Development history of the German rotary wing aircraft from the beginnings to the international community developments (= Die deutsche Luftfahrt. 3). 3rd, expanded edition. Bernard & Graefe, Munich et al. 1999, ISBN 3-7637-6115-2 , pp. 336–339, here p. 336.
  3. ↑ Niels Klußmann, Arnim Malik: Lexicon of aviation. 3rd, updated edition. Springer, Berlin et al. 2012, p. 230.
  4. ↑ a b Rc Heli Action. April 2013, ISSN  1869-9219 .