Contra-rotating propellers

A coaxial rotor is a rotor assembly of helicopters in which two counter rotating main rotors are arranged one above the other in a rotational axis. By getting canceling torques can be dispensed a tail rotor.

Use

At the beginning of the development of helicopters, the coaxial system has been widely used, since one of them the promised maximum efficiency, so the Gyroplane Laboratoire of 1933. The majority of the produced coaxial helicopter comes today from the Russian manufacturer Kamov, who specializes in this type of construction. Some types are also used in German-speaking countries as " crane" for precise installations, eg of mast, antenna or cable cars. Kamov produced ( e), among others,

  • Kamov Ka -8 "flying motorcycle "
  • Kamov Ka -10 NATO reporting name: " hat"
  • Kamov Ka -15 NATO reporting name: " Hen "
  • Kamov Ka -18 NATO reporting name: " Hog "
  • Kamov Ka -20 NATO reporting name: " Harp"
  • Kamov Ka -25 NATO reporting name: "Hormones "
  • Kamov Ka -26 NATO reporting name: " Hoodlum "
  • Kamov Ka -27 NATO reporting name: " helix A D"
  • Kamov Ka -28 NATO reporting name: "Helix"
  • Kamov Ka -29 NATO reporting name: "Helix -B"
  • Kamov Ka -31 NATO reporting name: "Helix"
  • Kamov Ka -32 NATO reporting name: "Helix -C "
  • Kamov Ka -37 drone
  • Kamov Ka-50 NATO reporting name: " Hokum A"
  • Kamov Ka - 50-2 Erdogan
  • Kamov Ka-52 Alligator
  • Kamov Ka -56 Osa / Wasp ( one-man mini- helicopter )
  • Kamov Ka - 92 concept design of an air wrench
  • Kamov Ka -115
  • Kamov Ka -126
  • Kamov Ka -137 drone
  • Kamov Ka -226

Lately, the coaxial rotor principle is thanks to new materials and production possibilities again larger interest of manufacturers. Sikorsky built the Sikorsky X2 (first flight 2008). The X2 has an additional pusher propeller at the rear, allowing the air wrench at a speed of up to around 460 km / h.

Operation

The lower rotor is driven by a hollow shaft, in the second drive shaft running to the upper, counter-rotating rotors. The two rotor layers are controlled via control rods to the respective blade holders, in order to adjust the angle of attack of the rotor blades during rotation can. However, the control linkage for the rotor top must be pivoted from a second swash plate between the rotor planes is mitbetätigt of the main swashplate through separate linkages to take the opposite direction of rotation into account (see Fig of Kamow Ka -32 in the article). Alternatively, electrical or hydraulic lines can run up into the shaft and control the upper rotor head by means of servos.

The flight around the pitch and roll axis is controlled as individual rotors on the cyclic pitch (see swashplate ). The rotation around the vertical axis (yaw axis ), however, achieved by opposing collective pitch, so that experiences a rotor with a higher angle of attack the greater the air resistance and thus produce more lift and more (counter ) torque to the fuselage, and therefore the produces desired yaw. When the other rotor is proportional produced with less angle of attack less reaction torque resistance and less lift, the total lift is not changed by doing this, the yaw control and the helicopter maintains substantially the flight altitude.

  • An advantage of this design over the conventional tail rotor configuration is that no separate torque compensation is necessary because cancel the moments of the two rotors. The system enables a particularly smooth hovering because no drift - a lateral thrust component of the tail rotor, which would compensate by means of roll control - occurs ( see also drift ).

The full engine power can be converted to buoyancy.

  • The disadvantage of this construction is the higher construction and maintenance costs for the two rotor heads with the more complex control of the upper rotor and the gearbox. The distribution of the coaxial system is limited by the higher cost (and possibly shorter maintenance intervals).

Model coaxial helicopter

In a simpler version of the model helicopters Koaxialrotors is used with a fixed blade pitch angle, since the lack of drift and the high intrinsic stability and facilitates operation in confined spaces or indoors nowadays. About the yaw axis is controlled by the ratio of the speed of the two electronically controlled electric motors, each driving one of the two counter-rotating rotors.

To the upper swash plate to the low center of gravity, the large distance between the rotor planes and also be omitted due to the use of a stabilizer bar to the upper rotor head; the design is so cost and weight saving.

Other multi- rotor systems

Other systems with double rotor helicopter, the tandem configuration, transverse rotors and the Flettner rotor double.

Helicopter rotor Axis of rotation Gyroplane-Laboratoire Kamov Ka-8 Kamov Ka-10 Kamov Ka-15 Kamov Ka-18 Kamov Ka-26 Kamov Ka-31 Gyrodyne Kamov Ka-115 Kamov Ka-126 Kamov Ka-226 Sikorsky Aircraft Swashplate (aeronautics) Servo (radio control) Leeway Rotorhead Intermeshing rotors
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