Tandem rotors

Tandem rotor (sometimes referred to as dual rotor) helicopters have two large horizontal rotor assemblies; a twin rotor system, instead of one main assembly and a smaller tail rotor.

Single rotor helicopters need a tail rotor to neutralize the twisting momentum produced by the single large rotor. Tandem rotor helicopters, however, use counter-rotating rotors, with each canceling out the other's torque. Counter-rotating rotor blades won't collide with and destroy each other if they flex into the other rotor's pathway.

This configuration also has the advantage of being able to hold more weight with shorter blades, since there are two sets. Also, all of the power from the engines can be used for lift, whereas a single rotor helicopter uses power to counter the torque. Because of this, tandem choppers are among some of the most powerful and fastest. The CH-47 Chinook for example, has one of the fastest top speeds of any helicopter in service.

List of tandem rotor helicopters

* Nicolas Florine (1933) Belgium
* Piasecki PV 3 Dog Ship, HRP-1 (1945)
* Piasecki PV 14 (1948)
* Piasecki H-21 (1949)
* Piasecki PV 17 (1950)
* Piasecki H-25 Retriever "HUP" (1952)
* Yakovlev Yak-24 (first flew 1952)
* Bristol Belvedere (1952)
* Piasecki PD 22 (H-21) (1953)
* Piasecki PV-15, YH-16 (1953)
* Bell Model 61 / HSL
* Boeing-Vertol 107-II (1958)
* CH-46 Sea Knight (1960)
* CH-47 Chinook (1961)
* Boeing-Vertol 347 (1970)
* Boeing-Vertol Model 234 (1980)
* Boeing-Vertol Model 360 (1987)

Transversal scheme

* Focke-Wulf Fw 61 (1936)
* Platt-Le Page XR-1 (1941)
* Landgraf H-2 (1944)
* Bratukhin G-3 (1946)
* Bratukhin B-11 (1948)
* Kamov Ka-22 (1959)
* Mil Mi-12 (1967)

Intermeshing scheme

* Flettner Fl 265 (1939)
* Kaman HH-43 Huskie (1947)
* Kaman K-MAX

ee also

* Coaxial rotors
* Rotorcraft
* Tiltrotor