page_title: Tandem rotors
section_title: List of tandem rotor helicopters
hierarchical_section_title: Tandem rotors / List of tandem rotor helicopters
caption_attribution_description: English: H-21B, 5017th Operations Squadron, Elmendorf AFB, early 1960s from http://www.elmendorf.af.mil/3wing/units/history/webdocs/H-21B.htm
context_page_description: Tandem rotor helicopters have two large horizontal rotor assemblies mounted one in front of the other. Currently this configuration is mainly used for large cargo helicopters.
  Single rotor helicopters need a mechanism to neutralize the yawing movement produced by the single large rotor. This is commonly accomplished by a tail rotor, coaxial rotors, and the NOTAR systems. Tandem rotor helicopters, however, use counter-rotating rotors, with each cancelling out the other's torque. Therefore, all of the power from the engines can be used for lift, whereas a single rotor helicopter uses some of the engine power to counter the torque. An alternative is to mount two rotors in a coaxial configuration. The first successful tandem rotor helicopter was built by Nicolas Florine in 1927.
  Advantages of the tandem-rotor system are a larger center of gravity range, and good longitudinal stability. Disadvantages of the tandem-rotor system are a complex transmission, and the need for two large rotors.
  The two rotors are linked by a transmission that ensures the rotors are synchronized and do not hit each other, even during an engine failure.
context_section_description: Bell HSL (1953)
  Boeing CH-47 Chinook (1961) - most-produced tandem-rotor helicopter (over 1,200 built)
  Boeing Model 360 (1987)
  Boeing Vertol 107-II (1958)
  Boeing Vertol CH-46 Sea Knight (1960)
  Boeing Vertol XCH-62 (1970s - not completed)
  Boeing Vertol Model 234 (1981)
  Bristol Belvedere (1958)
  Bristol Type 173 (1952)
  Chu CJC-3 (1952)
  Filper Beta 200 (1966)
  Filper Beta 400 (1967)
  Filper Helicopter (1965)
  HERC JOV-3 (1948)
  Jovair Sedan 4A (1963)
  McCulloch MC-4 (1951)
  Piasecki H-16 (1953)
  Piasecki H-21 (1949)
  Piasecki H-25/HUP Retriever (1952)
  Piasecki HRP Rescuer (1945)
  Piasecki PV-14 (1948)
  Rotorcraft XR-11 (1947)
  Yakovlev Yak-24 (1952)
caption: A Piasecki H-21B at Elmendorf AFB in the early 1960s
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