CH-46 Sea Knight

Tandem rotor helicopters have two large horizontal rotor assemblies mounted one in front of the other. These days this configuration is mainly used for large cargo helicopters^[1].

Single rotor helicopters need a tail rotor to neutralize the yawing moment produced by the single large rotor. Tandem rotor helicopters, however, use counter-rotating rotors, with each canceling out the other's torque. Therefore all of the power from the engines can be used for lift, whereas a single rotor helicopter uses power to counter the torque.^[2]

Advantages of the tandem-rotor system are a larger center-of-gravity range and good longitudinal stability^[3]. Disadvantages of the tandem-rotor system are a complex transmission^[4] 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.^[5]

Tandem rotor designs achieve yaw by applying opposite left and right cyclic to each rotor, effectively pulling both ends of the helicopter in opposite directions. To achieve pitch, opposite collective is applied to each rotor; decreasing the lift produced at one end, while increasing lift at the opposite end, effectively tilting the helicopter forward or back.^[6]

Tandem rotor aerodynamics is a complex subject. Tandem rotor helicopters have the advantage of being able to hold more weight with shorter blades, since there are two sets. However, the rear rotor works in the aerodynamic shadow of the front rotor, which reduces its efficiency. This loss can be minimized by increasing the distance between the two rotor hubs, and by elevating one hub over the other^[7][8]. Tandem rotor helicopters tend to have a lower disk loading than single rotor helicopters.^[9]

Tandem rotor helicopters typically require less power to hover and achieve low speed flight as compared to single rotor helicopters. Both configurations typically require the same power to achieve high speed flight.^[10]

[edit] List of some tandem rotor helicopters

Columbia Helicopters Boeing Vertol 107-II and Boeing 234

A Piasecki H-21B at Elmendorf AFB in the early 1960s

• HRP Rescuer (1945)
• Piasecki PV-14 (1948)
• HERC Jov-3 (1948)
• Piasecki H-21 (1949)
• McCulloch MC-4 (1951)
• Piasecki H-25/HUP Retriever (1952)
• Yakovlev Yak-24 (1952)
• Bristol Belvedere (1952)
• Piasecki H-16 (1953)
• Piasecki H-21 (1953)
• Bell HSL (1953)
• Boeing Vertol 107-II (1958)
• CH-46 Sea Knight (1960)
• CH-47 Chinook (1961)
• Jovair Sedan 4A (1963)
• Fliper Beta 200 (1966)
• Fliper Beta 400 (1967)
• Boeing Vertol XCH-62 (1970s - not completed)
• Boeing Model 234 (1981)
• Boeing Model 360 (1987)

[edit] See also

• Coaxial rotors
• Intermeshing rotors
• Rotorcraft
• Transverse rotors
• Tiltrotor

[edit] References

This article about aircraft components is a stub. You can help Wikipedia by expanding it. v • d • e