A tandem-rotor aircraft is an

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

with two large

helicopter rotor On a helicopter, the main rotor or rotor system is the combination of several rotary wings (rotor blades) with a control system, that generates the aerodynamic lift (force), lift force that supports the weight of the helicopter, and the thrust ...

assemblies mounted one in front of the other in the

horizontal plane Horizontal may refer to: *Horizontal plane, in astronomy, geography, geometry and other sciences and contexts *Horizontal coordinate system, in astronomy *Horizontalism, in monetary circuit theory *Horizontalidad, Horizontalism, in sociology *Hor ...

. This configuration is mainly used for large cargo helicopters. Such aircraft are often informally referred to as "Chinooks," after the

CH-47 Chinook The Boeing CH-47 Chinook is a tandem-rotor helicopter originally developed by American rotorcraft company Piasecki Helicopter, Vertol and now manufactured by Boeing Defense, Space & Security. The Chinook is a Military transport helicopter, heav ...

, one of the first widely adopted heavy-lift helicopters with a tandem-rotor configuration.

Design

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 rotor A coaxial-rotor aircraft is an aircraft whose rotors are mounted one above the other on concentric shafts, with the same axis of rotation, but turning in opposite directions ( contra-rotating). This rotor configuration is a feature of helicopt ...

s, and the NOTAR systems. Tandem-rotor helicopters, however, use counter-rotating rotors, with each cancelling out the other's

torque In physics and mechanics, torque is the rotational analogue of linear force. It is also referred to as the moment of force (also abbreviated to moment). The symbol for torque is typically \boldsymbol\tau, the lowercase Greek letter ''tau''. Wh ...

. 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 In physics, the center of mass of a distribution of mass in space (sometimes referred to as the barycenter or balance point) is the unique point at any given time where the weighted relative position of the distributed mass sums to zero. For ...

range and good

longitudinal stability In flight dynamics, longitudinal stability is the Flight dynamics (fixed-wing aircraft), stability of an aircraft in the longitudinal, or Aircraft principal axes, pitching, plane. This characteristic is important in determining whether an aircraft ...

. 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. 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 A collective is a group of entities that share or are motivated by at least one common issue or interest or work together to achieve a common objective. Collectives can differ from cooperatives in that they are not necessarily focused upon an e ...

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. 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.Rotary Wing Aerodynamics, W.Z. Stepniewski, p. 197. Tandem-rotor helicopters tend to have a lower

disk loading In fluid dynamics, disk loading or disc loading is the average pressure change across an actuator disk, such as an airscrew. Airscrews with a relatively low disk loading are typically called rotors, including helicopter Helicopter rotor, main ro ...

than single-rotor helicopters. 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.Rotary Wing Aerodynamics, W.Z. Stepniewski, p. 200.

Examples

* Bell HSL (1953) *

Boeing CH-47 Chinook The Boeing CH-47 Chinook is a tandem-rotor helicopter originally developed by American rotorcraft company Piasecki Helicopter, Vertol and now manufactured by Boeing Defense, Space & Security. The Chinook is a Military transport helicopter, heav ...

(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 The Boeing Vertol CH-46 Sea Knight is an American medium-lift tandem rotors, tandem-rotor transport helicopter powered by twin turboshaft aircraft engine, engines. It was designed by Piasecki Helicopter, Vertol and manufactured by Boeing Helico ...

(1960), military version of Vertol 107-II *

Boeing Vertol XCH-62 The Boeing Vertol XCH-62 (Model 301) was a triple-turbine, heavy-lift helicopter project designed for the United States Army by Boeing Rotorcraft Systems, Boeing Vertol. Approved in 1971, one prototype reached 95% completion before it was cancel ...

(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) * Hunt Rotary Aeroplane (1910) * Jovair Sedan 4A (1963) * McCulloch MC-4 (1951) * Piasecki H-16 (1953) *

Piasecki H-21 The Piasecki H-21 Workhorse/Shawnee is an American helicopter, the fourth of a line of tandem rotor helicopters designed and built by Piasecki Helicopter (later Boeing Vertol). Commonly called "the flying banana", it was a multi-mission helicop ...

(1949) * Piasecki H-25/HUP Retriever (1952) * Piasecki HRP Rescuer (1945) * Piasecki PV-14 (1948) * Rotorcraft XR-11 (1947) * Yakovlev Yak-24 (1952)

References

External links

* {{Commons cat inline Helicopter components *

Design

Examples

See also

References

External links