Contra-rotating propellers
Aircraft equipped with contra-rotating propellers (CRP)
Operation
When airspeed is low, the
A well designed contra-rotating propeller will have no rotational air flow, pushing a maximum amount of air uniformly through the propeller disk, resulting in high performance and low induced energy loss. It also serves to counter the
). Some contra-rotating systems were designed to be used at takeoff for maximum power and efficiency under such conditions, and allowing one of the propellers to be disabled during cruise to extend flight time.Advantages and disadvantages
The torque on the aircraft from a pair of contra-rotating propellers effectively cancels out.
Contra-rotating propellers have been found to be between 6% and 16% more efficient than normal propellers.[4]
However they can be very noisy, with increases in noise in the axial (forward and aft) direction of up to 30 dB, and tangentially 10 dB.[4] Most of this extra noise can be found in the higher frequencies. These substantial noise problems limit commercial applications. One possibility is to enclose the contra-rotating propellers in a shroud.[5] It is also helpful if the tip speed or the loading of the blades is reduced, if the aft propeller has fewer blades or a smaller diameter than the fore propeller, or if the spacing between the aft and fore propellers is increased.[6]
The efficiency of a contra-rotating propeller is somewhat offset by its mechanical complexity and the added weight of this gearing that makes the aircraft heavier, thus some performance is sacrificed to carry it. Nonetheless, coaxial contra-rotating propellers and
They are also being examined for use in airliners.[7]
Use in aircraft
While several nations experimented with contra-rotating propellers in aircraft, only the United Kingdom and Soviet Union produced them in large numbers. The first aircraft to be fitted with a contra-rotating propeller to fly was in the US when two inventors from Ft Worth, Texas tested the concept on an aircraft.[8]
United Kingdom
A contra-rotating propeller was patented by F. W. Lanchester in 1907.[9]
Some of the more successful British aircraft with contra-rotating propellers are the Avro Shackleton, powered by the Rolls-Royce Griffon engine, and the Fairey Gannet, which used the Double Mamba Mk.101 engine. In the Double Mamba two separate power sections drove one propeller each, allowing one power section (engine) to be shut down in flight, increasing endurance.
Another naval aircraft, the Westland Wyvern had contra-rotating propellers. The Martin-Baker MB 5 test aircraft also used this propeller type.
Later variants of the Supermarine Spitfire and Seafire used the Griffon with contra-rotating props. In the Spitfire/Seafire and Shackleton's case the primary reason for using contra-rotating propellers was to increase the propeller blade-area, and hence absorb greater engine power, within a propeller diameter limited by the height of the aircraft's undercarriage. The Short Sturgeon used two Merlin 140s with contra-rotating propellers.
The Bristol Brabazon prototype airliner used eight Bristol Centaurus engines driving four pairs of contra-rotating propellers, each engine driving a single propeller.[10]
The post-war SARO Princess prototype flying boat airliner also had eight of its ten engines driving contra-rotating propellers.
USSR, Russia and Ukraine
In the 1950s, the Soviet Union's
The NK-12 engine powers another well-known Soviet aircraft, the Antonov An-22 Antheus, a heavy-lift cargo aircraft. At the time of its introduction, the An-22 was the largest aircraft in the world and is still by far the world's largest turboprop-powered aircraft. From the 1960s through the 1970s, it set several world records in the categories of maximum payload-to-height ratio and maximum payload lifted to altitude.
Of lesser note is the use of the NK-12 engine in the
In the 1980s, Kuznetsov continued to develop powerful contra-rotating engines. The NK-110, which was tested in the late 1980s, had a contra-rotating propeller configuration with four blades in front and four in back, like the NK-12. Its 190-inch propeller diameter (4.7-metre) was smaller than the NK-12's 220–240 in (5.6–6.2 m) diameter, but it produced a power output of 21,007 hp (15,665 kW), delivering a takeoff thrust of 40,000 pounds-force (177 kilonewtons).[12] Even more powerful was the NK-62, which was in development throughout most of the decade. The NK-62 had an identical propeller diameter and blade configuration to the NK-110, but it offered a higher takeoff thrust of 55,000 lbf (245 kN). The associated NK-62M had a takeoff thrust of 64,100 lbf (285.2 kN), and it could deliver 70,700 lbf (314.7 kN) of emergency thrust.[13] Unlike the NK-12, however, these later engines were not adopted by any of the aircraft design bureaus.
In 1994, Antonov produced the An-70, a heavy transport aircraft. It is powered by four Progress D-27 propfan engines driving contra-rotating propellers. The characteristics of the D-27 engine and its propeller make it a propfan, a hybrid between a turbofan engine and a turboprop engine.
United States
The United States worked with several prototypes, including the
The US propeller manufacturer, Hamilton Standard, bought a Fairey Gannet in 1983 to study the effects of counter rotation on propeller noise and blade vibratory stresses. The Gannet was particularly suitable because the independently-driven propellers provided a comparison between counter and single rotation.[14]
Ultralight applications
An Austrian company, Sun Flightcraft, distributes a contra-rotating gearbox for use on Rotax 503 and 582 engines on ultralight and microlight aircraft. The Coax-P was developed by Hans Neudorfer of NeuraJet and allows powered hang-gliders and parachutes to develop 15 to 20 percent more power while reducing torque moments. The manufacturer also reports reduced noise levels from dual contra-rotating props using the Coax-P gearbox.[15][16][17]
Use in water
Recreational Boating: in 1982 Volvo Penta introduced a contra-rotating boat propeller branded DuoProp.[18] The patented device has been marketed since. After the Volvo Penta patents ran out, Mercury has also produced a corresponding product, MerCruiser Bravo 3.
Commercial ships: In traditional machinery arrangement contra-rotating propellers are rare, due to cost and complexity.
In 2004, ABB produced a product for large-power installations: the forward propeller is on a traditional shaft line, while the aft propeller is in an ABB Azipod.[19]
At lower power levels, contra-rotating mechanical azimuth thrusters are one possibility, convenient for CRP due to their inherent bevel gear construction. Rolls-Royce and Steerprop have offered CRP versions of their products.[20][21]
See also
References
- S2CID 110551942.
- ISSN 0015-3710.
- ^ Strack, W. C.; Knip, G.; Weisbrich, A. L.; Godston, J.; Bradley, E. (October 25–28, 1982). Technology and benefits of aircraft counter rotation propellers. Aerospace Congress and Exposition. Anaheim, California, USA: NASA. alternate url
- ^ a b Vanderover, J. S.; Visser, K. D. Analysis of a contra-rotating propeller driven transport aircraft (Report).
- ^ Truong, Alexander; Papamoschou, Dimitri (January 7, 2013). Aeroacoustic testing of open rotors at very small scale (PDF). AIAA Aerospace Sciences Meeting (51st ed.). Grapevine, Texas, USA. Retrieved August 5, 2016.
- OCLC 17508419. Archived (PDF) from the original on March 13, 2017. Retrieved February 2, 2019. alternate url
- ^ Kijk magazine, 1/2013
- ISSN 0161-7370.
- ^ Lanchester, F. W. (December 11, 1941). "Contra-props: Recollections of early considerations by advisory committee for aeronautics: A pioneer's 1907 patent: Suggestions for further research". Flight. Vol. 40, no. 1720. pp. 418–419. Retrieved 3 November 2015.
- ^ "Brabazon engine layout". The Bristol Brabazon - Engineering masterpiece or Great White Elephant. Aviation Archive: Aviation Heritage. Archived from the original on 23 September 2015. Retrieved 3 November 2015.
- ^ "General aviation world records". Fédération Aéronautique Internationale (FAI). Archived from the original on October 7, 2007.
- ^ "NK-110" (PDF). Ulyanovsk Higher Aviation School of Civil Aviation (in Russian). p. 48.
- ^ Zrelov, V. A. (2018). "Development of engines 'NK' large thrust on the basis of a single gas generator" (PDF). Dvigatel (in Russian). Vol. 115, no. 1. pp. 20–24.
- ^ Gatzen, B. S.; Reynolds, C. N. (September 9–14, 1984). Single rotation and counter rotation prop-fan propulsion system technologies (PDF). Congress of the International Council of the Aeronautical Sciences (14th ed.). –Toulouse, France. pp. 708–717.
- ^ "COAX-P: Counter rotating propeller gearbox". Sun Flightcraft. Retrieved July 18, 2019.
- ISSN 1368-485X.
- ^ "Willkommen bei Neura Jet". neurajet.at. Archived from the original on 22 December 2005. Retrieved 3 November 2015.
- ^ "The benefits of Duoprop". Volvo Penta Singapore. Archived from the original on July 31, 2016.
- ^ "Akashia & Hamanasu".
- ^ "Contaz azimuthing thruster". www.rolls-royce.com. Retrieved 14 June 2018.
- ^ "Steerprop : SP 10 ... 45 CRP". www.steerprop.com. Archived from the original on 19 March 2017. Retrieved 14 June 2018.
External links
- "Two propellers in tandem turning in opposite ways give warplanes new speed". ISSN 0161-7370.
- "Avro Shackleton". Aircraft.co.za. Archived from the original on November 19, 2005.
- Luftfahrtmuseum.com – Further information and pictures of contra rotators for the Fairey Gannet and Shackleton
- Spitfire PR.XIX startup by Steve Hinton at Chino, California. YouTube. Archived from the original on 2021-12-22.
- A History of Aircraft Using Contra-Rotating Propellers (Part 1) – Aircraft Engine Historical Society
- A History of Aircraft Using Contra-Rotating Propellers (Part 2) – Aircraft Engine Historical Society
- A History of Aircraft Using Contra-Rotating Propellers (Part 3) – Aircraft Engine Historical Society
- A History of Aircraft Using Contra-Rotating Propellers (Part 4) – Aircraft Engine Historical Society