Counter-rotating propellers

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Counter-rotating propellers
World War I Linke-Hofmann R.I German heavy bomber (1917) with counter-rotating propellers
He 177A Greif with counter-rotating propellers

Counter-rotating propellers, also referred to as CRP, are propellers which spin in opposite directions to each other.[1] They are used on some twin- and multi-engine propeller-driven aircraft.

The propellers on most conventional twin-engined aircraft spin clockwise (as viewed from behind the engine). Counter-rotating propellers generally spin clockwise on the left engine and counter-clockwise on the right. The advantage of such designs is that counter-rotating propellers balance the effects of torque and P-factor, meaning that such aircraft do not have a critical engine in the case of engine failure.

Drawbacks of counter-rotating propellers come from the fact that, in order to reverse sense of rotation of one propeller, either the engines must be adapted to turn in opposite directions or one propeller must have an additional reversing gearbox.

History[edit]

Counter-rotating propellers have been used since the earliest days of aviation, in order to avoid the aircraft tipping sideways from the torque reaction against propellers turning in the a single direction. They were fitted to the very first controlled powered aeroplane, the Wright flyer, and to other subsequent types such as the Dunne D.1 of 1907 and the more successful Dunne D.5 of 1910.

In designing the Lockheed P-38 Lightning, the decision was made to reverse the counter-rotation such that the tops of the propeller arcs move outwards, away from each other. Tests on the initial XP-38 prototype demonstrated greater accuracy in gunnery with the unusual configuration.

The counter-rotating powerplants of the German World War II Junkers Ju 288 prototype series (as the Bomber B contract winning design), the Gotha Go 244 light transport, Henschel Hs 129 ground attack aircraft, Heinkel He 177A heavy bomber and Messerschmitt Me 323 transport used the same rotational "sense" as the production P-38 did – this has also been done for the modern American Bell Boeing V-22 Osprey tiltrotor VTOL military aircraft design. The following German World War II aviation engines were designed as opposing-rotation pairs for counter-rotation needs:

The aerodynamics of a propeller on one side of an aircraft change according to which way it turns, as it affects the P-factor. This can in turn affect performance under extreme conditions and therefore flight safety certification. Some modern types, such as the Airbus A400M, have counter-rotating propellers in order to meet air safety requirements under engine-out conditions.

List of aircraft with counter-rotating propellers[edit]

Type Country Date Notes
Airbus A400M Atlas EU 2009 Four engines
Beechcraft 76 Duchess US 1974 Twin engines
Cessna T303 Crusader US 1978 Twin engines[citation needed]
de Havilland Hornet UK 1944 Twin engines
Dunne D.1 UK 1907 twin engines in fuselage on a common driveshaft
Dunne D.4 UK 1908 Single central engine
Dunne D.5 UK 1910 Single central engine
Fairey F.2 UK 1917 Twin engines
Gotha Go 244 Germany Twin engines
Heinkel He 177A Greif (fourth prototype onwards) Germany Twin engines
Henschel Hs 129 Germany Twin engines
Junkers Ju 288 Germany Twin engines
Linke-Hofmann R.I Germany 1917 four engines in fuselage
Lockheed P-38 Lightning US 1939 Twin engines
Messerschmitt Me 323 Gigant Germany Six engines
North American P-82 Twin Mustang US Twin engines
North American Rockwell OV-10 Bronco US Twin engines[citation needed]
Piaggio P.180 Avanti Italy 1986 Twin engines[citation needed]
Piper PA-31 Navajo (some variants) US Twin engines
Piper PA-34 Seneca US Twin engines
Piper PA-39 Twin Comanche C/R US Twin engines
Piper PA-40 Arapaho US Twin engines
Piper PA-44 Seminole US Twin engines
Vought V-173 Flying Pancake US 1942 Twin engines
Vought XF5U Flying Pancake US 1947 Twin engines
Wright Flyer and most other Wright models to 1916 US 1903 Single central engine.

See also[edit]

References[edit]

Notes
Bibliography
  • Gunston, Bill. Jane's Aerospace Dictionary. London, England. Jane's Publishing Company Ltd, 1980. ISBN 0 531 03702 9