Counter-rotating propellers (CRP) are propellers which turn in opposite directions to each other.Counter-rotating propellant analysis using a frequency domain panel method
/ref> They are used on some twin- and multi-

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...

propeller-driven

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 ...

. The propellers on most conventional twin-engined aircraft turn clockwise (as viewed from behind the engine). Counter-rotating propellers generally turn clockwise on the left engine and counterclockwise on the right. The advantage of such designs is that counter-rotating propellers balance the effects of

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 ...

and

P-factor Pfactor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller (aircraft), propeller,) wherein the propeller's center of thrust moves off-center when the aircraft is at ...

, 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 the rotation of one propeller, either one propeller must have an additional reversing gearbox, or the engines themselves must be adapted to turn in opposite directions. (Meaning that there are essentially two engine designs, one with left-turning and the other with right-turning parts, which complicates manufacture and maintenance.)

History

Counter-rotating propellers have been used since the earliest days of aviation, in order to avoid the aircraft tipping sideways from the

reaction against propellers turning in a single direction. They were fitted to the very first controlled powered aeroplane, the ''

Wright Flyer The ''Wright Flyer'' (also known as the ''Kitty Hawk'', ''Flyer'' I or the 1903 ''Flyer'') made the first sustained flight by a manned heavier-than-air powered and controlled aircraft on December 17, 1903. Invented and flown by brothers Wrigh ...

'', 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 Lockheed P-38 Lightning is an American single-seat, twin piston-engined fighter aircraft that was used during World War II. Developed for the United States Army Air Corps (USAAC) by the Lockheed Corporation, the P-38 incorporated a distinc ...

, the decision was made to reverse the counter-rotation such that the tops of the propeller arcs move outwards (counterclockwise on the left and clockwise on the right), 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 The Henschel Hs 129 was a ground-attack aircraft designed and produced by the German aircraft manufacturer Henschel Flugzeugwerke AG. Fielded by the ''Luftwaffe'' during the Second World War, it saw combat in Tunisia and on the Eastern Front. ...

ground attack aircraft,

Heinkel He 177 The Heinkel He 177 ''Greif'' (Griffin) was a long-range heavy bomber flown by the ''Luftwaffe'' during World War II. The introduction of the He 177 to combat operations was significantly delayed by problems both with the development of its ...

A heavy bomber and

Messerschmitt Me 323 The Messerschmitt Me 323 ''Gigant'' ("Giant") was a German military transport aircraft of World War II. It was a powered variant of the Messerschmitt Me 321, Me 321 military glider and was the largest land-based transport aircraft to fly during ...

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 The Bell Boeing V-22 Osprey is an American multi-use, tiltrotor military transport and cargo aircraft with both vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) capabilities. It is designed to combine the functionalit ...

tiltrotor VTOL military aircraft design. The following German World War II aviation engines were designed as opposing-rotation pairs for counter-rotation needs: * BMW 801A and B, and G/H subtypes * Daimler-Benz DB 604 * Daimler-Benz DB 606 * Daimler-Benz DB 610 * Junkers Jumo 222 The aerodynamics of a propeller on one side of an aircraft change according to which way it turns, as it affects the

. This can in turn affect performance under extreme conditions and therefore flight safety certification. Some modern types, such as the

Airbus A400M The Airbus A400M AtlasNamed after the Atlas (mythology), Greek mythological figure. is a European four-engine turboprop military transport aircraft. It was designed by Airbus Military, now Airbus Defence and Space, as a tactical airlifter with ...

, have counter-rotating propellers in order to meet air safety requirements under engine-out conditions.

List of aircraft with counter-rotating propellers

References

;Notes ;Bibliography * Gunston, Bill. ''Jane's Aerospace Dictionary''. London, England. Jane's Publishing Company Ltd, 1980. {{Aircraft gas turbine engine components Aircraft engines Propellers Aircraft configurations

History

List of aircraft with counter-rotating propellers

See also

References