Counter-rotating propellers
Encyclopedia
Counter-rotating propellers, found on twin- and multi-engine
propeller-driven
aircraft
, spin in directions opposite one another.
The propellers on both engines of most conventional twin-engined aircraft spin clockwise (as viewed from the pilot seat). 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
, eliminating the problem of the critical engine
.
In designing the Lockheed P-38, 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 German World War II Henschel Hs 129
ground attack aircraft, Heinkel He 177
heavy bomber and Messerschmitt Me 323
transport's counter-rotating powerplants used the same rotational "sense" as the production P-38 did.
Drawbacks of counter-rotating propellers come from the fact that, in order to reverse sense of rotation of one propeller, a gearbox needs to be used or the engine or engine installation must be different. This may increase weight (gearbox), or maintenance and spare parts costs for the engines and propellers, as different spare parts need to be produced in lower numbers, compared to a conventional installation.
Counter-rotating propellers should not be confused with contra-rotating propellers
that share common axes.
The following aircraft have counter-rotating propellers:
Single engine, chain driven propellers :
Twin-engine, 1 engine per wing :
At least four engines, two or more on each wing :
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
propeller-driven
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
, spin in directions opposite one another.
The propellers on both engines of most conventional twin-engined aircraft spin clockwise (as viewed from the pilot seat). 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
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
and p-factor
P-factor
P-factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller, that is responsible for asymmetrical relocation of the propeller's center of thrust when aircraft is at a high angle of attack.- Causes :When an aircraft is in...
, eliminating the problem of the critical engine
Critical engine
The critical engine of a multi-engine, fixed-wing aircraft is the one whose failure would result in the most adverse effects on the aircraft's handling and performance.- Description :...
.
In designing the Lockheed P-38, 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 German World War II Henschel Hs 129
Henschel Hs 129
The Henschel Hs 129 was a World War II ground-attack aircraft fielded by the German Luftwaffe. Its nickname, the Panzerknacker , is a deliberate pun—in German, it also means "safe cracker"...
ground attack aircraft, Heinkel He 177
Heinkel He 177
The Heinkel He 177 Greif was the only operational long-range bomber to be operated by the Luftwaffe. Starting its existence as Germany's first purpose-built heavy bomber just before the war, and built in large numbers during World War II, it was also mistakenly tasked, right from its beginnings,...
heavy bomber and Messerschmitt Me 323
Messerschmitt Me 323
The Messerschmitt Me 323 Gigant was a German military transport aircraft of World War II. It was a powered variant of the Me 321 military glider and was the largest land-based transport aircraft of the war...
transport's counter-rotating powerplants used the same rotational "sense" as the production P-38 did.
Drawbacks of counter-rotating propellers come from the fact that, in order to reverse sense of rotation of one propeller, a gearbox needs to be used or the engine or engine installation must be different. This may increase weight (gearbox), or maintenance and spare parts costs for the engines and propellers, as different spare parts need to be produced in lower numbers, compared to a conventional installation.
Counter-rotating propellers should not be confused with contra-rotating propellers
Contra-rotating propellers
Aircraft equipped with contra-rotating propellers, also referred to as coaxial contra-rotating propellers, apply the maximum power of usually a single piston or turboprop engine to drive two propellers in contra-rotation...
that share common axes.
The following aircraft have counter-rotating propellers:
Single engine, chain driven propellers :
- The Wright FlyerWright FlyerThe Wright Flyer was the first powered aircraft, designed and built by the Wright brothers. They flew it four times on December 17, 1903 near the Kill Devil Hills, about four miles south of Kitty Hawk, North Carolina, U.S.The U.S...
Twin-engine, 1 engine per wing :
- de Havilland HornetDe Havilland HornetThe de Havilland DH.103 Hornet was a piston engine fighter that further exploited the wooden construction techniques pioneered by de Havilland's classic Mosquito. Entering service at the end of the Second World War, the Hornet equipped postwar RAF Fighter Command day fighter units in the UK and was...
- Lockheed P-38 Lightning
- Heinkel He 177Heinkel He 177The Heinkel He 177 Greif was the only operational long-range bomber to be operated by the Luftwaffe. Starting its existence as Germany's first purpose-built heavy bomber just before the war, and built in large numbers during World War II, it was also mistakenly tasked, right from its beginnings,...
Greif (fourth prototype onwards) - Piper PA-31 NavajoPiper PA-31 NavajoThe Piper PA-31 Navajo is a family of cabin-class, twin-engine aircraft designed and built by Piper Aircraft for the general aviation market, most using Lycoming engines. It was also licence-built in a number of Latin American countries. Targeted at small-scale cargo and feeder liner operations and...
- Piper PA-34 SenecaPiper PA-34 SenecaThe Piper PA-34 Seneca is an American twin-engined light aircraft, produced by Piper Aircraft since 1971 and still in production in 2011.The Seneca is primarily used for personal and business flying.-Development:...
- Piper PA-39 Twin Comanche
- Piper PA-40 ArapahoPiper PA-40 ArapahoThe Piper PA-40 Arapaho was an American twin-engined cabin monoplane designed by Piper as a replacement for the PA-39 Twin Comanche C/R.Like most Piper products at this time, the PA-40 was named for a North American native tribe, in this case the Arapaho....
- Piper PA-44 SeminolePiper PA-44 Seminole|-Related content:Related development* Piper CherokeeComparable aircraft* Beechcraft Duchess* Gulfstream American GA-7 Cougar-External links:*...
- Cessna T303 Crusader
- Beech BE-76 Duchess
At least four engines, two or more on each wing :
- Messerschmitt Me 323Messerschmitt Me 323The Messerschmitt Me 323 Gigant was a German military transport aircraft of World War II. It was a powered variant of the Me 321 military glider and was the largest land-based transport aircraft of the war...
Gigant transport - Airbus A400MAirbus A400MThe Airbus A400M, also known as the Atlas, is a multi-national four-engine turboprop military transport aircraft. It was designed by Airbus Military as a tactical airlifter with strategic capabilities. The aircraft's maiden flight, originally planned for 2008, took place on 11 December 2009 in...
- first plane with propellers that counter-rotate on each wing
See also
- TiltrotorTiltrotorA tiltrotor is an aircraft which uses a pair or more of powered rotors mounted on rotating shafts or nacelles at the end of a fixed wing for lift and propulsion, and combines the vertical lift capability of a helicopter with the speed and range of a conventional fixed-wing aircraft...
- Counter-rotating rotors
- Intermeshing rotorsIntermeshing rotorsIntermeshing rotors on a helicopter are a set of two rotors turning in opposite directions, with each rotor mast mounted on the helicopter with a slight angle to the other, in a transversely symmetrical manner, so that the blades intermesh without colliding. The arrangement allows the helicopter to...
- Screw-propelled vehicle