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Counter-rotating propellers, also referred to as CRP, are propellers which spin in opposite directions to each other.  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 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.)
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.
|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|
|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.|
Bomber B was a German military aircraft design competition organised just before the start of World War II to develop a second-generation high-speed bomber for the Luftwaffe. The new designs would be a direct successor to the Schnellbomber philosophy of the Dornier Do 17 and Junkers Ju 88, relying on high speed as its primary defence. Bomber B would also be a much larger and more capable aircraft, with range and payload far greater than the Schnellbomber, besting even the largest conventional designs then under consideration. The winning design was intended to form the backbone of the Luftwaffe's bomber force, replacing the wide collection of semi-specialized designs then in service. The Reich Air Ministry was so optimistic that more modest projects were generally cancelled; when the project failed the Luftwaffe was left with hopelessly outdated aircraft.
The Junkers Ju 288, originally known within the Junkers firm as the EF 074, was a German bomber project designed during World War II, which only ever flew in prototype form. The first of an eventual 22 development aircraft flew on 29 November 1940.
The Jumo 211 was a German inverted V-12 aircraft engine, Junkers Motoren's primary aircraft engine of World War II. It was the direct competitor to the Daimler-Benz DB 601 and closely paralleled its development. While the Daimler-Benz engine was mostly used in single-engined and twin-engined fighters, the Jumo engine was primarily used in bombers such as Junkers' own Ju 87 and Ju 88, and Heinkel's H-series examples of the Heinkel He 111 medium bomber. It was the most-produced German aero engine of the war, with almost 70,000 examples completed.
Contra-rotating, also referred to as coaxial contra-rotating, is a technique whereby parts of a mechanism rotate in opposite directions about a common axis, usually to minimise the effect of torque. Examples include some aircraft propellers, resulting in the maximum power of a single piston or turboprop engine to drive two propellers in opposite rotation. Contra-rotating propellers are also common in some marine transmission systems, in particular for large speed boats with planing hulls. Two propellers are arranged one behind the other, and power is transferred from the engine via planetary gear transmission. The configuration can also be used in helicopter designs termed coaxial rotors, where similar issues and principles of torque apply.
Aircraft equipped with contra-rotating propellers, also referred to as CRP, coaxial contra-rotating propellers, or high-speed propellers, apply the maximum power of usually a single piston or turboprop engine to drive two coaxial propellers in contra-rotation. Two propellers are arranged one behind the other, and power is transferred from the engine via a planetary gear or spur gear transmission. Contra-rotating propellers are also known as counter-rotating propellers, although counter-rotating propellers is much more widely used when referring to airscrews on separate non-coaxial shafts turning in opposite directions.
The Focke-Wulf Fw 191 was a prototype German bomber of World War II, as the Focke-Wulf firm's entry for the Bomber B advanced medium bomber design competition. Two versions were intended to be produced, a twin-engine version using the Junkers Jumo 222 engine and a four-engine variant which was to have used the smaller Daimler-Benz DB 605 engine. The project was eventually abandoned due to technical difficulties with the engines.
The critical engine of a multi-engine fixed-wing aircraft is the engine that, in the event of failure, would most adversely affect the performance or handling abilities of an aircraft. On propeller aircraft, there is a difference in the remaining yawing moments after failure of the left or the right (outboard) engine when all propellers rotate in the same direction due to the P-factor. On turbojet and turbofan twin-engine aircraft, there usually is no difference between the yawing moments after failure of a left or right engine in no-wind condition.
The Daimler-Benz DB 603 was a German aircraft engine used during World War II. It was a liquid-cooled 12-cylinder inverted V12 enlargement of the DB 601, which was in itself a development of the DB 600. Production of the DB 603 commenced in May 1942, and with a 44.5 liter displacement figure, was the largest displacement inverted V12 aviation engine to be produced and used in front line aircraft of the Third Reich during World War II.
The tail rotor is a smaller rotor mounted vertically or near-vertically at the tail of a traditional single-rotor helicopter, where it rotates to generate a horizontal thrust in the same direction as the main rotor's rotation. The tail rotor's position and distance from the helicopter's center of mass allow it to develop enough thrust leverage to counter the reactional torque exerted on the fuselage by the spinning of the main rotor. Without the tail rotor or other anti-torque mechanisms, the helicopter would be constantly spinning in the opposite direction of the main rotor when flying.
Blade pitch or simply pitch refers to the angle of a blade in a fluid. The term has applications in aeronautics, shipping, and other fields.
A quadcopter or quadrotor is a type of helicopter with four rotors.
A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are referred to as a rotor. The International Civil Aviation Organization (ICAO) defines a rotorcraft as "supported in flight by the reactions of the air on one or more rotors".
P-factor, also known as asymmetric blade effect and asymmetric disc effect, is an aerodynamic phenomenon experienced by a moving propeller, where the propeller's center of thrust moves off-center when the aircraft is at a high angle of attack. This shift in the location of the center of thrust will exert a yawing moment on the aircraft, causing it to yaw slightly to one side. A rudder input is required to counteract the yawing tendency.
In aeronautics, a propeller, also called an airscrew, converts rotary motion from an engine or other power source into a swirling slipstream which pushes the propeller forwards or backwards. It comprises a rotating power-driven hub, to which are attached several radial airfoil-section blades such that the whole assembly rotates about a longitudinal axis. The blade pitch may be fixed, manually variable to a few set positions, or of the automatically variable "constant-speed" type.
The Messerschmitt Bf 161 was a 1930s prototype German reconnaissance aircraft.
Loss of tail-rotor effectiveness (LTE) occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.
Asymmetrical aircraft have left- and right-hand sides which are not exact mirror images of each other. Although most aircraft are symmetrical, there is no fundamental reason why they must be, and design goals can sometimes be best achieved with an asymmetrical aircraft.
The Kawasaki Ha40, also known as the Army Type 2 1,100 hp Liquid Cooled In-line and Ha-60, was a license-built Daimler-Benz DB 601Aa 12-cylinder liquid-cooled inverted-vee aircraft engine. The Imperial Japanese Army Air Service (IJAAS) selected the engine to power its Kawasaki Ki-61 fighter.
The Dornier Do 417 was a twin-engine multirole bomber. Developed in 1942, it emerged from the Luftwaffe's request for a medium bomber, a contest for which Dornier, Junkers, Heinkel, and Blohm & Voss competed. In the end, the Junkers Ju 188 was chosen, and the Do 417 was never entered production.