Contra-rotating propellers

Contra-rotating propellers
Contra-rotating propellers on a Rolls-Royce–Griffon–powered P-51 unlimited racer

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 (rotation about the same axis in opposite directions). 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 should not be confused with counter-rotating propellers—airscrews on different engines turning opposite directions.



When airspeed is low, the mass of the air flowing through the propeller disk (thrust) causes a significant amount of tangential or rotational air flow to be created by the spinning blades. The energy of this tangential air flow is wasted in a single-propeller design. To use this wasted effort the placement of a second propeller behind the first takes advantage of the disturbed airflow. The tangential air flow also causes handling problems at low speed as the air strikes the vertical stabilizer, causing the aircraft to yaw left or right, depending of the direction of propeller rotation.

If it is well designed, a 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 asymmetrical torque effect of a conventional propeller (see P-factor). Some contra-rotating systems were designed to be used at take off for maximum power and efficiency under such conditions, and allowing one of the propellers to be disabled during cruise to extend flight time.

Contra-rotating propellers have been found to be between 6% and 16% more efficient than normal propellers.[1] 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.[1] Most of this extra noise can be found in the higher frequencies. These substantial noise problems will limit commercial applications unless solutions can be found. One possibility is to enclose the contra-rotating propellers in a shroud. It is also helpful if the two propellers have a different number of blades (e.g. four blades on the forward propeller and five on the aft).[citation needed]

The efficiency of a contra-rotating prop is somewhat offset by its mechanical complexity. Nonetheless, coaxial contra-rotating propellers and rotors are moderately common in military aircraft.

Significant 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 though was in the US when two inventors from Ft Worth, Texas tested the concept on an aircraft.[2]

United Kingdom

Contra-rotating propellers of a Spitfire Mk XIX

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.

Later variants of the Supermarine Spitfire and Seafire used the Griffon with contra-rotating props as well. In the Spitfire/Seafire and Shackleton's case the primary reason for using contra-rotating propellers was so as 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. Whilst this also applied to the Gannet, in addition this aircraft's engine had two separate power-sections, each driving one propeller. The Short Sturgeon used 2 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.[3]

USSR, Russia and Ukraine

One of the quartet of contra-rotating propellers on a Tu-95 Russian strategic bomber

In the 1950s, the Soviet Union developed the Kuznetsov NK-12 turboprop. It drives an 8-blade contra-rotating propeller and, at 15,000 shp, it is the most powerful turboprop in the world. Four NK-12 engines power the Tupolev Tu-95 Bear, the only turboprop bomber to enter service, as well as one of the fastest propeller-driven aircraft. The Tu-114, an airliner derivative of the Tu-95, holds the world speed record for propeller aircraft.[4] The Tu-95 was also the first Soviet bomber to have intercontinental range. The Tu-126 AEW aircraft and Tu-142 maritime patrol aircraft are two more NK-12 powered designs derived from the Tu-95.

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 A-90 Orlyonok, a mid-size Soviet ekranoplan. The A-90 uses one NK-12 engine mounted atop its T-tail, along with two turbojets[citation needed] nestled in its nose.

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 U.S. worked with several prototypes, including the A2J Super Savage, the Boeing XF8B, the XP-56 Black Bullet and the tail-sitting Convair XFY and Lockheed XFV "Pogo" VTOL fighters and the Hughes XF-11 reconnaissance plane, but jet engine technology was advancing rapidly and the designs were deemed unnecessary.

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 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.[citation needed]

See also


External links

Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Contra-rotating — A Soviet Ka 32 helicopter with coaxial contra rotating rotors, in 1989 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… …   Wikipedia

  • Counter-rotating propellers — Not to be confused with Contra rotating propellers. Counter rotating propellers Opposite propeller blade section can be clearly seen on this Piper PA 44 Seminole Counter rotating propellers, found on twin and multi engine propeller driven… …   Wikipedia

  • Propeller — A propeller is essentially a type of fan which transmits power by converting rotational motion into thrust for propulsion of a vehicle such as an aircraft, ship, or submarine through a mass such as water or air, by rotating two or more twisted… …   Wikipedia

  • Curtiss P-60 — P 60 Curtiss XP 60C in flight, modified from second XP 60A, wit …   Wikipedia

  • Northrop YB-35 — YB 35 YB 35 prototype Role Strategic bomber Manufacturer Northrop …   Wikipedia

  • Fairey Gannet — Infobox Aircraft name= Gannet type=Anti submarine warfare aircraft manufacturer=Fairey Aviation Company caption=Fairey Gannet AS.4 of the Fleet Air Arm designer= H. E. Chaplin first flight=19 September 1949 introduced=1953 retired= 15 December… …   Wikipedia

  • Disk loading — The MV 22 Osprey tiltrotor has a relatively high disk loading, producing visible blade tip vortices from condensation of the marine air in this photo of a vertical takeoff …   Wikipedia

  • Westland Wyvern — infobox Aircraft name = Wyvern type = Carrier based strike aircraft manufacturer = Westland Aircraft caption = Wyvern S Mk.4 designer = Teddy Petter first flight = 12 December 1946 introduced = 1953 retired = 1958 status = primary user = Fleet… …   Wikipedia

  • Convair XFY Pogo — XFY Pogo Role Experimental VTOL fighter aircraft Manufacturer Convair …   Wikipedia

  • Torpedo — The modern torpedo (historically called an automotive, automobile, locomotive, or fish torpedo) is a self propelled explosive projectile weapon, launched above or below the water surface, propelled underwater toward a target, and designed to… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”