Contra-rotating propellers

The energy of this tangential air flow is wasted in a single-propeller design, and causes handling problems at low speed as the air strikes the vertical stabilizer, causing the aircraft to yaw left or right, depending on the direction of propeller rotation.

Some contra-rotating systems were designed to be used at takeoff for maximum power and efficiency under such conditions, and allowing one of the propellers to be disabled during cruise to extend flight time.

[6] The efficiency of a contra-rotating propeller is somewhat offset by its mechanical complexity and the added weight of this gearing that makes the aircraft heavier, thus some performance is sacrificed to carry it.

[7] While several nations experimented with contra-rotating propellers in aircraft, only the United Kingdom and Soviet Union produced them in large numbers.

[10] The post-war SARO Princess prototype flying boat airliner also had eight of its ten engines driving contra-rotating propellers.

It drives an eight-blade contra-rotating propeller and, at 15,000 shaft horsepower (11,000 kilowatts), it is the most powerful turboprop in service.

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 NK-62 had an identical propeller diameter and blade configuration to the NK-110, but it offered a higher takeoff thrust of 55,000 lbf (245 kN).

The United States worked with several prototypes, including the Northrop XB-35, XB-42 Mixmaster, the Douglas XTB2D Skypirate, the Curtiss XBTC, the A2J Super Savage, the Boeing XF8B, the XP-56 Black Bullet, the Fisher P-75 Eagle and the tail-sitting Convair XFY "Pogo" and Lockheed XFV "Salmon" VTOL fighters and the Hughes XF-11 reconnaissance plane.

However, both piston-engined and turboprop-powered propeller-driven aircraft were reaching their zenith and new technological developments such as the advent of the pure turbojet and turbofan engines, both without propellers, meant that the designs were quickly eclipsed.

[14] An Austrian company, Sun Flightcraft, distributes a contra-rotating gearbox for use on Rotax 503 and 582 engines on ultralight and microlight aircraft.

The manufacturer also reports reduced noise levels from dual contra-rotating props using the Coax-P gearbox.