What is the advantage of contra-rotating propellers?

Use of contra-rotating propellers recovers energy lost due to the motion of the air in the slipstream of the forward propeller and allows for an increase in power without a corresponding increase in propeller diameter. It will also help counter the torque effects of a high power piston engine.

Are contra-rotating propellers efficient?

Contra-rotating propellers have been found to be between 6\% and 16\% more efficient than normal propellers. 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.

Why do airplane propellers turn counter-clockwise?

In a counter-rotating installation, the propellers on the right wing turn counter-clockwise while those on the left wing turn clockwise. The principle advantage of counter-rotation is to balance propeller torque effects thus eliminating any problems associated with a Critical Engine.

How do twin propellers work?

On most twin or multi-engine propeller driven aircraft, the propellers all turn in the same direction, usually clockwise when viewed from the rear of the aircraft. In a counter-rotating installation, the propellers on the right wing turn counter-clockwise while those on the left wing turn clockwise.

How do contra rotating boat propellers work?

As contra-rotating suggests, twin props on a single shaft rotate in opposite directions. The prop pitch and loads are designed so that rotational energy in the wake is zero, while shaft vibration drops because the blades do not pass each other simultaneously.

How efficient are contra-rotating propellers and rotors?

The efficiency of a contra-rotating prop 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. Nonetheless, coaxial contra-rotating propellers and rotors have been used in several military aircraft, such as the Tupolev Tu-95 “Bear”.

When was the first contra-rotating propeller invented?

A contra-rotating propeller was patented by F. W. Lanchester in 1907. 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.

How do you troubleshoot a vibration in a propeller?

If a propeller vibration is suspected but cannot be positively determined, the ideal troubleshooting method is to temporarily replace the propeller with one known to be airworthy and then test fly the aircraft if possible. Blade shake is not the source of vibration problems.

Why did the Spitfire have a contra-rotating propeller?

In the Spitfire/Seafire and Shackleton’s case the primary reason for using contra-rotating propellers was 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. The Short Sturgeon used two Merlin 140s with contra-rotating propellers.