Counter-rotating propellers

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Counter-rotating propellers, are found on twin-engine, propeller-driven aircraft and have propellers that spin in opposite directions.

Generally, 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 counter-rotating propellers is to balance out 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, making both engines critical. Tests on the initial XP-38 prototype demonstrated greater accuracy in gunnery with the unusual configuration.

Counter-rotating propellers should not be confused with Contra-rotating propellers that share a common axis.

Some aircraft with counter-rotating propellers include:

• Piper PA-31 Navajo
• Piper PA-34 Seneca
• Piper PA-39 Twin Comanche
• Piper PA-40 Arapaho
• Piper PA-44 Seminole
• Cessna T303 Crusader
• Beech BE-76 Duchess
• Lockheed P-38 Lightning
• The Wright Flyer