Contra-rotating

Contra-rotating propellers are also common in some marine transmission systems, in particular for large speed boats with planing hulls.

The configuration can also be used in helicopter designs termed coaxial rotors, where similar issues and principles of torque apply.

Nonetheless, coaxial contra-rotating propellers and rotors are moderately common in military aircraft and naval applications, such as torpedoes, where the added maintenance cost is not a primary concern.

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

The U.S. worked with several prototypes, including the tail-sitting Convair XFY and Lockheed XFV "Pogo" VTOL fighters, but jet engine technology was advancing rapidly and the designs were deemed unnecessary.