The benefits of contra rotating propellers are well understood and common place in the marine and subsea propulsion sectors
Whilst developments in the fifties and sixties demonstrated the huge potential benefits of the arrangement in aircraft, piston and gas turbine powered contra rotating systems proved to be mechanically complicated, prone to failure and heavy. Their high cost prevented commercial development and only military aircraft such as the British built Fairey Gannet and Avro Shackleton were fitted with them.
The USA built fighters Convair XFY (Pogo) and the Lockheed XFV shown below were fitted with “torque free” contra rotating propulsion systems to allow vertical take-off.
Fast forward 50 years and the immense advances in electric motor technology, rising fuel prices and increasing concern over environmental issues once again favours contra rotating propeller propulsion for medium speed aircraft.