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. Some helicopters use contra-rotating
coaxial rotors mounted one above the other. The
H-43 Huskie helicopter uses non-coaxial
intermeshing rotors turning in opposite directions. The
F-35B variant of the
F-35 Lightning II strike fighter uses a lift fan with contra-rotating blades. == History ==