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Coaxial-rotor aircraft
Helicopter with two sets of rotor blades placed on top of each other / From Wikipedia, the free encyclopedia
A coaxial-rotor aircraft is an aircraft whose rotors are mounted one above the other on concentric shafts, with the same axis of rotation, but turning in opposite directions (contra-rotating).
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This rotor configuration is a feature of helicopters produced by the Russian Kamov helicopter design bureau.