The biggest helicopter in the world ever to be created is Russian Mil MI-12. NATO classified it as a Homer class aircraft. Only two were made. They were designed during the sixties.
The main goal of designing this helicopter was to lift more than 30.000 kg needed to transport parts for ballistic missiles. First prototype had its first flight on 10th July, 1967. It takes a crew of 6 people to operate it (pilot, copilot, navigator, flight engineer, radio operator and electrician). It has a capacity of 30.000 kg with the record weight of 44.200 kg lifted.
It is thirty seven meters long and has twin rotors with the thirty five meters diameter each. Fully loaded it weighs up to maximum of 97 tons. Maximum speed is 260 km/h, it can fly over 500 km without refill and the top height at which it can operate is 3.700 meters. The twin rotors were designed and put in place, thus eliminating the need for tail rotor.
The diameters of both rotors exceed wing span of Boeing 747-400 ! Since its first flight, this wonder of cold war Soviet engineering has even outperformed most of its projected capacities and broke several world records. Even today it holds the records.
Its designers from Mil Bureau won several awards for this design including prestigious Sickorsky Prize, given by the American Helicopter Society.
This award is given for outstanding achievements in helicopter design and technology. Despite all the awards and records, Soviet military never started production of these helicopters. This was so because these helicopters weren’t needed anymore as the main reason for their production i.e. the fast deployment and transport of ballistic missiles no longer existed.
This was the main reason. The second reason was extremely expensive production. This helicopter was later replaced by a smaller (and stronger) MI-26.