There are none bigger. The Mil Mi-12 is the largest helicopter ever built. Launched in the early 60’s by Mil Helicopters (Mil Moscow Helicopter Plant), named after its founder, Russian engineer Mikhail Mil, it made its first test flight in 1967.
Its dimensions are impressive, being as long as a Boeing 737, and its overall wingspan of 220 feet (67 m), is comparable to that of the A350. One unusual feature of the aircraft are its double-decker cockpits. The pilots are on the lower level, the navigator and the radio operator on the upper. Another distinguishing features are its two counter-rotating five-bladed rotors, allowing it to dispense with a tail rotor. Each rotor is supported on the wingtips of the unusual inverse taper wings.
Built during the Cold War, primarily to transport heavy nuclear missiles, its 21,200 ft3 (600 m3) freight compartment could hold a payload of 88,200 lbs (40 tonnes).
Although the Mil Mi-12 was presented at the Paris Air Show in 1971, the programme was stopped in 1974. Whilst no aircraft ever came off the production line, officially there were two prototypes produced, which today are on display near Moscow; one in the Russian Air Force museum and the other on the manufacturer's premises.