The Russian-built Mil V-12 is the world s largest helicopter, 28 metres in length and 4.4 metres in width and height and pair of rotors were mounted on transverse wings. Two prototypes were built in 1967 and though it never went into full production, the helicopter was able to carry a payload weighing over 40,000 kilograms to altitude. Development ceased in 1974 and both prototypes currently reside in air museums.