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.

Design limitations forced Mil to adopt a twin rotor system but design studies of a tandem layout, similar to the Boeing CH-47 Chinook, revealed major problems. The single rotor layouts also studied proved to be non-viable, leading to the transverse layout chosen for the finished article.

The transverse rotor system of the V-12, which eliminates the need for a tail rotor, consists of two Mi-6 transmission systems complete with rotors mounted at the tips of the approximately 30 m (98 ft) span inverse tapered wings. The prototype V-12s outperformed their design specifications, setting numerous world records which still stand today.