This monster is much bigger that any helicopter ever built: the Soviet Mil V-12 was a doubled version of Mi-6 fitted with greater fixed-wing airlift of An-22 and Il-76. It used a double set of Mi-6 dynamics: two sets of Mi-6 engines, gearboxes and lifting rotors side-by-side, with small overlap.
Rotor rpm decreased to 112; gearboxes connected by transverse shafting, axes tilted forward 4°30'; the helicopter was braced at root and tip to landing gears with torque reacting by horizontal bracing to rear fuselage.
Fuel was deposed in outer wings and two external tanks; optional ferry tanks in cabin. The fixed twin-wheel landing gear had main tyres of 1750 x 730mm, pneumatic brakes and steerable nose tyres 1200 x 450mm.
Crew door was in each side, three sliding side doors and full-section rear clamshell doors. It had an airplane tail with fin and tabbed rudder. The use of twin counter-rotating main rotors made not the tail rotor useless.
Flight deck had place for pilot in the left with engineer behind and co-pilot in the right with electric-system operator behind. The autopilot had three-axis autostab. The main cabin was 28.15m (94 ft) long, 4.4m square.
The first prototype crashed; the second flew in August 1969 to 2255 m (7520 ft) with a payload of 40,204.5 kg, after it had flown in February 1969 to 2,951 m (9,835 ft) with a cargo of 40,204 kg, records for payload and payload- to-altitude unbeaten to date.
The Mil Mi-12 (called V-12 in the Soviet Union and by the NATO Homer) is to date the world's largest helicopter, 28.15 m long and 4.4 m wide.
The Mi-12 project, begun in 1965, aimed to realize a vertical take-off aircraft that could carry missiles or other loads compatible with those carried by the four-engine An-22, but also troops. The maximum speed was of 260 km (162 mi)/h, with a 35400kg load and in a 500 km (315 mi) range. But Mi-12 was also intended for military purposes, like deployment in areas of Siberia rich in resources but with very poor communications.
V-12 could carry with an unobstructed cabin up to 120 passengers but tip-up seats are provided for just 50, as it was intended mainly for heavy-lift work, with accommodation just for drilling crews and missile crews.
Technical problems, rather than performance deficiencies, led to the abandonment of this helicopter in favor of the Mi-26. Just two examples of the Mil Mi-12 were built.