Mil V-12

The Mil V-12 (NATO reporting name: Homer), given the project number Izdeliye 65 ("Item 65"), is a prototype helicopter designed in the Soviet Union and the largest helicopter ever built. The designation "Mi-12" would have been the designation for the production helicopter and did not apply to V-12 prototypes.

Design studies for a giant helicopter were started at the Mil OKB in 1959, receiving official sanction in 1961 by the GKAT (Gosudarstvenny Komitet po Aviatsionnoy Tekhnike - State Committee on Aircraft Technology) instructing Mil to develop a helicopter capable of lifting 20 to 25 tonnes (22 to 28 short tons). The GKAT directive was followed by a more detailed specification for the V-12 with hold dimensions similar to the Antonov An-22, intended to lift major items of combat material as well as 8K67, 8K75 and 8K82 inter-continental ballistic missiles (ICBM).

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 Mil Mi-6 transmission systems complete with rotors mounted at the tips of the approximately 30 m (100 ft) span inverse tapered wings. Although the first use by Mil, the transverse system had been used by several of the early helicopters, including the Focke-Wulf Fw 61, Focke-Achgelis Fa 223 Drache and Kamov Ka-22 Vintokryl convertiplane.

Construction of the V-12 first prototype, after exhaustive testing with test-rigs and mock-ups including a complete transmission system, began at Panki in 1965. The airframe was largely conventional, using stressed skin construction methods with high strength parts machined from solid metal blocks. The large fuselage accommodated the 28.15 m × 4.4 m × 4.4 m (92 ft 4 in × 14 ft 5 in × 14 ft 5 in) cabin and crew section in the extreme nose, housing a pilot, co-pilot, flight engineer and electrical engineer in the lower cockpit, with the navigator and radio operator in the upper cockpit.

At the aft end of the fuselage access to the cabin is gained by large clamshell doors and a drop down cargo ramp with inbuilt retractable support jacks. Doors in the fuselage also give access to the cargo hold: two on the starboard side and three on the port side. Above the rear fuselage is a very large fin and rudder, with a moderately sized tailplane with dihedral fitted with end-plate fins (not fitted for the first flight).

The fixed undercarriage consists of large paired main-wheel units on oleo-pneumatic levered shock absorbers mounted at the junction of a strut system supporting the rotor systems and wings and connected to the centre fuselage by a tripod strut structure with the nose-leg attached aft of the crew section. A pair of bumper wheels are mounted at the rear of the fuselage keel and fixed support pads ensure that the cargo ramp is extended to the correct angle. Long braced struts also connected the transmission units to the rear fuselage forward of the fin. Cargo handling is done by means of a forklift or electric hoists on traveling beams.

The power system and wings are mounted above the centre fuselage with interconnecting shafts ensuring synchronisation of the main rotors which overlap by about 3 m (10 ft). Drag and lift losses are reduced by the inverse taper wings with minimum chord in regions of strongest down-wash. The interconnecting shafts also ensured symmetrical lift distribution in the event of an engine failure. To optimise control in roll and yaw the rotors are arranged to turn in opposite directions with the port rotor turning anti-clockwise and the starboard rotor turning clockwise, ensuring that the advancing blades pass over the fuselage.