Mil V-12

Mil

Industry	Aerospace
Founded	1959
Headquarters	Moscow , Soviet Union
Products	Helicopters

The Mil V-12 (NATO reporting name: Homer), internally designated as Izdeliye 65 ("Item 65"), is a Soviet-developed prototype helicopter and holds the distinction of being the largest helicopter ever constructed. The designation "Mi-12" was reserved for the production version and did not apply to the V-12 prototypes.

Design and development

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Mil V-12 displayed at the Central Air Force Museum

Initial design efforts for an oversized helicopter commenced at the Mil design bureau in 1959. Official approval came in 1961 from the GKAT (Gosudarstvenny Komitet po Aviatsionnoy Tekhnike — State Committee on Aircraft Technology), which mandated Mil to develop a rotorcraft with a lifting capacity between 20 to 25 tonnes (22 to 28 short tons). Following this directive, detailed specifications were issued for the V-12, including a cargo hold size comparable to that of the Antonov An-22, intended to transport substantial combat equipment as well as intercontinental ballistic missiles such as the 8K67, 8K75, and 8K82.

Due to design constraints, Mil opted for a twin-rotor configuration. However, initial studies of a tandem rotor layout, resembling that of the Boeing CH-47 Chinook, revealed significant challenges. Alternative single rotor designs were also investigated but ultimately deemed impractical, leading to the adoption of a transverse rotor arrangement for the final design.

The V-12’s transverse rotor system, which negates the requirement for a tail rotor, incorporates two complete transmission assemblies from the Mil Mi-6, each with rotors mounted at the ends of approximately 30 metres (98 ft) inverse-tapered wings. Although this was Mil’s first use of such a system, transverse rotors had been employed on earlier helicopters like the Focke-Wulf Fw 61, Focke-Achgelis Fa 223 Drache, and the Kamov Ka-22 Vintokryl convertiplane.

Construction of the first V-12 prototype began in 1965 at Panki following extensive testing on rigs and mock-ups, including full transmission assemblies. The airframe utilized conventional stressed skin construction with high-strength components machined from solid metal blocks. Its spacious fuselage measured approximately 28.15 by 4.4 by 4.4 metres (92.4 ft × 14.4 ft × 14.4 ft), featuring a crew compartment at the extreme front that housed a pilot, co-pilot, flight engineer, and electrical engineer in the lower cockpit, while the navigator and radio operator occupied positions in an upper cockpit.

Access to the cargo area at the rear was provided by large clamshell doors coupled with a fold-down ramp equipped with retractable support jacks. Additional doors offered entry to the cargo bay—two on the starboard side and three on port. A sizable fin and rudder were positioned above the rear fuselage, complemented by a moderately sized tailplane with dihedral and end-plate fins; these fins were not installed during initial flight tests.

File:Cockpit of Mil V-12 ‘CCCP-21142’ (24492250877).jpg

Lower cockpit of Mil V-12

The fixed landing gear featured large paired main wheels mounted on oleo-pneumatic shock absorbers attached where struts supporting both rotors and wings met. These struts connected to the central fuselage through a tripod framework; meanwhile, the nose gear was located just aft of the crew compartment. Rear bumper wheels were fixed to the fuselage keel, and support pads ensured proper extension angles for the cargo ramp. Additional braced struts linked transmission units to the rear fuselage ahead of the fin. Cargo handling was facilitated by forklifts or electric hoists mounted on traveling beams.

The powerplants and wings were positioned atop the central fuselage, interconnected by shafts that synchronized rotation between main rotors overlapping by about 3 metres (9.8 ft). The inverse taper wing design minimized drag and lift losses by reducing chord length in areas subjected to strong downwash. These interconnecting shafts also guaranteed balanced lift distribution if one engine failed. To optimize roll and yaw control, rotors rotated in opposing directions: port rotor turned counterclockwise while starboard rotated clockwise, ensuring advancing blades passed above the fuselage.

Each propulsion unit consisted of two Soloviev D-25VF turboshaft engines mounted beneath main gearboxes driving five-bladed rotors with diameters of approximately 35 metres (115 ft). Synchronization shafts extended wingtip-to-wingtip. Engine pods featured large access panels that opened for maintenance and doubled as platforms for servicing personnel.

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Mil V-12 exhibited at Central Air Force Museum in 2022

Piloting the V-12 posed considerable challenges due to its immense size and unique rotor layout. The pilot and co-pilot were seated in a lower cockpit offering extensive visibility through large windows. Control inputs were made using conventional cyclic sticks, collective levers, and rudder pedals. Roll was managed via differential collective pitch adjustments between left and right rotors to maintain lift and prevent unintended descent. Yaw control during hover or low speeds was achieved by tilting rotor discs forward or backward differentially according to desired direction; at higher speeds, yaw authority transitioned progressively to a large aerodynamic rudder mounted on the fin. Vertical movement was controlled by collective pitch changes affecting both rotors simultaneously, while sizeable elevators on the tailplane assisted in maintaining fuselage attitude and counteracting pitching moments caused by wings or rotor disc angle variations.

Due to structural aeroelasticity and significant friction forces within control linkages, a complex three-stage control system was necessary to reduce pilot input forces. The first stage involved direct mechanical linkage from pilot controls feeding into an intermediate powered stage equipped with low-powered hydraulic boosters; these then actuated high-powered rapid-response control actuators at main gearboxes that manipulated swashplates directly.

Operational history

The initial prototype's construction was finished in 1968. An early test flight on 27 June 1967 was cut short due to oscillations stemming from control difficulties; one of the main wheel sets struck the ground forcefully, causing a tire to burst and a wheel hub to bend. These oscillations were traced back to a harmonic vibration amplification within the cockpit floor, which fed back into the control column when a roll command was applied to the cyclic stick. Contrary to widespread but inaccurate reports in Western media, the aircraft was not destroyed.

The first prototype, registered as SSSR-21142, completed its maiden flight on 10 July 1968, departing from the Mil factory pad in Panki and landing at the Mil OKB test flight facility in Lyubertsy. In February 1969, this prototype achieved a record by lifting a payload of 31,030 kg (68,410 lb) to an altitude of 2,951 m (9,682 ft). Later, on 6 August 1969, the V-12 set another world record by hoisting 44,205 kg (97,455 lb) to an elevation of 2,255 m (7,398 ft).

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Mil V-12 at Groningen Airport in 1971

The second prototype was also built at the Mil experimental production site in Panki but remained idle in the workshop for an entire year awaiting engine delivery. Its first flight occurred in March 1973, traveling from Panki to the flight test center in Lyubertsy. Interestingly, this second unit carried the same registration number, SSSR-21142.

Both prototype V-12s surpassed their original design goals and established multiple enduring world records. Their success earned the designers distinguished honors, including the renowned Sikorsky Prize granted by the American Helicopter Society for exceptional contributions to helicopter technology. The V-12's design received patent protection across several countries, including the United States and United Kingdom. Despite these accomplishments, the Soviet Air Force declined to proceed with state acceptance trials for several reasons; chief among them was that the helicopter’s primary mission—rapid deployment of heavy strategic ballistic missiles—had become obsolete. This shift also contributed to a cutback in Antonov An-22 production.

During May and June 1971, the first prototype SSSR-21142 conducted a series of demonstration flights across Europe, culminating in its display at the 29th Paris Air Show held at Le Bourget, where it bore exhibit code H-833.

Development efforts for the V-12 ceased entirely in 1974. The first prototype remains preserved at the Mil Moscow Helicopter Plant located in Panki-Tomilino, Lyuberetsky District near Moscow, where it is still present as of 27 December 2023 at . The second prototype was transferred to the Central Air Force Museum, situated approximately 50 km (30 mi) east of Moscow, where it is available for public viewing.

World records

The Fédération Aéronautique Internationale (FAI) is responsible for validating these records. The initial V-12 prototype established eight global records in the FAI E1 General category, designated for turbine-powered rotorcraft. Of these, three records remain unbroken. The flight crews were as follows:

22 February 1969

Pilot - Vasily Kolochenko

Crew - L.V. Vlassov, V.V. Journaliov, V.P. Bartchenko, S.G. Ribalko, A.I. Krutchkov

6 August 1969

Pilot - Vasily Kolochenko

Crew - L.V. Vlassov, V.V. Juravlev, V.P. Bartchenkov, S.G. Ribalko, A.I. Krutchkov

Date	Record description	Result	Still standing
22 February 1969	Altitude achieved carrying a 15,000 kg (33,000 lb) payload	2,951 m (9,682 ft)	No
22 February 1969	Altitude reached with a 20,000 kg (44,000 lb) payload	2,951 m (9,682 ft)	No
22 February 1969	Altitude attained while transporting a 25,000 kg (55,000 lb) payload	2,951 m (9,682 ft)	No
22 February 1969	Altitude with a payload of 30,000 kg (66,000 lb)	2,951 m (9,682 ft)	Yes
22 February 1969	Heaviest load lifted to 2,000 m (6,600 ft)	31,030 kg (68,410 lb)	No
6 August 1969	Altitude reached carrying 35,000 kg (77,000 lb) payload	2,255 m (7,398 ft)	Yes
6 August 1969	Altitude with a payload of 40,000 kg (88,000 lb)	2,255 m (7,398 ft)	Yes
6 August 1969	Maximum load transported to 2,000 m (6,600 ft)	40,204 kg (88,635 lb)	No

Variants

V-12

The designation assigned by OKB to the two prototype models intended for the Mi-12 production variant.

Mi-12

The label reserved for the anticipated production model.

Mi-12M

An advanced iteration of the V-16 concept featuring a pair of 15,000 kW (20,000 hp) Soloviev D-30V (V - Vertolyotny - helicopter) turboshaft engines powering six-bladed rotors. This design aimed to carry 20,000 kg (44,000 lb) over distances up to 500 km (310 mi) or alternatively 40,000 kg (88,000 lb) across 200 km (120 mi). The Mi-12M project was discontinued at the mock-up phase following the cancellation of the V-12 development program.

Operators

• Aeroflot
• Soviet Air Forces (Planned)

See also

• Hotelicopter
• Yakovlev VVP-6

External links

• Information and images of the Mil V-12 at aviation.ru
• Details on Mil V-12 CCCP-21142 at Avia-dejavu.net
• Mil Mi-12 'Homer' photographs hosted on Airliners.net
• English-language video featuring the Mil-12