The Mil V-12 was a massive heavy-lift helicopter project taken on by the Soviet Union during the Cold War - even today (2015), it remains the largest helicopter ever built. Known in the Soviet Union under project "Izdeliye 65" and to NATO under the codename of "Homer", V-12 saw its first flight - an unsuccessful "hop" - in June of 1967 (its first successful test flight came a year later). Despite the promising nature of this large beast, particularly in the scope of Soviet military transportation service, the V-12 was not to be - cancelled after just a pair of prototypes had been completed.
Work on the V-12 began as early as 1959 when thought was given to a large transport helicopter to move upwards of 55,000 lb of cargo - men, machines, supplies, and particularly Soviet ICBMs ("InterContinental Ballistic Missiles"). The charge fell to the famous Soviet helicopter concern, Mil Design Bureau, whose engineers elected for a "transverse" rotor system arrangement - the main rotors fitted outboard of wing assemblies as opposed to an inline format (as in the Boeing CH-47 Chinook). The dual main rotors were also used to cancel the naturally occurring torque effect seen in single-rotor helicopters which negated the use of a tail rotor. Mockups and small-scale testing ensued into the mid-1960s to prove certain design aspects viable. Two paired Soloviev D-25VF turboshaft engines (four engines in all) were selected to power the helicopter and these engines each drove five-bladed main rotors while also providing the needed forward thrust for horizontal flight.
The finalized fuselage was streamlined in its general shape with a twin-deck approach, the primary flight deck being fitted at the nose of the aircraft for two pilots and two engineers while a secondary deck was sat over the nose housing a navigator and radioman. The fuselage took on a tubular shape from nose to tail with the tail being raised to allow for easier access to the cargo hold by way of clamshell doors. The empennage consisted of a sole vertical tail fin with low-set horizontal planes. To each of these horizontal planes were added vertical tail fins - though much smaller in overall dimension than the primary tail fin. The wing mainplanes were fitted over the fuselage spine near amidships and held dihedral (upward angle) from centerline. At their ends were the engine pairings (under) and main rotor assemblies (over). The undercarriage was fixed in place though wheeled, the main legs (double-wheeled) situated under the wings via a network of struts and the nose leg under the forward fuselage with a double-wheeled arrangement. The helicopter carried the AP-44 autopilot system and ROZ-1 navigational radar.
Internally, the cargo hold was to match that of the large Antonov An-22 ("Antei") strategic airlifter to an extent. It could seat 196 passengers if equipped as such or carry up to 88,000 lb of goods under maximum loads including military-grade wheeled vehicles or a mixed cargo set. Dimensions of the aircraft included a length of 37 meters, a wingspan of 67 meters, and a height of 12.5 meters. Maximum Take-Off Weight (MTOW) reached 231,485 lb.
The four Soloviev D-25VF turboshafts produced 6,500 shaft horsepower each while driving the twin 35-meter-diameter main rotor blades. Performance specifications included a maximum speed of 162 miles per hour, a cruise speed of 150 miles per hour, a ferry range out to 620 miles, and a combat range of 310 miles. Its service ceiling peaked at 11,500 feet.
Initial testing began in 1967 and ended in a hop of the machine due to oscillation issues which caused a hard landing- though damaged, the aircraft was not a total loss. Construction was completed for 1968 which allowed for more deeper testing to continue and ultimately led to an official first flight on July 10th, 1968. Its first payload test came the following year when a prototype hauled over 68,000 lb of goods airborne. The first prototype wowed audiences attending the 1971 Paris Air Show (le Bourget). The second prototype was not realized until March of 1973 after delays in acquiring its engines.
The V-12 continued to impress throughout its developmental life. However, the Soviet mission began to change and the system fell victim to no longer having a defined role to explain its development, procurement, and operating costs. As such, the V-12 program was cancelled after the two prototypes and no further work on the pair was done after 1974. For a time, the V-12 was also considered for industry and civilian transport service but this fell to naught as well. The Soviet military eventually adopted the Mil Mi-26 ("Halo") series in 1983 to fulfill its revised heavy-lift role.
V-12 served as the prototype designation which numbered just the two aforementioned aircraft. In serial production, the aircraft would have been given the designation of Mi-12. V-16 was a proposed super-heavy-lift variant of the V-12 and set to become the Mi-16 in production. This model was intended to haul up to 110,000 lb of goods utilizing six Soloviev engines with a three rotor configuration (later revised to twin-rotor design). A proposed revised version of the V-16 also emerged though with a slightly different engine set (Soloviev D-30Vs) as the Mi-12M but this mark joined the others in never seeing the light of day.
Despite the perceived failure of the V-12 program, the massive aircraft managed to find its way into the world aviation record books as it set multiple records dealing with payload-to-altitude during flights in 1969.
Fortunately, both of the completed prototypes were saved from the scrap heap - the first residing at the MIL Moscow Helicopter Plant (Moscow) and the second finding a home at the outdoor Monino Air Force Museum Display (Monino Airfield) as of 2015.