Steve Trichard

The Soviet Union has had the most amazing history of building huge, yet very successful helicopters, that dwarf the biggest the West has ever produced.

The Mi-26 (NATO reporting name “Halo”) is the biggest, heaviest, and most powerful helicopter ever to have gone into production. It created a new category in helicopter classification, known as super heavy-lift.

The sheer size and capabilities of the Mil Mi-26 are difficult to put into perspective. The Halo is effectively a C-130 Hercules with rotors as the cargo holds of the C-130 and Mi-26 are almost identical in size, with the Mi-26 being marginally bigger. The max payload of the Mi-26 is almost 1,000 kg more than that of the C-130.

Development

In 1922, with the founding of the Soviet Union, a massive country was created. It was three times the size of the USA, and with extreme climate and inhospitable terrain. The average monthly temperatures in Yakutsk in Siberia (population of 350,000), are +20°C in July and −37°C in December.

Almost 65% of the Soviet Union is covered by permafrost (frozen subsoil). The construction of roads and railways in many areas was uneconomical, impractical and, in some cases, impossible. Air travel therefore played a crucial role in linking population centres separated by huge distances.

To cater for air travel needs, by the end of the 1930s, Aeroflot had over 4,000 pilots and operated 3,000 aircraft. There were few airports, most with unpaved runways. This had a significant impact on the size and payload of fixed-wing aircraft that could be employed.

To address this limitation of fixed wing aircraft, rotorcraft were identified as a game changer. However, the worldwide experience and expertise of developing rotorcraft were minimal.

To develop aircraft the Soviets created Opytno Konstruktorskoye Byuros (OKBs). These “experimental design bureaus” were independent and unique, designing and constructing prototypes in a specific area of advanced technology. The OKBs were identified through a numbering system. The system followed no logical order or structure, creating intentional confusion.

The rotorcraft design bureaus included OKB-3 (Bratukhin), OKB-115 (Yakovlev), OKB-329 (Mil) and OKB-938 (Kamov). It is interesting to note that there were multiple OKBs dedicated to a specific technology which led to competing teams proposing similar designs.

The most successful rotorcraft design bureau was OKB-329. It was established in 1947 under the leadership of Mikhail Mil, who was also the lead designer. Informally the bureau was known as OKB Mil. Mil’s design philosophy was “make it simple, make it reliable, make it rugged, and make it work”.

OKB Mil designed the Mi-1 “Hare” helicopter which entered service in 1950. It was quickly followed by the Mi-4 “Hound” in 1953. Initially, the Soviets built most of their transport helicopters to move civilian personnel and equipment to remote areas of the Soviet Union. It provided Aeroflot with the means to assist in the exploitation of undeveloped regions.

In the early 1950s a joint civilian and military requirement was identified for a large transport helicopter. Specifications for this helicopter stated a range of 130 nm (240 km) with an 11,000 kg payload.

The requirements were at the furthest end of “possibility”. The OKB Mil team had to design and then direct the development of groundbreaking technology and products to satisfy the requirement. The design work began in 1952 and in June 1957 the Mil V-6 made its maiden flight.

When the Mil Mi-6 “Hook” went into production, it was powered by two Soloviev D-25V turboshaft engines producing 4,100 kW each (designed by OKB-19) and a five-blade main rotor with a 35-meter diameter.

Mil Mi-6 “Hook”

The Mi-6 was the world’s first twin-turboshaft helicopter and the first to exceed 300 km/h (162 knots) in level flight, a speed that was assumed to be beyond the capability of helicopters. With a maximum payload capacity of 12,000 kg (or 70 troops) and a Maximum Take-Off Weight (MTOW) of 42,200 kg, the Mi-6 was the world’s first heavy-lift helicopter.

Its most notable feature was stub wings, which were mounted high on each side of the fuselage. It provided 25% of the lift required during cruise flight. But during hover the stub wings increased the vertical drag, known as rotor blockage. As a result, the negative impact on the payload was close to 800 kg. For heavy-lift operations, the wings could be removed. Rolling take-offs and landings became operational procedure during flights at high All Up Weight (AUW).

By the time the production line was closed in 1981, 924 Mi-6s had been manufactured. The Mil Mi-6 remained in operational service until 2002 when the type certificate was withdrawn.

Mil V-12 “Homer”

In 1957 the Mil Mi-6 was the largest helicopter in the world, far out-sizing helicopters built in the West. But for the Soviet Union, the need to build a helicopter even bigger than the Mi-6 was a matter of national security.

The cold war was in full swing. Nuclear weapons guaranteed a tense but stable global peace based on the concept of Mutual Assured Destruction (MAD). This is a “strategic situation in which both sides possess the ability to inflict unacceptable damage upon the opponent at any time during the course of a strategic nuclear exchange, even after absorbing a surprise first strike.” (oxfordreference.com).

To absorb a first attack and strike back, the missile launch sites had to be secret. The Soviet military deployed their land-based Intercontinental Ballistic Missiles (ICBMs) all over the country. The enormous size of the Soviet Union was ideal for hiding missiles, but the massive first-generation missiles had to be transported to launch sites by train. Railways were built with the sole purpose of transporting the missiles.

By 1960, American U-2 spy planes conducting high-altitude reconnaissance flights over the Soviet Union were beginning to uncover the location of Soviet ICBM sites. It was relatively easy as the U-2 used the purpose-built railways to pinpoint the missile launch sites.

The Soviets could no longer hide their land-based nuclear weapons so they devised a plan to airlift the missiles into the Soviet wilderness. This would make it almost impossible for spy planes to track down missiles hidden in over twelve million square kilometres of forests. But to make the plan work, the Soviets needed a giant helicopter.

The concept was to use the Antonov An-22 “Cock” turboprop 80,000 kg payload transport aircraft in combination with a 30,000 kg payload helicopter. The An-22 would transport the missile over long distances to a remote airfield, from which the helicopter could transport the missiles hundreds of kilometres into the vastness of Soviet territory.

OKB Mil started design studies in 1959 for the giant helicopter, after receiving a directive to develop a helicopter that can airlift a 30,000 kg payload over 270 nm (500 km). It was specified that the height and width dimensions of the cargo bay must be similar to that of the Antonov An-22.

Mil’s solution was a transverse rotor design, in which the complete main gearbox, uprated engines and rotor assemblies of the Mi-6 were located at the tip of extensively braced fixed wings. The flight deck layout was split, with the pilots in the lower cockpit and the navigator in the upper cockpit.

Construction of the first prototype started in 1965, designated Mil V-12. During the first test flight in 1967, a hard landing damaged the left main landing gear. The second test flight took place a year later, having addressed the oscillation issues experienced during the first test flight.

In 1971, the Mil V-12 was displayed at the Paris Air Show, much to the surprise of the world. NATO was caught unawares. They were not sure what the Soviet Union planned to do with the massive helicopter.

The helicopter exceeded all design specifications, setting numerous world records which still stand. The Mil designers received the American Helicopter Society’s Sikorsky Prize for “outstanding achievements in helicopter technology”.

Although an engineering success, acceptance by the military was not forthcoming. With the development of spy satellites and lighter ICBMs, the requirement for a 30,000 kg payload helicopter lost its relevance.

With a crew of six, the Mil V-12 “Homer” had a capacity of 196 passengers or a payload of 40,000 kg. It was huge, with a length of 37 m and a wingspan of 67 m across the rotors. It was as high as a 4-storey building. Maximum take-off weight was 105,000 kg.

The Mil V-12, the largest helicopter ever built, never went into production, with only two prototypes constructed.