Steve Trichard continues his story on Russia’s massive super-heavy helicopters

Although the Mil V-12 was the largest helicopter ever built, it never went into production, with only two prototypes constructed. The requirement for a heavy-lift helicopter therefore still existed.

The Mi-6 design was by then 25 years old and so OKB Mil was already designing and planning the next generation of heavy-lift helicopters.

Development started in the early 1970s. The design requirements were ambitious. Mil Moscow Helicopter Plant received a directive to produce a helicopter with a load capacity more than double that of any existing operational helicopter, in other words, a helicopter with twice the cabin and payload capability of the in-house Mil Mi-6.

Furthermore, the requirement stated that the empty weight of the helicopter must be less than half its MTOW.

The Mil design team concluded that only a single-rotor helicopter configuration would be able to satisfy the weight requirements.

They required an engine of at least 8,000 kW and a gearbox that could transfer the output of two of these engines to the rotors. It was a huge challenge as nothing like that was already in existence.

The engine design and development were done at the Progress Design Bureau (formerly OKB-478) with lead designer Vladimir Lotarev. The powerplant that was produced was the 8,500 kW Lotarev D-136 turboshaft engine, manufactured by Motor Sich in Zaporizhzhia, Ukraine.

Mil’s gearbox supplier was not able to design the required gearbox. So the Mil Design Bureau developed a “non-planetary, split-torque design” gearbox rated at 14,800 kW. The gearbox delivers the engine power to the unique eight-blade main rotor, with a diameter of 32 metres.

To meet the empty weight requirement being less than half the max all-up weight, aluminium-lithium alloys are used throughout the helicopter. The helicopter’s empty weight is 28,200 kg and its MTOW is 56,000 kg.

The prototype hovered for the first time on 14 December 1977, with production starting in October 1980. The initial production rate was thirty helicopters per year.

The Mi-26 design incorporated all the features of a modern transport aircraft. The cargo hold is box-shaped, a feature maintained throughout the length of the loading area. There are two 2,500 kg winches installed in the roof to position cargo as required by the loadmaster.

Loading is accomplished through a clamshell door and loading ramp located at the rear of a fuselage. The helicopter can kneel, thereby lowering the fuselage to ease cargo loading.

The internal fuel tanks, with a capacity of 12,000 kg, are situated beneath the cargo hold floor. Notably , the Mi-26 cargo bay is marginally bigger than a Hercules C-130’s cargo bay.

The main landing gear has sensors to measure the weight of the helicopter, displayed at the flight engineer’s workstation. The crew can observe the cargo sling loads with closed-circuit television cameras (CCTV).

The Mi-26 has a standard crew of five, being the pilot, copilot, navigator, flight engineer, and loadmaster. The navigator and flight engineer workstations are behind the pilot seats. Unusually for a helicopter, the cockpit and a four-seat passenger compartment are pressurised and the helicopter is fully air-conditioned.

The cargo compartment can accommodate 82 troops, or 20,000 kg of cargo. The Mi-26 can cargo sling a maximum external load of 20,000 kg.

The operational range, with maximum payload, is 318 nm (590 km), at a cruising speed of 138 knots.

The Mi-26 is highly regarded by users for its ease of handling, which is much contributed to by the excess of engine power.

Mi-26 Notable Operational Employment

To address the massive radiation leak from the Chernobyl nuclear disaster in April 1986 was a requirement that only the Mi-26 could satisfy. It required a cargo sling of air filters, weighing 15,000 kg each, with a cable length of 244 m (800 ft). It was a huge challenge to the aircrew and the task was successfully completed by test pilots from the Mil factory. Thirty Mi-26 helicopters were used at Chernobyl, and most of these helicopters are forever stored within the reactor exclusion zone due to radioactive contamination.

It is interesting to note that the crew of the helicopters seems to have been relatively unaffected by their heroic efforts to reduce the spread of radiation. An in-depth Wikipedia s article lists the 31 more or less immediate deaths from the disaster and it does not have any air crew members. It is speculated that while some may have suffered some delayed cancers, it was at a rate not detectable in the background cancer rate that we all risk.

Another notable deployment is that in early 2002, a civilian Mi-26 was contracted to recover two U.S. Army CH-47 Chinook helicopters from a mountain in Afghanistan.

Mi-26 Upgrade Challenges

By 2019 more than 380 Mi-26 helicopters had been built with the latest production derivative being the Mi-26 T2. The T2 is fitted with a comprehensive glass cockpit, eliminating the flight engineer and navigator stations.

In the early 2010s, upgrade plans included a new engine, being the Motor Sich D-136-2, rated at 9,120 kW to improve hot-and-high performance.

After the annexation of Crimea by Russia in 2014, the supply of engines to Russia stopped. However, a “workaround” was established to supply D-136 engines and spares to Russia, albeit on a limited scale. The supply stopped with the arrest of high-ranking officials of Motor Sich by the Ukrainian government.

The destruction of the Motor Sich engine manufacturing plant by Russian forces in May 2022 put an end to any chance of the D-136-2 or the new generation D-127, powering the upgraded Mi-26.

Even before the annexation of Crimea, the Russian Aviation Industry was tasked to develop a home-grown Russian engine. Development was slow, and a change in the preferred supplier extended the development timeline even further, with the first flight only expected in 2025.

Until the Kuznetsov PD-8V is operational, the Mi-26 fleet will be forced to fly with the original D-136 engine, sourced from existing stock. This will have a major impact on the serviceability of all Mi-26 helicopters operated around the world.

Soviet Union’s early rotorcraft development

OKB-3 (Bratukhin) designed and developed eight experimental helicopters during the 1940s, culminating in the B-11. The helicopters all featured the transverse rotor layout. The B-11 was a competing design for the Mil Mi-1.

OKB-115 (Yakovlev) developed the Yak-24 ‘Horse’ during the early 1950s. It is the only Yakovlev helicopter design that reached operational status. The paper-exercise Yak-60 is noteworthy as it was a competing design for the Mil V-12.

Yakovlev is well-known for the development of fixed-wing aircraft and more than a hundred Yak designs went into production. Russia produced 61,000 fighter aircraft during WWII of which 38,000 were built to Yak designs.

OKB-938 (Kamov) designed the Ka-22, with the first flight in 1959. The “gyrodyne” had the unique ability to change between vertical and horizontal flights. However, this change was a complicated and delicate process, which only highly skilled pilots could master.

The prototype reached a speed of 195 knots and lifted a payload of 16,500 kg. The lower part of the nose could “swing” away to facilitate loading. It was a competing design for the Mil Mi-6.

 Kamov continued developing helicopters and it fills a niche in the world helicopter market with its coaxial rotor products.

Last Thoughts

The Mil helicopter company was, and still is, highly successful. Ninety-five percent of the helicopters in the former Soviet Union were built to Mil designs.

Mil merged with Kamov and Rostvertol to form Russian Helicopters in 2006 and the Mil brand name has been retained.