If the Mi-26 did not exist in the USSR, it would have to be invented. With the advent of a rotorcraft of this class, it turned out that everyone needed it: border guards and army aviation, rescuers and builders, civil aviation and firefighters. The Mi-26 passed through Afghanistan, the Chechen conflicts, the liquidation of the Chernobyl disaster and the development of hydrocarbon deposits in Western Siberia.
The idea for the appearance of the Mi-26 came after a thorough analysis of the work of the predecessor of the Mi-6, which took to the skies in 1957 and by the beginning of the 70s already poorly met the needs of both the military and business executives.
Mi-26 in the latest modification
The tasks of transporting bulky cargoes weighing 15-20 tons over 500-800 kilometers came to the fore. Among other things, this was due to the appearance in the USSR of the heavy transport An-22, which delivered the overall cargo to the unpaved airfield, but there was nothing special to transfer to the destination - the project of the super-heavy B-12 helicopter was turned off even before it went into production. According to calculations, about 85% of all cargo for a promising helicopter should have been new and promising models of equipment for motorized rifle troops, which in some cases had to be delivered to an area located 1000-1500 meters above sea level.
Naturally, the first thought of the design headquarters was the idea of modernizing the old Mi-6 by installing more high-torque D-25VF engines. Each such engine produced 6500 hp, but in the end the payload increased only to 13-14 tons. The main reason was the ceiling of the capabilities of the Mi-6 five-bladed propeller, which, in fact, put an end to the modernization of the old helicopter.
The choice of the concept of the new car coincided with a tragic event: on January 31, 1970, Mikhail Leontyevich Mil died. Chief Designer Marat Nikolayevich Tishchenko gathered a team around him, which faced the problem of the scheme of a heavy helicopter. Three layouts were considered: the classic single-screw (the trademark of the Mil Design Bureau), the two-screw transverse and longitudinal. For example, a machine with transversely located rotors was supposed to have blades from the Mi-8. The longitudinal twin-rotor helicopter was supposed to be equipped with propellers with diameters of 23 and 35 meters. But such schemes had a couple of drawbacks - low weight efficiency and a large take-off weight, which did not fit into the terms of reference. The longitudinal layout of the helicopter, so beloved by the Americans at that time, in addition to the above, did not satisfy the engineers with the complexity of the transmission and production, as well as the vibrations that are inevitable for such an arrangement. The priority was given to Mil's classic single-rotor design with a tail rotor in the tail boom and a host of design innovations. The project received the Mi-6M index, but in 1970 it was far from the final definition of the layout. Interestingly, according to preliminary calculations, the mass of the car in all variants was close to 70 tons, and the engineers needed to reduce this parameter by 20 tons at once. How to do this, no one knew either in the Mil Design Bureau or in any other helicopter-building office in the world.
The solution to the problem was entrusted to OP Bakhov. Work in the design bureau began to boil. Competing groups of engineers were created, working on the same components, diagrams and assemblies. The main criteria were set: flight speed, weight return and reduced performance. The last criterion was proposed personally by Tishchenko. Special methods have been developed for assessing the mass of dynamic units - blades, bushings and transmission. In total, in over a year, nine layouts were developed using new design techniques.
TVD D-136 (modification AI136T) at the MAKS-2009 air show
In the summer of 1971, everything was decided - after all, a single-rotor machine with a screw diameter of 32 meters and a normal take-off weight of 48 tons was supposed to rise into the air. At the Zaporozhye engine-building plant in KB "Progress", under the leadership of F. M. Muravchenko, they began to develop the D-136 gas turbine engine, the pair of which in the Mi-26 was supposed to develop about 20,000 hp. with. Such power was required to lift 20 tons of cargo into the sky with a static ceiling of 1500 meters. The base for the D-136 was the double-circuit D-36 used on airplanes. The undoubted advantage of the new power unit was the low specific fuel consumption - only 0.196 g / (hp * h), which became the foundations of many future successes of the heavy machine.
By the end of the summer of 1971, the promising machine received the name Mi-26, the factory designation "product 90", and the design headquarters of the Moscow Helicopter Plant. Milya began to develop a preliminary project. At that time, the helicopter was the first product of the third generation, distinguished primarily by its transport efficiency, surpassing all existing machines in this parameter. The weight return reached an incredible 50% - the predecessor Mi-6 had only 34%, and the carrying capacity in general doubled. By the end of December 71, the preliminary project was approved, for further work it was necessary to involve TsAGI, LII, VIAM, NIAT, TsIAM with a lot of other small offices.
The finished draft design was presented at the end of 1972, having previously bypassed the rotorcraft being developed at the Ukhtomsk Helicopter Plant in the competition. A distinctive feature was the development of the outer skin of the fuselage by the method of defining surfaces with curves of the second order - this is how the recognizable "dolphin-like" appearance of the Mi-26 appeared. An important layout point was the location of the power plant above the cockpit in front of the main gearbox, which made it possible to balance the rather large tail of the helicopter. The engineers managed to convince the customer in the person of the Ministry of Defense to abandon heavy weapons, wheel drive, a pressurized cabin, as well as the fantastic ability of engines to run on low-quality diesel fuel. Almost simultaneously with the protection of the "sketch", they began to assemble the first model of the car in the main assembly shop of the cost center under the supervision of the deputy chief designer I. S. Dmitriev. At the same time, some points of the plan had to be corrected - the turbine unit for starting the engines was moved from the ceiling to the floor of the cockpit, the keel design was changed and the passage to the tail gearbox was “punched”. The main cockpit accommodated the commander, pilot, navigator, flight technician, and the second compartment housed four people accompanying the cargo and a flight mechanic.
Mi-26 carries the Mi-10 "flying crane" helicopter on the external sling
The cargo compartment had a length of 12.1 m, a width of 3.2 m and a height of 2.95 to 3.17 m. Any military equipment weighing up to 20 tons freely entered the womb of the Mi-26, and a similar mass was attached to the external sling … The airborne version accommodated 82 soldiers or 68 paratroopers, and the ambulance carried 60 wounded on a stretcher and three medics from the battlefield.
A separate piece of work on the Mi-26 was the development of stands for testing parts and assemblies of a promising helicopter. In general, the volume of preliminary calculations carried out by the cost center specialists was unprecedented for the domestic aviation industry. Only in this way was it possible to create a truly outstanding helicopter.
