The history of helicopter engineering in our country has deep roots dating back to the beginning of the last century. Unfortunately, initially the USSR did not attach much importance to the development and construction of helicopters, which led to a significant lag behind the United States. Everything changed after the Korean War. Then it turned out that the Americans with high efficiency used helicopters for reconnaissance and sabotage activities. Therefore, the country's leadership ordered the immediate acceleration of the development of domestic rotorcraft.
By the mid-50s of the last century, the legendary Mi-6 was created, aka “Cow”. Until now, this helicopter is considered the champion among helicopters in terms of size and tonnage of cargo carried. But few people know that the USSR also created the B-12 helicopter (also known as the Mi-12), the carrying capacity of which was supposed to exceed that for the legendary “Cow”!
Brief information about creating a machine
After the creation of a truly gigantic Mi-6 helicopter, all the leading engineers and designers of the design bureau, headed by M.L. Milem, continued to believe that the possibilities of increasing the size and weight of rotorcraft were far from exhausted. In addition, the army and the national economy, like air, needed new aircraft. The direction of their take-off was supposed to be vertical, and the ability to carry goods - 20 tons or more. By a decree from above, Mil Design Bureau was given a carte blanche to develop a new helicopter, the creation of which started in 1959.
In 1961, the official terms of reference were published. It assumed the creation of a helicopter capable of lifting loads weighing at least 20 or 25 tons. But even the B-12 helicopter is far from the limit of the demands of the Soviet military and landowners. So, at the same time, a variant of the machine capable of lifting 40 tons of cargo (V-16 / Mi-16) was being worked out at the OKB. Note that similar projects were worked out by the Americans, but they didn’t get any further than the sketches. But the work of Mil OKB finally convinced the CPSU Central Committee of the reality of creating such a helicopter.
In 1962, the terms of reference were once again finalized. Engineers were instructed to focus on creating a helicopter with a cargo compartment, similar in characteristics to that of Antonov Design Bureau aircraft. It was assumed that the new machine will also be used for long-distance transportation of various military equipment, including 8K67, 8K75 and 8K82 ballistic intercontinental missiles . That's what the Mi-12 was created for, a helicopter mainly for military purposes.
First layout options
Almost all domestic and western helicopter-related luminaries believed that a well-studied and well-proven longitudinal scheme would be best suited to create such a helicopter. In order to study its capabilities, the Yak-24 was taken from the army. And in the USA, for this purpose, they purchased a Boeing-Vertol V-44. It was on their example that engineers in real conditions investigated the problems of the mutual influence of rotors. Specialists needed to find out how two engines behave at once in different flight and operating conditions, how it is most advantageous to use all the advantages of the longitudinal scheme, while avoiding its main disadvantages. Synchronous screws became a feature of B-12. Since the tests revealed a real danger of overlapping load-bearing elements, they had to be positioned with minimal overlap. For this, I even had to sacrifice some of the aerodynamic qualities of the new car.
As a result, the fuselage completely ceased to meet the requirements of the technical specifications, as it became too large and bulky. But even this circumstance was not the main drawback of this design. The main and fatal miscalculation of the engineers was that the air intakes of one group of engines were almost close to the exhaust openings of the other. Already during the tests it was found out that the engines in such conditions are prone to the development of surging. And this in real flight conditions is fraught with stall and instant loss of controllability. Thus, the Mi-12 is a helicopter, during the development of which the designers faced numerous difficulties.
In addition, further analysis of the longitudinal pattern led to disappointing conclusions: it does not allow reaching the maximum possible flight ceiling. The speed and weight of the load lifted were also not up to par. It was also found that if two of the four engines failed, the car would fall into free fall. And it was proved that when reaching the flight ceiling and when flying at low temperatures, the power of the motors decreases sharply. That is why the designers unanimously decided to abandon the longitudinal scheme.
Continued research
M. L. Mil himself proposed a close examination of the prospects for other fuselage design schemes. First, experts proposed the use of a well-studied single-screw layout. But in subsequent tests it was found out that the scheme with a jet drive of the rotor would have to be abandoned (due to excessively large dimensions). But the mechanical drive turned out to be a catch. In the process of testing, it turned out that the design of the gearbox is too complex. At first, they tried to cope with the problem by taking two conventional devices from the Mi-6 and placing them on one bearing shaft.
In order to unify, the engineers even used standard Mi-6 blades for the construction of the screw. At the same time, only butt-shaped tips of a longer length were used. So the B-12 (helicopter) tried to unify as much as possible with the rest of the equipment in order to reduce the cost of its creation and maintenance. Alas, in a timely manner to create something like this was almost impossible. It was then that the decision was made to begin manufacturing a freely located turbine with a vertically directed shaft. She was placed directly under the main gearbox. The gas generator was connected to it through a special gas pipeline.
In this embodiment, the structural essence of the turbine itself was greatly simplified, since it no longer required bevel gears. The problem was that the manufacture of a low-speed gearbox with a diameter of just over four meters is also an extremely difficult task. After all, the latter had a tendency to self-destruction. It is possible, incidentally, that the helicopter crash in Syria (04/12/16.) Occurred precisely because of the failure of the motor gearbox.
Approach to the transverse structure design
Faced with all these specific difficulties, in 1962 the Mil Design Bureau specialists finally decided to abandon the idea of “single-engine experiments”. They again returned to the scheme with two engines. True, this time it was decided to work out a variant with a transverse arrangement of motors. This is exactly what the "12" helicopter became, the photo of which is in our article.
Of course, in this case, there were some complicated problems. All this was compounded by the fact that no one had ever built helicopters of such sizes in the world. Accordingly, the Soviet engineers had to take on the hard work of the pioneers. However, scientists in Western countries have repeatedly tried to create rotorcraft precisely according to this scheme. But over and over again they failed.
Even a number of domestic experts from TsAGI believed that it was not worth messing around with the transverse arrangement of motors. Mil himself and his colleagues were not at all scared. Competent specialists confidently created the first draft and substantiated its viability before the government commission. After that, the largest helicopter in the world, the Mi-12, received a "ticket to life."
Vibration control
Again, the team fully took into account the invaluable experience accumulated by the OKB I.P. Bratukhin's employees. The most difficult was the design of a fairly lightweight and durable consoles rotor groups. The variant with the classic rectangular airplane wing had to be discarded immediately, since with the required dimensions of the helicopter this part of the structure was unnecessarily heavy and cumbersome. It was required to create a console that would be completely spared the problem of spontaneously occurring wandering vibrations, as well as other instabilities. But the most dangerous was the possibility of developing dynamic air resonance, which was especially susceptible to screws on an elastic base. Because of this, the B-12 helicopter, the characteristics of which we describe, had every chance of falling apart in the air.
When the work with the first prototype was completed, the initial tests were decided to be carried out directly in the workshop, so that some gross flaws, if any, could be fixed right away without wasting time. To achieve the effect of flight, special dynamic cords and vibrators were used that simulate the resonant sensations that occur when the screws rotate. It should be noted that even for this invention of all employees alone it was safe to reward, since nothing like this had been done before in the global aircraft industry. Soon, test results confirmed the correctness of all calculations. And already by 1967, the helicopter was recognized as fully prepared for real flight tests.
Basic characteristics of the helicopter
So, the B-12 helicopter was a four-engine transport vehicle built according to the revolutionary transverse scheme. Propeller groups were borrowed from the Mi-6. They were mounted on the long ends of the consoles. Unfortunately, this solution was not entirely correct, since the Mi-6 screw, which also did not differ in particularly small sizes, was clearly insufficient. I had to force the engines. More precisely, the Solovyov Design Bureau created a separate version of the D-25F motor, the power of which was immediately increased to 6500 liters. from. I had to tinker with the wings, which, to ensure the best aerodynamic performance, were given a V-shaped section.
Directly in the center section, a revolutionary design gearbox was installed, which was used to break the transmission shaft. Its uniqueness was not even in the excellent synchronization of all the screws, but in the excellent work of the swashplate and the ability to distribute the voltage so evenly that it was allowed to fly even with two failed engines on one side! Fuel was pumped both in wing and in separate mounted tanks. The effectiveness of such a solution was proved when the world's largest Mi-12 helicopter made a one-time flight from Moscow to Akhtubinsk.
Fuselage characteristics
The fuselage was manufactured according to the conceptual scheme of a semi-monocoque. As one of the foreign experts who was allowed to inspect the helicopter aptly put it, inside it looked like a “giant Gothic cathedral”. The entire front part was occupied by the cockpit, which was two-story and provided unprecedented comfort for pilots at that time. In total, the crew had six men. And four of them were located on the first floor, the rest - on the second. The tail section had a descent power gangway and closing flaps.
This design made it possible (with the help of powerful electric winches) to lift even light tanks aboard, without putting much effort into it. After all, the B-12 helicopter, whose purpose was purely military, was obliged to have such an opportunity. About 200 soldiers in full dress or 158 wounded (provided that no less than ¾ were on a stretcher) could be accommodated in the huge central compartment. Under the fuselage was the tail, made like an airplane, equipped with elevators. Particularly important was the rudder, which can significantly increase the accuracy of control of the rotorcraft in flight. He worked through a synchronizer at the same time as the mechanism controlling the pitch of the screws.
In general, the control circuit of the V-12 has since remained typical for all helicopters with a transverse structure. So, the lifting force was regulated precisely by changing the pitch of the rotors. It also allowed controlling the skew of the helicopter. The machines were responsible for the longitudinal balancing indicators, in a cyclic step (by changing its indicators) it was possible to correct the direction of the helicopter.
Reliability is first and foremost!
The entire helicopter control and wiring system was designed taking into account possible deformations and high rates of friction. That is, the emphasis was immediately placed on wear resistance. It was designed in two cascades. So, there were basic and additional hydraulic amplifiers, as well as many automatic synchronizers, greatly simplifying the control of a helicopter with four engines. The main hydraulic system was located in the same compartment as the main gearbox. The most important amplifiers, in addition, were powered by backup systems located in the right and left engine nacelles. There were three hydraulic systems in total. Each of them was not only completely autonomous, but also duplicated separately. In short, the largest helicopter in the world, the Mi-12, was also the most reliable.
The chassis of the car from the moment of the first sketches was offered three-support. Under the left and right farms, respectively, had their own racks. Under the cockpit was the main one. For the first time in the domestic aircraft industry, shock absorbers of the “hybrid” type were used: on hydraulics and pneumatics. In addition, there were auxiliary tail supports that were involved in loading heavy equipment. Fundamentally new navigation systems have been developed for the new helicopter, which allow charting in the most adverse weather conditions. In addition, there was an autopilot and a system that automatically corrects the rotational speed of the screws. So the helicopter V-12, the design of which we describe, can be safely ranked among the most advanced examples of technology.
First flights and start of testing
At the end of June 1967, the car first flew into the air. It should be noted that already in the first flight it was found out that there is a different, special system of oscillations, when the vibration was transmitted directly to the controls. This was due to miscalculations of designers who, through a direct kinetic connection, connected control and engine drives. Because of this, the giant who had just taken off in the air was forced to make an emergency landing. All defects were quickly analyzed and eliminated by increasing the overall rigidity of the structure. So, the B-12 helicopter, the advantage of which was a tremendous payload, was completely rehabilitated.
It should be noted that the advanced four-engine transverse circuit fully proved itself in the course of further tests. In total, the helicopter flew 122 times. Another 77 times for a long time hung in the air. The reliability of the systems and the high pilot qualities, originally laid down in the calculations, were fully confirmed. The pilots were delighted with the simplicity of controlling a huge machine. And the military was surprised at the low voracity of the engines.
There is evidence that flight tests were conducted on two engines, which the machine also successfully passed. But the main triumph of the designers was the fact that with weight dimensions close to the Mi-6, the helicopter had a load capacity increased by 7.2 times! Thus, the V-12 helicopter (manufacturer - OKB Mil) had every chance of a successful “career” in the USSR Air Force. In 1970, he made a flight from Moscow to Akhtubinsk and vice versa, after which state tests were considered successful. At the end of the year, a special commission recommended the launch of the helicopter in a series. So why is there no B-12 in the sky of modern Russia? The helicopter, unfortunately, turned out to be unclaimed.
End of story
During the verification process, some design flaws were revealed, due to which its refinement was greatly delayed. In addition, the second copy of the helicopter from 1972 to 1973 stood in the hangar, as suppliers delayed the manufacture of engines. He differed from his brother in a much more rigid structure and reinforced controls. Unfortunately, for a number of reasons, in 1974, the program for the creation and development of a unique helicopter was completely curtailed.
Despite its unique characteristics, the V-12 helicopter did not enter serial production and operation. First, originally created for the transport of heavy ballistic missiles, it has lost its “target niche”. Heavy self-propelled systems have been developed. Secondly, the very concept of rocket-based missiles also underwent dramatic changes due to a sharp increase in their power. It was not necessary to bring them closer to the territories of the potential enemy.
Thirdly, some of the ICBMs being developed simultaneously with the B-12 and specially designed for it turned out to be frankly unsuccessful and were never adopted. In other cases, it was much cheaper to send military cargo on the ground. Fourth, the plant in Saratov, the only one on which it was possible to deploy equipment for the production of helicopters as soon as possible, since 1972 has been “over the head” loaded with other state orders. There was simply no production capacity left.
Total
Thus, the B-12 is a helicopter, which in many ways was ahead of its time, but ended up "in the wrong place." If such a machine were created in the early 60s, then, most likely, work would definitely be found for it. Priorities changed in the 1970s, and the unique design was unclaimed. But the B-12 helicopter, the history of which we described, gave the pilots invaluable experience.