Mi-12 Homer - Development
Everything began in the distant 1959 when the interests of the national economy and the armed forces came together, which needed the transportation of one-piece cargoes of over 20 tons with the use of vertical takeoff and landing aircraft and the Mil Design Bureau, in which the then Mi-6 heavyweights were not considered the pinnacle of progress.
The Mil Design Bureau was able to present convincing arguments in the reality of the construction of a superheavy helicopter, and on May 3, 1962, the Council of Ministers of the USSR issued a decree on the development of the V-12 (V vertolet = helicopter) with a cargo cabin similar to the cargo cabin of the giant An-22 aircraft designed by OKB OK. Antonova.
The assignment for the design of the helicopter "for the transport of non-load cargoes of 25 t" was issued, not with the aim of hitting the world or wiping the nose of the Americans. This was the most important state task. It was necessary to provide the potential for a retaliatory nuclear strike in any scenario of conflict with the United States. But in the early 1960s, rocket missile complexes were only being created, and the hope for submarines and strategic bombers in the conditions of total dominance of the potential enemy in the oceans and the surrounding airspace was rather illusive. Calculations showed that a sudden nuclear strike across the USSR would become disarming.
It was intended to be used as a complement to the Antonov An-22 heavy transport aircraft, which by operational necessity could not directly approach the battlefield. Instead of landing of the An-22 to close to the battlefield, cargo would be relayed by the giant helicopter capable of carrying heavy loads.
After the creation of the largest in the world helicopter Mi-6 the chief designer and the key personnel of OKB im. M.L.Mil by no means considered it exhausted the possibility of further increase in sizes and load capacity of helicopters. National economy and especially armed forces frequently needed the transportation of nondetachable loads with a mass of more than 20 t with the aid of the flight vehicles for vertical takeoff and landing. The first studies on the creation of the superheavy helicopter, which received designation V-12 (Mi-12), or article 65, began in OKB in 1959. After two years the chairman of State Committee for aviation equipment P.V.Dementev officially affirmed the task for the study of helicopter by load capacity 20- of 25 Tons.
The firm simultaneously examined the possibility of designing a larger machine, capable of raising loads to 40 tons, named V-16 (Mi-16).
In the same years the design of similar helicopters was conducted also at the most important American firms, but there further the stage of preliminary design the matter did not go. However, the studies of [milevtsev] convinced the government in reality of building superheavy helicopter, and on May 3, 1962. followed the decision of the Council of Ministers of USSR about the development V-12 with the cargo compartment, analogous to the cargo compartment of gigantic aircraft An-22, projected by OKB O.K.Antonov. Helicopter had to transport different types of combat materiel with a mass of up to 25 t, including the newest strategic ballistic missiles of 8K67, 8K75 and 8K82.
The deputy chief designer on V-12 was assigned N.T.Rusanovich, in 1968 he replaced M.N.Tishchenko and G.V.Remezov became chief designer. The chief flight-test engineers were D.T.Matsitskiy and V.A.Izakson-Elizar. The majorities of domestic and foreign competent authorities considered what for the helicopter of large load capacity to most rationally use a lontitudinal configuration. For studying the special features of this layout the flying station of Plant #329 obtained an army Yak-24 and acquired in the USA helicopter Boeing-Vertol V-44. With them were investigated the problem of the reciprocal effect of rotors and distribution between them of power, determination of the required power of the engines under conditions of flight, were evaluated to the possibility of flight with the slip and the like in parallel the designers of OKB M.L.Mil created the first project V-12, in which longitudinally power plants Mi-6 were located connected by the synchronizing shaft with the overlap of rotors.
Because of the danger of collision of their five-blade rotors they arranged with the minimum overlap. In connection with this the fuselage came out bulky and longer. A fundamental deficiency in the layout consisted in the fact that the air ducts of rear paired engines were located in the zone of the exhausts of front power plant - appeared the danger of the surge of engines. The analysis of the special features of lontitudinal configuration showed that it led to the low values of the service ceiling, speed and rate of climb, impossibility to continue flight with the failure of two engines and sharp worsening in the flight performances on the service ceiling and with an increase in the temperature of surrounding air, and also to a number of other undesirable consequences. Therefore it was necessary to reject the lontitudinal configuration.
On the solution M.L.Mil began a study of other layouts. Single-rotor designs were the most studied. The experience of the tests of helicopter V-7 made it necessary to exclude the layout with the blade-tip drive, which seemed initially to offer large load capacity. With the retention of the power drive the problem of the design of the main rotor gearbox became complex. Designers attempted to solve it, after arranging two main rotor gearboxes from Mi-6 one above others with the drive to one general shaft. The rotor with a diameter of 38 m was assembled of eight blades from Mi-6 on the root tips of the increased length. However, the creation of the main rotor gearbox of the layout within the limited periods proposed was improbable.
Then the idea of the free turbine of large diameter with the vertically located shaft arose. Turbine had to be located under the main rotor gearbox on the common vertical axis. The gas generator of engine was connected with the turbine by gas conductor - "Ulita". In this case the construction of the main rotor gearbox significantly simplified because of the absence of bevel gears, but the production of slow turbine with a diameter of 4,5 m required also sufficiently much time.
Therefore in 1962. the specialists of OKB M.L.Mil decided to return to the idea "of the doubling" of power plants Mi-6, but no longer on the longitudinal, but according to transverse layout. The development of superheavy twin-rotor helicopter placed before Mil a number of the complex problems, specific for the transverse layout, which moreover were aggravated by the large dimensions of the projected apparatus. As is known, precisely these problems became the reason of the failures of many talented design associations in different countries, which were being attempted to build the helicopters of transverse layout. The number of the most important specialists of the aircraft industry, including of the prominent scientists of TsAGI (Central Institute of Aerohydrodynamics im. N Ye Zhukovskiy), they considered that this layout was hopeless. Nevertheless, M.L.Mil and its adherents undertook solution of this problem and confidently defended their rightness before the competent government commissions.
With designing superheavy V-12 the designers of OKB M.L.Mil maximally considered the experience of the building of the helicopters of OKB of I.P.Bratukhin. The most difficult of the problems transverse layout there was the design which ensure minimum inductive losses from the blowing with rotors, and in also the time of rigid and durable consoles for the power plants. From the semicantilever rectangular "aircraft" wing, used on some helicopters and rotorcraft, it was necessary to immediately reject because of its large mass and significant thrust losses of rotors while hovering. It was necessary to create the cantilever truss of this construction, which would exclude the appearance of the self-excited fluctuations, high alternating voltages and vibrations, and also of other forms of the dynamic structural instability of, including one of the dangerous - air resonance of rotor on the elastic support. The probability of its occurence on the helicopter of transverse layout increased because of the presence of heavy nacelles with the engine-propeller units at the ends of the consoles, in consequence of which the natural frequencies of oscillation of construction occurred commensurate with the frequency of the rotation of rotors.
With the aid of the method of calculation developed in the OKB of design parameters from the conditions guaranteeing minimum mass and exception of the possibility of the appearance of air resonance, by the middle of 1963 the rigid and light construction of truss console with the wing was designed, whose contraction was less than one (end chord of more than root). M.L.Mil called it "the wing of reverse contraction". This solution ensured minimum wing chord in the zone of the maximum induced velocities of flow from the rotors and maximum chord near the screw axes, which decreased the losses of lift from the blowing of wing and prevented the backflow of the air flow. This form gave, in comparison with usual with wing, a gain in the payload of approximately nine tons and made it possible to provide the required load capacity. The created design concept of helicopter was designed as invention, and patents in the USA, Great Britain and number of other countries were obtained to it.
One serious task was the selection of the direction of rotation of rotors. Studies showed that for "harmonious" combination of transverse and azimuth guidance it is necessary to ensure such rotation of rotors, during which the advancing blades of rotors would be passed above the fuselage.
Studies on the dynamically similar models V-12 were conducted for checking the calculations of the rigid and frequency characteristics of the construction of the airframe. Then began the building of full-scale test bench for the finishing of the carrier system, transmission and power plant. The testings of model helicopters in the wind tunnels of TsAGI were conducted. To the developments many subsidaries were assigned.
In April 1965. the decision of the Council of Ministers about the building of the first experiment helicopter followed. At the firm M.L.Mil they considerably strengthened production and experimental bases, state was supplemented with new colleagues, while preparation for the release of the first troop series of five helicopters V, was begun at the Saratov aircraft plant. At the end the same year in the full-scale mock-up V-12 military customer investigated the possibility of positioning 36 types of heavy combat technology. In April 1966 the state commission finally approved full-scale mock-up, and assembling the first prototype began.
After the completion of assembling the first flying copy underwent frequency tests directly to assembly shop. They hung up it on the shock cords to the special portals, the imitators of blades and vibrators established on the rotor hubs. Similar basic research were conducted for the first time in the practice of world helicopter construction. They confirmed the results of the calculations of hardness and vibrations, and at the beginning of the summer of 1967 the first flying model was acknowledged ready to flight tests.
On June 27, 1967. test pilot V.P.Koloshenko for the first time raised V-12 into air from the plant area in Pankakh. But instead of applauding, those present at the factory site in Pankov outside Moscow witnessed a flight accident. The heavy machine, having made several fluctuations at a low altitude, hit the main support of the landing gear on the ground. So, at the price of the broken chassis, it was possible to detect the type of auto-oscillations of the "control system-construction" circuit, unknown before in helicopter construction. In sight of the numerous spectators, among whom was located the design project leader, the rotary-wing giant, after completing several fluctuations at the small height, "roughly" landed to one wheel. Damages were insignificant - pneumatic tire and wheel rim was destroyed; however, emergency served as occasion for the appearance in the foreign press of information about allegedly the occured destruction of helicopter. In this flight was noted the new, unknown earlier form of auto-oscillations of the type "system control - construction". They were its reasons: the kinematic constraint of control knob with the flight deck through the hand of pilot, and also the agreement of the natural frequencies of oscillation of the control run and construction of helicopter.
New dynamic phenomenon was analyzed and after insignificant structural modifications it is rapidly removed by an increase in the hardness of control system. To get rid of the defect it was possible, having made the wiring of the helicopter control system more rigid. At the same time, additional keels appeared on his stabilizer. In this form, the machine began vertical lifts in the air in December of the same year.
After these improvements, which increased also the effectiveness of control, from December 1967 began systematic lifts. The V-12 completed overflight from the plant area to the MVZ flight-test station. The entire program of plant tests was executed in the month without complications, to what they to a considerable extent contributed very good theoretical preparation and the experimental finalizing of entire project. Dynamic system did not need finishing, since with the creation V-12 were used the worked out in the operation aggregates of power plant and carrier system from the helicopter Mi-6.
In the autumn of 1968 the V-12 entered into the Flight- research institute the first stage of joint official tests. They passed satisfactorily to a strict correspondence with the program. Modifications concerned predominantly the equipment of helicopter. They were established additionally to the specially designed autopilot AP-44 the experimental autopilot VUAP-2, which more lately replaced by AP-34B1, radar "pilotage", external fuel tanks and the like furthermore, on V-12 were tested, instead of the all-metal blades from Mi-6, the new blades of composite construction - a steel longeron with the glass-plastic by nose section and the ending with the foiled honeycomb filler.
On February 22, 1969 in the course official tests the crew of V.P.Koloshenko established the absolute world record of load capacity, after raising load 31 t to the height of 2350 m, and on August 6 the same year it was fixed new salient reaching of the Soviet helicopter construction: the crew of V.P.Koloshenko on the V-12 raised load 40.2 to height 2250 m. this record it was not overlapped, until now, and hardly in the next decades will appear the rotary-wing apparatus, capable of competing with the giant, created by OKB M.L.Mil. In all on V-12 established seven world records. For the creation of the heavy helicopter V-12 OKB M.L.Mil the second time it was rewarded with the I.I.Sikorsky prize by the American Helicopter Society for the salient achievements in the helicopter technology.
The selected transverse layout and the concept "of the doubling" of power plants completely justified itself. V-12 successfully underwent all planned plant tests, carried out 122 flights and 77 hoverings. In which completely were confirmed calculated flight-performance data and the reliability of systems. It distinguished good piloting characteristics both by the switch oned and turned-off autopilot, the low required power of engines in the progressive flight, the high indices of the controllability under the conditions of autorotation, the low level of vibrations and noise, the comfort of pilot's cab. Helicopter demonstrated the ability to continue the flight of during the malfunction two engines, the possibility of a considerable increase in the load capacity with the running take-off. Despite the fact that in comparison with the predecessor the volume of cargo compartment V-12 increased 7,2, its specific weight characteristics proved to be at the level of indices Mi-6. By the distance flight Moscow-Akhtubinsk-Moscow in 1970. ended the first stage of the joint official tests V-12. At the end October of the same year state commission recommended the neglecting of it into series production.
In May - June 1971, the V-12 successfully was demonstrated in the 29th international salon of aviation and cosmonautics in Le- Le Bourget on by Paris, where it was acknowledged "as the star of salon". Then demonstration flights in Paris, Copenhagen and Berlin followed. In the foreign press they were enraptured by the new reaching of the Soviet helicopter construction: "Heaviest in the world helicopter Mi-12. darkens almost all other exhibits in Le- Le Bourget. This giant according to the sizes is more than double, and by the weight more than four times exceeded the American very heavy helicopters Sikorsky SN-53 Boeing-Vertol Chinook.
"Before the technical-engineering reaching, such as is helicopter Mi-12, it is possible to remove hat", stated the son of the great founder of the series helicopter construction I.I.Sikorsky, S.I.Sikorsky, Vice President of "Sikorsky corporation". "Development of technology teaches us that during its estimation it is not possible to use an excellent degree. Helicopter Mi-12 is one of the exceptions, which confirm rule. The discussion deals with the helicopter to the excellent degree."
Unfortunately, foreign specialists hurried to rename V-12 in Mi-12 (this designation they appropriated to a machine, as a rule, after its entering into the aviation subdivisions), since, in spite of the successful completion of the first stage of State tests and "Parisian triumph", the finishing of the V-12 was not completed. The second copy of the V-12 was assembled in 1972 in the MVZ experimental production, but for an entire year it stood in the shop in the expectation of engines. Only on March 28, 1973. it accomplished the first upsurge into air, and it they next day outdistanced to the flying station for continuing official tests. It differed from the first copy, which passed at this time sorting and flaw detection, in terms of the more rigid elements of control and as the intensive tail struts. The crew of the second helicopter headed test pilot G.V.Alferov. Understudy flew successfully, but customer unexpectedly refused to accept V-12 to the second stage (stage "B") of State tests.
In 1974. all work on the finishing of two experiment machines was stopped. The first copy V-12 remained to "eternal storage" at the plant, and the second was transmitted to the VVS museum at Monino.
It is said that during the years of creation and testing of the V-12, M.N. Tishchenko, Mikhail Mil's successor, revised his views on the B-12 and came to the conclusion that the tasks assigned to this machine can largely be solved with using a prospective single-rotor helicopter, which later became the Mi-26.
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