M-50/M-52 Bounder - Design
According to the task, "the 50th" had to reach a speed of 1,800 km / h at cruising -1500-1600 km / h at altitudes of 14-15 km. Practical range system with a bomb load of 5000 kg was estimated at 13,000 km. It took about a year to prepare the preliminary design, but already in the summer of 1955, the line of work on "50" had changed dramatically. It now required a "clean" long-range bomber with increased cruising speed, calculated with four turbofan engine NK-6 or HP-9 turbojet. The March 1956 government decree set THD M16-17. The designers of DB-23 spared no effort for optimal aerodynamic design of the aircraft.
In wind tunnels 39 different models wer tested and the results clearly favored a canard ["duck"] layout. The “duck” type scheme was revived, according to which aircraft were built at the dawn of aviation technology, such as the first Flyer of the Wright Brothers. Historically, this term covered aircraft with canards equipped with elevator. Unfortunately, this is not explained to students aviation universities. As a result, not only in periodicals, but in special documents, there appears the "newspaper duck" - airplanes, whose canards used either to improve the landing characteristics, or to balance the machine. This control in the pitch channel by means of elevons.
A canard system in aerodynamics is considered one of the most difficult, and therefore its preliminary testing by DB-23 occupied about a year. This was a huge period of disputes, construction models, queuing in wind tunnels, and finally analysis of the materials. It seemed that the final shape of the aircraft had matured, but the designers settled on the classical scheme with a triangular wing with a relative thickness of 3.5%. The reason is not in any tradition or inertia of thinking, and the unwillingness of management TsAGI deal with this problem. At the suggestion V.A.Fedotova, one time head of the firm, and Yu.E.Ilenko, two engines placed on the pylons under the wings, and two on the wing tips.
When creating a new aircraft, there are always a lot of questions to answer, so it is necessary to conduct scientific research. The creators of the M-50, not having analogs, tried to combine seemingly incompatible requirements. At high speed turbojet engines of those years were required to provide not only high supersonic speed, but also a huge range. For plans to become a reality, the designers decided to reduce the crew to two people, leaving the pilot and navigator located in an armored cab. The seats of the crew were one after another, in tandem, with the landing and bailout (in the fashion of those years) carried out through hatches in the bottom of the fuselage.
To solve problems arising in flight, it was necessary to completely automate the aircraft and its management, putting, in fact, the two-person crew in control of the flight. It used as a backup hydromechanical control, in which the translational movement of the pedals and steering column converted into rotational and passed through a high-speed shafts are driven by hydraulic actuators to the rudders and ailerons. If necessary, the design provided for transition to manual control at any stage or flight mode. For motor control, probably the world's first used-wire system with triple redundancy was used. This wager on automation meant that the existing hardware components all benefiting from it would negate the weight of equipment and power sources. To get out of the vicious circle, the heads of the radio-electronic industry were tasked to accelerate work on the miniaturization of equipment. Airplane people in turn proposed to use three-phase alternating current on the aircraft instead of the traditional sources of DC Generators.
The plane featured, in modern parlance, a flight and navigation system. The equipment consisted of three radio stations: connected "Planet" team - RSIU-3M and emergency - "Cedars-C". In addition, the board had an SPU-6 intercom, PB-5 and PB-25 high and low altitude altimeters, SRZO-2 interrogator-transponder, "Sirena-2" tail protection station and more.
The future M-50 was calculated to fly in the speed range of the landing 270km/h to 2,000 km/h at an altitude of 16000m on a range (with refueling in flight) to 15000km. Maximum take-off weight of the aircraft at startup accelerators reached 253 tonnes, of which the share of fuel was 170 tonnes. In flight, could be carried out at least two refueling sessions, the first of which was scheduled for removal of about 2000 km from the aerodrome of departure. At the same time in all modes it was required to ensure sustained and controlled flight. The result is the all-moving tailplane.
Those familiar with aerodynamics knew that in the transition from subsonic to supersonic flight, the aerodynamic center of pressure of the wing is shifted toward the tail. This effect, which often led to disaster of the first jet aircraft, forced a search for new ways to preserve the required reserve longitudinal stability. So there was a proposal to change, depending on the flight conditions, the center of gravity of the aircraft by pumping fuel from one tank to another group.
On M-50 for the first time in the USSR, an automatic control system of the center of gravity in flight by pumping fuel between the fuselage and wing groups caisson-tanks was used. The need for this arose because the transition to supersonic flow over the wing pattern changes, and the center of pressure (conditional fulcrum net lift) moves back, leading to the appearance of diving moment. Without pumping fuel compensation diving moment would require increasing the size of the horizontal tail and, accordingly, would have led to an increase in aircraft weight and drag. The author of this decision was L.Minkin. On the M-50 supplementary fuel poured into the empty tanks from pressurized compartments of the fuselage and wing. This solution, applied for the first time on M-50, then became in widespread use at supersonic machines, including Tu-144 and the "Concord".
"Working on the project M-50" recalled L.L.Selyakov, "with problem solving to create a fully automatic flight control systems on almost "neutral" plane, I insisted on the incompatibility of large, bulky arms control, which was a traditional steering column with fully automatic system. I suggested creating a control unit with a handle on the type of existing "drill" autopilot handle by which the navigator guides the plane to the target. Requirements for TsAGI were the need for strict compliance with the standards for the efforts and strokes per unit overload when creating automatic control systems completely unnecessary and harmful. Unfortunately, TsAGI prevailed, Myasischev did not support me, and the system Absu-50 performed with classical motion and demanded efforts ..."
Initially it was assumed that the area of managed stability did not exceed 5% of the area of the wing. It was believed that once the stability margin is small, the need to manage and moments will be small. However, it soon became clear that in the case of a device failure artificial plane centering on a number of modes lies in the region of instability. Landing "50" in this case was decisive, and the area of the horizontal stabilizer increased twice. Using a central keel helped reduce its area, weight, aerodynamic drag and improve the behavior of the aircraft on takeoff and landing in a crosswind.
Through the use of electronics, one of the nation's first achievements on the M-50 heavy bomber was reducing the crew to two people. Pilot and navigator sitting one behind the other in the forward fuselage. This innovation allowed to save several tons of aircraft take-off weight, limiting its 210,000 kg.
Bomb weapons with a maximum mass of 30 tons were located in the cargo compartment, where it was also planned to suspend the M-61 guided missile with folding wings, with a launch range of up to 1000 km (it was also created in the Vladimir Myasishchev Design Bureau).
What to do if airfields are destroyed by the enemy? This issue had become one of the main problems in military aviation. New supersonic aircraft could no longer take off from the dirt strip and demanded a good and long concrete strip, too vulnerable to enemy attacks and requiring a long repair. This attracted attention to the development of vertical takeoff and landing aircraft. But the problem of destroying runways affected not only tactical aviation - atomic weapons made it possible to easily “out of the game” even one of the largest airfields of strategic aviation, and the development of missiles made even the deepest bases vulnerable. This problem was solved in two ways: projects of strategic amphibian bombers were developed, the runways of which could not be destroyed, on the other hand, the possibility of ensuring the take-off of bombers without a long take-off was investigated. These works went on both sides of the ocean. So in 1960, the Myasishchev Design Bureau conducted research to ensure fast take-off for the supersonic bombing of the M-50. In total, several launch options were worked out, most of them were supposed to use rocket boosters or other special acceleration devices. M-50 with rocket boosters in a transport vehicle was supposed, with the help of machines, to ensure the mobility of bombers and their launch from almost anywhere. In addition, the cars provided a slight additional acceleration. Use for dispersal of a bomber of a hydrocart and rocket accelerators. This design allows the use of a conventional bomber to take off from the water, without the need to develop special strategic seaplanes. Later, the development experience of the launch system for the M-50 was already used in the M-52 project, for which a point-start scheme (detaching an aircraft from a place without acceleration) using rocket boosters with a total thrust of up to 360 tons was created.
Lack of practical experience of piloting aircraft with a delta wing led to the creation of analog simulator in which test pilots acquainted with the management of future machines, while studying their flight.
Despite all the measures taken to reduce the weight of the airframe, production did not meet the specified limits, which led to an increase in weight of the structure that helped a little application for the first time in domestic practice of seamless, followed by milling, the cladding panels. manufacturing techniques mastered many elements only and it is not surprising that some of them weighing four tons of billets had to make weight 40 tons All these costs weigh down the aircraft.
Previously used and proven technical solutions, such as a bicyle landing gear, slotted flaps and many other things, previously tested on the M-4 and 3M, allowed performing takeoff at angles of attack greater than at the beginning of the takeoff. To reduce the roll-out distance after landing ski brakes were provided.
Originally the aircraft was created as a means to deliver bombs, but early on the designer tried to hang cruise missiles, in particular, to develop a planning bureau in the rocket "45B". In 1958, A.D.Nadiradze proposed to equipe the M-50 with ballistic missiles.
Particular attention was given to the engines. Because of them, largely depended upon whether the aircraft reaches a pre-determined speed and the design range. It was very important that the specific fuel consumption at cruising does not exceed 1.12 kg / kgf.h. Only in this way was is possible to obtain a predetermined range. The M-50 was originally designed with four turbofan NK-6 turbojet or WD-9A, and then the next Council of Ministers decree they were replaced by engines P.F.Zubtsa M16-17 (RD16-17). By the beginning of 1961, the NK-6 was the most powerful Soviet turbojet. In the dry weight of 3500 kg, it was calculated the original thrust augmentor was 22000 kgs. High performance to a large extent was achieved by higher turbine inlet temperature to 1130 K. In November 1960, at the stand it demonstrated 22400kgs thrust with a specific fuel consumption at afterburner 1.72 kg / kgf.h. However, it soon became clear that to ensure 50-hour operating life, it would be necessary to reduce thrust augmentor to 19,000 kg, and maximum - up to 13000 kg.
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