The Soviet Union was one of the first in the world to create heavy four-engine bombers. In the early thirties, TB-3, created by A. N. Tupolev, ascended into the sky. In the mid-30s, this four-engine giant was considered a miracle of its time. Not a single country in the world then had anything like this in service, and hundreds of such machines sailed over Red Square on holidays. These giants were rightfully called airships and even "air battleships". The all-metal TB-3 was made according to the advanced technology for that time - with corrugated aluminum skin, the strength and rigidity of which was significantly higher than that of smooth sheets. But such a cladding also had a significant drawback: it sharply increased the resistance due to the large area of the so-called “wetted” surface. "Corrugations" significantly reduced the range and speed of flight.
For its time, the TB-3 heavy bomber was certainly good, but by 1933 it became clear that with the rapid development of aviation, this aircraft would become obsolete in a couple of years. By this time, the ways for the further development of aviation had already been determined. The advent of wing mechanization, retractable landing gear, and powerful aircraft engines created conditions for increasing the specific wing loading and thus for a sharp increase in the maximum flight speed. The world level of production technology made it possible to switch from trusses with corrugated sheathing to semi-monocoque ones with smooth airframe sheathing.
Therefore, it is not surprising that in 1933-1934. In the midst of the serial construction of the TB-3 aircraft, the idea arose to overhaul the aircraft or release a new one on its basis in order to achieve a significant improvement in its performance in the light of new requirements.
In 1934, at plant number 22, during the serial construction of the TB-3, it was decided to overhaul the aircraft so that it would meet the new requirements. At this time, the team of V. M. Petlyakov under the general guidance of A. N. Tupolev began the development of a heavy four-engine bomber TB-7, and Tupolev did not consider work on the development of TB-3 promising for himself. Therefore, plant No. 22, on its own initiative, supported by the commander-in-chief, invited a group of teachers and engineers of the Air Force Academy (about 20 people) to carry out this work. The group was headed by Professor of the Academy Viktor Fedorovich Bolkhovitinov; the group included MM Shishmarev (design and strength calculations), Ya. M. Kuritskes (aerodynamics), and others. Later, on the basis of this group, the OKB was organized. When creating a bomber, it was necessary to meet very stringent technical requirements: speed - not less than 310 km / h, service ceiling - 6000-7000 m, payload - up to 5000 kg.
The influence of TB-3 of the late series was outwardly quite sensitive, and V. F. Bolkhovitinov considered the new car precisely as a development of the TB-3. But at the same time, the designers tried to find use in it for all the aircraft-building innovations of that time. The fuselage was not a rectangular cross-section, but a semi-monococcus. In order to save weight, the wing was made one-piece, although the design of the spars was almost entirely borrowed from the TB-3. Engines - four AM-34RNB. Chassis - foldable into large fairings. The initial armament consisted of four ShKAS turret machine guns and one BT machine gun, but in the future they were planned to be replaced with six ShKAS and a ShVAK bow cannon. Bomb load - 5000 kg. An APR-3 radio direction finder was installed on the DB-A. The project involved the installation of the AVP-10 autopilot. Communication between the crew members was carried out using pneumatic mail and an aircraft intercom. To ensure landings at night, the aircraft provided for the placement of underwing torches.
Work on the design and construction of the aircraft, which received the name DB-A (Long-Range Bomber - Academy), was carried out promptly, and already in November 1934 the prototype was ready. Its maiden flight took place in May 1935. Factory tests were carried out from the end of 1935 to March 5, 1936. They showed that the DB-A with four AM-34RNB engines had significantly higher flight characteristics compared to the TB-3, from which it hardly differed in design and size. These characteristics were achieved thanks to the improvement of the general aerodynamics of the aircraft, in particular, the use of smooth skin, semi-retractable landing gear, closed cabins and shooting installations, as well as due to the internal suspension of bombs. With a flight weight of 19500 kg, DB-A could perform horizontal flight on two engines at an altitude of 2500 m, on three engines the ceiling was 5100 m. DB-A had a very high aerodynamic quality - its value reached 15 units. Thus, the calculations of the designers were fully confirmed, and the speed achieved during the test was even higher than the assumed one - 330 km / h, by 40 km / h. At the same time, the increase in speed also had a shadow side: the load on the rudders increased sharply. The car, which appeared at the junction of two eras of aircraft construction - ending the period of giants-slugs and beginning the era of aerodynamically clean high-speed aircraft - remained too many traditional solutions. Of course, the control system DB-A lacked the boosters-hydraulic boosters that appeared much later, and in order to solve this problem, cable pulleys were introduced into the aileron control system based on the test results.
The success of the DB-A was undeniable, and it was decided to use the modified version of this aircraft to establish various records. On November 10, 1936 pilots M. A. Nyukhtikov and M. A. On May 14, 1937 pilots G. F. Baidukov and N. G. Kastanaev with navigator-radio operator L. L. with a test load of 5 tons, setting two international speed records of 280 and 246 km / h at distances of 1000 and 2000 km with a load of 5 tons.
The results of the records and the excellent characteristics of the machine suggested that it be used for a transarctic flight - across the North Pole to America. In early June 1937, Baidukov introduced the famous pilot of the Hero of the Soviet Union S. A. Levanevsky to Bolkhovitinov and to the leading factory test pilot DB-A Kastanaev, who agreed to show the car in flight right there. Dressed with a needle, with an attentive and intent gaze, Levanevsky gave the impression of a well-mannered aristocrat. While preparations were underway for the flight, he was very restrained and silent. Kastanaev lifted the plane, gained altitude, then dived to gain speed and over the airfield, at a low altitude he laid a very sharp turn - he put his wings almost perpendicular to the ground at an angle of 90 degrees. Having deafened the airfield personnel with the roar of four forced engines, he steeply went up. The plane was empty, refueled for demonstration purposes only. Kastanaev easily succeeded in spectacular figures unusual for a heavy bomber. Watching the flight, Levanevsky was transformed. Nobody expected such a violent reaction from the silent guest. The plane had not yet landed, but Levanevsky was beaming, radiating delight and literally rushed to Bolkhovitinov: “Give, give me this car! Show this to the Americans! They never dreamed of it! " Indeed, the Americans did not have cars of this class. They have just begun to create the first "flying fortress" - "Boeing-17". Levanevsky knew very well the American technology of that time. Seeing such a heavy and elegant plane in the air, he realized that this “novelty” could surprise anyone.
For a record flight, the aircraft was equipped with new AM-34RNB engines, which passed two-hundred-hour bench tests and assigned the polar aviation index N-209 to it. During the training period, the crew performed a test flight along the Shchelkovo - Baku - Shchelkovo route. At this stage, special attention was paid to practicing takeoff. The fact is that for such a long-distance flight, 16.4 tons of fuel were required (which was almost twice the norm), and the total mass of the aircraft exceeded 34.7 tons. With this reserve, the DB-A could fly about 8440 km.
All work was completed by August 1937. Judging by the memorandum of the director of the aircraft plant, the plane was thoroughly prepared for flights in the Arctic. They even installed an anti-icing system, with the help of which the propeller blades were washed with alcohol. The composition of the crew was also approved. The commander of the ship was S. A. Levanevsky, the second pilot was N. G. Kastanaev, in the recent past, test pilot of the Research Institute of the Air Force of the Red Army, the navigator was the famous polar explorer V. I. Levchenko, the radio operator was the engineer of the Research Institute of the Air Force N. Ya. Galkovsky, flight mechanic - engineer N. N. Godovikov, second flight engineer - G. T. Pobezhimov.
On a quiet August evening in 1937, a four-engine Soviet airship DB-A took off from the Shchelkovo airfield and headed north.
The flight proceeded normally for almost a day (8:17 pm). Radio communication between the command post and the aircraft remained stable and was carried out in accordance with a previously agreed plan. The only alarming thing was that, starting from the middle of the Barents Sea, the plane was sailing in overcast conditions. After passing the North Pole, Levanevsky directed the car along the 148th parallel, in the direction of the city of Fairbanks in Alaska.
At 14 hours 32 minutes, a radiogram was received, in which it was reported that due to damage to the oil line, the rightmost engine was out of order. Then the connection deteriorated sharply. Over the next three hours, two more radiograms were received at the command post. From them it was possible to understand only that the flight continues. Then the connection was cut off completely …
Despite the undertaken large-scale searches, in which 24 Soviet and 7 foreign aircraft participated, no traces of the missing expedition could be found. Only nine months later, in May 1938, the government commission decided to stop further searches.
But work on the long-range bomber VF Bolkhovitinov continued. In March 1936, a new DB-2A aircraft entered for testing. On the second DB-2A aircraft were installed: new forced AM-34FRN engines with turbochargers and variable pitch propellers, a fully retractable landing gear (without "pants"), a new central tower installation and two additional ShKAS machine guns in special cabins located in engine nacelles, which provided a circular fire. In addition, the cockpit was made higher to improve visibility. The bomber's crew increased to 11 people. The second copy developed practically the same speed as the first, and its flight weight reached 28 tons. The power-to-weight ratio of the machine made it possible to freely fly even with one engine off at a speed of up to 292 km / h. The practical ceiling of the DB-2A turned out to be close to the calculated one - with a flight weight of 21.5 tons, it was 5100 m. In 1938, after eliminating a number of shortcomings and replacing engines with AM-34RNV, state tests were completed, and the aircraft was recognized as promising, and since the appearance of serial TB-7 was delayed indefinitely, Bolkhovitinov's bomber was recommended for serial production.
As a development of DB-A, in March 1936 Bolkhovitinov developed a project of a BDD aircraft with four M-34FRN engines of 1200 hp.sec., wingspan - 36.2 m, length -26.0 m, wing area - 180 m2, pressurized cabins, flight weight - 20,000-27,000 kg, weight return - 38%, specific wing load - 111 - 150 kg / m2, at a power of 5-6, 7 kg / l, s., Speed at the ground-350 km / h, at an altitude of 4000 m - 400 km / h, at an altitude of 8000 m - 460 km / h, ceiling - 9, 0-11, 0 km, time to climb 5000 m - 10, 5 min, 8000 m - 17, 4 min.
In December 1939, tactical and technical requirements (TTT) were developed for the TK-1 heavy cruiser - a modification of the DB-2A with four M-34FRN engines, with powerful weapons (3 ShVAK guns, 5 ShKAS machine guns and 8 PCs) with unprecedented ammunition (3 thousand shells and 11 thousand cartridges). For a similar TK-4 aircraft, the following were assigned: a crew of 11 people, bombs - 5000 kg and an flight weight - from 16880 to 23 900 kg. But all these machines never made it out of the design stage.
In 1938, a series of 16 DB-A aircraft was laid, of which 12 were delivered in 1939. The installation of new engines and additional equipment by almost a ton increased the mass of production vehicles - while the center of gravity shifted forward, which improved the longitudinal stability of the vehicle. Unfortunately, the engine builders did not fulfill their obligations - the M-34FRN engine did not develop its rated power. And yet the speed of the bomber reached 346 km / h at an altitude of 6 thousand meters, he could freely perform turns with a roll of up to 60 °.
At the same time, all the upgrades and improvements that DB-A underwent could not bring its data in line with the dramatically changed requirements for this kind of machines. Built at the junction of two eras, the long-range bomber carried too many outdated concepts. The heavy bomber TB-7, built at the A. N. Tupolev Design Bureau by the brigade of V. M. Petlyakov, became a machine that fully meets the new conditions. Nevertheless, the TB-7 aircraft was difficult to manufacture, it was produced with long interruptions, was taken out of production twice and was restored again. The total number of TB-7s built and the pace of its production could not satisfy the USSR Air Force in any way, therefore the possibility of producing several more series of DB-2A was repeatedly considered. And the last time the question of resuming the production of DB-A was raised in 1942. Serial DB-2A did not take part in hostilities. In mid-1941, four aircraft were evacuated beyond the Urals, for some time using them as military transport vehicles.
References:
Yakubovich N. At the junction of epochs // Model-constructor.
Yakubovich N. Long-range bomber "Academy" // Wings of the Motherland
Shunkov V. Red Army.
Yakubovich N. Academic bomber // Wings of the Motherland.
Kaminsky Yu., Khazanov D. Grave cross // Aviamaster.
