The high-altitude experimental aircraft project began in 1935. The BOK-7 or SR (from the Russian acronym for Stratospheric Reconnaissance Plane – Стратосферный Разведчик – СР) was designed based on experience gained with the BOK-1 and was generally similar to the BOK-1.
Originally conceived as a stratospheric reconnaissance aircraft, it ended up being developed as a record-setting aircraft. It began to be projected in 1935 as a development of the BOK-1.
The BOK-7 was designed as a stratospheric reconnaissance aircraft, hence its name SR (Стратосферный Разведчик), capable of photographic reconnaissance at heights of 14 – 16 km. Because it was designed as an airplane for military use, it was decided to equip it with weapons. The BOK-7 was designed with two ShKAS machine guns in the wings and two other machine guns defending the rear hemisphere. The possibility of transporting 400 kg of bombs was also envisaged.
In 1937 these original plans were modified. It was decided to build two copies as a development of the BOK-7, the first intended to establish a world height record and the second in the military version, originally known as BOK-8.
The BOK-7 from the structural point of view was designed similar to the BOK-1. The main difference was that in this new model the airtight cabin was designed as an integral part of the aircraft structure. Two domes with several skylights protruded above the fuselage, one located over the pilot’s station and the other over the observer’s position.
The initial project envisaged the use of a fixed landing gear with trouser-type fairings, but during development a similar gear was returned to that used in the BOK-1, with drop-type fairings on the wheels.
Until mid-1938 the construction of the BOK-7 was developed at Factory No.35 in Smolensk. Then, with the decision to transfer the BOK to KB-29, the unfinished plane was transferred to the Moscow suburb of Podlipki. In September 1938 Alexander Alexandrovich Mikulin delivered the AM-34FRN engine with two turbochargers requested for its structure, with which the assembly of the aircraft was completed. On December 20, the construction work on BOK-7 was completed and on the 28th of that month a first short-duration straight-line flight took place.
There is no data about the first test flight of the BOK-7, but it is known that for its successful completion the KB-29 collective was awarded and its main constructor NN Kashtanov received a cash prize.
The BOK-7 was tested at the end of 1938 and presented performances not very different from those of the BOK-1, therefore the tests were not concluded. The test pilots were IF Petrov and PM Stefanovski. The fundamental reason for abandoning the tests was due to the fact that they failed to exceed expectations of setting new world height records. Again, the blame fell on the power plants.
In the spring of 1939, it was decided to use the BOK-7 and BOK-11 airplanes to prepare the crews for long-haul flights. For this reason, on 24 May 1939 the aircraft was delivered to pilot Gromov. Various crews that included Gromov, Yumashiev, Spirin, Baidukov, Beliakov, among others; They lived for several days in the airtight cabin of the plane, based on the ground, checking the feasibility of executing the complete life cycle. This served as training for the projected long-haul flights on the BOK-15.
During these tests everything worked without problems. The cabin proved its ability to be airtight. The air losses due to the few holes for the cables and control systems were compensated by the delivery of the oxygen system. However, it was decided to add an additional compressor in the future that worked powered by the engine.
The BOK-8 was designed as an armed development of the BOK-7. The conception of a military aircraft operating in the stratosphere brought with it the impossibility of using defensive systems of the traditional type. The weaponry was made impossible to handle in the thick pressurized suits and diving suits. It was necessary to develop a defensive weapons control system that could be operated from the pressurized cabin. This task was successfully solved in 1938 with the design and laboratory testing of the first remote weapon control system.
The new armament control set consisted of a synchronized electro-automatic sighting system with collimator designed by Riezunov and located in the second turret above the navigator’s cockpit and a system capable of controlling fire from the sealed cockpit designed by the engineers. VS Kostishkin and KB Zhbanov, who operated a machine gun located on the fuselage, outside the cockpit.
The installation of this system was carried out on the BOK-7. It is noteworthy that this remote fire control system was developed long before the appearance of similar systems in the United States on Boeing B-29 Superfortress bombers. The development was materialized in the BOK-11.
Later, on the basis of the BOK-7, the BOK-10 projects were developed for a high-altitude reconnaissance plane, BOK-12, an atmosphere research plane and the BOK-13 as a passenger plane. All these variants did not go beyond the project table.
BOK-7
Powerplant: 1 M-34FRN 890hp
Wingspan: 32.40 m
Length: 14.85 m
Wing area: 81.4 m²
Empty weight: 3400 – 3600 kg
Takeoff weight: 4814 kg
Maximum speed at 9000 m: 350 km / h
Landing speed: 86 km / h
Practical ceiling: 15,200 m
Accommodation: 2
All Aero 