The Soviet Union was the largest state on the planet, and already in the 1930s actively claimed the title of superpower. But within the framework of the race between countries, the authorities of the USSR needed to constantly maintain this image through the implementation of ideas that would show the capitalist camp the viability and power of socialism. Soviet engineers and developers did their best to match the large-scale ambitions of the party elite, creating truly ambitious projects, although some of them were never implemented. This is exactly what the K-7 transcontinental plane was - a huge flying fortress.
The 1930s in the USSR quite rightly began to be called "the time of the searchlights" - it was during this period that the largest number of grandiose giant projects were created, which were supposed to personify all the strength and power of a huge country. Aircraft designers in this matter did not lag behind their colleagues from other fields. One of them was Konstantin Kalinin, who, as the head of the design bureau, by the beginning of the 30s of the 20th century, had created a number of new, successfully tested aircraft.
But one of the most promising ideas of the designer was the concept of the so-called "flying wing". The essence of the idea was that the fuselage role here was played by an empty wing. It housed both the cargo and the crew. This unusual design made it possible not only to reduce the weight of the aircraft itself, but also to increase its payload. According to Novate.ru, Kalinin himself considered the concept of a "flying wing" ideal for large vehicles.
Carried away by this idea, in 1928 KB Kalinin presented a project of a transcontinental giant aircraft, one wingspan of which was to be at least 50 meters. The ambitious party leadership liked the grandiose idea, and two years later the construction of the first prototype began.
In 1932, the project already had a complete package of technical documentation and a full-size model. After that, it took another nine months to build the first model of the K-7 fortress aircraft. And at this stage the first difficulties began. It turned out that the military-industrial complex of the USSR was not yet able to provide such a huge liner with engines of the required power. And even an increase in their number in the final version to 7 did not solve the main problem - the giant plane turned out to be very heavy.
Despite this, another military modification of the K-7 was released. She had almost ideal armament for a huge aircraft - sixteen machine guns and cannons installed around the perimeter. Such foresight of the developers made it possible, if necessary, to shoot through the entire surrounding space from several points at once. Also, the plane could carry more than 6 tons of cargo - for example, a bomb load or armored vehicles for further dropping it with parachutes.
The first tests of the transcontinental giant gave very encouraging results - the aircraft's flight characteristics were satisfactory for such a huge machine. Even the memories of one of the first K-7 test pilots M. Snegirev have survived: “The car in the air obeyed the rudders well. It was easy to operate. I couldn't even believe it. Pull the steering wheel slightly and the car immediately responds!"
However, after the first successful test, the success of the ambitious project ended.On one of the following flights, a tragedy occurred: during the landing approach, the plane stopped obeying and crashed. The victims of the disaster were 15 crew members of the K-7.
The cause of the disaster was the destructive effect of vibrations on the tail of the aircraft, which arose due to the so-called yaw (instability) of the machine in flight, especially at low speeds. And at that time, neither technologies nor materials to compensate for these processes simply did not exist.
Interesting fact:the issue of vibration due to aircraft yaw has been present on virtually every aircraft in the flying wing design.
The future of the ambitious transcontinental giant K-7 turned out to be unenviable: the decision of the USSR government to subject the Soviet aircraft industry to a qualitative transformation put an end to the project of a flying fortress, and it was frozen and then finally closed.
And the fate of its author was completely tragic: in 1938, when the wave of "Great Terror" reached the military-industrial complex, Konstantin Kalinin was arrested on charges of anti-Soviet activities and espionage and shot. The Soviet aircraft designer was rehabilitated only in 1955.