5 most mysterious military aircraft of the Soviet Union and Russia

The Soviet Union and Russia once had many ambitious fighter aircraft projects, but were forced to cancel them for various reasons.

The only prototype of the giant bomber K-7. Photo: Wikipedia.

Throughout the history of Soviet and Russian military aviation, there have been many mysterious aircraft designs that were designed to gain an advantage over their rivals around the world. However, some projects were canceled before they were even conceived, while others ended after just a few test flights, according to RBTH.

Kalinin K-7

The giant Kalinin K-7 bomber was developed in the 1930s and was the largest aircraft in the Soviet Union at that time, with a wingspan of up to 53 m and equipped with 7 AM-34 piston propeller engines. In addition to its bombing capabilities, the K-7 could also carry passengers after modifying the fuselage.

The K-7's design was considered quite unusual for the 1930s, equipped with two vertical tails and large underwing compartments for landing gear and machine gun pods. The passenger version had seats arranged in wings up to 2.3 m thick. The fuselage was welded from a high-strength steel alloy frame.

Each K-7 is 28 m long, has a wingspan of 53 m, is 12.4 m high and has an empty weight of 24 tons. The civilian passenger version has seating for 120 people and 7 tons of cargo. The military transport version can also accommodate 112 fully equipped soldiers. Meanwhile, the K-7 bomber variant carries 8 20 mm automatic cannons, 8 7.62 mm machine guns and a maximum of 9.6 tons of bombs.

Construction of the first K-7 prototype began in Kharkiv in 1931 and took two years to complete. The first test flight, on August 11, 1933, revealed severe instability and vibration in the K-7, caused by the resonance effect between the engine and the airframe. Engineers solved the problem by shortening and strengthening the tail, but the vibrations were not completely eliminated.

After seven safe test flights, the K-7 prototype crashed on November 21, 1933, when its vertical tail collapsed. The accident killed 14 people on board and one person on the ground. The cause of the accident was never made public, but many suspected sabotage. Two more prototypes were ordered, but the K-7 project was terminated in 1935, before either could be completed.

Zveno

The Zveno (Chain) project was developed by the Soviet Union from the early 1930s until the start of the Great Patriotic War in 1941. The main idea was to use a TB-3 heavy bomber as a mothership, carrying up to five small Polikarpov I-16 fighters to increase combat radius and save fuel.

The small aircraft could be attached to the TB-3 from the ground or connected in the air, before the bomber would take them to the combat area far beyond the normal operating radius. The I-16 fighters would separate from the mother aircraft, attack the enemy and return to land at Soviet airfields.

Zveno-PBS version with two I-16 fighters. Photo: Wikipedia

Each I-16 could carry up to two 250 kg bombs when suspended under the TB-3's wings. Normally they were not capable of taking off on their own with such a large weapons load.

Despite several successful campaigns in the early stages of World War II, the Zveno project was not expanded. The TB-3 bomber was quickly phased out of production due to its age, while the I-16s were soon replaced by more modern fighters.

Sukhoi T-4

In 1963, the Soviet government issued a request for a strategic bomber to counter the XB-70 Valkyrie being developed by the United States. Three design bureaus (OKBs) Sukhoi, Yakovlev and Tupolev proposed their projects, of which Sukhoi's T-4 version was selected for trial production.

The Sukhoi T-4 was capable of cruising at speeds of up to 3,200 km/h, three times the speed of sound (Mach 3). This helped Sukhoi's design beat its rivals Yakovlev and Tupolev. After the review phase in June 1964, the first Sukhoi T-4 prototype was built.

The development of the T-4 required a great deal of research to create the technology that met the requirements. Notable among these were the method of manufacturing materials and titanium welding techniques to ensure the aircraft could withstand Mach 3 speeds. According to Sukhoi, nearly 600 inventions were published and applied during the development of the T-4.

The Sukhoi T-4 was made of titanium and stainless steel. It was the first Soviet aircraft to be equipped with a fly-by-wire electronic control system with four redundant channels, along with a traditional mechanical control system for safety. The T-4's fly-by-wire technology was later used on the Su-27 fighter line and upgraded versions such as the Su-30 and Su-35.

The first T-4 prototype, serial number 101, took off on August 22, 1972, piloted by Vladimir Ilyushin and navigator Nikolai Alfyorov. Test flights lasted until January 19, 1974. Only 10 flights were made, with a total flight time of 10 hours and 20 minutes. In mid-1974, the Soviet Ministry of Aviation Industry ordered the Sukhoi T-4 to be discontinued. The project was officially canceled on December 19, 1975.

One of the reasons for the cancellation of the T-4 project was that the US had abandoned the XB-70 Valkyrie, the aircraft’s main competitor. In addition, the Soviet Air Force’s demand for 250 T-4s was considered unrealistic. The funds for building the bomber could have been used to produce more practical aircraft in large numbers.

Mi-30

The most famous hybrid helicopter in the world today is the Boeing V-22 Osprey, designed in the 1980s. However, not many people know that the Soviet Union tried to develop this type of weapon since 1972. With the ability to take off vertically and fly like a fixed-wing aircraft, and a cargo capacity of two tons, the Mi-30 is a potential project to replace multi-purpose helicopters such as the Mi-8.

A prototype of the Soviet Mi-30 hybrid helicopter. Photo: Wikipedia.

The first prototype of the Mi-30 project was scheduled to be launched in 1986, but the economic and political turmoil in the Soviet Union led to the project being canceled. A total of four Mi-30 prototypes were built, but three of them lost control and crashed during transport. The cause of the crash is unknown.

Su-47

In 1983, the Soviet leadership decided to launch a forward-swept fighter project and assigned the program to the Sukhoi OKB. However, the collapse of the Soviet Union caused the budget for this project to be completely cut, forcing the Sukhoi OKB to use its own budget to continue developing the fighter model.

On 25/0/1997, the experimental version with the designation S-37 made its first flight. In 2002, the Russian Air Force decided to change the name of this aircraft model to Su-47 Berkut (Golden Eagle).

Compared to traditional swept wings, the inverted wing design offers advantages in lift, high maneuverability at low speeds, as well as reduced take-off and landing length. To overcome the common disadvantage of the inverted wing design, which is the uneven distribution of forces on the wing, the Su-47 uses carefully processed composite materials to prevent torque, while still allowing the wing to maintain superior aerodynamic properties.

However, composite materials still do not guarantee durability. Although up to 90% of the components are made from composite materials,The Su-47's wings are still at risk of breaking off from the body.if flying at too high a speed. Besides, the pair of D-30F11 engines are not powerful enough for the Su-47 to have supercruise capability.

Limited technology and high cost in the context of the difficult Russian economy prevented the Su-47 from being mass produced. However, OKB Sukhoi still used the only prototype to test modern technologies, then deployed these technologies on the PAK-FA stealth aircraft project, with the product being the current Su-57 fighter.

According to VNE