USSR (1938-1940)
Experimental long-range bomber – One prototype
With the rapid expansion of Soviet aviation in the 1930s, radical new design concepts were constantly being developed, producing a number of eccentric designs that hoped to break the mold. Among the many different concepts, one particularly unusual design emerged in the form of a twin-fuselage, bat-winged aircraft created by Viktor Nikolayevich Belyayev.
This aircraft, known as the Belyayev DB-LK, featured two fuselages, connected by a central wing section with a glazed rear cone. Despite its unconventional layout, testing showed that the DB-LK was a stable and reliable aircraft. However, the Soviet aviation industry at the time prioritized more conventional designs for long-range bombers with the onset of war, which ultimately doomed the project before it could progress further.
History
Following the end of the First World War and the later Russian Civil War, a new nation emerged from the remnants of a once-mighty empire: the Soviet Union. During the 1920s, it began the slow process of rebuilding its shattered industry. In order to recover, the Soviet political and military leadership decided to prioritize large-scale industrial development, and enormous financial resources, manpower, and raw materials were committed to achieving this goal. As a result, new technologies were quickly introduced, leading to a period of rapid industrial expansion.
The aviation sector also benefited from this renewed focus. A series of new projects, both civilian and military, were initiated to rebuild and modernize the nation’s air capabilities. Before the First World War, in the now-lost Russian Empire, there had been considerable developments in airliner design. However, progress was halted by the outbreak of the First World War, and the devastation caused by the subsequent Civil War. By the early 1920s, the aviation industry’s infrastructure was in ruins, and many of its original engineers and experts had either fled the country or been killed.
By the 1930s, new experts were eager to test various ideas and concepts. Among them was Viktor Nikolayevich Belyayev. Born in 1896 (Moscow, Russian Empire), Belyayev showed a strong interest in aviation from an early age and was an enthusiastic engineer. During the late 1920s, he worked with Andrei Nikolayevich Tupolev’s Experimental Design Bureau, and later with Aeroflot, the Soviet civil aviation operator.
Belyayev had a particular fascination with a bat-wing, sometimes also described as a butterfly wing shape, design, featuring a slightly forward-swept wing with tips that curved gently backward. At the time, aviation worldwide was marked by the introduction of numerous experimental and innovative concepts. With such rapid technological progress, there was plenty of room for improvement and innovation, and eccentric ideas found fertile ground for development. Belyayev believed that this bat-wing configuration could significantly improve longitudinal stability while also reducing overall drag.
Like many other aircraft engineers who often lacked adequate funding, he decided to test his ideas using simple and inexpensive gliders. In 1920, he built a fully operational glider. In 1933, he managed to construct a glider designated BP-2. It used the bat-wing layout and also featured an unusual twin-tail assembly connected by an extended elevator. The glider was tested in a flight from Crimea to Moscow, towed by a Polikarpov R-5. The tests were successful, which encouraged Belyayev to continue experimenting with new fuselage designs. He was particularly interested in an unconventional twin-fuselage arrangement.
The Development of a New Project
Following his research and experimentation with glider design, Belyayev eventually felt that he had gathered enough knowledge and design experience to put his ideas into practice. In 1934, he began working on a new twin-fuselage, 10-seat transport aircraft. Each fuselage was fitted with a 750-hp engine.
In addition to developing new wing designs, Belyayev also theorized methods to significantly reduce aircraft drag. Conventional twin-engine aircraft had their engines mounted on the wings, which inevitably created drag that could not be eliminated. Belyayev’s new concept was to extend the engine nacelles and use them as the fuselage itself. This meant that no additional structural elements had to be attached to the wing, thereby removing unnecessary drag and creating a more aerodynamically efficient aircraft.
In the late 1930s, the Soviet Air Force issued a requirement for a new long‑range bomber. Belyayev decided to take this opportunity. He essentially reused his original civil aircraft design and adapted it for military use. In 1938, he approached the Soviet Air Force with his proposal for a new long-range bomber. This time, he received approval to construct a working prototype, which was completed rather quickly by November 1939. The resulting aircraft made use of his earlier concept: it featured two fuselages that, technically speaking, functioned more like elongated engine nacelles.
The aircraft received a simple designation: DB-LK. While not entirely clear, this was most likely an abbreviation of Dalniy Bombardirovshchik – Letayushcheye Krylo, meaning Long-Range Bomber — Flying Wing. It is also often referred to by its designer’s name as the Belyayev DB-LK. During the testing phase, it also carried the nickname Kuritsa (Eng. Chicken), given by the test pilot who was afraid to fly it.
Experimental Flights
Once the DB-LK prototype was completed, it was cleared for its first flight tests. While Belyayev may have had doubts about the realization of the entire project, he likely never expected that, despite the vast size of the Soviet Union, not a single test pilot was willing to fly his plane. At this time, most pilots were still flying older biplane designs, and many were often reluctant to test newer aircraft. For example, some even hesitated to fly low-wing monoplanes, which were still unfamiliar to many aviators. This hesitation stemmed both from a general fear of experimental aircraft and, to an even greater degree, from an ingrained belief that proven older designs were superior to new, untested ones. In any case, Belyayev unexpectedly found himself unable to secure a willing test pilot.
This situation dragged on until 1940. That year, the Soviet Directorate of the Air Scientific Test Institute issued an official order assigning pilot M. A. Nyukhtikov to test the aircraft. There was little point in keeping a fully functional machine sitting idle on the ground. To support the pilot during the trials, lead engineer T. T. Samarin and test observer N. I. Shaurov were also assigned to the project.
After several initial flights, Nyukhtikov reported that the aircraft’s controls were heavy and difficult to operate. In addition, he noted that the landing gear should be strengthened. A commission of the Scientific Test Institute, led by A. I. Filin agreed that the control system needed refinement but rejected the pilot’s concerns regarding the landing gear. This decision proved premature, as only a few days later, during a flight test involving Filin himself, one of the landing gear legs collapsed.
Sudden End of the Project
After a series of test flights, the DB-LK, despite its unconventional, inverted-gull twin-fuselage design, proved to be an airworthy and well functioning aircraft. During testing, the DB-LK could easily reach speeds of up to 488 km/h (303 mph) at an altitude of 5 km (16,400 ft). When fully loaded, it was also capable of climbing to around 8.5 km (28,000 ft). In total, more than 100 test flights were conducted without any major incidents, demonstrating that the overall design was sound.
Complaints from the test pilots focused on the limited visibility experienced by both the pilot and the navigator. Despite this, the DB-LK was viewed as an aircraft with significant potential for future service within the Soviet Air Force.
Then, suddenly, the project was shut down. This occurred for several reasons, though not necessarily because of flaws in the design. By late 1940, war was raging in Western Europe between Germany and Britain, and a wider conflict seemed increasingly possible. The Soviet leadership did not want to take risks with an aircraft considered highly unorthodox. The DB-LK’s twin-fuselage layout likely contributed to these concerns. Instead, the authorities decided to focus production efforts on the more conventional and already-established IL-4 bomber. With that decision, all work on the DB-LK stopped. Its final fate is unclear, but it was likely scrapped.
Technical characteristics
The DB-LK featured an unconventional overall layout, lacking a traditional central fuselage. Instead, the crew stations, armament, and most of the onboard equipment were housed inside two elongated engine nacelles that terminated in glazed tail cones (gondolas), somewhat reminiscent to the aft section of the later German Fw 189. In practical terms, these extended nacelles functioned as the aircraft’s fuselage. Each semi-monocoque structure was built from a framework of metal frames and longerons, covered with duralumin skin. The two glazed cones could be mechanically rotated 360°, boosted by small electric motors mounted on top of the fuselages. This was designed to provide the best possible angle for the rear gunners, while retaining aerodynamic shape.
The DB-LK’s wings featured a distinctive layout. In addition to the characteristic “batwings,” the aircraft incorporated a central wing section positioned between the two fuselages. The wings were slightly forward-swept and ended in backward-curved tips. Structurally, they consisted of a light metal stressed-skin construction over a conventional airframe. The outer wing panels used a Göttingen 387 airfoil profile, while the center section employed a CAHI (TsAGI) MV-6bis profile. The wing leading edges were curved at an angle of –5° 42′.
The rear tail assembly was mounted on the central wing section between the two fuselages. It consisted of a single vertical fin with a large rudder. Above the rudder, a small horizontal stabilizer was installed, fitted with two large elevators, one on each side.
The landing gear retracted rearward, with one wheel (900 × 300 mm) housed in each fuselage section. During later testing, this arrangement was redesigned, and the gear was modified to retract forward instead. The entire landing gear system was hydraulically operated. A small fixed tailwheel (450 × 150 mm) was installed at the bottom of the tail unit.
The DB-LK was powered by two Tumansky M-87B 14-cylinder radial engines, each delivering 950 hp. These drove three-bladed variable-pitch propellers. It was planned to replace them with the more powerful 1,100 hp M-88 engines, or even the 1,700 hp M-71, but these upgrades were never implemented as the project was ultimately cancelled. Fuel was stored in both the wing and fuselage tanks, with a total capacity of 3,444 liters (910 US gallons)..
Behind each of the two engines, a cockpit with a rear-sliding canopy was installed. The DB-LK was designed to be operated by a crew of four: the pilot, navigator, and two rear gunners. The pilot occupied the left cockpit, and the navigator the right. The gunners were positioned in the two rear glazed cones, with one of them also serving as a radio operator. Crew members entered their positions through the roof hatch doors.
Given its role as a long‑range bomber, Belyayev intended for the aircraft to have a fairly respectable defensive armament for its day, consisting of six machine guns. Both rear glazed tail cones were fitted with mounts for twin 7.62 mm (.30 in) ShKAS machine guns. These weapons had a firing arc of –10° to +10° in all directions. However, the gunner could rotate the glazed cones themselves, allowing him to reposition the guns and further increase the weapon’s effective defensive arc.
In addition to these four rear-mounted machine guns, two more were installed in the leading edge of the center section and operated by the pilot. Altogether, approximately 4,500 rounds of ammunition were carried for all six weapons.
For attacking ground targets, bombs were to be employed. The bomb bays were located behind the landing‑gear doors in each of the nacelles. Each of the two bomb bays could carry up to 1 tonne (2,200 lb) of bombs, or alternatively four 250 kg (550 lb) or two 500 kg (1,100 lb) bombs per bay, four in total. In addition, a container with 59 smaller bombs could have been used instead. Lastly, an additional external bomb rack capable of carrying up to one tonne could be attached to the central wing section.
Cocnlusion
The Belyayev DB-LK is one example where the overall visual design essentially killed the project. The aircraft itself had no unresolvable flaws. In fact, it demonstrated generally good flight performance. It carried a large bomb payload, and its defensive armament, while not covering every angle, was still respectable. Most importantly, it did not suffer any major problems during the initial test flight phase.
Its main downside was its unusual overall appearance, which may have caused significant concern among industry decision-makers when it came time to consider a production order. It can be assumed that this was one of the key reasons it was cancelled, along with its prototyping being interrupted by the start of the Second World War. Soviet authorities preferred more conventional, proven designs and did not want to commit to a highly unorthodox aircraft that had no equivalent or prior service experience anywhere in the world.
| Belyayev DB-LK specifications | |
| Wingspan | 21.6 m / 70 ft 10 in |
| Length | 9.8 m / 32 ft 1 in |
| Wing Area | 56.9 m² / 612 ft² |
| Engine | 2x Tumanskii M-87B 950 hp 14 cylinder radial engines |
| Empty Weight | 6,000 kg / 13,230 lbs |
| Maximum Takeoff Weight | 10,670 kg / 23,530 lbs |
| Fuel Capacity | 3.444 l |
| Maximum Speed | 490 km/h / 300 mph |
| Cruising Speed | 395 km/h / 245 mph |
| Range | 1.270 km / 790 mi |
| Maximum Service Ceiling | 8,500 m / 27,890 ft |
| Climb speed | Climb to 5,000 m in 13.6 minutes |
| Crew | Pilot, navigator, and two gunners |
| Armament |
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Illustration
Credits
- Article written by Marko P.
- Edited by Henry H.
- Illustrations by Oussama Mohamed “Godzilla”
Source:
- Y. Gordon and B. Gunston (2000), Soviet X-Planes, Midland Publishing
- D. Nešić (2008), Naoružanje Drugog Svetskog Rata SSSR, Beograd
- Y. Gordon and D. Khazanov (1999), Soviet Combat Aircraft Of The Second World War, Midland Publishing
- B. Gunston (1996), The Osprey Encyclopedia Of Russian Aircraft 1875-1995, Osprey Aerospace
- W. Kopenhagen (1989) Sowjetische Bombenfluhzeuge , Transprees