USSR (1938-1940)
Experimental Long-Range Bomber – 1 Prototype Built

In the late thirties and early forties, the Soviet aviation industry had developed and tested a variety of aircraft design concepts, some quite peculiar. While generally unknown around the world, a number of these strange aircraft would represent a serious departure from anything resembling their contemporaries. Such is the case with Victor Nikolayevich Belyayev’s DB-LK experimental long-range bomber.

History

Victor Nikolayevich Belyayev, March 1896 – July 1953, began working for the Department of the Marine Experimental Aircraft Construction, OMOS, in 1925, where he gained his first experience in aircraft design. In the following years, he worked for the Central Aerohydrodynamic Institute, TsAGl, and Tupolev. During this time, he became an advocate for tailless aircraft designs. He also argued that the so-called “batwing”  or “butterfly”, offered better performance, due to their reduced drag and better stability, than regular wing designs.

The “batwing” design possessed a slightly forward-swept wing with back curved tips. Belyayev managed to construct a glider, designated BP-2, which was equipped with this kind of wing design in 1933, on which he tested this concept. During its test flight, it was successfully towed in the air from Crimea to Moscow, where it proved to have good stability and control during flight.

The next year, Belyayev participated in the competition for a new Soviet military transport plane design. His design was unusual, as it consisted of a large wing and two nacelles,  powered by Tumanskii M-87B 950 hp (708 kW) engines. His design was not approved nor did he build a working prototype. However, four years later, he would reuse this project and adapt it for the role of a long-range bomber. In 1938, he designed the DB-LK long-range flying wing bomber, which the TsAGl approved and ordered the construction of a fully operational prototype. The prototype was built the following year by factory No.156 and by November 1939 it was ready for testing.

Technical Characteristics

The DB-LK had an unusual overall design with no classical fuselage. Instead, the crew, armament, and other equipment were located in the two extended engine nacelles that ended in glazed tail cones (gondolas), somewhat similar to the later German Fw 189. The two extended engine nacelles were, technically speaking, the plane’s fuselage. The semi-monocoque fuselages were constructed by using a combination of metal frames and longerons covered with a duralumin sheet. The DB-LK was designed in this unusual configuration in the hope of reducing the overall drag and weight and thus increasing its speed and range.

The DB-LK’s wings had a unique design, where beside the “batwings” there was an additional center wing section between the two fuselages. Also, the wings were slightly swept to the front with back curved tips. The wings consisted of an airframe covered with light metal stressed-skin. The outer wings had a Gottingen 387 profile, while the center section had a CAHI (TsAGI) MV-6bis profile. The wing edges were curved at an angle of -5° 42′.

The rear tail was located on the middle section wing between the two fuselages. The tail consists of one fin and a large 20 ft2 (1.9 m2) rudder. Above the rudder, a smaller tailplane with two, one on each side, large elevators was placed.

One Tumansky M-87B 950 hp (708 kW) 14-cylinder radial engine was installed at the front of both nacelles. For these engines, three-bladed propellers with variable pitch were used. It was planned to upgrade these two with much stronger 1,100 hp (820 kW) M-88 engines, or even the 1.700 hp M-71, but this was never implemented. The fuel was stored in the wing and fuselage tanks, with a total fuel load of 3.444 l.

The landing gear retracted rearwards, with one wheel (900 x 300 mm) in each fuselage. During later testing, the landing gear design was changed with a forward retractable one. This whole landing gear system was operated hydraulically. There was a small fixed rear wheel (450 x 150 mm) located at the bottom of the tail unit.

The DB-LK was to be operated by a crew of four: the pilot, navigator, and the two rear gunners. The pilot position was in the left cockpit and the navigator in the right. The gunners were positioned in both rear glazed cones. One of the two gunners was also the radio operator. The crews entered their positions through roof hatch doors. The two glazed cones could be mechanically rotated 360° by using a small electric engine located at the fuselage top, but the sources do not specify why this was done.

Both rear glazed tail cones had a recess where a twin  7.62 mm (.30 caliber) ShKAS machine gun mount was installed. These machine guns had a -10 to +10 field of fire in all directions.  Besides these four machine guns, there were two additional ones forward mounted in the leading edge of the center section. These two machine guns were operated by the pilot. In total, around 4,500 rounds of ammunition were provided for these machine guns. The bomb bays were located behind the landing gear doors in each of the two nacelles.

Depending on the sources, the load capacity of the bomb carried is different. The authors Yefim G. and Dimitri K. note that the bomb load was 1000 kg (2,200 lb) with another 1000 kg that could be carried on external racks. According to Bill G., the capacity of each bomb bay (in each fuselage) was one 1000 kg (2.200 lb), two 500 kg (1.100 lb), or smaller bombs with a total of 1000 kg (2.200 lb) weight.

 

Flight Tests

While being completed in November 1939, the first extensive flight test would only begin the following year. This was due to the unwillingness of the test pilot to fly this plane. He did not believe that it was safe to fly due to its unorthodox design. During this time, the plane received the nickname “Kурица” (chicken).

In order to move the entire project testing through this roadblock, the Soviet Direction of the Air Force Scientific test institute, GK Nil WS, appointed M. Nyuikhtikov as the main test pilot, supported by aircraft engineer and test pilot T. T. Samarin and N. I. Shaurov. Under the new leadership, the tests were carried out in the spring of 1940. During the new leadership, the DB-LK was extensively tested in over 100 flights.

During these flights, the pilots managed to reach speeds of 245 mph (395 km/h) at sea level and 300 mph (490 km/h) at an altitude of 16,400 ft (5,000 m). The DB-LK needed a 2,030 ft (620 m) long airfield for landing and taking off. However, the  DB-LK was never truly trialed with a fully loaded payload. The numbers presented above would have likely been different with a full payload of equipment.

The test pilot Nyuikhtikov, after flying on the DB-LK, pointed out some issues with the plane’s design. The main problems were the inadequate overall flight-control system, poor visibility for the pilot and the navigator, especially on the ground. He also noted the poor construction of the landing gear. These reports were examined by the Nil WS Commission led by A. I. Filin. They agreed that the control system should be improved, but Filin had a positive opinion on the landing gear construction. Ironically, during a test flight, where Filin was the pilot, there was a landing gear malfunction during the landing when one of the front wheels broke free, after a possible collision with a treetop. The aircraft was only lightly damaged and the testing continued, but this led to a change in the landing gear design.

There were also other problems mentioned during the tests, like uncomfortable cockpits, low-level of fire protection, structural problems, a limited firing arc of the rear-mounted defense machineguns, and the tendency for the crew compartments to be filled with exhaust fumes from the engines. To solve these issues, there were plans for the DB-LK improvements, with stronger engines, wings, and various other modifications, to be completed by late 1940 but they were probably never implemented.

Conclusion

Despite plans for more testing and improvements, unfortunately for the DB-LK design team, they never got a chance to do so. In late 1940, the Nil WS Commission gave orders for the cancellation of the DB-LK program. The main reason for this was the decision for the production of the Il-4 as the main Soviet long-range bomber.

 

Belyayev DB-LK specifications
Wingspan	70 ft 10 in / 21.6 m
Length	32 ft  1 in /  9.8 m
Wing Area	612 ft² / 65.9 m²
Engine	2x Tumanskii M-87B 950 hp (708 kW) 14 cylinder radial engines
Empty Weight	13,230 lbs / 6,000 kg
Maximum Takeoff Weight	23,530 lbs / 10,670 kg
Fuel Capacity	3.444 l
Maximum Speed	300 mph / 490 km/h
Cruising Speed	245 mph / 395  km/h
Range	790 mi /  1.270 km
Maximum Service Ceiling	27,890 ft / 8,500 m
Climb speed	Climb to 3,000 m in  8 minutes
Crew	Pilot, navigator, gunner and radio operator/gunner
Armament	Six 7.62 mm ShKAS machine gun Two 1,000 kg bombs or Four 500 kg bombs

Gallery

Illustration by Godzilla

Credits

• Article written by Marko P.
• Edited by Stan L. & Henry H.
• Illustration by Godzilla

Sources

• Y. Gordon, D, Khazanov (1999), Soviet Combat Aircraft Of The Second World War, Midland Publishing
• Yefim G. and Bill G (2000), Soviet X-Planes, Midland Publishing
• Peter G. D. (2015), Soviet Aircraft Industry, Fonthill Media
• D. Nešić (2008), Naoružanje Drugog Svetskog Rata SSSR, Beograd.
• Aviamuseum