Ilyushin DB-4

Ilyushin DB-4

Company type	Aircraft prototype
Industry	Aerospace
Predecessor	Ilyushin DB-3
Founded	early 1940s
Headquarters	Moscow , Soviet Union
Products	Long-range bombers (prototypes)

The Ilyushin DB-4 (DB - Дальний бомбардировщик - Dalniy Bombardirovshchik, meaning long-range bomber) also known as TsKB-56 (TsKB - Tsentral'noye Konstruktorskoye Byuro, or central design bureau) was a Soviet twin-engine bomber developed in the early 1940s. Conceived as an advancement of the Ilyushin DB-3, it aimed to replace its predecessor; however, only two prototypes were constructed. Issues with the engines and the necessity to prioritize production of existing aircraft following the German invasion of the Soviet Union in June 1941 prevented further manufacturing.

Design and development

During the late 1930s, the Ilyushin design bureau (OKB) was assigned to create a successor to its twin-engine, long-range bomber, the Ilyushin DB-3. The bureau simultaneously worked on two projects: the TsKB-56 and the DB-3F (which later became known as the Ilyushin Il-4). While the DB-3F represented a straightforward upgrade of the DB-3, the TsKB-56 was designed to be larger and heavier to fulfill demands for enhanced performance and increased bomb capacity. Featuring a high-mounted wing to house an extensive bomb bay, the DB-4 was equipped with retractable tailwheel landing gear. Its radial engines were set to be replaced by innovative Klimov M-120 powerplants—18-cylinder liquid-cooled engines arranged in an inverted "Y" configuration with three banks of six cylinders—offering a takeoff output of 1,800 hp (1,346 kW). The crew complement consisted of four members: pilot, navigator, dorsal gunner, and radio operator. Defensive weaponry included three ShKAS machine guns positioned in the nose, dorsal turret, and ventral hatch. The spacious bomb bay could accommodate up to 1,000 kg (2,200 lb) of ordnance.

The initially intended M-120 engines encountered significant difficulties, prompting their replacement with 1,400 hp (1,044 kW) Mikulin AM-37 V12 engines for prototype testing. The first prototype, featuring a single vertical stabilizer, took to the air on 15 October 1940 under the control of test pilot Vladimir Kokkinaki. The second prototype, completed in November 1940 with twin vertical tails and originally powered by M-120 engines, had these swapped for AM-37s before its maiden flight on 20 February 1941.

Flight evaluations revealed shortcomings in low-speed stability and fuselage flexing due to its large bomb bay. These issues were addressed by enlarging tail surfaces and reinforcing the fuselage structure. Although the AM-37 engines were an evolution of the earlier Mikulin AM-35 model, they suffered from reliability problems. Alternative powerplants such as the Shvetsov M-71, M-82 radial engines, and the Charomskiy ACh-30 Diesel engine were considered but never installed. Following the onset of the German invasion in 1941, production of the DB-4 was halted. Manufacturing facilities were relocated eastward from Moscow and redirected toward producing urgently needed aircraft like the Il-2 ground attack plane and Il-4 bomber. The two DB-4 prototypes remained operational as experimental platforms supporting development efforts for improved Il-4 variants and the subsequent Ilyushin Il-6 bomber.

References

• Gordon, Yefim, Dmitry Komissarov and Sergei Komissarov. OKB Ilyushin: A History of the Design Bureau and its Aircraft. Hinkley, UK: Midland Publishing, 2004.
• Gunston, Bill. The Osprey Encyclopedia of Russian Aircraft 1875–1995. London: Osprey, 1995.