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Background
Spoiler
The Bolkhovitinov DB-A represents a significant advancement in the field of aircraft design. In contrast to the TB-3, it features a streamlined exterior, metal propellers with ground-adjustable blade angles, Schrenk landing flaps, a retractable tail, and semi-retractable main landing gear wheels. Additionally, it includes a bomb bay measuring 6x2 meters, a Tur-8 mechanized shielded turret, a fixed stabilizer, and a cockpit that is enclosed except for the position of the rear gunner.
The semi-monocoque structure of the fuselage allowed for a considerable increase in internal volume while maintaining the same dimensions as the TB-3. Located beneath the center section of the fuselage, the bomb bay is capable of accommodating up to 3,000 kg of ordnance, with configurations including eight 250 kg bombs, six 500 kg bombs, two 1,000 kg bombs, or twenty-four 100 kg bombs. Additionally, provisions were made for the attachment of VAP-500 and VAP-1000 airborne discharge devices, as well as RRAB rotary-dispersal bombs.
At the front of the fuselage, a Tur-8 turret equipped with a ShKAS machine gun is situated, while the central section houses a Tur-Aldis turret featuring a 20 mm ShVAK cannon. The tail section is equipped with mounts for ShKAS machine guns. The total ammunition capacity includes 3,000 rounds for the machine guns and 250 rounds for the cannon.
The power plant was equipped with M-34RN engines, complete with a gearbox and supercharging system. Although the project was intended for the enhanced M-34FRN engines, these were not available until a later date.
Initially, the DB-A engines utilized two-bladed wooden propellers, measuring 4.35 meters in diameter, sourced from the TB-3. This configuration resulted in a reduction of flight performance compared to the anticipated specifications. Eventually, these propellers were substituted with three-bladed variants, measuring 4.1 meters in diameter, taken from the ANT-25 aircraft.
The aircraft featured a tricycle landing gear design, complemented by a tail wheel. The main landing gear was fitted with single wheels, each measuring 2000x450 mm. To facilitate operations in winter conditions, specialized skis were planned; however, these were never produced, and during testing, skis from the TB-3 were utilized instead.
The DB-A, based on its performance metrics from factory evaluations, demonstrated a marked superiority not only over its predecessor but also in comparison to the nearest foreign four-engine bomber, the Farman-222. This enhancement in flight performance can be attributed to an increase in aerodynamic efficiency, which peaked at a maximum value of 15.
Bolkhovitinov, along with Baidukov, expressed strong opposition to the proposal of utilizing the sole DB-A undergoing flight tests for a transpolar mission. They contended that it was a military bomber ill-suited for northern operations. In response, Bolkhovitinov convened a team of designers in the office of B.N. Tarasevich, the director of the aircraft plant, to inform them that the government had approved Levanevsky’s request, permitting the DB-A to undertake the Moscow-North Pole-Alaska route on June 5. The aircraft was designated with the polar aviation index “USSR-H-209.” At this point, the DB-A had accumulated a total flight time of 115 hours.
Stalin, who held Sigismund Aleksandrovich Levanevsky in high regard, permitted him to select his aircraft for the journey across the North Pole. The pilot declined the Tupolev models and chose the heavy four-engine bomber DB-A, designed by Viktor Fedorovich Bolkhovitinov, which was assigned the tail number “USSR-H-209” and the call sign “RL” (Radio Levanevsky). To prepare the military aircraft for the flight, modifications were necessary: the machine-gun turrets were removed, the navigator’s canopy was fully enclosed, and the bomb bay was converted into a cargo hold. The designer himself opposed this decision, believing that his aircraft was not suitable for such an expedition, as it was one of the initial experimental models.
On August 12, 1937, the aircraft designated “USSR - H-209” departed from Moscow. The intended flight path included Moscow - Arkhangelsk - Rudolph Island - North Pole - Fairbanks (USA). Following a refueling stop in Fairbanks, the aircraft was planned to continue to New York. The day after its departure, on August 13 at 13:40, the aircraft successfully reached the North Pole.
Approximately one hour later, the crew transmitted a radio communication, which was later interpreted as follows:
“I-RL, 14 hours, 32 minutes. The right outer engine has failed due to an oil system malfunction. We will proceed on three engines. Altitude 4600. We are navigating through continuous cloud cover. Levanevsky.”
The aircraft subsequently vanished, and its coordinates remain unknown. Efforts to locate it have been unsuccessful.
Technical Data
Specifications
Crew - 7
Length - 24.4 m
Height - N/A
Wingspan - 39.5 m
Empty Weight - 15,400 kg
Max Takeoff Weight - 21,900 kg
Powerplant - 4 x Mikulin M-34RN Piston Engine (713 kW each)
Max Speed - 280 km/h at Sea Level, 330 km/h at 4,000 m
Service Ceiling - 7,220 m
Range - 4,500 m
Takeoff Distance - 400 m
Landing Distance - 300 m
Landing Speed (Flaps Deployed) - 80 km/h
Armament
1 x 20mm ShVAK Autocannon in Dorsal Turret (250 rpg)
1 x 7.62mm ShKAS Machine Gun in Nose Turret (1,000 rpg)
1 x 7.62mm ShKAS Machine Gun in Tail Turret (1,000 rpg)
1 x 7.62mm ShKAS Machine Gun in Ventral Turret (1,000 rpg)
(?) 1 x 7.62mm ShKAS Machine Gun in each Engine Nacelle (Rumored)
Up to 3000 kg of Bombs;
24 x 50 kg Bombs
8 x 250 kg Bombs
6 x 500 kg Bombs
2 x 1000 kg Bombs
Images
Spoiler
Spoiler
DB-A Bolkhovitinov long-range bomber (airpages.ru)
Bolkhovitinov DB-A - Wikipedia
(Book) The Osprey Encyclopedia of Russian Aircraft 1875-1995.