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TB-7, Pe-8 (ANT-42) Heavy bomber - Design

The TB-7 was the first Soviet second generation bomber, in the same cohort as the Western B-17. This aircraft had streamlined forms, retractable landing gear, smooth lining, a relatively thin wing profile. All these qualities provided a significant reduction in aerodynamic drag compared to TB-3. The predecessor first generation Tupolev Tu-3 was obsolete on arrival. A product of the late 1920s, the Tu-3 first flew in 1930, and was the world’s first strutless (cantilever wing) monoplane bomber. But with a first flight only four years later, the TB-7 had roughtly twice the 2000 km range, twice the maximum payload of 2000 kg of bombs, and twice the top speed of 200 km/h.

A speed of 400 km / h was required at 12,000 meters and the transport of two tons of bombs at a distance of 3,800 km or four tons to 1,200 km. It was clear that in order to meet the specifications, it would be essential to change the approach that led to the box-shaped and highly cluttered TB-3. The new TB-7 had a metal construction that matched high speed and accessibility, with massive wings and a specially designed hull, which in some cross-section resembled pear. The machine commander and the second pilot sat behind each other in the upper cabin, and in the glassed bow, instead of a third crew member, who served as navigator, bomber, and front shooter. Behind him was a pair of boarding engineers and a radio operator. The remaining members were five gunners, for apart from the total "normal" three shots in the upper and lower part of the center of the hull and in the tail, the aircraft had two unusual firing positions at the rear of the internal motor gondola [the assumption being that any encounter with enemy fighters would place the fighters in a tail chase of the faster bomber].

Due to the absence at that time of suitable high-altitude engines, a rather original decision was taken: to add a fifth Klimov M-100 engine called ACN (aggregat nodulum) to the four Mikulin AM-34FRN engines, exclusively for the rotation of a centrifugal supercharger, which ensures the supercharging and altitude of the four engines. In June 1935, the technical requirements for the central supercharging unit (ATSN) were worked out. It was certainly an original idea, but the entire system was very large, heavy and disturbed, so his tests were prolonged.

In the spring of 1938, the second prototype was completed; the AM-34FRNV engines were a bit more powerful, the "chin" (or the glassed protrusion below the front of the aircraft) disappeared, and the lower body fuselage was modified so one of the gunners had disappeared. In accordance with the observations revealed during the test of the experimental aircraft, the design of the understudy was improved. AM-34FRNB engines (on the first serial AM-34FRNV) and ATSN with M-100A were installed on the plane. The weight of the empty aircraft increased by 635 kg, the capacity of the fuel tanks increased from 8250 to 8750 kg. Flight-technical data changed little, and the understudy was adopted as a standard for the construction of an experimental series of 5 copies. The range of flight mass in the operation of the aircraft was set from 24,000 to 32,000 kg.

It was recommended to replace the central supercharging engine with the individual installation of turbochargers on each AM-34FRNV engine. It was clear to everyone that the plane was very good, that the first high-altitude high-speed bomber was created, fully meeting the requirements of its time and anticipating the development of this class of aircraft for several years to come. But this bomber needed reliable engines of sufficient power and altitude.

This engine was the high-altitude AM-35A in 1200 hp. The initial production machines were fitted with AM-35A inlines with 1,350 HP each. The scheme involving the M-100 engine in the fuselage to drive a blower system was not used in production machines. With these engines the plane TB-7 since 1940 began to be built serially. Chief designer of the plant IF Nezel was appointed responsible for mass production. After the death of VM Petlyakov in 1942, the name of the Pe-8 was approved for the aircraft. The size and design of the aircraft did not change during its existence.

The view was that (in retrospect it was wrong) the diesel engines from the designer Alexei Caromskı would be suitable for the extension of the range. Its aggregates M-40 and M-30 (later AC-30B) should provide outputs of over 1,100 kW and a range of almost 5,500 km. The Air Force Command was enthusiastic, and in 1940 and 1941, several small TB-7 series were created with these engines.

Following the initial production aircraft, Pe-8s were then built with Charomskii M-30 and M-40 two-stroke diesels, which proved unreliable to the point of unacceptable, leading to retrofit of AM-35As. Ultimately, problems with delivery of the AM-35A forced conversion to Shvestsov M-82 air-cooled radials, with 1,850 HP each. The refit of the air-cooled engines required considerable redesign of the engine nacelles. Air crews liked the greater power provided by the M-82s but found the old AM-35As more reliable.

The wingspan was 39.01 m, its area is 188.68 square meters, the length of the aircraft was 23.59 m, the area of the horizontal tail is 29.28 square meters, vertical 11.30 square meters, the width of the fuselage is 1.6 m, its height is 2.5 m. m. The chassis with two-post shock absorption, retracted into the nacelle by backward movement, the wheels are 1600x500 mm, the tail is 700x300 mm, unassembled. In the forward part of the fuselage a rotating machine-gun turret with two SHKAS machine guns, two heavy machine guns BT in rifle installations behind the nacelles and two cannons SHVAK- 20 in the stern and in the fuselage behind the rear wing spar. In the cockpit the pilot places were located one after another and were closed by an oblong "lantern", slightly shifted to the port side.

Armament was not selected immediately, initially dominated by light machine gun ShKAS, then they were gradually replaced by heavy ShVAK guns. The serial production aircraft of 1941 with the AM-35A engine had a mass of an empty aircraft of 19,986 kg, a flight of 27,000 kg in its normal state and 35,000 kg in a transhipment aircraft; its full load was 15,014 kg, weight return 42.9%, with a crew of 8 - 11 people. The total fuel reserve at the beginning of 10,800 kg, later was brought to 13,025 kg, the oil - up to 670 kg, the normal bomb load was 2000 kg, with an overload of 4000 kg.

Fuel tanks were located in the wing - in the center wing five tanks between the wing spars, in the consoles - five tanks between the spars and two tanks in the socks, and only 19 tanks. With two tons of bombs with full fueling, the maximum range of the Pe-8 was: with the AM-35A engines - 3,600 km, with the M-40 or M-30 - 5460 km, with the M-82 - 5800 km. In special cases, the range of flight could be greater. For example, in the flight of E. K. Pusen 24 - 30 May - 2 June 1942 in England and the United States and back with a diplomatic mission. For this flight additional tanks and oxygen tanks were installed. There was a reservation in the plane: two armored seats of pilots' seats and the same thickness (9 mm), small tiles to protect the navigator and riflemen in the nacelle.

The passenger variant of Pe-8 (Pe-8 ON, 2 were built + 2 were planned to built), was equipped with 12 comfortable sleeperette in central cabin with windows, 3 sofas in sleeping-cabin, toilet room, bar-room, small coatroom and luggage compartment under sleeping-cabin. All cabins had soundproofing, individual venting, air heating (special water radiators heated floor air by warm from engines), oxygen equipment for each place (16 l per men for 8 h of flight at 6000-8000 m), central and individual lighting. New floor was developed to allow enter in full height. Both Pe-8 ON were equipped with pneumatic ice-protection "Goodrich" system for wings and fins (also liquid ice-protection systems for pilot's windows and propellers as serial bombers had) because diesels ACh-30B didn't allow to use usual heating ice-protection for wings/fins. Pe-8 ON had additional oil tanks, improved fuel and cooling systems of engines; it could continue flight on each two engines from four.

The quality of Pe-8 was very good because of its low serial production and strict control (that was almost "handmade" aircraft also taking into consideration its technology of production), early ANT-42/TB-7 of 1938-1941 had even much better quality than Pe-8 of 1941-1944. But the later aircraft had more powerful engines - M-40 or ACZ-30B engines with a capacity of 1500 HP - which nearly doubled maximum range and payload.




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Page last modified: 30-08-2018 17:21:22 ZULU