Editing Ilyushin DB-3 (section)

==Design and development==
The genesis of the DB-3 lay in the BB-2, [[Sergey Ilyushin]]'s failed competitor to the [[Tupolev SB]]. Ilyushin was able to salvage the work and time invested in the BB-2's design by recasting it as a long-range bomber, again competing against a [[Tupolev]] design, the [[Tupolev DB-2|DB-2]], to meet the stringent requirements of an aircraft capable of delivering a {{convert|1000|kg|abbr=on}} bombload to a range of {{convert|3000|km|abbr=on}} at a maximum speed no less than {{convert|350|km/h|abbr=on}}. He had redesigned the BB-2 to take advantage of the radial [[Gnome-Rhône Mistral Major]] 14Kdrs engine, for which the Soviets had purchased a license in 1934 as the M-85, and had begun construction of the prototype of the BB-2 2K-14 as the TsKB-26 that same year.<ref>Gordon, p. 81</ref>

The TsKB-26 was more of a proof-of-concept vehicle to validate Ilyushin's ideas on how to obtain long range than an actual bomber prototype. To speed the construction process, it had a wooden fuselage and fin with metal wings and tail surfaces. It made its first flight in the summer of 1935 and proved to be stable, easily controllable and highly maneuverable; it performed the first [[Aerobatic maneuver|loop]] made by a twin-engined aircraft in the Soviet Union.<ref name=g2>Gordon, p. 82</ref> It went on to set six world records in its class, generally in payloads to height and speed over a {{convert|5000|km|abbr=on}} closed circuit.<ref name=g2/>

The real prototype of the DB-3 was called the TsKB-30 and it was completed in March 1936. It had a number of improvements over the TsKB-26, notably an all-metal structure, an extended nose, an aft-sliding canopy with a fixed [[windscreen]] and improved engine cowlings. It passed the State acceptance trials and was ordered into production in August 1936 as the DB-3,<ref name=g2/> although some sources refer to this initial series as the DB-3S for ''seriynyy'' (series-built).<ref name=g4>Gordon, p. 84</ref>

The DB-3 was not a simple or easy aircraft to manufacture as Ilyushin had pushed the limits of the available construction technology to make it as light as possible. For example, the [[Spar (aviation)|spar]] in each wing panel had four parts which had to be riveted together and there were numerous welds that each had to be inspected by an [[X-ray generator|X-ray machine]], with many failures. In addition the internal riveting of small-diameter tubing was also a difficult and time-consuming process.<ref name=g3>Gordon, p. 83</ref>

The bomb bay was designed to carry ten {{convert|100|kg|abbr=on}} FAB-100 bombs, but heavier bombs could be accommodated on external bomb racks up to a total of {{convert|2500|kg|abbr=on}} on short-range missions. The defensive armament for the three crewmen consisted of three {{convert|7.62|mm|1|abbr=on}} [[ShKAS machine gun]]s. One in the tip of the nose manned by the bombardier-navigator and the two others protecting the rear. The rear gunner manned both the gun in the SU dorsal turret and the gun in an LU ventral hatch.<ref name=g3/>

Flight tests of the second example pre-production aircraft, conducted May–October 1937, revealed that it was slightly inferior to the TsKB-30 in performance, but still exceeded its requirements by a considerable margin. It attained a speed of {{convert|390|km/h|abbr=on}} at an altitude of {{convert|5000|m|abbr=on}}. It could carry a bombload of {{convert|500|kg|abbr=on}} to a range of {{convert|4000|km|abbr=on}} and a {{convert|1000|kg|abbr=on}} bombload to a range of {{convert|3100|km|abbr=on}}. In comparison, the [[Heinkel He 111]]B then in production was {{convert|10|-|20|km/h|abbr=on}} slower and could carry only {{convert|750|kg|abbr=on}} of bombs to a range of {{convert|1660|km|abbr=on}} and {{convert|1500|kg|abbr=on}} to a distance of {{convert|910|km|abbr=on}}. This performance arguably made it the best twin-engined bomber in the world already or entering service in 1937.<ref name=g4>Gordon, p. 84</ref> 45 DB-3s were built that year at Factory No. 39 in [[Moscow]] and No. 18 in [[Voronezh]] and the aircraft entered service with the [[Soviet Air Forces|VVS]].<ref name=g4/>

During 1938 the improved M-86 engine, rated at {{convert|950|hp|kW}} for takeoff, replaced the M-85 on the production line. Aircraft with this engine are properly referred to as DB-3 2M-86, but are sometimes referred to as the DB-3A, after the three-step upgrade program planned for the aircraft. Other minor changes were introduced over the course of the year. Factory No. 126 in [[Komsomolsk-on-Amur]] also began producing DB-3s in 1938.<ref>Gordon, pp. 85–86</ref>

During 1938–39 the [[Tumansky M-87]]A engine was introduced on the production line in a gradual transition as were VISh-3 [[Controllable pitch propeller|variable-pitch]] [[propeller (aircraft)|propeller]]s. The M-87 had the same horsepower rating at takeoff as the M-86, but produced more power at higher altitudes. The M-87B further increased power at altitude and was introduced in 1939–40. These aircraft were known as the DB-3B as part of the second stage of the upgrade program. The last production batches in 1940 had the [[Tumansky M-88]] that produced {{convert|1100|hp|kW}} for takeoff. These increased the maximum speed to {{convert|429|km/h|abbr=on}} at {{convert|6800|m}}.<ref>Gordon, p. 86</ref>

===Nomenclature===
Great confusion exists in the sources, including original Soviet documents, about the names commonly used for the DB-3. Formally the Soviet designation system used a two-letter abbreviation to designate the role of the aircraft, then a number for the model in that sequence followed by the number of engines, and the engine used. So SB 2M-100A is decoded as twin-engined fast bomber, first in the series, equipped with M-100A engines. Shorter abbreviations were informally used, but the use of them is not consistent between sources. For example, the listing for the strength of the VVS on 1 June 1941 shows a mixture of DB-3A and DB-3 aircraft, with the former predominating.<ref>{{cite web|url=http://www.rkkaww2.armchairgeneral.com/weapons/Airforce_41.xls|title=Airforce_41.xls|access-date=2009-09-07|archive-url=https://web.archive.org/web/20060831040324/http://www.rkkaww2.armchairgeneral.com/weapons/Airforce_41.xls|archive-date=2006-08-31|url-status=dead}}</ref> But this does not match the account in Gordon where the DB-3A designation is used for one of the oldest versions of the DB-3. And where are the DB-3Bs?