Editing Yermolayev Yer-2 (section)

==Development==
[[Robert Ludvigovich Bartini|Roberto Bartini]] had designed and built the [[Bartini Stal-7|Stal-7]] airliner whilst he was the chief designer at the ZOK NII GVF ({{langx|ru|Завод Опытных Конструкций Научно-Исследовательского Института Граждаского Воздушного Флота – Zavod Opytnykh Konstrooktsiy Naoochno-Issledovatel'skogo Institoota Grazhdanskogo Vozdooshnogo Flota|lit=Factory for Special Constructions at the Scientific Test Institute for the Civil Air Fleet}}). The performance of the Stal-7 was exceptional, particularly in respect to its payload: at gross overload weight over 56% of the total weight was payload.<ref name=g4>Gordon, p. 354</ref> During flight trials with maximum all-up weight the prototype crashed on takeoff in early 1938, resulting in the arrest of Bartini and his imprisonment in a [[Siberian]] [[Gulag]] in February 1938.<ref>Gunston, p. 42</ref> The Stal-7 lay unrepaired until [[Vladimir Yermolaev]] was appointed as chief designer at [[Yermolaev|OKB-240]] after Bartini's arrest, with the task of transforming the Stal-7 design into a long-range bomber, a task made easier since Bartini had reserved space for a bomb bay in the fuselage. After repair the Stal-7 carried on with the flight-test programme, including a record-breaking nonstop flight on 28 August 1939 when it flew [[Moscow]]—[[Yekaterinburg|Sverdlovsk]]—[[Sevastopol]]—Moscow; a distance of {{convert|5,086|km|mi|abbr=on}} at an average speed of {{convert|405|km/h|abbr=on}}.<ref name=g4/>

Preliminary design of the '''DB-240''' ({{langx|ru-Latn|dahl'niy bombardirovschik|lit=long-range bomber}}), as the bomber version was designated, was completed by the beginning of 1939 and the construction of two prototypes began the following July. The DB-240 retained little apart from the general layout of the Stal-7 as the structure was almost completely redesigned. The pilot's cockpit was offset to port to improve his downward view and the navigator/bomb aimer sat in the extensively glazed nose with a {{convert|7.62|mm|adj=on|sp=us}} [[ShKAS]] machine gun, the radio operator sat below and to starboard of the pilot and the dorsal gunner in a partially retractable turret with one {{convert|12.7|mm|adj=on|sp=us}} [[Berezin UB]]T machine gun. Another ShKAS was fitted in a ventral hatch. Up to {{convert|2000|kg|abbr=on|0}} of bombs could be carried in the bomb bay and two {{convert|500|kg|adj=on|0}} bombs could be carried externally. Up to {{convert|4600|kg|abbr=on|0}} of fuel could be carried. The DB-240 had been designed to use the experimental [[Klimov VK-106|Klimov M-106]] [[V12 engine]]s, but the less-powerful [[Klimov M-105]] engine had to be substituted because the M-106 was not available.<ref name=g5>Gordon, p. 355</ref>

The DB-240 prototype flew for the first time on 14 May 1940 and began its State acceptance tests on 27 September 1940. The weaker engines prevented the DB-240 from reaching its designed performance.  It could only attain {{convert|445|km/h|abbr=on|0}} at {{convert|4250|m|abbr=on|0}} instead of the expected {{convert|500|km/h|abbr=on|0}} at {{convert|6000|m|sp=us|0}}. Its defensive armament was deemed inadequate and other problems included an excessively long take-off run and engine defects. However, these did not offset its virtues of a heavy bomb load and long-range ({{convert|4100|km|0|sp=us}} carrying {{convert|1000|kg|abbr=on|0}} of bombs). It was ordered into production at Factory No. 18, in [[Voronezh]], as the Yermolayev Yer-2.<ref name=g5/>

Manufacture began in March 1941, with approximately 50 aircraft delivered by 22 June 1941. These aircraft were about {{convert|5|-|8|km/h|abbr=on}} slower than the prototype and their normal weight increased {{convert|1220|kg|abbr=on|0}} to {{convert|12520|kg|abbr=on|0}}. Production was terminated in August 1941 with only 128 built to allow the factory to concentrate on the higher-priority [[Ilyushin Il-2]] ground-attack aircraft.<ref>Gordon, pp. 355–56</ref>

A Yer-2 was modified with experimental [[Mikulin AM-37]] engines, a reinforced undercarriage, armored seats for the navigator and gunner, and 12.7&nbsp;mm UBT machine guns in place of its original ShKAS weapons. It first flew in July 1941 and was able to reach {{convert|505|km/h|abbr=on|0}} at {{convert|6000|m|abbr=on|0}}, but the range was reduced to {{convert|3500|km|abbr=on|0}} carrying {{convert|1000|kg|abbr=on|0}} of bombs. One significant problem with this version was the excessive takeoff roll which hindered operations from grass airstrips.<ref>Gordon, p. 357</ref> The engine was unreliable, however, and had cooling problems that the Mikulin [[OKB]] did not have the resources to resolve so it was cancelled in October when the factory was forced to evacuate from Moscow by the German advance.<ref>{{Cite book|last=Kotelnikov|first=Vladimir|title=Russian Piston Aero Engines|publisher=Crowood Press|location=Marlborough, Wiltshire|date=2005|page=110|isbn=1-86126-702-9}}</ref>

The [[Charomskiy M-40]]F Diesel engine was also evaluated in a Yer-2 in 1941. This engine, like all Diesels, offered a greatly reduced [[Brake specific fuel consumption|fuel consumption]] compared to a standard gasoline-powered engine, but at a great penalty in weight. These engines increased the gross takeoff weight to {{convert|13500|kg|abbr=on|0}} which required the undercarriage to be reinforced and the wing area increased to keep the same [[wing loading]]. The M-40F-powered aircraft reached a maximum speed of {{convert|430|km/h|abbr=on|0}} at {{convert|6050|m|abbr=on|0}}. However, the M-40 was not yet ready for service use and the project was cancelled.<ref name=g8>Gordon, p. 358</ref>

The aircraft/engine combination did have enough potential that development work continued using the closely related, but more mature, [[Charomskiy ACh-30]]B Diesel engine. The cockpit was modified to accommodate two pilots side-by-side and the wing and tailplane areas were increased. The 12.7&nbsp;mm UBT machine gun in the dorsal turret was replaced by a {{convert|20|mm|adj=on|sp=us}} [[ShVAK cannon]] and the nose and ventral ShKAS machine guns were exchanged for 12.7&nbsp;mm UBT machine guns. Up to {{convert|5460|kg|abbr=on|0}} of fuel could be carried. The Yer-2/ACh-30B was placed into production at Factory No. 39 in [[Irkutsk]] at the end of 1943 and the first production aircraft was submitted to its State acceptance trials the following month. Some excess aircraft were converted as Yer-2ON VIP transports.<ref name=g8/>