Yermolayev Yer-2

Roberto Bartini had designed and built the Stal-7 airliner whilst he was the chief designer at the ZOK NII GVF (). 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. 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. The Stal-7 lay unrepaired until Vladimir Yermolaev was appointed as chief designer at 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—Sverdlovsk—Sevastopol—Moscow; a distance of at an average speed of . 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 at instead of the expected at . 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 ( carrying of bombs). It was ordered into production at Factory No. 18, in Voronezh, as the Yermolayev Yer-2. A Yer-2 was modified with experimental Mikulin AM-37 engines, a reinforced undercarriage, armored seats for the navigator and gunner, and 12.7 mm UBT machine guns in place of its original ShKAS weapons. It first flew in July 1941 and was able to reach at , but the range was reduced to carrying of bombs. One significant problem with this version was the excessive takeoff roll which hindered operations from grass airstrips. 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. The Charomskiy M-40F Diesel engine was also evaluated in a Yer-2 in 1941. This engine, like all Diesels, offered a greatly reduced fuel consumption compared to a standard gasoline-powered engine, but at a great penalty in weight. These engines increased the gross takeoff weight to 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 at . However, the M-40 was not yet ready for service use and the project was cancelled. The aircraft/engine combination did have enough potential that development work continued using the closely related, but more mature, Charomskiy ACh-30B Diesel engine. The cockpit was modified to accommodate two pilots side-by-side and the wing and tailplane areas were increased. The 12.7 mm UBT machine gun in the dorsal turret was replaced by a ShVAK cannon and the nose and ventral ShKAS machine guns were exchanged for 12.7 mm UBT machine guns. Up to 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. ==Operational history==

The Yer-2 was not in squadron service when Germany invaded on 22 June 1941, but the 420th and 421st Long-Range Bomber Regiments (—DBAP) were formed shortly afterwards. However neither regiment flew any operational missions until later in the summer. Three crews from the 420th DBAP bombed Königsberg during the nights of 28–29 and 30 August – 1 September from Ramenskoye Airport, southeast of Moscow. On 1 October 1941 63 Yer-2s were in service, but only 34 were operational. The 420th DBAP had flown 154 sorties by the beginning of November (6 in August, 81 in September, 67 in October) and had lost 30 of its 40 aircraft. Over half of these (19) were due to non-combat losses. Losses were extremely high over the autumn and winter as they were inappropriately committed against German tactical frontline targets during the Battle of Moscow at low altitudes and only 12 were in service on 18 March 1942. The survivors were flown, in ever dwindling numbers, until August 1943 when the last few aircraft were transferred to schools by the 2nd Guards DBAP and the 747th DBAP. The Yer-2 was placed back into production at the end of 1943, but none of the new bombers had been issued to combat units by 1 June 1944. However 42 were in service on 1 January 1945 and 101 on 10 May 1945 after the war ended. It remained in service with Long-Range Aviation units until replaced by four-engined bombers like the Tupolev Tu-4 in the late 1940s. ==Variants==

;DB-240 :Two prototypes of the Yer-2 series with two 1,050 hp M-105 engines. ;Yer-2 :Production version with two M-105 engines, 128 built. ;Yer-2/AM-37 :One aircraft re-engined with two prototype 1,380 hp Mikulin AM-37 engines, the fastest of all Yer-2s. ;Yer-2ON :(−Special Assignment) Two aircraft from the Yer-2/ACh-30B production line were modified with a 12-seat VIP cabin, military equipment removed and long-range fuel tanks in the bomb-bay. A third aircraft was converted from a Yer-2 (1941 production) and used for shuttle flights between Irkutsk and Moscow. At least one other source instead applies the Yer-4 designation to a 1943 prototype that he states did not enter production. However, his description otherwise matches the aircraft that other sources identify as the prototype that led to the Yer-2/ACh-30B production series, including its engine choice, extended wingspan, cannon armament in the nose, and development timeline. ;Yer-6 :The designation Yer-6 was applied to two different aircraft in some documentation: :* The first was a Yer-2 tested with M-40F engines in 1941. Fifteen flights had been made before the outbreak of war with Germany. :* The designation was re-used for a Yer-2 fitted with special engine mounts that allowed for M-40F, M-ZO, or AM-38F engines to be fitted without any further modifications. ==Operators==

; • VVS (—Soviet Air Forces) • ADD (—Long Range Aviation) • 420th Long-Range Bomber Aviation Regiment, later the 748th Long-Range Bomber Aviation Regiment • 421st Long-Range Bomber Aviation Regiment, later the 747th Long-Range Bomber Aviation Regiment • 747th Long-Range Bomber Aviation Regiment • 748th Long-Range Bomber Aviation Regiment, later the 2nd Guards Long-Range Aviation Regiment • 327th Long-Range Bomber Aviation Regiment • 329th Long-Range Bomber Aviation Regiment ==Specifications (Yer-2/ACh-30B)==