The Yermolayev Yer-2 () was a long-range Soviet medium bomber used during World War II. It was developed from the Bartini Stal-7 prototype airliner before the war. It was used to bomb Berlin from airbases in Estonia after Operation Barbarossa began in 1941. Production was terminated in August 1941 to allow the factory to concentrate on building higher-priority Ilyushin Il-2 ground-attack aircraft, but was restarted at the end of 1943 with new, fuel-efficient, Charomskiy ACh-30B aircraft Diesel engines.
Although designed as a long-range medium bomber it was flown on tactical ground-attack missions during the Battle of Moscow with heavy losses. The survivors were flown, in ever dwindling numbers, until August 1943 when the last examples were transferred to schools. However, the resumption of production in 1943 allowed the aircraft to resume combat operations in April 1945. The Yer-2 remained in service with Long-Range Aviation until it was replaced by four-engined bombers such as the Tupolev Tu-4 at the end of the 1940s.
Development
Roberto Bartini had designed and built the Stal-7 airliner whilst he was the chief designer at the ZOK NII GVF ( — "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. 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 .
Preliminary design of the DB-240 (—"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 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 Berezin UBT machine gun. Another ShKAS was fitted in a ventral hatch. Up to of bombs could be carried in the bomb bay and two bombs could be carried externally. Up to of fuel could be carried. The DB-240 had been designed to use the experimental Klimov M-106 V12 engines, but the less-powerful Klimov M-105 engine had to be substituted because the M-106 was not available.
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.
Manufacture began in March 1941, with approximately 50 aircraft delivered by 22 June 1941. These aircraft were about slower than the prototype and their normal weight increased to . 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.
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.