The long-range bomber Er-2 (originally designated DB-240) was developed on the basis of the 12-seat high-speed passenger aircraft "STAL 7", created under the leadership of R.L. Bartini and released in 1936. This aircraft had excellent flight data, confirmed in several flights within the USSR. In particular, in 1939 the crew under the command of pilot N.P. Shebanova made a circular non-stop flight, flying 5068 km at an average speed of about 405 km / h, which was higher than the world achievement for a flight on a closed route.

According to the combination of its parameters, "STEEL 7" was certainly a promising aircraft. He had excellent aerodynamic properties and high weight return. Its dimensions were somewhat larger than those of the DB-3. Unfortunately, "STEEL 7" did not go into serial production. In 1938 R.L. Bartini, like many other workers in the aviation industry, was arrested on completely ridiculous charges. When the idea arose to create a long-range bomber on the basis of this aircraft, all work on the alteration of the machine was entrusted to V.G. Ermolaev, who was one of the leading designers in the R.L. Bartini Design Bureau.

The power plant.    The DB-240 was designed for the advanced M-106 liquid-cooled engines, with which this bomber could have a range of 5000 km and a maximum speed of 500 km / h at an altitude of 6000 m, which was 70 - 80 km / h higher than the speed of the then main long-range bomber DB-3F. But the development of the M-106 was delayed and the designers were forced to urgently redo the project for less powerful and high-altitude, but already produced series for the M-105 engines.

The forced replacement of the power plant significantly reduced the combat capabilities of the DB-240. noticeably decreased its speed and altitude. However, there were no other serial engines more suitable for this aircraft at that time.

The design of the bomber's power plant was radically revised compared to that used on Stal-7. So, instead of frontal radiators located under the engines, the DB-240 received tunnel radiator installations in the cantilever parts of the wing with adjustable shutters at the exit. The entrances to the tunnels were made in the zone of high velocity pressure created by the propellers, and the exits were made in the vacuum zone, approximately in the middle of the console chord. The tunnels, which had optimal diffuseness, ensured effective cooling of water and oil coolers and at the same time created low resistance. The entire cooling system was tested on a specially created ground stand by Yu. Edelshtein, which was not often practiced at that time.

The engine compartment was blown by the oncoming flow, taken through the holes in the toes of the spinners of the screws. Some increase in speed was hoped to be obtained through the use of jet exhaust pipes. From the point of view of aerodynamics, the DB-240 engine installation with M-105 engines was the height of perfection: cigar-shaped hoods with original recessed hood locks and a minimum of elements protruding into the stream provided the lowest possible resistance. Combined production of fuel from all gas tanks was carried out with the organization of a common collector at the bottom of the service tank. To do this, gasoline from low-lying tanks in the engine compartments and consoles was pumped into the supply tank by pumps, and from the console tanks it came by gravity.

The DB-240 was a cantilever all-metal monoplane with a reverse gull wing. The fuselage is triangular in cross-section with rounded corners. To increase the flight range with a normal bomb load of 1 ton, an additional gas tank was provided in the free space of the bomb bay. Crew - 4 people: pilot, navigator and two gunners. The cockpit was shifted to the left of the axis of symmetry, which gave a better view. To reduce aerodynamic drag in cruising flight, the upper turret with a BT heavy machine gun and the lower hatch installation of the ShKAS rapid-fire machine gun were retracted into the fuselage, which gave a speed gain of 15 km / h. The design of the bomber was significantly different from the design of "STEEL 7" and was based on the use of the plasma-template production method.

The tests of the DB-240 were completed in the fall of 1940, and the Voronezh Aviation Plant began organizing its mass production.

Despite the insufficient power of the engines, the Yer-2 had a number of advantages over the DB-3F. At low and medium altitudes, its maximum speed was 30-50 km / h more. With the same bomb load of 1 ton, the range of the Yer-2 exceeded the range of the DB-3F by almost 20%, moreover, at a cruising speed of 395 km / h versus 340 km / h. Compared to the DB-3F, the Er-2 bomber was simpler in terms of piloting technique. But due to the relatively low altitude of the engines, the performance of combat missions on the Yer-2 was associated with a great risk, since the likelihood of anti-aircraft artillery fire and interception by enemy fighters increased, and the dependence on weather conditions on the route increased.

Photo	Description
	Drawing DB-240
	The first prototype DB-240 during production tests

Bibliography

• "The history of designs of planes in USSR 1938-1950" /Vadim Shavrov/
• "Avia Master # 2 1999 " /Al. Medved, Dm. Khazanov/
• "Planes of Stalin falcons" /Konstantin Kosminkov and Dmitriy Grinyuk/