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Aviation Diesels for Yer-2
Alexander Medved and Dmitry Khazanov
Aviation diesel engines in the early forties were a source of special pride for domestic engine builders. Only in the USSR and Germany, diesel engines were "brought" to the level of development, which made it possible to proceed to flight tests and even to the construction of serial aircraft equipped with this type of power plant. But if in Germany the main emphasis in creating an aviation diesel was on increasing reliability, then in the USSR it was on achieving the highest power. In our country, the use of aircraft diesel engines was considered the most promising for long-range and heavy bombers. For aircraft of these classes, the requirements for efficiency and high unit power of the "engine" were in the foreground. Since the maximum takeoff weight of a twin-engine long-range bomber at that time was estimated at 16-18 tons, in order to obtain good take-off qualities and a sufficiently high cruising speed (about 400 km / h), it was required to “remove” at least 1500-1800 h. p. from each of the two shafts of 750 h.p. In the first place, the activities of domestic "diesel" design bureaus were aimed at obtaining just such characteristics.
The most important advantages of diesel engines were considered to be significantly lower fuel consumption compared to carburetor engines, as well as the lower fire hazard of kerosene (diesel fuel) compared to flammable aviation gasoline. In addition, diesel fuel has a high density, so more fuel (by weight) can be poured into tanks of the same capacity. The disadvantage of a diesel engine is that it is much heavier than a carburetor counterpart of the same power. This is due to the large shock loads characteristic of the combustion process of fuel that is ignited by compression. Diesels have worse acceleration compared to gasoline engines. To start them, a powerful starter is required, much heavier than that of a carbureted engine.
The main contribution to the creation of aviation diesel engines in the USSR was made by the department of oil engines of CIAM, which was headed by Andrey Dmitrievich Charomsky before his arrest. In 1936-1937. this team developed the AN-1A diesel engine with a power of 900 hp, which, thanks to the monitoring station, was maintained up to an altitude of 2500 m. The engine passed flight tests on a TB-ZD aircraft. In the future, two independent teams were engaged in finalizing the design of the AN-1A. One of them, headed by V.M. Yakovlev, worked at the famous Kirov plant in Leningrad and improved the M-40 engine (the former name was AN-1R, after the arrest of A.D. Charomsky, it was smeared on all the blueprints of the drawings and replaced with a new one). The degree of secrecy of diesel engines was considered so high that people's commissars A.I. Shakhurin and L.P. Beria personally gave access to the relevant documentation. Because of this, there was even a scandal when the military representatives (after all, they were from another department - the people's commissariat of defense) at the plant for a long time could not get acquainted with the products, the quality of which was required to be controlled "according to the situation."
The second design bureau, organized at the Moscow plant No. 82, was a “sharashka”, the actual head of which was the “enemy of the people” A.D. Charomsky (but in the documents of the NKAP of that period his name did not appear anywhere, the director of the plant was nominally responsible S.I. Zhilin and chief engineer A.G. Takanaev). The diesel engine developed by the "zeks" was called the M-30. The development of both models (M-40 and M-30) was carried out in one general direction: while maintaining the working volume, cylinder diameter and piston stroke, the designers sought to increase the take-off power and engine altitude through the use of two-stage turbochargers (TK-88 on the M-40 and TK-82 on M-30). Four TCs were installed on each engine; at this stage, the motors did not have drive superchargers. In the future, such a decision was recognized as erroneous, but in the middle of 1940 the shortcomings of the scheme had not yet been recognized, and the results obtained were overestimated. The successful completion of bench tests of the M-40 was followed by the decision to launch their mass production in addition to the Kirov plant also at the Kharkov Tractor Plant, and later at Plant No. 751. In addition, V.M. Yakovlev was tasked with boosting the engine to 1500 hp. in takeoff mode and up to 1250 hp. at nominal. This version of the engine was designated M-40F.
In May 1940, the M-30 engine with similar technical characteristics was ready at Charomsky's "outlet". Both engines were flight tested, however, of a limited volume, on two BOK-15 aircraft. Before the May (1940) resolution of the Defense Committee under the Council of People's Commissars, both engines were intended mainly to achieve a political result - a round-the-world non-stop flight of a Soviet aircraft under the control of M.M. Gromov. The technical parameters of the aircraft-motor complex could ensure the fulfillment of this task, provided that the engine could withstand at least 100 hours of continuous operation at rated power. However, in the summer of 1940, neither the M-30 nor the M-40 had such a resource yet. The Defense Committee issued a new task to engine builders: in August 1940, to conduct state tests of both types of diesel engines on the stand, and in October-December, install them on TB-7 and DB-240 aircraft, and then proceed to flight tests.
Difficulties in fine-tuning pushed back the deadlines for the implementation of the tasks of the Defense Committee. Only in November 1940, after the bench tests of the M-40 diesel aircraft engine were completed, did OKB-240 develop a draft design, and on March 17, 1941, under the chairmanship of the head of the Air Force Research Institute, Major General A.I. Filin, in the presence of Ermolaev and Ozimkov, the a meeting of the mock-up commission for a new aircraft, but with forced diesel engines M-40F. The maximum bomb load of the machine was set equal to 6000 kg, while one FAB-2000 was supposed to be suspended inside the fuselage, and two more - on under-wing holders !! Such an armament option at that time was considered too heavy even for a four-engine TB-7 (only in the second half of the war, Pe-8 aircraft with ASh-82F engines, in exceptional cases, began to make sorties with six tons of bombs on board). Without waiting for the start of testing, the leadership of the NKAP, with the blessing of the Council of People's Commissars, planned the serial production of "diesel" DB-240s, starting from the third quarter of 1941. As already mentioned, in total, Voronezh plant No. 18 was supposed to produce 90 machines by the end of this year 2, and in 1942 - to build 800 aircraft!
In mid-April, 1941, the Yer-2 aircraft with M-40F diesel engines was brought to the airfield and made a number of taxiing and approaching. Based on the results of testing, it was necessary to replace the hydraulic cylinders for lifting the main landing gear. During the next run, the crutch formed, the tail spinner turned out to be dented. Both nodes had to be replaced. The first flight of the aircraft was held back by the absence of a factory pilot: by this time, N.P. Shebanov had retired from factory No. 240, and another was not appointed. Without Ermolaev, the solution of this issue was delayed. The chief designer himself in the spring of 1941 was almost constantly in Voronezh at a serial plant. Only in early May, pilot L.A. Dudkin was allowed to fly on the Er-2 2M-40F. He made several flights, the machine in the air behaved normally. On May 15, a pilot from the LII NKAP Shilev drove the machine to Ramenskoye to the institute's test airfield. Here she ended up in the company of "distant relatives" - TB-7 with diesel engines M-30 (serial number 4227) and M-40F (serial number 4225). All diesel aircraft flew infrequently, mainly due to the revealed low reliability of turbochargers, in which the bearings continually crumbled and the blades “flyed”. This cup did not pass and Er-2: at the end of May, both of its motors failed and were sent to the manufacturer.
G. M. Shiyanov was appointed the lead pilot for Yer-2 with M-40F in the LII NKAP. Before the start of the war, he managed to complete 15 flights, while he had to change turbochargers and exhaust manifold covers more than once. In addition, increased oil consumption was revealed, and therefore it was necessary to significantly increase the volume of oil tanks. Since June 7, the ongoing tests by government decree were transferred to the category of joint tests with the Air Force Research Institute, for which military overflight pilots arrived in Ramenskoye. At the same time, the machine in some "internal" documents of the Design Bureau received a new name - Er-6. Later, under this designation, an aircraft with a “universal” engine mount passed, which made it possible to mount the M-40F, or M-30, or AM-38F engine on it without any changes.
On July 23, 1941, the head of the LII NKAP, M.M. Gromov, approved the act of testing the Er-2 aircraft with M-40F engines. The purpose of the tests was to check the maximum speed range of the machine with a flight duration of about 17-20 hours. The maximum take-off weight of the machine was estimated at 16500-17000 kg, which was clearly overestimated. In reality, an aircraft with such a mass, with diesel power limited by CIAM in terms of maximum specific fuel consumption, could not take off from the ground, therefore its take-off mass could not exceed 15,000 kg. In accordance with the calculations, the maximum speed of the machine was supposed to be 480 km / h, during the tests it was possible to get only 448 km / h. Leading engineer N.S. Rybko explained the lack of speed by the lower nominal power of the engines, the unaccounted for interference of the open shutters of the cooling system and the wing, as well as the non-retractable tail wheel.
Due to the poor throttle response of diesel engines, takeoff power was set only at the end of the takeoff run, because of this, the takeoff run and takeoff distance increased by 220-260 m against the calculated values. In addition, the diameter of the propellers was also recognized as insufficient, which had already increased to 3.8 m. But the wing of the aircraft had to be redesigned specifically for diesel machines, increasing the span of the center section. Screws with a diameter of 4.1 m were mounted on the understudy Er-2 2M-40F, due to which it was planned to obtain a take-off run reduced by 150 m and an increased range. However, this machine was built only in October 1941. Due to the lack of knowledge of the M-40F engines, no flights were made in 1941, and later it was converted in the interests of the Yer-2 2M-30 program. The third machine, designed to install M-40F or M-30 diesel engines, began to be built in the summer of 1941, but then it was dismantled during the evacuation of plant No. 240 to Kazan.
As for the first Yer-2 with the M-40F, it, like the diesel TB-7s, became hostage to the engine, which seriously undermined its reputation during the raid of the 81st Air Division on Berlin on the night of August 10, 1941. Only one TB-7 (with M-30 diesels) out of seven flying machines (the eighth crashed during takeoff) managed to return to the Pushkin airfield, all the rest suffered to some extent due to defects in the M-40F diesels. It is characteristic that all the shortcomings of the power plant, which the leadership of the NKAP willingly turned a blind eye to before the Berlin fiasco, “suddenly” came to light and became sufficient reason for the almost complete curtailment of the diesel program. True, at first only the M-40F was considered discredited, and the penance was imposed on Charomsky's engines a little later. The main reasons for criticism were their unstable work at low costs and in the planning mode.
With the onset of cold weather, these and other difficulties with ensuring the normal operation of diesel engines were revealed with renewed vigor. “When starting, the motors shake violently, some cylinders or one block begin to work, and only after warming up to 60 ° all cylinders work, - it was noted in the test report. At an altitude of more than 4000 m, when the flow rate drops to 70-90 kg / h, the motors or individual units spontaneously turn off. on suction did not provide flashes in part of the cylinders, which led to a sharp decrease in the speed of the TC and a further decrease in air pressure behind them. In addition, the motors vibrated strongly (the cause was considered to be the dynamic imbalance of the moving parts) and caused nasty small shaking of the entire aircraft structure.
Another unpleasant feature of diesel engines was the overly complicated technique of landing the machine. Usually, the engine is throttled during gliding to avoid speed acceleration. But the diesel engine with injection from the TC, for the above reasons, did not want to work steadily on "low gas". Asymmetric engine thrust in this flight mode is absolutely unacceptable, so the test pilots had to land "in a glider", that is, with the engines turned off. Of course, this was unacceptable for combatant pilots. Suffice it to recall that even such an outstanding master as V.P. Chkalov fell victim to an error in the calculation when landing with a failed engine.
Nevertheless, Ermolaev hoped to finalize the machine, in connection with which on August 5, 1941 he wrote a letter to the people's commissar of the aviation industry A.I. Shakhurin it is necessary to continue the work of our plant for the creation of long-range bomber aircraft and we ask you ... to give the team of our plant an opportunity to finish fine-tuning the Yer-2 2M-40F aircraft." However, the fate of the M-40F was practically decided by an unsuccessful raid on Berlin.
In the autumn of 1941, the Germans blocked Leningrad and the continuation of work on the M-40F aircraft diesel engines at the Kirov Plant became impossible. The Kharkov Tractor Plant was completely reoriented to the production of T-34 tanks and V-2 diesel engines for them. For these reasons, the M-40F program was curtailed, and in the first half of 1942, any improvements to the Yer-2 with this version of the power plant ceased. The plan to resume production of diesel Yer-2s at plant No. 18 was not implemented either, although the designers of the Ermolaev Design Bureau in the first half of 1941 transferred a complete set of drawings to Voronezh.
By the beginning of the summer of that year, about 200 aircraft diesel engines had already been built in the USSR, including up to 150 M-40 and M-40F by the Kirov Plant and KhTZ, and up to fifty M-30 by Plant No. 82. At the first stage, TB-7 aircraft manufactured by Kazan plant No. 124 began to be equipped with these engines. In the second place, the consumers of diesel engines were "Yer". Since at the beginning of 1941 the serial production of Yer-2 with diesel engines was only planned, and the TB-7 version already existed in metal, the team of I.F. The first results of the operation of engines with compression ignition, it must be admitted, turned out to be gloomy. During the tests, only 22% of the M-40 engines and 10% of the M-30 engines were able to operate for more than 50 hours, while approximately every third diesel engine failed without serving even 10 hours!
1 Plans for the production of the M-40F in 1941 provided for the construction of 1,500 diesel engines at the Kirov Plant and 750 at the Kharkov Tractor Plant.
2 This number varied from ruling to ruling, but never exceeded 100 machines.
Aircraft | Glossary | USSR | Bartini | Yermolaev | DB 240 | Yer-2 | Yer-2 | Yer-2ON | Photos & Drawings Combat Use Combat Use | Yer-2 | Diesels for Yer-2 |
GKO - Gosudarstvennyy Komitet Oborony - State Defense Committee
LII - Letnyy issledovatel'skiy institut - Flight Research Institute
NKAP - Narodnyy komissariat aviatsionnoy promyshlennosti - People's Commissariat of Aviation Industry
TC - Turbo Compressor
DBA - Dal'ne bombardirovochnaya aviatsiya - Long-range bomber aviation
VVS KA - Voyenno vozdushnyye Sily Krasnoy Armii - Air Force of the Red Army
CIAM - Tsentral'nyy institut aviatsionnogo motorostroyeniya - Central Institute of Aviation Motors
FAB - Fugasnaya avibomba - High-Explosive Bomb
KhTZ - Khar'kovskiy Traktornyy Zavod - Kharkov Tractor Plant
The M-30 engine was designed by A.D. Charomsky, taking into account the already identified shortcomings of the M-40. In particular, monoblock cylinders were designed (one of the defects of the M-40 was the knocking out of an aluminum gasket in the gas joint of the blocks), a more rigid crankshaft, new connecting rods and a reinforced crankcase were used, the design of which took into account French experience. To do this, Charomsky and his staff had to carefully study all the "subtleties" of the Hispano-Suiza HS12Y engine, which became the basis for a whole family of domestic M-100 / M-105 aircraft engines.
In general, the M-30 engine turned out to be easier to manufacture and operate compared to the "fortieth". Its design in terms of power was more rigid, and with a smaller mass, the motor, after appropriate refinement, became more reliable, allowing forcing without any special alterations. In December 1940, he passed 100-hour state tests, and in June 1941, commission 150-hour tests on the machine. And yet, the "thirty", like all new products, suffered from a large number of, albeit small, but unpleasant defects. She also inherited the most important drawback of the M-40: the tendency to self-shutdown when flying at cruising speed at an altitude of more than 4000 m.
Plans to equip the experimental Yer-2 with M-30 engines in 1941 were not implemented due to the outbreak of war, the redirection of plant No. 240 to mass production of small bomb clusters KMB-2 production of 1000 pieces per month) and its subsequent evacuation to Kazan. In addition, OKB-240 spent a lot of effort on bomber variants with M-40F and AM-37 engines, not to mention production vehicles. Only after returning to Moscow in the spring of 1942 did Ermolaev focus on the M-30 diesel engine.
And the situation around the engine of A.D.Charomsky during this period was not easy. Disappointed with the results of the operation of diesel TB-7s, the leadership of the NKAP and the country (as usual, it could not do without the highest officials of the state) in February-March 1942 decided to liquidate the last of the enterprises involved in aviation diesel engines - plant No. 82. This decision was motivated by the need to strengthen the production base of plant No. 45, which duplicated the production of AM-38 engines for Il-2 attack aircraft. In a difficult situation, the only ally of the “dieselists” was the Air Force of the spacecraft represented by the head of the Main Directorate of Orders and Technical Supply, Brigadier N.P. Seleznev. He sent a letter to the head of the aviation department of the Central Committee of the All-Union Communist Party of Bolsheviks Vavilov, in which he petitioned for the cancellation of the “crushing” decision of the State Defense Committee No. 1440ss of March 14, 1942. In particular, Seleznev wrote:
"Aviadiesel M-30, tested in combat operations on a TB-7 aircraft, confirmed the positive qualities of a diesel engine.
To eliminate the main defect of the motor: self-shutdown when planning at altitudes of more than 4000 m, plant No. 82 designed a combined boost to the M-30 engine: from a turbocharger and a driven centrifugal supercharger. Such a motor was manufactured and at the beginning of March 1942 successfully completed 50-hour bench tests. To decide on the launch of the M-30 with combined supercharging in a series, only small flight tests need to be carried out.
The M-30 engine has a development perspective and can be brought up to a power of 1750 hp within 4-5 months.
... Plant No. 82, the only one in the USSR for the production of aircraft diesel engines, has extensive experience in fine-tuning diesel engines and manufacturing small series, has the necessary equipment and technology for mass production, has qualified personnel who have absorbed the culture of aircraft diesel building and are able to establish mass production in the next 4-5 months."
Despite this letter and even the fact that by an earlier GKO resolution No. 1207ss dated January 24, 1942, plant No. 82 was obliged to produce a serial M-30 diesel engine with combined supercharging by May 1, 1942, the decision to liquidate the enterprise entered into force. The chief designer for the M-30 at CIAM (there was such an interesting position) Tulupov tried to appeal to the highest officials of the state and wrote another letter, this time to L.Z. Mekhlis. The result was the same.
But the whole chain of amazing decisions is not over yet. In less than three months, on June 4, 1942, the same GKO issued decision No. 1866ss, in which the NKAP was proposed to organize a new plant No. 5003 ... "for the production of small series of aircraft diesel engines." At the same time, now plant No. 45 was ordered to urgently transfer special "diesel" equipment to a new plant, and the latter - to convert two Yer-2s by July and five TB-7s under the M-30 by August! However, neither the NKAP, nor the State Planning Committee of the USSR, nor Plant No. 45 complied with the instructions of the highest governing body of the country. Charomsky and his colleagues had to “take the rap” themselves, bit by bit collecting the necessary machines and tools. Naturally, the efficiency of work throughout 1942 turned out to be extremely low.
In February-March 1942, after almost a six-month stay in Kazan, Plant No. 240 was reevacuated to Moscow. And then it turned out that the former territory of the plant and even its number were "expropriated" by the design team of S.V. Ilyushin. Ermolaev tried to "fight for the truth", but as a result, the current situation was consolidated by order of the NKAP No. 304 of April 21, 1942. Ermolaev, along with the drawing economy and the machine park, were "in limbo." However, soon their situation was "significantly eased" - the machines and equipment were taken away. Only in July, the territory "B" of plant No. 240 and the building of the evacuated Library Institute of the People's Commissariat of Education were transferred to a seriously reduced team. Of the workers at this point, only 70 people remained, and from the machines - as many as five! The plant, in essence, began life anew under the new number 134. The first tasks for the workers were the conversion of two damaged Yers delivered from the front to AM-35A engines and one more to AM-37 engines. After refurbishment, all three vehicles were handed over to the 747th Air Regiment of Colonel Gusev.
By September 1942, a new version of the Yer-2 bomber with M-30B engines was ready "in metal", which received No. 4. Today it is not easy to figure out why experimental vehicles with the M-40 were “ignored” when calculating the numbers, in any case, it is known that the machine number 3 is the copy used in the statistical tests. From copy No. 2 with AM-37 engines, the new version of Er-2 differed not only in the motor unit. Thus, the midsection of the fuselage has increased by increasing it in the lower part by 70 mm. The increased size of the bomb bay made it possible to hang up to 20 FAB-100 bombs or eight FAB-250 bombs inside, four half-tons were another suspension option. Three external bomb racks made it possible to hang 1000-kg explosives on each lock, and at the midpoint, if necessary, the aircraft could also lift a two-ton bomb !! The bomb bay doors, when opened, retracted inside the fuselage, moving along the sides (as on the American Liberator). Instead of the entrance hatch of the shooters, which simultaneously served for the release of the lower defensive installation, two separate ones were introduced, while the hatch installation was mounted in a permanently released position, covered with a fairing. Instead of the TAT-BT upper turret, the TUM-2 installation with UBT machine guns was mounted on the aircraft. The pilot's canopy cap was increased in width by 100 mm, the bent side windows were replaced with flat ones, but the visor remained the same in shape. The design of the lantern provided for the possibility of emergency dropping of the top and side panels. Aircraft wing: consisted of six separate structural parts, not counting the tips: two consoles, two engine bays and two center section bays docked to the fuselage.
The letter "B" in the name of the engine meant that the pressurization was carried out in a combined way: in addition to the two left turbochargers, Charomsky supplied the diesel with a drive supercharger borrowed from the AM-38 engine. This event ensured stable operation of the engine at reduced fuel consumption and at high flight altitudes. In connection with the use of VISH-24 propellers with a diameter of 4.1 m, the engine nacelles had to be spread wider, while the wingspan increased to 22.79 m. rudders increased by 0.18 m². The mechanism for cleaning and releasing the chassis was made electro-hydraulic. Changes were made to the engine cooling system and the aircraft fuel system. The weight of the empty machine has increased to 10325 kg (which is almost one and a half tons more than that of the Er-2 2AM-37), and the maximum takeoff (calculated) - up to 17650 kg4! The composition of the crew did not change and included a pilot, navigator, gunner and gunner-radio operator.
Only in February 1943, the aircraft was presented for testing at the Air Force Research Institute. They were conducted by the leading engineer engineer-lieutenant colonel N.K. Kokorin and the leading pilots Colonel Alekseev and Major V.V. Lisitsin. According to the pilots, the aircraft was easy to pilot in almost all modes. Its maximum speed, compared to the AM-37 version, decreased to 429 km / h, but the estimated maximum flight range exceeded that originally set for the Yer-2 and reached a fantastic 5,500 km. The bomber became noticeably more tenacious, because kerosene, unlike gasoline, caught fire in the air extremely reluctantly. The total mass of armor reached 180 kg, while the pilot received a 15-mm armored back. The upper turret was equipped with an electric drive, which greatly facilitated the work of the shooter (360 ° rotation was carried out in just 6 seconds) and increased the accuracy of fire. In a letter to the head of the Air Force Research Institute, Lieutenant-General P.A. Loskutov, dated June 1, 1943, Yermolaev indicated that the new version of his bomber was twice as large as the Il-4 in the number of bombs delivered to the target. In addition, Yer-2 had an advantage over Ilyushin's aircraft in terms of flight speed - both near the ground and at altitude. In particular, with a flight range of 3000 km, the Il-4 could take on board 1000 kg of bombs, and the Er-2 2M-30B - 2000 kg.
At the same time, the shortcomings of the Er-2 2M-30B were also noted - low rate of climb, long takeoff distance, inability to fly without loss of altitude on one engine with a flight weight of more than 14200 kg. The machine turned out to be overweight, the engine power was again not enough. When working on the ground, due to the lack of minimum speed controls, taxiing was difficult. For the same reason, planning before landing had to be carried out with the engines turned off.
And yet, during the tests, the operation of the engines did not cause any particular complaints from the crews of the Air Force Research Institute. According to the test results, it was noted that “maintenance of M-30B engines by ground personnel in winter and summer is easier than maintenance of gasoline engines due to the absence of an ignition system and carburetors in the presence of a reliable injection equipment. The fuel equipment (TN-12 fuel pump and TF-1 injectors) installed on the M-30B worked reliably and had no defects during the entire test period."
On April 14, 1943, Colonel A.D. Alekseev started on the "Yer" for a non-stop flight along the route Moscow-Omsk-Moscow at a distance of 4500 km with a load of 1000 kg. The take-off weight of the machine was 17700 kg, 4900 kg of kerosene splashed in the tanks. Alekseev had to return due to a meeting with a thunderstorm in the Elabuga region. The flight on the route Ramenskoye-Kazan-Sverdlovsk and back was more successful, its total length was 3950 km. In the hope of improving take-off properties in the second half of July 1943, experimental four-blade propellers AB-9EL-116 were installed on the aircraft, but the expectations were not met. Moreover, with the new propellers, the flight speed even decreased. But the new ball bow rifle mount with a UBT machine gun designed by factory No. 134, tested on the same machine, turned out to be more successful than the previous domed one (designed by I.I. Toropov), and later became serial.
According to the ADC command, the experimental Yer-2 with M-30B engines generally met the requirements for a long-range bomber. In the tradition of the time, without waiting for the end of the full program of fine-tuning the machine, the GKO, by its decree No. 4170 of September 21, 1943, resumed mass production of the Er-2, this time at plant No. 39 in Irkutsk, which had previously produced the Il-4. So Ermolaev for the second time “turned around” S.V. Ilyushin, who at that time was developing a new long-range bomber Il-6.
Outwardly, the new Ilyushin machine strongly resembled the enlarged Il-4. In terms of the composition of the bomber armament, it did not differ from the Yer-2 2M-30B, but the defensive armament was noticeably more powerful: five 12.7-mm UBT machine guns or three Sh-20 cannons. The specific parameters of the bombers with the same engines were very close, but the process of fine-tuning the engine installation for the Ilyushins was much more difficult, and in the end they lagged behind the Yermolaevs by about half a year.
3 The fact is that by that time another aircraft factory with No. 82 already existed in Moscow (on the territory of factory No. 81). In essence, the 500th plant, according to its staffing of the main workers, represented the special pre-war 82nd.
4 In fact, during the tests, the aircraft flew to the maximum range with a takeoff weight of 16190 kg, with a large takeoff weight, due to the rear centering, the aircraft becomes insufficiently stable, which greatly complicates piloting.