Aviation of World War II
SB-RK / Ar-2
The war in Spain showed the insufficient speed of the Soviet "high-speed bombers". An attempt to extend the life of the SB was the creation of an experimental MMN aircraft with M-105 engines. It was presented for state tests in September 1939. It differed from the SB bis 3 aircraft in engines, a more perfect shape of the forward fuselage, reduced by 8.5 sq.m. the area of the detachable parts of the wing, a significantly increased area of the flaps and horizontal tail, as well as the design of the detachable parts of the wing using beam spars and ribs stamped from a sheet.
Based on the experience of creating and flight testing the MMN aircraft, the Arkhangelsky brigade developed the latest modification of the SB - the dive bomber SB-RK (expanded wing, wing-radiators or SB with radiators placed in the wing), which completed the development of one of the most massive and famous combat aircraft of the world in the 1930s. It was as a dive bomber that the SB-RK type showed good results. The Red Army Air Force did not have such machines at that time, and the experience of fighting at the beginning of World War II in Poland and Finland showed both the need to hit small targets and the advantages of Germany, which had a specially designed single-engine dive bomber Ju-87.
Outwardly, the RK differed from the SB in the presence of aerodynamic brake grilles under the wing on its front spar, an improved shape of the engine nacelles, and a reduced height of the vertical tail.
The brake grilles, made of steel pipes, had an oval section. When entering into a dive, after opening the valve of the air system, the brake grids deviated to a position perpendicular to the flow. The release of the gratings was signaled to the pilot by mechanical indicators - “soldiers” emerging from the wing skin in the area between the 10th and 11th ribs. Entering into a dive was carried out by simultaneously deflecting up the trimmers of the elevators. When the bomb release button or the duplicate command button was pressed, the trimmers returned to their original position.
The front part of the fuselage of the SB-RK was completely redesigned, with an increased view to the pilot and navigator, providing direct communication between them (i.e., the pilot and navigator could exchange gestures or transmit something to each other). The pilot is shifted to the left to get a forward view when entering a dive through the glazing of the navigation cockpit, his instrument panel is mainly grouped on the right side of the cockpit. The pilot's canopy opens back up. The navigator's glazing area has been significantly increased and a second control with a folding steering wheel has been installed.
* - Under other data 12.640m
** - Under other data 7.1min
Armament. The aircraft was armed with 4 ShKAS machine guns (two of them at the rear upper and lower points) and could carry up to 1500 kg of bombs (with external suspension).
The NU-type bow gun mount (called NU-DB3F in a number of documents, since it is being developed primarily for a new modification of the DB-3F bomber) has one ShKAS machine gun with a supply of 500 rounds of ammunition. The ShKAS machine gun in this installation was mounted in a special ball head, the so-called. "Apple", allowing firing forward in a cone of 50 °. The machine gun is powered by a flexible sleeve from a cartridge box on the starboard side of the navigational cockpit.
The upper aft machine gun mount designed by Toropov with shelling only the rear hemisphere received the designation TSS-1 (high-speed aircraft turret), equipped with a K-8T collimator sight, has a supply of 1000 rounds of ammunition. The turret was a semi-circle (sector), along which a carriage with a machine gun head moved. In the stowed position, the machine gun was mounted on the port side, in the lantern there was a small cutout for this position. Upper lantern, so-called. "Turtle", when firing, moved back on rollers along the rails and partially rose up to protect the shooter from the oncoming air flow. The shelling from the TSS-1 could be carried out 90 ° to the left and right, up to 60 °, down to 30 °.
For the defense of the lower hemisphere, a retractable MV-2 turret with a ShKAS machine gun, with an OP-2L sight, with a supply of 600 rounds of ammunition, was installed on the SB-RK. The MV-2 was mounted on a special frame (cradle), which rose up in the stowed position. In the central part of the frame, in the area of the machine gun handle, there was a copier limiter that prevented it from getting into its crutch wheel. When transferring the MV-2 to a combat position, the two lower glazed doors opened, after which the machine gun, together with the cradle, fell out. Aimed shooting from the MV-2 made it possible to fire at 30 ° to the sides, vertically from 4-5 to 55 °.
For dropping bombs of 250 kg or 500 kg caliber, new NP-1 holders were equipped under the center section of the SB-RK. The bombs were fastened in the area of the center of gravity for one central lock and were additionally fixed with the help of side stops.
For aiming, the navigator was equipped with the NKPB-3 sight (for bombing at night and at low altitudes) and the OPB-1M sight. The pilot was equipped with a PBP-1 collimator sight, designed for dive bombing.
The weight of the empty aircraft was 4430 kg, the flight weight - 6650 kg, and with overload - 7800 kg. Its speed at an altitude of 4700 m was 480 km / h, cruising was 320 km / h, it gained 3000 m in 7.25 minutes. The ceiling was 10100 m. The flight range was 1500 km.
In accordance with the government decree on the renaming of combat aircraft, in the order of the NKAP dated December 9, 1940, the SB-RK was renamed Ar-2 (the first letters of the chief designer's surname and the even number "2", with which the numbering should have started all machines of any design bureau, if they were bombers, attack aircraft, reconnaissance aircraft and transporters). This is explained by the fact that all work on SB aircraft, starting from the design, was carried out by the team of A.A. Arkhangelsky - until 1936 under the leadership of A.N. Tupolev, and since the spring of 1938 independently at the factories.
Despite the fact that the flight speed of the Ar-2 has increased due to more powerful engines, a smaller wing area and improved aerodynamics of the airframe (as well as rate of climb and ceiling), the available information about the tests of the Messerschmitt Bf109E fighter purchased in Germany, said that that this was clearly not enough. Ar-2 was inferior to him in speed by more than 60 km / h. By the way, the German influence also touched the Ar-2, and not only in the concept of its appearance: such a technical solution as an automatic aircraft entry and exit from a dive, similar to that installed on the Ju 88, was mastered in production at the Moscow plant N 213 and was used on it and Pe-2.
According to an extract from the control log of the People's Commissariat of the Aviation Industry of the USSR "Dynamics of Aircraft Production" in 1940, 71 Ar-2s were produced. Decree of the Council of People's Commissars of the USSR and the Central Committee of the All-Union Communist Party of Bolsheviks "On the program for the production of aircraft and aircraft engines in 1941" N 2466-1096ss of December 7, 1940 established the program for the production of 1000 Ar-2 2M-105 in 1941 for the People's Commissariat of Aviation Industry, including 300 in the first quarter, 300 in the second, 250 in the third and 150 in the fourth. From the first quarter of 1942, the release of this aircraft was no longer expected. An extract from the control log of the People's Commissariat of the Aviation Industry of the USSR for the production of aircraft in 1941 indicates that 122 Ar-2s were manufactured at the 22nd aviation plant in the first quarter, including 100 in January, 20 in February, and in March - 2. "Plan of current military orders for the NPO, the NKVMF and the NKVD for aviation weapons for the II quarter of 1941" (Appendix N1 to the Decree of the Council of People's Commissars of the Union of the USSR N 908-383ss of April 12, 1941) contained information on the supply of 3 Ar -2 for the People's Commissariat of Defense. There are detailed data from the "Plan for the retraining of the flight personnel of the Red Army Air Force units on the new materiel for 1941." dated February 19, 1941 on the receipt by the relevant units of the Ar-2 aircraft and on the timing of the retraining of these units. 11 formations were to complete their studies by May 1, 1941. The new-generation Pe-2 bomber that replaced the Ar-2 was created in a big hurry, by converting a high-altitude long-range fighter into a dive bomber. It retained the great speed of its prototype, but compared to the older SB and Ar-2 had a small bomb load and a relatively short range.
In parallel with the refinement of the SB-RK 2M-105, the Arkhangelsk Design Bureau began to develop a new high-speed short-range bomber SBB. At first, the new aircraft had index C (under this designation, the aircraft model was purged at TsAGI), but soon the aircraft index was replaced by B. The aircraft was conceived as a cardinal modification of the serial SB with increased flight performance and continuity in production technology. When designing it, the experience of creating MMN, SB-RK, and later Ar-2 was used. The SBB crew included a pilot, a navigator and a gunner-radio operator.
The main advantage of the new aircraft was significantly improved aerodynamics. The general layout and combat scheme of the bomber B were similar to the SB aircraft, but with a two-fin tail. In order to "maximize the speed of the aircraft," the load per unit area of the wing in the normal version of the combat load was increased to 149 kg / m² and up to 162 kg / m² in the reloading. In this regard, the wing area has been reduced to 40 m². The wing has become shorter and slightly narrower in comparison with the SB wing. At the same time, to ensure the necessary landing speed, it was supposed to use TsAGI flaps, which were a cross between conventional flaps and Fowler flaps. The wing profile was chosen as a high-speed NACA-22 type with a relative thickness at the root of 14.7% and at the tip of 8%.
The design of the SBB assumed the widespread use of open profiles instead of pipes, stamping, load-bearing skin. The skin of the SBB aircraft, and especially the wing, was smooth with flush riveting. The nose of the wing and its upper part between the spars of the wing had a sheathing of bakelite plywood glued to a metal frame. It was assumed that such a wing design should provide the necessary strength and good aerodynamics.
The fuselage was made in the form of a well-streamlined "blimp form", which, according to experts, was the most advantageous in terms of aerodynamics.
Water radiators were located inside the center section of the wing with an entrance in the toe of the center section and an exit at the rear. Moreover, it was supposed to use aluminum ribbed-type radiators designed by the Leningrad SKV NKAP.
The tail support was carried out retractable in flight. The design of the aircraft provided for a significant simplification of technology in comparison with the SB aircraft. Open profiles were used on the SBB, including spars (instead of pipes on the SB). Open riveting was used throughout the car. A number of elements were made by stamping. The number of welded assemblies was reduced with their replacement by stamped ones from duralumin and steel.
The spars of the center section were steel channels with shelves interconnected by braces made of pipes, and in some places by a sheet.
The spars of the detachable part of the wing were made of two pressed corners riveted together with a shelf bent in section. The upper and lower belts were interconnected by a smooth sheet, supported by vertical corners-racks.
The ribs were stamped from sheet duralumin. The upper wing skin between the spars, working in compression, was reinforced from the inside with corrugation. This section of the upper skin of the center section "was not cut", but passed through the fuselage entirely through. For the same purpose, in order not to make any cutouts in the lower part of the wing, they refused to retract the landing gear into the wing.
For the "correct operation" of the bearing part of the skin, the docking of the weaning with the center section was carried out not at four points, but along the entire contour of the shackle in the area between the side members.
The use of load-bearing skin ensured greater survivability of the aircraft and made it possible to better "perform the surface and maintain the wing profile."
The margin of safety according to the calculation was provided in the case of Ak equal to 8 instead of 1 for the SB aircraft.
The M-105 with a TK-2 turbocharger was considered as the main engine of the SBB power plant. In addition to it, it was supposed to use the M-106 engine.
By this time, the M-105 had already passed 50-hour state tests, and the TK-2 turbocharger was installed on the SB aircraft with M-103 engines for flight tests.
In the future, in order to further improve the aerodynamics of the aircraft, it was supposed to install the M-105TK upside down. In this case, the layout of the engine installation and the radiator was improved and space was freed up in the wing to accommodate gas tanks instead of radiators. On this issue, there was an agreement with the engine builders of the 26th plant. However, in the future, such an option for a motor installation was abandoned, as it did not have significant advantages for a bomber aircraft over a traditional engine installation.
In both versions, it was supposed to use three-bladed propellers of the 3-SMV-2 type variable in flight with a diameter of 3.25 m.
The normal bomb load was 600 kg, in overload - 1000 kg (including 800 kg inside the fuselage). The nomenclature of aerial bombs included air bombs of calibers from 2.5 to 250 kg. At the same time, small fragmentation and incendiary bombs of 2.5-15 kg caliber, as well as chemical ampoules, were loaded into cassettes of small bombs. High-explosive bombs of 250 kg caliber and pouring aircraft devices of the VAP-200 type were hung only on external bomb racks. The reloading version of the bomb load was obtained using 10 FAB-100s, of which 8 were located in the fuselage, and a couple of “hundredths” were placed on external bomb racks.
Small arms included one UltraShKAS normal-caliber machine gun in the navigator's bow mount and one UltraShKAS or ShVAK-12.7 heavy machine gun on the kingpin at the gunner-radio operator. The ammunition load of the navigational machine gun was 600 rounds, and the gunner-radio operator - 800 rounds for the UltraShKAS and 300 rounds for the ShVAK.
The normal flight weight of the SBB with the M-105TK engines was 5961 kg, and with the M-106 engine - 5851 kg. The estimated maximum flight speed with the M-105TK engines was to be 455 km/h near the ground and 612 km/h at an altitude of 9000 m, with the M-106 engines - 587 km/h at an altitude of 7000 m.
The rate of climb of the bomber with the M-105TK was expected to be higher than in the version with the M-106 engines - the SBB 2M-105TK climbed to a height of 5000 m in 5.5 minutes, and the SBB 2M-106 in 6 minutes.
In both variants, the takeoff run with normal flight weight without the use of flaps was 350 m. Landing speed did not exceed 118 km/h.
The flight range of the SBB at a speed of 0.8 from the maximum did not exceed 880 km in the version with M-105TK engines and 970 km for the version with M-106 engines. In the reloading option for fuel, the maximum flight range with a take-off weight of 6466 kg could be no more than 1500 km.
To increase the flight range, the project provided for the suspension under the wing of outboard drop fuel tanks for 520 kg of fuel. In this case, the takeoff weight of the aircraft reached 7025 kg.
In November 1939, after discussing the layout of the SBB, a decision was made to build the aircraft. According to the Decree of the Defense Committee of March 4, 1940, two copies of the B-1 and B-2 were built. The first option corresponded to the high-speed bomber variant, and the second to the dive bomber. The B-2 aircraft differed from the B-1 in a wider fuselage and a somewhat different layout of the forward fuselage.
The prototype B-1, which was powered by serial M-105 engines, was completed by October 1940, after which factory tests began. On October 20, the B-1 was taken to the airfield of the 22nd plant, ground work and taxiing were carried out. Bearing in mind the sad experience of testing the SPB 2M-105, accompanied by disasters and numerous forced landings due to the fault of the M-105 engines, it was decided to perform the first B-1 flights under the factory test program from a large airfield. The aircraft was transported to the Central Airfield, where test flights were made on October 30. The flights showed the readiness of the B-1 for the first flight, however, due to the lack of a TsAGI conclusion on flutter, they did not dare to release the aircraft on the first flight. After receiving the conclusion from TsAGI, the pilot Yu. K. Stankevich on November 6 performed the first flight on the B-1. After completing 6 flights, which were generally successful, they decided to overtake the car in the summer back to the airfield of the 22nd plant in Fili. On November 26, 1940, after landing at the Fili airfield, the left landing gear strut broke while taxiing.
In the meantime, at the end of October 1940, M. A. Lipkin lifted into the air the BB-22PB dive bomber, which, with a flight weight of 5962 kg, showed a speed of 533 km / h at an altitude of 5100 m. 4 FAB-100 or 2 FAB-250.
Preparations for factory testing of the lead serial dive bomber PB-100 manufactured by plant No. 39 were in full swing. The first flights under the factory test program were scheduled for the first ten days of December.
It was at this time, on November 18, 1940, that a meeting of the joint commission of the NKAP, Air Force and TsAGI was held, during which, based on a comparison of the main characteristics of the PB-100, SB-RK, BB-22PB and B bombers, it was concluded that it was advisable to launch into serial production as the main dive bomber of the Air Force of the KA aircraft PB-100 and on the preservation in the BB-22 series (to secure the "weave", since it was built from non-deficient materials). With regard to the B-1 aircraft, it was indicated that the latter, compared with the PB-100, with the same engines and initial defensive weapons, has significantly better takeoff and landing characteristics and rate of climb. However, no decisions on B-1 (on the termination or on the intensification of work on the aircraft) were made by the commission. According to the conclusion of the commission, "...aircraft B, compared to the PB-100, is one year late and has not yet passed the tests."
Such a cautious behavior of the commission is quite understandable. On the one hand, the members of the commission may have already understood that in the event of war, the well-established technology of the B bomber and its good take-off, landing and aerobatic qualities would play an almost decisive role in the rapid deployment of mass production of combat vehicles and the training of wartime flight personnel. , which has in all respects a weak initial flight training. In addition, the launch of the Pe-2 bomber, which was rather difficult for the Soviet aviation industry, into mass production still concealed many pitfalls, but it was still not necessary to expect good results from the BB-22PB 2M-105. But, on the other hand, how the B-1 would behave in the future, and especially its motor installation, was still not completely clear. The members of the commission wisely decided not to take risks - "Better a tit in the hand than a crane in the sky." The decision on the B-1 was postponed "for later", and Arkhangelsky was left with a chance to bring his bomber to flight-combat condition.
Taking advantage of the accident, the Arkhangelsk Design Bureau decided, along with the repair of the landing gear, to make a number of changes to the aircraft design based on the results of the first test flights. In an updated form, the B-1 bomber again went on a test flight only on February 20, 1941. From March 24 to July 9, 1941, factory tests were carried out, during which test pilot Yu. K. Stankevich reached maximum speed at an altitude of 4900 m 540 km/h It was expected that after the elimination of some design flaws, the speed of the bomber would increase to 560-565 km / h.
On April 10, order No. 309 was followed by the NKAP, according to which the entire design team of A. A. Arkhangelsky was transferred to the 32nd plant Despite the difficulties associated with moving and settling in a new place, in the summer of 1941 the second version of the SBB was built - dive bomber B-2. It was assumed that, compared with the B-1, its maximum speed at the estimated altitude would be 40-60 km / h more.
At the same time, in connection with the success of the "103" and "103U" bombers during tests at the Research Institute of the Air Force of the KA, the interest of the military and the NKAP in aircraft B was steadily declining, and the outbreak of war interrupted all work on this aircraft. A. A. Arkhangelsky himself, by order of the NKAP No. 823 dated August 9, 1941, was transferred to aircraft factory No. 156 to organize the repair and restoration of serial SB bombers. Later, the design bureau of A. A. Arkhangelsky was evacuated to Omsk in October 1941, and the B-1 aircraft was sent to the rear in December 1941. What happened to him next is unknown.
High Speed Bomber
Analyzing the operating experience in combat units, the experience of combat use, as well as the experience of mass production, Arkhangelsky planned to carry out a radical modernization of the SB in two stages: at the first stage, by improving the aerodynamics and VMG of the serial SB, to reach a speed of 500 km / h - a small modernization of the SB aircraft, and at the second stage, by creating an essentially new aircraft on the basis of the SB, to achieve a maximum speed of 600 km / h - a major modernization of the SB aircraft.
By May 16, 1939, the MMN 2M-105 aircraft was manufactured. From July 1 to August 16, 1939, the MMN passed State tests at the Air Force Research Institute. The name of the aircraft meant "small modification of the aircraft "N". The fact is that the factory designation of the aircraft SB was "N".
The MMN aircraft was a development of a production aircraft built according to the SB bis 3 type. The main differences were as follows:
Motors M-105 with three-blade propellers VISH-22E were installed.
The area of the wing has been reduced by changing the design of detachable parts of the wing.
The nose of the fuselage has been made more aerodynamic. The pair of machine guns was replaced by one ShKAS machine gun with increased firing angles.
A second control is installed in the navigator's cockpit.
The shielded MV-3 turret was installed instead of the TUR-9 turret, and the hatch for the lower firing mount was completely closed.
The landing gear emergency release crane is installed in the cockpit
Additional gas tanks with a capacity of 205 liters are installed in the cantilever parts of the wing.
The areas of the ailerons and empennage have been slightly increased, and the area of the flaps has been significantly increased (by 40%). A noticeable external difference was the peculiar form of vertical plumage.
All electrical equipment is shielded and the aircraft is fully metallized.
During the tests, the following flight data were obtained. With a bomb load of 500 kg (bombs inside the fuselage), with a normal takeoff weight of 6420 kg, the maximum speed near the ground was 405 km / h, and at an estimated altitude of 4200 m - 458 km / h. Climb time 5000 m - 9.3 min. The practical ceiling is 9000 m. The takeoff run is 520 m, and the run with deflected flaps and using the brakes is 665 m.
With a bomb load of 1000 kg (4 FAB-250), the takeoff weight was 7420 kg, the maximum speed near the ground was 383 km/h, and at an estimated altitude of 4200 m it was 425 km/h. Time to climb 5000 m - 13.8 min. Practical ceiling - 8000 m.
The aircraft had a length of 12.78 m, a height of 4.7 m, a wing span of 18.0 m. The wing area was 48.214 m², which provided a specific wing load of 133.5 (104) wing area - 43.56 (34.00) hp / m². Specific load on power - 3.23 (2.90) kg / hp. In parentheses for comparison are the data for the production aircraft SB No. 2/201.
Despite the increase in horizontal flight speed compared to serial SB aircraft, a negative verdict was expressed in the conclusion based on the test results: "The MMN 2M-105 aircraft designed by engineer ARKHANGELSKOY did not pass the state tests due to insufficient maximum speed, low defense capability, and underdevelopment of weapons and equipment, complicating landing properties ... At present, according to flight data, the MMN aircraft is already far behind, because in 1940 a medium bomber with a speed of the order of 500 km / h and more is needed. "
The conclusion was signed by the Head of the Research Institute of the Air Force of the Red Army, a military engineer of the 1st rank, Losyukov, and the Head of the 1st department of the Research Institute, a military engineer of the 1st rank, Rudintsev and others.
It was noted in the conclusions that: "The flight performance of the MMN aircraft in level flight, climb and maneuverability are similar to those of the production aircraft SB. The takeoff is characterized by a significant increase in the takeoff run and the need for long-term holding, which requires a good airfield. Landing is much more difficult than production aircraft, because approach to the ground at a speed of 180 km / h is required even with the flaps extended, due to the high mileage. These deteriorations in piloting technique are mainly caused by a decrease in the wing area. "
Let's pay attention to the fact that the MMN navigation cabin resembles Polikarpov's VIT-1 navigation cabin. In developing the navigational cockpit for the VIT, Polikarpov set the task of simultaneously obtaining good aerodynamic contours of the aircraft, providing a good overview for the navigator and making his cockpit spacious enough to ensure the convenience of firing from the ShVAK nose gun in the 40 ° sector.
At MMN, such a cabin was highly appreciated during state tests. So, in the conclusions in paragraph 3 it is indicated: "The new F-1 gives the fuselage a more favorable aerodynamic shape and creates good conditions for the navigator for visibility and bombing. There are a number of improvements in the navigator's cockpit:
the lower hatch has been increased for the convenience of climbing in and jumping out;
The astronomical sunroof is equipped with a retractable visor;
personal communication between the navigator and the pilot is provided through the opening window;
second aircraft control set".
Along with this, there were also major defects in the installation, the main of which were:
strong blowing into the machine-gun gap, worsening the working conditions of the navigator even in comparison with serial SBs;
unsatisfactory location of the dashboard;
forward-up visibility distortion through the convex part of the plexiglass".
In addition, the machine gun had insufficient firing angles and insufficient vertical maneuverability. The commission stated that in the form presented, the MMN bow installation cannot be put into service.
The installation of the MV-3 turret was generally approved, as the gunner-radio operator's cabin became more spacious, and the conditions for the gunner's work improved significantly.
At the same time, it was pointed out that the absence of a hatch installation makes the lower hemisphere completely undefendable. "The blind sealing of the lower hatch in the F-3 leads to the fact that the most vulnerable zone - under the tail of the aircraft - is not only not shot through, but also not visible. At the same time, it is very difficult for the gunner-radio operator to jump out with a parachute."
The commission drew attention to the fact that the installation of the MV-3 turret fully provides the shooter with the opportunity to "work with a hatch machine gun."
As for the quality of factory production, it was assessed as unsatisfactory: "The putty is fragile, after a while it cracks and falls off in layers. The fitting of hoods, hatches, tapes, etc. was done carelessly with dents, bulges and cracks."
At the same time, quite satisfactory operation of the engine cooling system and oil system was noted, as well as many advantages in the aircraft piloting technique - satisfactory longitudinal, directional and lateral stability of the aircraft, aircraft stability in turns and in level flight, excellent behavior during takeoff and landing . Horizontal flight on one motor was possible up to an altitude of 3000 m.
By December 1939, the 2nd copy of the MMN aircraft with 2 M-104s (MMN-2) was ready. There is no record of his trial. It is only known that in January 1940 he began to fly.
Such a detail is curious: at about the same time, the German company Dornier manufactured a high-speed bomber Do17Z-1 about the same class, like MMN, with two Bramo 323 engines with a power of 900 hp each. During 1939-1940. 506 copies of these aircraft were manufactured. According to the German historian Novara, with a bomb load of 500 kg, its maximum flight speed near the ground was 350 km / h, and at an estimated altitude of 4700 m - 426 km / h. And only in the Do17Z-2 modification with engines of the same power as the M-105, the maximum speed increased by about 35-40 km / h, and the maximum bomb load increased to 1000 kg.
That is, in terms of speed and maximum bomb load, it was worse than the MMN aircraft. Meanwhile, Do17Z aircraft took an active part in the initial period of the Great Patriotic War.