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Arjanguelsky MMN
In early 1939, the construction bureau headed by Arjangelsky at Factory No.22 was working hard to improve the design of the SB fast bomber. The experience of the fighting in Spain, and the experiences of serial production allowed development work along two fundamental lines:
- The first and less complex (called Minor) was aimed at achieving improvements in the aerodynamics with the aim of obtaining a speed of 500 km / h.
- The second (called Major), which included modifications in the construction and, if necessary, the development of a superior model capable of reaching speeds of 600 km / h.
By decision of the Defense Committee of the 5 of May of 1939 is demanded of the bureau Arjanguelsky --- "... present state test on June 15 , a model SB modernized with two engines Klimov M-105 and the following results: Speed maximum at 4500 m - 470 km / h and practical ceiling of 9500 m. A second example with two M-104 engines to be presented on July 1 with the same results as the previous model, excluding the maximum speed, which should be 470 km / h at 7000 meters. " ---.
The modernized model should begin production at Factory No.125 with deliveries beginning in April 1940. Factory No.22 had to prepare to start the production of copies with a Klimov M-106 engine from January 1940 and from March all the SBs to be delivered had to have this engine, which would allow reaching 500 km / h at 6500 m. height.
The armament also had to be modified with --- “ a frontal ShKAS machine gun with 500 shots and in the upper middle position an Ultra-ShKAS with a cassette for 500 additional shots above the 800 shots of the ' SB. The weaponry in the lower hatch had to be removed. " --- The bomb load capacity had to also be modified to accommodate a capacity of 1000 kg in the following variants: 8 bombs of 100 kg in the interior bay and two bombs of 100 kg under the wings or 4 bombs of 250 kg (two interiors and two exteriors) or 3 500 kg bombs (one in the hold and two under the wings.
Detail of the MV-3 ​​turret at the MMN.
The 16 of May of 1939 finished the preparation with two motors Klimov M-105 which was renamed Arjanguelsky MMN (In Russian: Архангельский ММН). The name stood for Minor Modification of Object N (Малая Модификация самолета "Н") - as the SB was factory known.
The main differences with the standard SB consisted of:
Use of Klimov M-105 engines with ViSh-22E three-bladed propellers
Decrease in wing area by 8 m².
Modifications in the wing structure to facilitate the production process.
Changes to the nose of the device to improve aerodynamics. The two bow machine guns were replaced by a single ShKAS with a greater firing angle.
Double controls in the navigator's position.
The TUR-9 nacelle was replaced by the armored MV-3 ​​and the lower firing point was permanently closed.
The manual landing gear removal system was moved to the cockpit.
New fuel tanks were introduced towards the wing end with a capacity of 205 liters. Total fuel capacity was increased to 2000 liters
The area of ​​the ailerons and the shape of the vertical tail surface were slightly modified.
From 1 July to 16 of August of 1939 state tests were conducted by the engineer of the second rank test pilot Efimov. Khripkov. The results of the tests showed that with a cargo of 500 kg of bombs in the hold and normal takeoff weight of 6420 kg, the speed at sea level was 405 km / h and the calculated height of 4200 m - 458 km / h. The ascent time to 5000 meters was 9.3 minutes and the practical ceiling was 9000 meters.
With the calculated load of 1000 kg (four FAB-250 bombs) the takeoff weight reached 7240 kg, the speed at sea level - 383 km / h, at 4200 meters - 425 km / h and the ascent time to 500 meters - 13.8 minutes. The practical ceiling dropped to 8000 meters.
Despite the increase achieved in relation to the series SB, the result of the tests was negative since it was considered that the speed obtained did not satisfy the established requirements. It was also noted the poor defensive capacity and the deterioration of the landing performance. As a conclusion of the test plan report, it was written:
[...] « The flight characteristics of the MMN in horizontal flight, rate of climb and maneuverability are similar to those presented by the SB series specimens. Take-off is characterized by an increase in the run and greater action on the part of the pilot, which makes a good aerodrome necessary. Landing is more complex compared to the standard aircraft, as an approach is required at a speed of 180 km with flaps extended due to excessive running. This worsening of the results is motivated by the reduction of the wing surface. »
As an interesting detail, it is noteworthy that the report expressed its dissatisfaction with the decision to eliminate the lower firing point and the total closure of the hatch, which left the lower rear hemisphere completely unattended. The change in the upper shooting point was rated as highly positive.
In December 1939 the preparation of the second, known as MMN-2 was completed, this time with the Klimov M-104 powerplant. No documents have been found on the flight tests of this model, but it is known that it flew in January 1940.
Engines: 2 Klimov M-105 1050 hp
Wingspan: 18.0 m
Wing area: 48,214 m²
Length: 12.78 m
Height: 4.7 m
Empty weight: 4820 kg
Maximum takeoff weight: 6420kg
Wing loading: 133.5 kg / m²
Power load: 3.23 kg / hp
Speed ​​at sea level: 360 km / h
Speed ​​at 4200m: 458 km / h
Cruising speed: 398 km / h
Landing speed: 160 km / h
Ascent speed: 538 m / min
Ceiling: 9000 m
Range: 760 km
Take-off run with 500 kg: 520 m
Landing run with 500 kg and use of brakes: 665 m
Accommodation: 3 crew
Armament: 1x 7.62 mm ShKAS machine gun in the nose and 1c 12.7 mm UltraShKAS in a MV-3 ​​ turret in dorsal position.
Bonbload: 1000 kg
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