Tupolev SB in Soviet Service. Part Four.

 

The Tupolev PS-41 was a civilian version of the SB 2M-103. It was developed by Aeroflot in 1939 and by December 1940 forty-nine machines were in service. As civilianized as it was, every defensive armament, as well as armour plating and bomb release systems were deleted, with the exception of the cartridge case ejector tunnel, which remained in the nose. Many PS-41s had an additional antenna mast placed in front of the canopy frame. When serving with Aeroflot, most of them were left in bare metal with civil registration codes and Aeroflot's logo (albeit not always present), painted in black.

From early 1940 onwards, many PS-41s were assigned to Aviaarktika (Aeroflot's Polar Aviation Division). This organization served in the USSR's most northern region under extreme conditions, hence the non-retractable ski undercarriage the PS-41 were equipped with. Most of them were painted in orange or had their noses or engine cowlings painted red to increase their visibility. 

Shortly after the German Invasion of the USSR in June 1941, Aeroflot's PS-41 were pushed into service with the Civil Air Fleet (GVF in Russian acronym) under VVS (Soviet Air Force) command. Some PS-41s were assigned to liaison squadrons, operating from bases in Moscow and northern USSR. They were used for liaison duties between the Central Military Headquarter in Moscow and the Transcaucasian Front. They were also employed as liaison to link Moscow with the newly established industrial centers east of the Ural mountains. 

In combat, the PS-41 was also used, taking advantage of its high speed, to resupply beleaguered Soviet defenses in the Leningrad area, to supply the city with mail, medicines and military staff. 

As more modern Soviet bombers as the Tupolev Tu-2 or the Petlyakov Pe-2 became available, some former SB 2M-103 bombers were converted to PS-41 standard and assigned to GVF, to ease the acute shortage of transport planes the VVS suffered all along World War 2. 

Overall, the PS-41 served well and became VVS' main high speed transport during the war. It was kept on service for a short period of time after the conflict, until it was gradually replaced by more modern types like the Ilyushin Il-12 or the Lisunov Li-2.

There was an extended range sub-variant, called PS-41 bis designed for mail transport. It featured a pair of external wing mounted fuel depots in lieu of the bomb racks. Those depots allowed for an increased range of 1.180 km (733 miles). 

The Tupolev SB-RK was a regular SB 2M-100A fitted with two Klimov M-105R engines. This served as the initial prototype for the ground attack variant of the SB which eventually became the Arkhangelsky Ar-2. 
The Tupolev SBB was an attempt made by Arkhangelsky to modernize the SB design. It featured smaller wings and an almost complete new redesign with twin tail. The only prototype flew for the first time in September 1940. It was tested against the Pe-2 prototype and the Yakovlev Yak-4 and was discarded due to unsatisfactory performance. Some few attempts were made to attract VVS' attention on the type but the interest was lost.

There was another test aircraft based on the frame of the Tupolev SB. Igor P. Tolstikh an engineer from TsAGI (Central Aero and Hydrodynamics Institute) led a team to investigate a tricycle undercarriage (based on implanting a nose-wheel) in 1940. This landing gear configuration, however, wasn't new in the USSR as another aircraft, Kharkov KhAI-4 employed a nose-wheel back in 1934. 
A heavily modified SB 2M-103 was the basis for the nose-wheel arrangement. This experiment was never intended to be put into mass production, as it was just an study to improve future Soviet bombers.
The nose section was heavily modified to incorporate a large nose-wheel with two bracing struts. The main non-retractable undercarriage was repositioned to the rear.
It was test flown by the famous Soviet test pilot Marc L. Gallai on taxiing and landing flights, who praised the new arrangement as it made it much easier to take off and land, than the conventional tail-wheel bombers. 
TsAGI's prototype, nicknamed as 'Pterodactyl', was assigned to the NII (Flight Research Institute) located at Kratovo, near Moscow, in late 1940. Tests continued until 1941, when Germany launched Operation Barbarossa, invading the USSR in June. The first Soviet bombers with tricycle landing gear arrangement, didn't see the light until after the end of the war, namely the Tupolev Tu-12. 

Sources:

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/prototypes/SBB.htm