OKB Sukhoi BB-1 (Su-2) "Ivanov" Short-Range Bomber with M-88 engine.
In December of 1940, the BB-1 was renamed the Su-2, after designer Pavel Osipovich Sukhoi, and began to be constructed with the M-88 engine.
This engine, developed in the Tumansky OKB, was an upgrade of the M-87. The M-88 retained the original design scheme (air-cooled, radial, 14-cylinder) and had a takeoff power capacity of 1100 hp.
However, unreliable operation caused serious problems. The M-88 was continually suffering from piston burnouts, shaking, and increased oil consumption. Oil splatters leaking from the engine would splash on the cabin's transparent bottom, under the navigator, making it more difficult to aim bombs. In addition, the decision to replace the plexiglass canopy with celluloid was a mistake, as the new material quickly lost its transparency, reducing visibility. Nevertheless, the crew did appreciate the warm, closed cabin.
Some of the Su-2s were equipped with rockets. Instead of bombs under the wings, five unguided PC-82 or PC-132 rockets could be installed in each location.
A new variant of the Su-2 was released in early 1941, featuring the M-88B engine. This modification improved the aircraft's performance. The oil cooler was moved to the midsection and the shape of the hood and suction pipe were changed. The plane's armament was somewhat reduced to facilitate construction. Instead of four ShKAS guns in the winds, two guns were installed, with 850 rounds of ammunition per gun. The bulky MB-5 tail turret was replaced with a TSS-1 turret, with a ShKas 7.62mm machine gun and 900 rounds of ammunition. However, the turret suffered from a number of problems, including a limited angle of fire and difficulty firing when in an air stream. In the spring of 1941, 250 aircraft were produced with the TSS-1. Afterwards, the MB-5 was used. Bomb and rocket payloads remained unchanged.
The Red Army Air Force began to use the Su-2 in combat during the second half of 1940. By the beginning of World War II on June 22, 1941, 213 Su-2s were in service.