Combat operations during the first years of the Second World War revealed the need for a special aircraft to support ground troops distant from base airfields and to strafe communications far in the enemy's rear. The single-engined attack aircraft serving with the VVS had armament of inadequate power and lacked the required range. Not only was powerful armament needed, but the crew's safety was important and they had to be well protected against enemy fighter attacks.

Design of the aircraft began in 1912 in the Urals (Molotov city), at Plant No.79 (the Arkady Shvetsov engine manufacturing plant), where the design bureau and production base had been evacuated. Next year the Su-8 (DDBSh - Dvukhmotornyi Dalny Bronirovannyi Shturmovik - twin engined, long range armoured attacker) two-seater, powered by two 2.200 hp (1,641 kW) Shvetsov M-71F air-cooled engines, was completed. As the bureau was then returning to Moscow's Tushino airfield, the dismantled aircraft was loaded on a barge and towed there along the Kama, Volga and Moscow rivers. After it had been reassembled at Tushino airfield the tests began there and were continued at the LII, with Nikolay Fikson as pilot.

The Su-8 had extremely powerful gun and bomb armament. Four 45 mm OKB-16 cannon with 50 rounds each were installed as а central battery under the fuselage. The cannon were intended for suppressing the forces of German armour, which had the most up-to-date vehicles in their inventory. For use against infantry there were four 7.62mm ShKAS machine guns in each outer wing panel, with 2,400 rounds for each pair. To protect the aircraft from attacks from the rear, a similar machine gun with 500 rounds was mounted in the qunner/radio operator's LU-100 movable hatch, and a 12.7mm UBT machine gun was mounted in the upper UTK-1 turret. The bombs were attached to carriers in six centre-wing bays. Each bay contained one bomb of 3301b (150kg) or a few of lighter weight, the maximum load being 1,984 lb (900 kg). In overload the aircraft could carry three bombs weighing a total of 1,102 lb (500kg) externally under the fuselage, bringing the maximum bomb load to 3,086 lb (1,400 kg).

At a normal take-off weight of 27,365 lb (12,413kq) the operational range was 372 miles (600km), and the maximum range was 932 miles (1,500km). The Su-8 had a rather high maximum speed for such a heavy aircraft; 310mph (500km/h) at sea level and 341 mph (550 km/h) at altitude. Its service ceiling was 29,500 ft (9,000 m).

The aircraft had a composite structure. Its forward fuselage was made entirely of armoured steel of 1/16 to 6/10 in (4 to 15mm) thickness, and the cockpit windshield and the headrest were made of 2 ½ in (64mm) thick armoured glass. The central fuselage section was made of Duralumin, with armour protection for the gunner/radio operator. The tail section was a semi-monocoque structure comprising a plywood covered wooden frame. The armour, which weighed 3,703 lb (1,680 kg) in total, protected the crew, engines, fuel tanks, oil tanks, oil coolers and propeller cylinders from the ffire of the large calibre guns. The single-spar wing, of 645 ft² (60m²) area and NACA-230 aerofoil section, and having a high thickness/chord ratio, consisted of an all-metal centre section including the engine nacelles and two detachable outer panels with metal spars, wooden ribs and plywood covering.

The outer panels were attached to the engine nacelles with 7° dihedral. In addition to the main spar, the wing had a metal web carrying attachment points for the four-section flaps and the ailerons. The port aileron had an adjustable trim tab, To enhance slow speed controllability the designers provided automatic slats along the outer wing leading edges. The empennage consisted of an all-metal tailplane with fabric covered elevators and endplate fins. The rudders were horn balanced, and an adjustable trim tab was fitted to the port rudder. The aircraft had the simplest possible undercarriage which retracted hydraulically into the engine nacelles.

Once the design of the DDBSh was completed and building of the first prototypes had begun, the Sukhoi Design Bureau began to develop the Su-6. Minimal changes, such as removal of the cannon battery and engine armour, and the introduction of a third crew member, enabled medium bomber and high altitude reconnaissance versions of the aircraft to be considered. At that time (1944) the DDBSh had successfully undergone its manufacturer's and state tests, but it was decided not to put it into production. There was no longer any need for the attack aircraft because the war was now being waged close to Germany's borders, and Hitler's defeat was close and inevitable.

Photo	Description
	Drawing Su-8
	Su-8 with M-71F

Bibliography

• The history of designs of planes in USSR 1938-1950 /Vadim Shavrov/
• Attack aircrafts of Red Army /Vladimir Perov Oleg Rastrenin/
• Attack aircrafts Su-2. /Dmitriy Khazanov, Nikolay Gordyukov/