Sukhoi Su-7

Su-7BKL

The Sukhoi Su-7 (NATO designation Fitter) was a swept wing, turbojet-powered fighter-bomber used by the Soviet Union and its allies.

Development

Su-7s of the Polish Air Force.

The prototype, designated S-1 'Strela,' first flew on 7 September 1955, and was first revealed to the world at the 1956 Aviation Day at Tushino. Its wing planform was devised during the Korean War by TsAGI, the Soviet aeronautics bureau. It was a 62-degree swept wing with Fowler flaps, conventional tail, and Sukhoi's distinctive petal-style rear-fuselage air brakes. The very large, area ruled fuselage was built around the dimensions of the Lyulka AL-7 turbojet, with 88 kN (19,800 lbf) afterburning thrust. Despite its dimensions, internal volume for fuel and avionics were extremely limited. The engine was fed by a nose-mounted intake with a translating shock cone containing the SRD-5M ('High Fix') ranging radar.

The Su-7, given the NATO reporting name 'Fitter-A,' was originally intended as a fighter to counter NATO's F-100 Super Sabre and F-101 Voodoo fighters, in service with the USAF. It was armed with two NR-30 30 mm cannon in the wing roots, with 70 rounds per gun. In keeping with the vogue for unguided rocket armament, early models had provision for an under-fuselage rocket pack, but this was quickly abandoned. The Su-7 entered service in 1958, but in 1959 it was decided, that a basic Soviet fighter would be MiG-21, and a production of Su-7 fighters was canceled after building less than 200 machines. As the Su-7B, the 'Fitter' soon found its metier as a ground-attack fighter-bomber, entering frontline service in 1961. In the Soviet service, its primary purpose became carrying of tactical nuclear weapons.

The Su-7's combat capabilities were limited. With a tiny internal fuel volume of 2,940 l (647 imp gal), its operational radius, even with drop tanks, was poor - seldom more than about 300 km (200 miles), and it had almost no useful range at all with maximum ordnance. Take-off and landing speeds were also very high, requiring long runways. Su-7BKLs had provision for JATO, but this only made logistics even more complicated, so it was rarely used. An additional problem with early models was that the afterburner took six to seven seconds to light, a handicap in combat.

In its favor, the 'Fitter' was very easy to fly, with docile handling characteristics. Its controls were notoriously heavy, but it was forgiving and predictable. The thirsty engine provided exceptional rate of climb and low-level speed. Furthermore, the entire aircraft was extraordinarily tough and robust, easy to service and cheap to operate (except in fuel consumption). Despite its limitations, it was popular with pilots. The Su-7 saw combat service in the Six Day War in 1967, the War of Attrition, and conflicts between India and Pakistan. Although used mostly in the ground attack role, an Indian Air Force Su-7 did shoot down a Pakistani Shenyang F-6 (Chinese copy of the MiG-19) in 1971.

The limitations of the Su-7, particularly in take-off distance, led the Soviets to pursue the swing-wing Su-17, but the Su-7 remained in service through the 1980s. It was exported in the thousands to some Soviet Bloc and Warsaw Pact nations as well as many other air forces. In addition to the USSR, users were: Afghanistan (about 120), Algeria, Czechoslovakia (about 60), Egypt, India (about 160), Iraq, North Korea, Poland (46), South Yemen, and Syria, possibly Bangladesh.

Variants

The first production version was the Su-7 fighter. After it was repurposed as a fighter-bomber, production switched to the Su-7B. In this role it carried bombs and unguided rockets on two underwing pylons, each rated for 500 kg (1,100 lb) (later increased to 750 kg (1,660 lb)) and two side-by-side fuselage pylons, rated for 500 kg (1,100 lb). With tanks, total maximum load was only 1,000 kg (2,200 lb). The factory designation of all attack Su-7 variants was S-22.

Su-7BKL landing gear and UB-16 57 mm rocket launcher

The Su-7B was superseded in production in 1963 by the Su-7BM, with a more powerful and reliable AL-7F1-150 engine with 10,000 kgf (98 kN, 22,000 lbf) thrust ("BM" stands for bomber - modified in Russian). In Soviet service, this was the first variant to carry tactical nuclear weapons. In 1965 it was superseded in production by the Su-7BKL (KL stands for "kolyesa i lyzhi" i.e. wheels and skids, which improved the 'Fitter's' rough field capability with larger tires, provision for rocket-assisted take-off with two SPRD-110 JATO rockets of 29.4 kN (13,300 lbf) thrust, and an unusual set of sprung skid attachments for the main landing gear, spreading the load on a larger surface area once the main wheels sank deeper into the ground. It also added twin braking parachutes, and a new AL-7F1-250 engine. From 1969, Su-7s were fitted with additional 2 underwing pylons, rated for 250 kg (552 lb; some of the produced aircraft were modified this way as well). The Su-7BKL was the most numerous model, about 500 were built by 1971. The export model, basing upon the Su-7BM with some further modifications, was the Su-7BMK, produced from 1965 for non-Warsaw Pact users.

A two-seat trainer was also built, the Su-7U (NATO 'Moujik'), and an export variant the Su-7UMK. The two-seater removes the leading fuselage tank, reducing fuel capacity by some 200 kg (440 lb), but is otherwise combat-capable. Visibility from the rear seat was poor.

A prototype swing-wing version, the Su-7IG of 1966, became the basis for the later Su-17.

Specifications (Su-7BKL)

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