Sukhoi Su-15: The Boeing Killer

Introduction

After its resurrection in 1953 under the new number OKB-51 (opytno-konstrooktorskoye byuro – experimental design bureau) the Moscow-based design office headed by Pavel O. Sukhoi started work in two main areas, developing a supersonic tactical fighter for the Soviet Air Force (VVS – Voyenno-vozdooshnyye seely) and a supersonic interceptor for the Air Defence Force (PVO – Protivovozdooshnaya oborona). At that time two distinct design schools, or scientific methods, existed in the Soviet Union with regard to high-speed flight. One was headed by Professor Vladimir V. Stroominskiy, an avid proponent of swept wings; the other was led by Professor Pyotr P. Krasil’shchikov, who favoured delta wings. Both types of wings had their merits, therefore OKB-51 worked in both directions at once, designing the single-engined S-1 tactical fighter and the T-3 interceptor which featured considerable structural and systems commonality; the S and T stood for strelovidnoye krylo (swept wings) and treugol’noye krylo (delta wings) respectively. The two aircraft eventually evolved into the famous Su-7 Fitter-A fighter-bomber and the Su-9 Fishpot-B missile-armed interceptor (known in-house as the T-43) respectively, the latter type entering service in October 1960. The Su-9 further evolved into the T-47 interceptor featuring a more powerful fire control radar and longer-range missiles, which entered service in February 1962 as the Su-11 Fishpot-C.

In the second half of the 1950s the Western world began fielding new airborne strike weapons systems, forcing the Soviet Union to take countermeasures. In particular, new state-of-the-art interceptors possessing longer range and head-on engagement capability were required for defending the nation’s aerial frontiers. Creating such an aircraft appeared a pretty nebulous perspective, considering that many a promising programme for the re-equipment of the VVS and the PVO was terminated when Nikita S. Khrushchov was head of state.

A late-production Su-9 interceptor armed with four RS-2-US missiles.

In this generally troubled climate the outlook for the Sukhoi OKB seemed quite favourable at first. however, By mid-1961 it became obvious that the first-line units of the VVS and the PVO had run into big problems with the Su-7B and Su-9, the appallingly low reliability of the Lyul’ka AL-7F afterburning turbojet being one of the worst. In the first 18 months of service, more than 20 aircraft were lost in accidents, more than half of which were caused by engine failures. The PVO began lobbying for the production entry of the Yakovlev Yak-28P Firebar interceptor on the grounds that it was twin-engined, ergo safer. The State Committee for Aviation Hardware (GKAT – Gosudarstvennyy komitet po aviatsionnoy tekhnike) amended its production plans accordingly, and in the three years to follow GKAT’s aircraft factories were to manufacture only twin-engined interceptor types – the Yak-28P and the Tupolev Tu-128 Fiddler long-range heavy interceptor. Additionally, the rival OKB-155 headed by Artyom I. Mikoyan had begun trials of the promising MiG-21PF Fishbed-D light tactical fighter/interceptor powered by a single Tumanskiy R11F2-300 afterburning turbojet which, though less powerful than the AL-7F, was much more reliable. Consequently on 27th November 1961 the Soviet Council of Ministers (= government) issued a directive ordering Su-9 production to be terminated in 1962 and cutting the Su-11’s production run dramatically for the benefit of the Yak-28P.

Thus OKB-51 was now facing not just further programme cuts but the daunting prospect of being closed altogether for a second time as unnecessary. Considering the disdainful attitude of the nation’s political leaders towards manned combat aircraft, the chances of developing all-new aircraft were close to zero; all the OKB could do was modernise existing designs, and then only if state-of-the-art missile armament was integrated did these plans have any chance of success.

‘10 Red’, the tenth production Su-11, armed with two R-8M medium-range AAMs.

The P-1 experimental interceptor – the first Sukhoi jet with lateral air intakes.

This was the situation in which the Sukhoi OKB began development of the T-58 single-engined interceptor – the first aircraft to have this designation. To win support at the top echelon the project was disguised as a ‘further upgrade of the Su-11’. The OKB-339 avionics design bureau offered two alternative radars for the T-58 – the Oryol-2 (Eagle-2), an upgrade of the Su-11’s RP-11 Oryol radar, and the brand-new Vikhr’ (Whirlwind). However, both radars were too bulky to fit inside the shock cone of an axisymmetrical nose air intake as used on the Su-11; hence the radar occupied the entire fuselage nose, the AL-7F-2 engine breathing through two-dimensional (rectangular-section) lateral intakes with vertical airflow control ramps – a design that was not yet fully explored in the Soviet Union at the time. By then OKB-51 already had some experience with lateral air intakes, having used them on the P-1 delta-wing two-seat experimental interceptor of 1956 and the T-49 experimental interceptor of 1959 (basically a modified Su-11).

The conical radome mated with a basically cylindrical forward fuselage that was flattened from the sides in the cockpit area and flanked by the air intakes which blended smoothly into a centre fuselage of basically cylindrical shape. The rear fuselage structure, wings, tail unit and landing gear were identical to those of the Su-11. The armament consisted of two air-to-air missiles (AAMs).

Prototype construction began at MMZ No.51 in July 1960. But then the military started demanding ever-higher performance; the T-58 was required to have allaspect engagement capability (that is, in both pursuit and head-on mode) against targets flying at up to 27,000 m (88,580 ft) and 2,500 km/h (1,550 mph). In keeping with a Council of Ministers directive drafted in November 1960 the interceptor was to be equipped with the Vikhr’-P radar and the Polyot (Flight) ground controlled intercept (GCI) system and armed with two K-40 AAMs; the choice of the missile type was dictated by the military who also envisaged this weapon for Mikoyan’s new interceptors. The aircraft was allocated the service designation Su-15. It was the core of an aerial intercept weapons system provisionally designated T-3-8M2 because the aircraft would be armed with K-8M2 AAMs (a product of Matus R. Bisnovat’s OKB-4) pending availability of the intended K-40s; the K-8M2 was a refined version of the K-8M which, unlike its precursor, had all-aspect engagement capability.

Still, time passed but the promised K-40 missile was nowhere in sight. OKB-51 continued development of the interceptor with the alternative Oryol-2 radar and K-8M2 AAMs, but the work on the T-58 project was suspended in the summer of 1961. ‘For want of a missile the fighter was lost’? Well, not exactly.

Acknowledgements

The book is illustrated with photos by Yefim Gordon, the late Sergey Skrynnikov, Sergey Popsuyevich, ITAR-TASS, the Novosti Press Agency (APN), as well as from the archive of the Sukhoi Company JSC, the M. M. Gromov Flight Research Institute (LII), the personal archive of Yefim Gordon and from the following web sources: www.karopka.ru, www.scalemodels.ru, www.rumodelism.com, www.scalemates.com, www.modellversium.de, www.modelclub.gr, www.hyperscale.com, www.aircraftresourcecenter.com, www.ipmsusa3.org, www.arcair.com, www.jonbryon.com, www.ebay.com. Line drawings by the late Vladimir Klimov. Colour drawings by Andrey Yurgenson.

The Su-15 is born

As an insurance policy in case the single-engined T-58 was rejected, in late 1960 OKB-51 prepared a new version of the project envisaging installation of two 7,200-kgp (15,870-lbst) R21F-300 axial-flow afterburning turbojets side by side in the rear fuselage; this engine was developed by OKB-300’s new Chief Designer Nikolay G. Metskhvarishvili. The PVO General Headquarters insisted that the twin-engined version (likewise officially designated Su-15) be equipped with the Vikhr’-P radar and armed with two K-40 AAMs, even though using the Oryol-2 radar and K-8M2 AAMs would allow the interceptor to enter service much sooner.

The general arrangement and internal layout was finalised in 1961. The powerplant was changed at this stage. Firstly, the single-engined version was indeed rejected, the customer expressly demanding twin-engine reliability; secondly, the R21F-300 turned out to have serious design flaws and was abandoned in 1962. This prompted the Sukhoi OKB to select the proven R11F2-300 to power the T-58. Accommodating the two R11F2-300s in the rear fuselage presented no problem; OKB-51 already had some experience with a similar engine installation on the T-5 development aircraft of 1958 (basically a modified Su-9).

Contrary to normal Soviet practice, no project chief was assigned to the T-58D until the mid-1960s; General Designer Pavel O. Sukhoi resolved the key issues related to the interceptor’s design, while the problems arising in the course of day-by-day work were handled by his deputy Yevgeniy A. Ivanov.

The T-5 development aircraft – a twin-engine experimental derivative of the Su-9. This view shows the wider rear fuselage accommodating two R11F-300 turbojets side by side.

In the course of 1961 the OKB completed the detail design of the interceptor whose inhouse designation was now amended to T-58D, the D suffix standing for either dvigateli (engines, as a reference to the new twin-engine powerplant) or dorabotannyy (modified). The prototype and the static test airframe were converted from the unfinished airframes of the cancelled single-engine T-58 sans suffixe; stock Su-11 subassemblies modified to match the new area-ruled fuselage (which was the only major component designed from scratch) were used to save time. Another important change occurred at this point; since the K-40 AAM had been selected as the main weapon for the Mikoyan Ye-155P heavy interceptor (the future MiG-25P Foxbat-A), it was agreed that the T-58D (Su-15) would be armed with two K-8M2 missiles in semi-active radar homing (SARH) and infra-red homing versions, provided that a further improved version of the Oryol-2 radar designated Sobol’ (Sable) was used.

Since the T-58D was a lot heavier than the Su-11 while having the same wing area, field performance would clearly deteriorate. To compensate for this the designers decided to use blown flaps instead of the Su-11’s area-increasing Fowler flaps, the air for these being bled from the engine compressors. The landing gear was reinforced to cater for the higher weight.

The general belief was that the T-58D would have to deal primarily with single low-manoeuvrability targets flying at altitudes of 2,000-24,000 m (6,560-78,740 ft) and speeds up to 2,500 km/h (1,550 mph). Without a significant advantage in speed the interceptor stood no chance of destroying such targets in pursuit mode; hence highspeed targets were to