Su-15 Development History

Background

In the early 1960s in the Soviet Union, fighter aircraft were developed as part of an interception system to destroy incoming bombers. The interception system consisted of a network of ground radars, ground controlled intercept (GCI) system, medium range air-to-air missiles, and an airborne launch platform for the missiles equipped with powerful radar. Contemporary intercept aircraft by other design bureaux than Sukhoi were the Yakovlev Yak-27 'Flashlight' and Yak-28 'Firebar', Tupolev Tu-128 'Fiddler' and the highly successful Mikoyan MiG-25 'Foxbat'.

Predecessors

The Su-15 was a development of Sukhoi's tailed-delta Su-9 and Su-11 interceptor fighters. The Su-9 'Fishpot-B' developed in the late 1950s was a successful fighter with just over 1,000 aircraft produced between 1957 and 1962. The limited range of the TsD-30T radar and K-5MS led Sukhoi to develop the Su-11 with new Oryol radar and K-8M missile. The Su-11 'Fishpot-C' first flown in 1958 entered series production in 1962 at Novosibirsk. After the series production of 112 aircraft, the Su-11 production was ceased because of its poor performance and flight handling, caused by its heavy nose shifting the centre point of gravity forward disrupting the design's balance.
In the mean time, Sukhoi experimented new configurations. The first of these was the P-1, a two-seat interceptor study featuring lateral air intakes. The P-1 was first flown on 12 July 1957, but the program ended on 22 September 1958 after tests were stopped earlier because of engine troubles.
Sukhoi's T-5 was the result of a study for an alternative propulsion system for the Lyul'ka AL-7 and delayed AL-9 single turbojets. The Su-9 prototype (T-3) was modified with a new rear fuselage with side-by-side arrangement of two Tumanskii R-11F-300 turbojets. First flown on 18 July 1958, tests ended on 1 June 1959. The increased weight of the rear had caused the centre point of gravity to move aft.
Based on the Su-11, the T-49 experimented an alternative radar/intake arrangement. The radar was protruded forward, while the air intakes were placed at each sides of the radome. Maiden flight on 10 January 1960, tests soon stopped following a non-fatal accident.

Early Development

In second quarter of 1960 Sukhoi proposed the Su-15-40 interception system, consisting of the Su-15 aircraft, Vikhr-P radar (reduced version of the Smerch radar of the Tu-128) and K-40 (AA-6 'Acrid') missiles. Compared to the Su-11-8M complex, the new system offered better range, maximum launch distance and could launch from any direction including head-on. Construction of five Su-15 (designated T-58) prototypes began in mid-1960, equipped with a single AL-7F2 engine and rectangular side air intakes, based on experience with the P-1 and T-49.
On 5 February 1962, the resolution approving the Su-15 construction passed, but required it to be a modernised Su-11. The 'first stage' Su-15 aircraft were to be equipped with modernised armament system from the Su-11, consisting of the Oryol-D58 radar and K-8M1 missiles. 'Second stage' aircraft were to be equipped with the new Smerch-AS (Taifun) radar and K-8M2 (R-98) missiles.

Delayed Production

Sukhoi failed to retain its place in the work schedule of the Novosibirsk factory. Yakovlev's Yak-28P 'Firebar' replaced the Su-11 on the production line at Novosibirsk. 443 aircraft were built between 1962 and 1967. The Su-15 needed to be largely superior to the Yak-28P in order to have it enter series production. The Su-15 proved much better with the exception of its range. The Yak-28's configuration of engines in underwing nacelles limited its performance and flight handling. In 1964 Yakovlev introduced the Yak-28-64 with a configuration similar to the Su-15, but to no avail.
State acceptance tests of the T-58-8M1 interception complex started in August 1963, later the K-8M1 missiles were followed by the K-8M2. On 3 April 1965 the T-58-8M2 was officially commissioned and designated Su-15-98 consisting of the Su-15, RP-15 (Oryol-D58) radar and R-98 (K-8M2) missiles. In 1966 series production at Novosibirsk began, the first pre-series Su-15 made its first flight from Novosibirsk on 6 March 1966. The superiority of the Su-15 over the Yak-28P was obvious and the production line was cleared.

Service Entry

In 1967 the first Su-15 entered service with the 148th Pilot Combat Training Centre of the Soviet Air Defence Forces ( Protivo Vozdushnaya Oborona - PVO) at at Savasleyka. 611th IAP at Dorokhovo, near Moscow, was the first operational unit to receive the Su-15 and began military operational tests in September 1967 with 10 series production aircraft which continued until July 1969. The Su-15 gradually replaced the Sukhoi Su-9 and Su-11 and Yakovlev Yak-25M and Yak-28Ps.

Design Improvements

While the Su-15 was in series production, a number of improved design features were developed, tested and subsequently introduced with a new production series. The most important change in the basic Su-15 variant was the new cranked wing design, as discussed in the Description, and later the addition of short range weapons. Another improvement was the new ogival radome on late production Su-15TMs, as discussed earlier as well. Unlike the West, the Soviets did not perceive these improved production series aircraft as new variants.

Two-Seat Version

Development of a two-seat training version of the Su-15 began in 1965 as soon as the Su-15 was approved for serial production. In 1965 the PVO preferred a combat capable trainer, and in October that year the committee approved the U-58 design which only differed in having a two-seat cockpit. A U-58 prototype was planned to be built in 1967, but the choice of radar delayed the production. The U-58 had originally be planned with the Korshun-58, a development of the Oryol radar. However in 1967, the Taifun radar was favoured.
A two-seat trainer was desperately needed, since the single-seat Su-15s were rolling of the production line. Development of the trainer was divided in a simple U-58T training version without radar and reduced avionics and a fully capable U-58B.
The U-58T featured a lengthened fuselage, two-seat cockpit, slightly reduced internal fuel capacity, and lacked the radar and weapons. The U-58T prototype made its first flight on 26 August 1968 and completed state acceptance tests on 3 July 1970 receiving the Su-15UT designation. Series production was started in the same year and continued until 1972.
The U-58B prototype with Taifun radar made its first flight on 24 June 1970, but tests were stopped soon because of the forward shift in gravity caused by the radar.

'Second Stage'

The Su-15-98 system was named the first stage of the Su-15 interceptor programme. With the new Taifun radar and R-98M missile, the new Su-15TM would create the Su-15-98M interception system to operate with the modernised Vozdukh-1M CGI system. On 31 Janary 1969 the first T-58T modernised interceptor with Taifun radar started its test programme. Other modifications are described in the Description and Variants parts. Before testing had been finished, series production began and 10 Su-15T aircraft were produced in 1970-1971, before it switched to the T-58M with Taifun-M radar, designated Su-15TM for service. This new version of the Taifun corrected some problems encountered during testing. The Taifun-M was far more powerful than the Oryol radar which resulted in a longer range, but also neccessary adjustments to the radome shape.

Last variant, Su-15UM Trainer

The last variant to enter series production was the Su-15UM trainer. This new combat capable trainer was based on the Su-15TM. This time the fuselage length and internal fuel tanks remained unchanged from the Su-15TM and only the radar and some avionics were removed to accomodate the instructor cockpit. Although just like the Su-15UT, it did not carry the radar, it was combat capable using the heat-seeking R-98MT and R-60 missiles as well as the gun pods. The last two were introduced to all Su-15s versions by now. The U-58TM prototype was first flown on 23 April 1976 and state acceptance tests had been completed by 25 November 1976. A small number of Su-15UM were produced between 1976 and 1979.

The End of Development

The introduction of transistors meant the end of the Su-15 development as well as the production of armed variants. Production stopped in 1975 with only the Su-15UM trainer being produced until 1979. In the 1970s the Sapfir-23 radar had been developed for the MiG-23 'Flogger' using transistor technology and Doppler effect. The MiG-23 radar could distinguish low flying targets against the ground, such a look-down/shoot-down capability was impossible for the Su-15TM. Sukhoi attempted to make the Su-15TM more capable against low flying targets by introducing the SAU-58-2 flight control system, enabling very low-level flight. However the MiG-23 also proved to have much better performance. From the MiG-23ML the MiG-23P interceptor version was developed for the PVO by integrating it systems with the Vozdukh-1M CGI system.

For more variant specific information, photos and unsuccessful developments go to the Variants overview.