History, Development, and Use
of the SU-15 'Flagon' Interceptor Aircraft

This section will cover the history, development, and use of the Sukhoi Su-15 'Flagon' interceptor.  In this section you will find where the aircraft has been used, when it was designed, its limitations and abilities, and how it functions.

 

Brief Operational History

As the 1950's came to an end the Soviet air defense forces found themselves facing a wide array of threats from Western aircraft.  While Soviet interception capabilities had been improved with the introduction of the Su-9 all-weather supersonic interceptor and the Tu-128 long range fighter,  these aircraft would be useless against fast high flying aircraft like the SR-71 and XB-70 bomber which were planned by the United States.

These Western aircraft could fly higher and faster than any existing Soviet interceptor, so a requirement for a suitable interceptor was issued in 1962.  The Mikoyan-Gurevich design bureau produced a design for a Mach 3+ interceptor with a powerful radar and long range missiles known as the MiG-25.  The Sukhoi design bureau also submitted a design.  It was slightly slower than the MiG aircraft (Mach 2.1), but still had exceptional performance, long range missiles, and was easier to produce.  It was felt that both aircraft would complement eachother and were both  accepted for production.

To develop the new aircraft Sukhoi would drew heavily upon his earlier designs, most notably the Su-11 and his experimental T-37 which flew in 1960.  The T-37 had given him a great deal of data about high speed flight as well as some experience in the construction of aircraft made of titanium.  The Su-11 would provide the base of the new aircraft, and many of its components would be incorporated into the new interceptor.  Sukhoi designated the aircraft the Su-15 and work began in 1963.

When it emerged from its hanger the following year it showed many similarities to the Su-11.  The aircraft used the same AL-21F engines as its predecessor.  It also had the same airbrake system, tail, cockpit assembly, and landing gear.  As with the Su-11 the tail had to be removed if the engines were to be changed.  Even with all these similarities the aircraft had some new features.  The most noticeable was the large radome housing the Uragan 5B radar.  The aircraft was also noticeably longer than its predecessor and its wings were a 60 degree delta as opposed to the 57 degrees of the Su-11.  The prototype first flew sometime between 1964 and 1966.

The Su-15 was first flown in public during the 1967 Aviation Day show.  It was painted black and flown by test pilot V. Ilyushin who was the son of the head of the Ilyushin design bureau.  Later that year a group of eleven Su-15 participated in an aerial display during the Domodedovo air show.  They were painted in the colors of the 'Golden Hawks' aerobatic team and trailed colored smoke during the demonstration.

In 1968 the first early Su-15 interceptors entered squadron service with the IA-PVO (interceptor aviation of the air defense forces).  Western observers quickly designated the new aircraft the 'Flagon-A'.

Shortly after the introduction of the SU-15 it was decided to determine if the aircraft could benefit from vectored thrust technologies.  These technologies had been demonstrated in Great Britain by the Hawker Siddeley 'Harrier' in 1963.  Pavel Sukhoi felt that he could apply these principles to his Su-15 to dramatically reduce the amount of runway it required to take off.

Work on the experimental STOL version began in the mid-1960's.  The aircraft, known as Su-15VD*, was fitted with three lift jets in the fuselage covered by small hinged doors.  Its fuselage was also lengthened to accommodate the new lift jets.  The most noticeable change was in the design of the wings, which had been changed to a compound delta configuration fitted with a small wing fence.  This new design gave the aircraft better lift and maneuverability at altitude.  The aircraft's ailerons were also enlarged to give better lateral control.  

The Su-15VD was a purely experimental aircraft and as such it was never fitted with radar or air-to-air missiles.  When the West became aware of the aircraft in 1967 they designated it the 'Flagon-B'.

Even though the Flagon-B never made production two other versions of the Flagon entered service in the late 1960's.  The first of these was a two-seat trainer version called the Su-15U, but known to NATO as the Flagon-C.  Most of these incorporated the compound delta design of the Su-15VD, although some had been observed with the original simple delta design.

The other production version was the Flagon-D which was simply a Flagon-A with a longer fuselage, the new wing design, and the larger ailerons.  This Su-15 variant and all Flagon's that followed were often referred to as Su-21's by NATO observers who did not know its true bureau designation.  Su-21 was never a Sukhoi bureau designation for the 'Flagon'.

Beginning in mid-1973 the first major production variant since the Flagon-A was introduced.  It was designated the Flagon-E by NATO and bore many outward similarities to the earlier Flagon-D.

This version had been fitted with powerful Tumansky R-13F-300 engines each of which produced 14,550 pounds of thrust.  The main air inlets were completely redesigned, and twenty ram air inlets were also placed around the engine areas.

Other outward changes were made in the landing gear which had been strengthened.  The forward landing gear had also been redesigned to have two smaller wheels rather than the single large wheel of the original model, although the front nosewheel bay doors retained the characteristic bulge of the earlier types.  Tire pressure on all the wheels was also increased.  Aircraft armament was increased with the addition of two air-to-air missile pylons.  It also had the ability to mount GSH-23L gun pods in place of drop tanks if required to.

More importantly the avionics of the Flagon-E were upgraded.  The aircraft mounted the SRO-2M IFF system (NATO designation 'Odd Rods') and the Sirena 3 radar warning system. and the SRO-2M IFF system.  Internal flight electronics were also improved.  It is believed that this variant was the first to mount the improved 'Twin Scan' radar system.

The final version of the Su-15 emerged in 1976.  It differed from earlier models by having a larger ogival radome which offered lower drag than the previous conical radome.  This version was designated the Flagon-F by NATO observers.

Throughout the 1970's the Su-15 formed the backbone of the IA-PVO fighter regiments.  Over the years they had many encounters with patrolling NATO and even civilian aircraft.  One of these incidents occurred in 20 April 1978 when a Soviet pilot flying an Su-15 intercepted a South Korean airlines Boeing 707 that had strayed far off course.  It later forced the aircraft to land.  The interception occurred in daylight which allowed the Su-15 to be photographed by a passenger on the airliner.  It would not be the last interception of a civilian aircraft.

On 1 September 1983 the Su-15 would again gain world attention during an encounter with another Korean airliner.  The incident began when the Korean aircraft, KAL 007 began flying directly for the Soviet border.  Interceptors were quickly sent to meet it, one of which was flown by Lt. Colonel Ossipovich  who made several attempts to contact the aircraft which did not respond.

When the aircraft crossed the Soviet border Lt. Colonel Ossipovich moved in front of the airliner and flashed the international signal for crossing a state border.  He also fired four warning bursts from the gun on his Su-15.  The airliner made no attempt to contact the Soviet aircraft and never changed course.  It was then that Lt. Colonel Ossipovich then fell back and fired two missiles, both of which struck their target.  At the time the incident brought widespread condemnation on the Soviet Union and caused the IA-PVO to change its interception policies.  It was only during the 1990's that the South Korean Airline would accept full responsibility for the incident.

Nearly 1000 Su-15 Flagon's of all variants were in service in the early 1980's but its limitations were becoming more clear.  The aircraft was in serious need of longer range missiles and lacked a  look-down/shoot-down radar which would be critical to the interception of low flying bombers. The Sukhoi design bureau decided not to upgrade the aircraft as its replacement (the Su-27 'Flanker') was already in the later stages of development.

The introduction of the Su-27 in the mid-1980's signaled the end of the venerable Su-15, many of which were withdrawn from active service when the new planes arrived.  By the end of the decade very few Su-15's remained in service.  All were eventually retired in 1992 due to both budget requirements and the changing threat situation following the Soviet collapse.  The Su-15 was never exported or operated by a foreign air force.

*VD stands for vertikalnye dvigatel or vertical engines

  

Tactical Use and Limitations

In the event of war the Su-15's of the IA-PVO were expected to remain on alert until ground radar stations detected an intruder.  The aircraft would then rapidly climb to the required altitude and rush at Mach 2+ to engage its target.  The Su-15's used by Frontal Aviation would be employed in a similar role, but would generally engage front line fighters and bombers overflying the front.

The Su-15 'Flagon' was well equipped to carry out these missions when it was introduced in the 1960's.  It filled the gap between the MiG-25 'Foxbat' and other Soviet interceptors of the era.  The powerful engines gave the aircraft greater speed and altitude in excess of any other Soviet fighter except the MiG-25.  This allowed it to engage all but the fastest and highest flying targets.  The plane was also much more maneuverable than the MiG-25.  It also had the ability to fight in close with its 23mm gun.

Even so the aircraft suffered from a number of limitations.  The first of these was the Uragan 5B radar which was rapidly outclassed by better systems.  Even when the Su-15 switched over to the more modern 'Twin Scan' radar it still lacked the look-down/shoot-down capability that was so critical at the beginning of the 1980's.  The aircraft's reliance on AA-3 'Anab' missiles even when better weapons such as the AA-6 'Acrid' became available was another limitation.

   

Deployment Chronology

The Su-15 gave the Soviet interceptor forces an extremely fast all-weather fighter to replace its older aircraft.  It did all this while costing less than the more specialized MiG-25 'Foxbat'.  Here you can see what aircraft the Su-15 'Flagon' replaced and what aircraft eventually replaced it in the high speed interceptor role.  You can find out more about these aircraft if we have them on our site by clicking on the links below.

The Su-15 'Flagon' replaced... Su-15 'Flagon' The Su-15 'Flagon' was  replaced by...
Su-11 'Fishpot' Su-27 'Flanker'

 

Sources Cited

Here are some of the most informative sources that we have used in compiling this information for you.  We hope you can find them as useful as we have.