Updated: 6/18/2017; Authored By Dan Alex; Content ©www.MilitaryFactory.com
Sukhoi set about on some preliminary work in trying to utilize the existing Su-7 airframe for the all-weather strike task. It was quickly realized that the Su-7's airframe was ill-suited for the amount of additional avionics and equipment that would be required in making the Fitter a right "fit" for the role. As a result, other designs solutions were entertained.
While introduction of the Fitter did well to strengthen the Soviet Air Force's aging fleet of fighters, there was no true solution in beefing up her long-range bomber arm. In the inventory remained the aged Ilyushin IL-28, introduced in 1950 and categorized as a medium bomber. The Yakovlev Yak-28 "Bewer"/"Firebar"/"Maestro" series was unveiled in 1958 and first flew in 1960, intended to become the answer to the growing Soviet question. However, once in service, the Yak-28 was quickly noted for its disappointingly short operational ranges and small payload capabilities - two qualities critical to a successful bomber design in the Cold War. Additionally, weapons firing and general munitions delivery accuracy left something to be desired by the Soviet Air Force. Regardless, some 1,180 such systems were placed into circulation and the type was developed to fulfill a variety of battlefield functions.
The F-111 Outshines Them All
Soviet personnel were not blind to the aviation progress being made in the United States as per their USAF General Dynamics F-111 Aardvark twin-engine, swing-wing, two-seat fighter-bomber. The aircraft began its life in 1964 and was officially introduced in 1967, pioneering a variety of technological advancements in the realm. The F-111 featured a terrain following radar (as opposed to terrain avoidance radar), variable sweep of her swing-wing assemblies and an afterburning turbofan engine. Swing-wing capabilities allowed an aircraft to vary its drag during different phases of flight - landing, take-off, cruise.
While practical in both use and design, a "swing-wing" approach often involved a complicated set of internal working functions that had to be incorporated into an already complicated aircraft design. Only a few aircraft have ever fielded variable sweep wings and this included such notables as the Grumman F-14 Tomcat, Panavia Tornado, Rockwell B-1 Lancer and Tupolev Tu-160 "Blackjack" - all appearing some time later. Terrain following radars served the aircraft by allowing it to fly at supersonic speeds just underneath the perceived radar screen and deliver munitions from this low altitude with accuracy. It should be noted, however, that the F-111 itself overcame a variety of obstacles during her development - these being both political and technological in nature - to become the 560+ examples delivered to the USAF. Success, it seemed, came at a cost from any angle. On the other hand, the new breed of military aircraft being fielded by the Americans now outclassed just about any Soviet offering at the time.
Of similar note here is the technological advancements made in the world of surface-to-air detection and engagement - also playing a key role in the growing Soviet long-range bomber need. The current crop of Soviet bombers were ill-suited in their operations against such newer active defenses being fielded by NATO allies. For the Soviets, what once appeared to be a small hole in the dike initially had now exploded to become a bleeding chasm of desperation to some extent.
Sukhoi set to work to fulfill the new Soviet air arm requirement. They set their eyes on a long-range interdiction bomber design mimmicking the performance capabilities of the American F-111 without the complicated swing-wing functionality. The culmination of this early design work revealed the S-6, a mockup delta-wing model design fitting a pair of side-by-side Tumansky R-21F-300 turbojet engines. The aircraft would be piloted by a crew of two personnel seated in tandem, this helping to achieve a slimmer forward profile. While the design was ultimately reviewed, the progress was eventually nil as the "Puma" nav-attack system development was lagging sorely behind. Further tests of the mockup also revealed some key limitations that would ultimately doom the S-6 as a viable solution.
The S-58VD Flying Laboratory
1964 saw the Sukhoi firm press their attention onto the "S-58M", a modified form of their Su-15 "Flagon" interceptor product. By this time, the Soviet Air Force came back with a revision to their original requirement and sought an airframe with STOL (Short Take-Off and Landing) capability. This provided for something of a mechanical nightmare to the internal design layout of the new Sukhoi aircraft. Not only was the type to feature two afterburning turbojet engines for the supersonic speed requirement, she was now required to showcase STOL qualities through the implementation of four smaller turbojet engines for improved vertical ascension. The powerplants of choice became a pair of Tumansky R-27F-300 base engines and four Kolesov RD-36-25 series turbojets to fulfill the vertical thrust role. The radar of choice came under the "Orion" name. An existing Su-15 airframe was converted for the new engine arrangement to become the developmental "S-58VD". The new S-58VD was given a wider cross-section to make room for the crew of two seated side-by-side as well as the wider radar system to be mounted in the nose. Comparatively, the S-58VD shared a general overall external appearance to the Su-15 it was developed from (including the dual Tumansky engine layout and single vertical tail fin) but the wider forward profile quickly differentiated the type from the original.
The S-58VD featured a long, relatively flat nose cone ahead of the two-man cockpit. The pilot and co-pilot sat under a canopy not unlike that as featured in the F-111 Aardvark. Each professional sat in "zero-zero" Zvezda K-36D series ejection seats, allowing for ejections at any airspeed and at any altitude (in contrast to earlier seat designs that required certain speed and altitude minimums). The streamlined fuselage contoured rather elegantly into the squared-off rear body. Rectangular intakes were fitted to either side of the fuselage and this boxy shape carried on to the aft portion of the airframe. Wings were fixed and swept along their trailing edges in a sort of "double-delta" format, with each wing featuring a pair of underwing weapon stations. The tail section was dominated by the single vertical fin and applicable horizontal tail surfaces to each aft fuselage side (the latter all-moving surfaces). The undercarriage was conventional and made up of two double-tired main landing gear legs and a nose landing gear leg fitted a pair of smaller wheels. Of particular note in the S-58VD design were the four RD36-35 lift engines buried within the middle portion of the fuselage at about amidships. The upper panel of each intake sported doors meant to open and aspirate the engines when they were activated for STOL flight. The developmental aircraft was now assigned the more formal designation of "T-6" in 1965.
The S-58VD design itself would go on to become a flying laboratory of sorts, collecting STOL data from 1966 into 1969. Her captured information proved invaluable and showcased a loss of operational range over the gain of her STOL capability. Lift engines were always something of a peculiar love affair with aircraft engineers since the prospect of vertical flight was born with Leonardo Da Vinci. However, in 1960s terms, the devices required to achieve such flight were still rather large contraptions taking up vital internal space and making up critical weight increases for very little tactical gain. The areas within such an aircraft were best suited for the carrying of internal fuel stores to feed thirsty afterburning turbojet engines. Control of the S-58VD during the STOL process was also noted to be adequate at best, requiring much attention and direct pilot interference. True STOL operation would not be realized until the arrival of the subsonic British Harrier jump jet and perfected to an extend by the upcoming stealthy Lockheed F-35 Lightning II.
The T6-1 Prototype
The initial T6 prototype became the "T6-1", completed in May of 1967 and launched for the first time on July 2nd of that year. Initial evaluations were conducted sans the four lift jets to do away with early complexities during in-flight performance testing. The lift jets were not installed on the T6-1 until October of 1967 and the primary Tumansky R-27F-300 turbojet engines were later replaced in whole by a new pair of Lyulka-brand AL-21F series engines.
The F-111 Raises Eyebrows
The Soviet Air Force vision for the new aircraft was decidedly different than the T6-1 being offered from Sukhoi. Testing revealed that the design - in her current form - lacked the desired function sought. The 1967 display of the American F-111 Aardvark at the Paris Air Show only served to drive home the painful point - her variable wing, low-level flying was duly noted by aircraft firms all over the world - Sukhoi and her Soviet overseers being no exception. Her variable geometry wing design proved the swing-wing concept sound for a powerful mount such as the Aardvark. The Sukhoi firm finally steered itself in the direction of applying a similar swing-wing style function to their T6.
The T6-2I Prototype
Work on a new T6 prototype began on August 7th, 1968, producing the T6-2I. The T6-2I was essentially the T6-1 airframe mated to a new variable geometry wing system though the four lift jets were formally dropped. First flight was achieved on January 17th, 1970 and testing continued on until 1976, covering some 300 total flights. Seventy-three flights were made by T6-2I in 1971 and covered basic flight dynamics incorporating the various wing sweep settings. Only later were more complex systems thrown into the mix (including the automated flight system) and most evaluations were handled at low altitudes. A second swing-wing prototype, the T6-3I, was included beginning in late 1970. The T6-3I completed 90 flights in 1971 and contributed 300 flights of her own. A fourth swing-wing prototype, the T6-4I, began evaluation service on June 16th, 1971 but was lost to accident in 1973 after completing just 120 flights. Final evaluation of the T6 program concluded in 1976 with various landing scenarios to test out the airframe during rough-field, unpaved operations.
Further development of the T6 eventually included the incorporation of the "Puma" nav-attack system coupled with the "Orion-A" attack radar. Terrain avoidance was handled by the Relyef radar and featured an automatic flight guidance system. The design was furthered into production-standard forms within time. Even before the new aircraft had completed her various test regimes, however, the Soviet Air Force - happy with what it saw in its IL-28 replacement - quickly ordered the type for production under the designation of "Su-24".
Production was selected to begin at Factory No. 153 at Novosibirsk. The first production Su-24 went airborne on December 31st, 1971, with test pilot Vladimir Vylomov at the controls. Early Su-24s ("Fencer-A") were fielded in small numbers and this limited to trials units, leaving the Fencer-Bs as the true initial production face of the line. Fencer-C came online some time later and sported improved avionics. Though differences between the three were many, they were more-or-less minor enough to not warrant new designations from Sukhoi. Only NATO required the varying "Fencer" designations for their own nomenclature.
Her rush to delivery produced a few teething problems from the start, forcing several - though multiplying - modifications to be enacted (both to current and former aircraft) based on operational feedback from crews. Such changes included the enlarging of an internal fuel tank to increase the aircrafts range. Another included am aerodynamic revision of key rear fuselage surfaces in an effort to reduce airframe drag. The brake chute was relocated and a ram-air inlet was installed at the base of the tail fin. While early Su-24s sported variable intake ramps within their intake openings, this was later dropped to improve maintenance requirements and save on weight. The removal of these devices dropped the overall speed of the Su-24 from Mach 2.18 to Mach 1.35 - as devastating as this may have appeared, the expected low-level operations of the Su-24 suffered little in the move. The countermeasure capabilities of early Su-24s were progressively updated to include improved radar warning and missile launch warning coupled with integral onboard jamming equipment.
The Su-24 would not be formally accepted into service until February 6th, 1975. Her slab-sided fuselage eventually earned her the nickname of "Suitcase" from her crews. The West would not find out about the Su-24 until perhaps 1974 to which the incorrect designation of "Su-19" was assigned. Interestingly, this mistake would not be officially corrected until 1981. In true NATO fashion, the codename of "Fencer" was applied to the Su-24 - "F" being for "Fighter" ("B" was reserved for Bombers as in the "Brewer", "Bear", "Bison" etc...). It was not until the Soviet Air Force began arriving at East German air fields in 1979 did many of the fantastic Western estimates about the new Soviet aircraft finally dissolve.
The Su-24's external design owed much to both the T6 prototypes as well as the Su-15 "Flagon" from which it was directly developed from. She sported a long oblong fuselage with flat surfaces along all her sides save for the upper surface. The cockpit was situated aft of the nose assembly housing the important radar suite. The operators (pilot and systems officer) sat in a side-by-side arrangement under a glass canopy featuring relatively light, unobtrusive framing. There was a forward canopy portion split at the center and a main canopy portion that opened as individual assemblies, each hinged along their respective rear frames. The pilot and his radar operator entered/exited the aircraft by way of individual "clip-on" ladders to the left and right sides of the forward fuselage. This was a necessity for the Su-24 sat a good distance from the surface of the tarmac - herself measuring some 20-feet, 4-inches in overall height. By any measure she proved a very large design when viewed up close. As in her prototype, the air intakes were mounted along the sides of the fuselage and sported rectangular openings to aspirate their respective turbojet engines buried further aft in the fuselage. Of note here was use of splitter plates to divert "dead air" away from the intake mouth and fuselage sides. Interestingly, the rounded curves of the forward fuselage quickly gave way to the true Soviet-style Cold War-era design of sharp angles and flat, featureless surfaces found further aft. The tricycle undercarriage remained largely unchanged from the prototypes.
Wings were high-mounted affairs, fitted amidships in the design and stemming from short 69-degree swept "wing gloves". Wing sweep was noticeably drastic when the assemblies were in their full retraction form, giving the Su-24 airframe an arrowhead-like quality. Wingspan went from a wide 57 feet, 10 inches extended length to a more manageable 34 feet when fully swept. The preset wing sweep positions were noted as 16-degrees, 35-degrees, 45-degrees and 69-degrees. These allowed for the respective applicable flight functions covering landing/take-off, two altitude-sensitive cruise modes and a straight-line "dash" setting. There were four weapons hardpoints assigned to the wings, two to each underside. Other hardpoints would be centered in on the fuselage.
The empennage featured a single large vertical tail fin with noticeable sweep along the leading edge, less so along the trailing edge. The horizontal planes were all-moving surfaces and set to either aft fuselage side. There were ventral strakes positioned well-aft under each engine compartment. The engines exhausted through a pair of circular rings at the rear.
The Fencer (taking the Su-24MK as our model) fitted a single Gryazev/Shipunov GSh-6-23 series 23mm internal cannon with approximately 500 rounds of ammunition. The cannon was set along the starboard side of the fuselage. While limiting to some extent, the Su-24 was designed as a ground strike platform and built around speed - not intended to get into the fanciful head-to-head dogfights with the expected Western fighters. Her mission was to simply evade enemy radar and unleash her payload in unsuspecting targets in range - thusly her biggest enemies would be enemy radar and surface-to-air missile installations.
The Su-24 was cleared to wield up to 17,640lbs of external ordnance across her eight hardpoints (nine in a later production model). The two outermost (underwing) stations swiveled to match the currently-selected wing sweep - that is, they were designed to always face directly forward regardless of the wing sweep being utilized by the pilot - this helped to maintain the aircrafts aerodynamic aspect. There were an additional two fixed weapons stations under the wing gloves as well as four underfuselage stations. The two inner underwing stations were "plumbed" to accept fuel delivery using external droptanks.
The Su-24 could make use of 4 x Kh-23 "Kerry" (radio-directed) or 4 x Kh-25ML "Karen" (laser-guided) air-to-surface missiles. Up to two Kh-28 "Kyle", Kh-58 "Kilter" or Kh-31P "Krypton" anti-radiation missiles figured prominently into the Su-24 arsenal. Additional munitions included the Kh-29L/T "Kedge" laser/TV-guided missiles and the Kh-59 "Kingbolt" TV-guided missile.
Drop ordnance was made up of the KAB-500KR TV- and KAB-500L laser-guided bombs as well as whatever conventional bombs were made available in the Soviet inventory at the time. Point ordnance came in the form of 55mm S-5, 80mm S-8 or 120mm S-13 rocket pods as well as cannon pods of varying calibers.
Perhaps more important to students of the Cold War was the Su-24s clearance to field tactical nuclear-tipped bombs if required. Droptanks can take up the inner underwing weapon stations. Self-defense was handled by a up to four of AA-8 "Aphid" or (later) AA-11 "Archer" air-to-air missiles.
Performance of the Su-24 (Su-24MK) centered around her powerful pair of Saturn/Lyulka AL-21F-3A series turbojet engines delivering 16,860lbs of thrust each on dry and 24,675lbs of thrust with afterburner. She could hit a maximum speed of 815 miles per hour (roughly Mach 1.07) at sea level and up to Mach 1.35 at higher altitudes. Radius was limited to 1,725 miles for ferry operations and about 590 miles in a combat radius (this without external fuel tanks).
The "Fencer-A" was the initial production Su-24 discovered by NATO. Fencer-B were the Su-24s featuring the revised rear fuselage among the other noted enhancements. Fencer-C designations were used by NATO to label improved countermeasures capability. None of these first three Fencer models were given a separate designation by Sukhoi, all collectively falling under the "Su-24" designation.
The Fencer-D was the Su-24M ("M" translating to "Modified"), featuring integrated chaff/flare countermeasures dispensers as well as noticeable wing fencing, usually along the wing gloves but placement differed on some production units. Munitions capabilities were greatly expanded beginning with this model. This included the addition of the Kaira-24 (Grebe) laser designator (at the expense of some internal fuel stores, thus limiting range somewhat) for use with precision guided ordnance delivery replacing the original electro-optical sighting system. Adoption of the Kaira-24 did away with the former required external designator pod. A collapsing in-flight refueling probe was affixed to the starboard side of the forward fuselage, improving tactical range substantially and putting the Su-24 on par with her Western counterparts. The fuselage was lengthened out some 30-inches (officially 29.9-inches) and the radome was revised in shape. Perhaps the greatest benefit of the new aircraft lay in the implementation of a new weapons control system known under the name of PNS-24M "Tiger" NS. A ninth hardpoint was added to the design. Defensive measures were also improved with the new "Karpaty" system, incorporating the "Mak" infrared sensor on the upper fuselage surface amidships. Work on these improved Su-24s began in 1971, producing the initial T6-M8 prototype which flew some time later on June 29th, 1977. The first production Su-24M went airborne on June 20th, 1979 with full acceptance into service coming in 1983.
The Su-24MK (Fencer-D) became simply the export version of the base and improved Su-24M models. By the middle of the 1980s, Sukhoi OKB received government permission to sell a "scaled down" version of the Su-24 to Arab allies. First flight was achieved on May 30th, 1987 under the prototype designation of T6-MK. The Su-24MK became officially available for export on May 17th, 1988 with production running into 1991. Of course these systems were sold to nations without the true avionics, IFF (Identification Friend or Foe) and weapons packages as found on the Soviet aircraft. The installed digital processing computer was the TsVM-24 series. This made for a less-functional, perhaps even less-lethal end product in the long run. Recipients of this Fencer became Algeria, both Iran and Iraq, Libya and Syria.
The Su-24MR (Fencer-E) became the dedicated tactical reconnaissance platform of the Su-24 series. The Soviet Air Force began to see a growing need to replace its outgoing reconnaissance aircraft with more modern types. Their current crop of aircraft lacked the needed operational ranges and utilized outdated equipment for the task. Sukhoi delivered two modified Su-24 airframes for evaluation as T6M-26 and T6M-34 (later becoming T6MR-26 and T6MR-34 respectively). First flight was conducted in September of 1980, and the new version entered service in 1983. Notable differences between the Su-24MR and the attack Su-24s was the deletion of the Orion-A attack radar suite as well as the laser target designator. Essentially, most of her ground attack equipment was removed including her internal cannon, this replaced by internal reconnaissance cameras. Additionally, three of the external hardpoints were dropped. Infrared and TV sensors were installed as was a panoramic camera fitted into a slightly smaller and shorter nose. An oblique camera was fitted to the lower fuselage. The nose showcased a slightly new external look as it housed a SLAR (Side-Looking Airborne Radar) and dielectric panels covering reconnaissance equipment. Collectively, the reconnaissance suite was known under the designation of "BKR-1" and was developed by the Moscow Institute of Instrument Engineering. For its time, the Soviets claimed it was the best of its type anywhere in the world, allowing for operations in all-weather, day or night, with image reproduction at near-photographic quality ranging out to over four times the altitude of the aircraft. Structurally, the wing root fencing was deleted. Most Su-24MRs are quickly identified by their use of external recce pods along their weapon stations.
Su-24MP (Fencer-F) signified the dedicated ELINT (ELectronic INTelligence) model variants. Work on this derivative began in 1976 and involved the T6M-25 and T6M-35 prototypes, becoming the T6MP-25 and T6MP-35 respectively. First flight of the model was achieved on November of 1979. The type was officially marked as ready on April 7th, 1983. These airframes could be identified by the addition of more antenna protrusions but were allowed to keep their internal 23mm cannons. The Su-24MP was traditionally armed with up to four AA-8 air-to-air missiles and is believed to have existed in only 10 production examples though some sources state the total as high as 20 aircraft.
The Su-24 was shipped beyond Russian borders to Soviet allies and satellite states. Algeria operated some 39 total Su-24s of which 36 are believed operational today. Angola was a rumored operator, having received perhaps 12 Su-24s by way of Belarus. Azerbaijan was noted for their 11 Su-24s in service. Belarus operated at least 34 of their own Su-24s after the fall of the Soviet Union. Between 24 and 36 Su-24s are thought to have been received into the inventory of the Iranian Air Force, some being captured Iraqi mounts following the 1991 Gulf War. No Iraqi Su-24s exist today. Kazakhstan operated at least 25 Su-24s while Libya purchased some 8 examples. Syria may have operated 20 Su-24 types at one time. It is believed that Uzbekistan still operates some ex-Soviet Su-24s left over from the fall of the Soviet Union.
Ukraine remains the second largest Su-24 operator with some 230 total examples believed in circulation as of late 2008.
Russian maintains the Su-24 in her aging air force ranks, making up 415 total examples as of late 2008. Over 300 of these serve with the Air Force while less than 100 of these form elements of the Russian Navy.
Once in operational status across the Russian inventory, the Su-24 proved a bear to maintain. Her complex infrastructure, while an impressive feat for Sukhoi OKB in itself, brought along with it the minute attention to detail required by her ground crews. The complexities inherent in her swing-wing design coupled with her computer-controlled internal functions made for one difficult horse to keep happy. The Su-24 was, in essence, the first Soviet combat aircraft to feature systems under control from onboard computers.
Despite these technological drawbacks, her pilots quickly found a lot to like in their new Su-24s when compared to their outgoing Yakovlev Yak-28s and Mikoyan MiG-27 "Floggers". She was a well thought-out design and especially endeared by those airmen charged with long flights abroad - her automatic terrain flight system proving handy in such sorties. Her cockpit offered up a good field of view from within and a few ergonomic amenities were noted. The variable wing sweep lived up to her STOL expectations and high-wing loading produced a fairly comfortable low-altitude journey. Additionally, the Su-24 fielded quite a bit of power at full afterburn from her dual engine configuration. Her handling was remembered as somewhat forgiving and responsive though still requiring a steady trained hand. The weapons hauling capability of such a system was a story all its own when compared to previous Soviet offerings.
Notable actions of the Su-24 in Soviet service began in 1984 with operations over Afghanistan. Su-24s operated from bases in southern USSR and were charged with tackling fixed fortifications being used by the Mujaheddin. The Fencer delivered as promised and was noted for her precision, range and variable weapons loadouts. However, as the war evolved, there was much less need for the high-speed, precision antics of such an aircraft and a diminished role soon followed. The Soviet war in Afghanistan turned more into an intimate affair requiring the use of close-air support aircraft such as the Sukhoi Su-25 "Frogfoot". Regardless, of all the Su-24s fielded in anger during the war, none were lost to enemy ground fire - the few that were lost were reportedly victims of accidents involving maintenance.
Additional activity yielded similar results in the Russian anti-rebel campaign against Chechen targets throughout the volatile 1990s. It is believed that the aircraft played a role in airstrikes against Georgian targets in South Ossetia during the limited August 2008 conflict as well.
The Su-24's Future
From a technological standpoint, the Su-24 is a design that met its last fruitful day sometime yesterday. Her 1960s origins almost dictate such action but financial limitations and modernization programs within the Russian Federation have kept the Fencer relevant in the last decade. However, to the West, the F-111 Aardvark has already been retired from service with the USAF and the Su-24 could hardly be considered a contender on today's "stealth" battlefields. The Su-24 is scheduled to be replaced in the long run (at least within the Russian Air Force) by Sukhoi's Su-34 "Fullback" two-seat, twin engine, fixed-wing fighter bomber. The aircraft fulfills a similar role but sports a bevy of modern and advanced features that make the Su-24 wholly archaic in nature. At $36 million US dollars apiece, there have only been twelve Su-34 examples produced even though its first flight occurred sometime in mid-1990.
For the interim, the Su-24M and Su-24MK production models are being given modernization assessments to keep them viable. The updates will include incorporation of "all glass" cockpits featuring a HUD (Heads Up Display) and MFDs (Multi-Function Displays). Compatibility with the AA-11 "Archer" short-range, air-to-air missile is expected. There will also be a digital moving map display and helmet-mounted sights for pilots (this currently en vogue on many modern jet fighters worldwide). It is believed that testing of upgraded Su-24s began as early as 1999.
The Russians have deployed their most advanced versions of the Cold War-era Su-24 int he skies over Syria during the Syrian Civil War which began in 2011. They have been responsible for most of the bombing runs seen against opposition forces. In 2015, a Turkish jet downed an Su-24 which caused Russia to deploy Su-35 air defense fighters for protection.
Service Year: 1974
Type: Long Range Strike / Attack Aircraft
National Origin: Soviet Union
Manufacturer(s): Sukhoi OKB - Soviet Union
Production Total: 1,400