The Sukhoi Su-25 (NATO Codename Frogfoot) is often identified as a direct counterpart of the A-10 Warthog. Indeed, the two share many of the same design criteria (both are slow, maneueverable, and heavily armored), and many have noted the superficial similarities between the Su-25 and the Northrop YA-9A, loser of the A-X competition. A more comprehensive analysis of the Su-25 will, however, reveal that it was designed quite a different mission than "tank busting"—which is the raison d'etre of the A-10A. First, a bit of background...
The Soviet Air Force during World War II developed a line of specialized close air support aircraft. Heavily armored, and armed with cannon, bombs, and unguided rockets, these Shturmoviki (specifically the Ilyushin Il-2 and Il-10) served as flying artillery in support of fast moving tank columns, and as fire brigades to seal off advances by German Panzer formations. The Il-10 Shturmovik served through the middle 1950s, and saw action in the Korean War. But the advent of Khrushchev's "Revolution in Military Affairs", and its emphasis on nuclear warfare, saw the demise of the Shturmovik in Soviet service.
By the early 1970s, Soviet doctrine had come to recognize the possibility of protracted conventional (non-nuclear) war in Central Europe, and renewed interest was given to the use of airpower in direct support of the ground forces. This was provided either by obsolescent fighters like the MiG-21 (NATO Codename Fishbed), specialized attack aircraft like the Su-7/-17 Fitter, or ground attack variants of front-line fighters like the MiG-27 Flogger. Only after the US initiated the A-X competition did the Soviet Air Force show real interest in a specialized, heavily armored attack aircraft--a "Bronyirovanni Shturmovik" (armored assaulter). The project was pushed forward by the Sukhoi design bureau, despite a relatively low priority. The T-8-1 prototype aircraft first flew in February 1975, and available pre-production aircraft were used in Afghanistan in 1979-80. Production aircraft were then manufactured at a low rate, and the first service squadrons were formed in 1984. These were formed into 3-squadron Otdelnyi Shturmovoi Aviatsionnaya Polki (OShAP), or Independent Storm Aviation Regiments. Several of these saw active service throughout the Afghan War, suffering several losses to US Stinger missiles in the hands of Mujahidin guerrillas.
Surprisingly, the Su-25 was acquired only by three of the Warsaw Pact nations—Bulgaria, Czechoslovakia and Hungary—none of which would be major players in the Central Front confrontation for which the aircraft was designed. It may be that Warsaw Pact air staffs had the same reservations about the survivability of a slow jet as their USAF counterparts. Export sales were also limited; few were picked up by Iraq and North Korea, but many were transferred to Afghanistan after the USSR withdrew from that country in 1989.
By all accounts, the Su-25 was a very successful design, faster than the A-10, highly maneuverable, and very rugged. Many were damaged in Afghanistan, but only a handful were actually shot down. Why, then, was this aircraft relegated to relative obscurity?
The answer may lie in the evolution of Soviet military doctrine regarding what the U.S. calls close air support (CAS); i.e., the use of aircraft to attack targets in direct contact with friendly ground forces. The turning point may have been the 1973 Yom Kippur War, in which the Israeli air force suffered heavy losses to battlefield air defenses while trying to repeat its 1967 performance as "flying artillery". After that war, the Israelis reconsidered their CAS philosophy, concluding that the pilot workload in the face of serious air defenses was simply too great to ensure survival. Instead, Israel began to place much more emphasis on the attack helicopter armed with anti-tank guided missiles. Helos, it was felt, could coordinate directly with the ground forces, and were inherently more effective and survivable by virtue of their ability to maneuver "nap of the earth" (NOE). Coming to similar conclusions were the West German Luftwaffe and the staff of the Soviet Air Force, both of which began to downplay fixed-wing CAS in favor of a rotary wing approach.
To this end, the Soviet Union transferred most light, medium and attack helicopters out of Frontevaya Aviatsiya (Frontal Aviation-FA) of the Soviet Air Force, and into Armeskaya Aviatsiaya (Army Aviation-AA) units controlled directly by ground force commanders. With this decision, much of the rationale for a Shturmovik seemed to disappear.
In USAF doctrine, tactical air-to-ground operations fall into three main battle area categories: CAS, performed within 1-5 km on either side of the Forward Edge of the Battle Area (FEBA); battlefield interdiction (BAI), attacks on tactical and operational targets such as enemy artillery and second echelon formations (from 5-50 km behind the FEBA); and deep interdiction, attacks on enemy logistic and transportation infrastructure, carried out more than 50 km behind the FEBA.
Soviet doctrine appears to have been somewhat different, in that there are four separate attack zones. CAS (in the US sense) is generally performed by helicopters. In between the CAS and the BAI zones was an intermediate zone in which the main targets are enemy battlefield forces not in direct contact with Soviet forces. Behind that are the traditional BAI and deep interdiction zones. While BAI and deep interdiction could be performed quite well by specialized high-speed strike aircraft such as the Su-24 Fencer and MiG-27 Flogger, and CAS was assigned to helicopters, the area between the CAS and BAI zones seemed to require a different sort of aircraft. In that region, air defenses would be as dense as in the forward area, and targets dispersed and difficult to spot. Aircraft operating in that zone would therefore have to loiter a relatively low speeds, be highly maneuverable (to avoid defenses and engage fleeting targets), and, obviously, be able to sustain considerable damage and return to base. In short, this was a mission ideally suited to the Su-25.
Su-25 Design Analysis
The main operational variant, Su-25 "Frogfoot-A", is a twin-engine, single-seat aircarft with an unswept, tapered, shoulder-mounted wing. The pilot sits in a heavily armored cockpit behind a bullet-proof windscreen. The clamshell canopy is faired into the spine of the slab-sided fuselage, limiting visibility to the rear (unlike the A-10, which has a bubble canopy for 360° vision). In contrast, the pilot's view forward is exceptional because of the downward-sloping nose profile (known in Russian as the "Utka", or duckbill. The same basic nose design is also used on the MiG-27 Flogger ground attack variant of the MiG-23 fighter. In the tip of the nose is an electro-optical sensor package that includes a low-light television, a laser spot tracker (like Pave Penny), and, in contrast to the A-10, a laser rangefinder / designator. Thus, unlike the A-10, the Su-25 has a modicum of night attack capability, is able to launch laser-guided weapons without external designation, and conversely, can also designate targets for other aircraft.
The engines, two 9,925-lb. st. thrust Turmanskiy R-195 turbojets, are buried in the wing roots, much like the Northrop YA-9A prototype. This configuration provides low drag, and makes for easy access and maintenance, but is more prone to foreign object damage (FOD) and presents a higher infrared (IR) target than the high-mounted engine pods of the A-10A. The choice of engine types in the two aircraft is in itself enlightening. The 9,065-lb st. thrust TF-34 of the A-10A is a high-bypass turbofan, selected for its fuel efficiency and cool efflux (to minimize vulnerability to IR-guided missiles). In contrast, the R-195 is low bypass ratio turbojet, generating more thrust, but at a cost of much higher fuel consumption and a hotter exhaust plume.
As in the A-10, most of the fuselage is occupied by fuel tanks and avionics compartments; other fuel tanks are located in the wings. In addition to the cockpit, the engine compartments and at least some of the fuselage fuel cells are armored. The degree of armor protection in general seems to be inferior to that of the A-10, but the threat against which the Su-25 was designed (20-35mm cannon) was less potent than the 23mm cannon of the Shilka.
As in the Northrop YA-9A—but in marked contrast to the A-10—the Su-25 has a conventional single-rudder tail. The twin rudder configuration of the A-10 was chosen to enhance survivability through redundancy, and also to mask the engines from IR missiles from the sides and below. With its low-mounted engines, this was not necessary in the Su-25. The overall effect, then, is a more streamlined design that emphasizes speed and power over endurance and survivability.
The defensive systems of the Su-25 are considerable, but not nearly as extensive as those of the A-10A. The standard radar warning receiver is the Sirena-3, which provides 360° detection of ground and airborne radars. A cockpit display shows bearing and approximate range based on signal strength, plus an identification of threat by type using simple warning lamps. As initially delivered, the Su-25 had only a small number of chaff/flare dispensers. As a result of Afghan war experience, two 128-cartridge dispensers were added to the upper surfaces of the air intakes (published reports indicate that the upward ejection of countermeasures improves the chances of seducing a missile away from the low-mounted engines). However, in the basic Su-25, the Sirena-3 is not linked to the countermeasures dispenser; the pilot must decide when and how many cartridges to pop on his own.
In addition to passive countermeasures, the Su-25 was designed from the start with two dedicated air-to-air missile pylons. Initially, these carried the IR-homing R-60 (AA-8 Aphid), a short-range missile roughly comparable to the second-generation AIM-9J/P Sidewinder. There is reason to believe that it is also capable of launching the newer R-73A (AA-11 Archer), a highly advanced IR missile considered superior in most respects to the latest AIM-9M Sidewinder. Thus the Su-25 has considerable ability to defend itself against enemy fighters, should these care to get into a dogfight.
Offensive Systems
The primary weapon of the A-10 is the GAU-8A Avenger 30mm cannon; the aircraft is in fact built around the gun. The Su-25 does indeed carry a twin-barrel 30mm gun with 250 rounds, built into the left side of the fuselage, but it has a much lower rate of fire and muzzle velocity than the GAU-8, and does not fire specialized armor-piercing ammunition like the PGU-14 API round. Thus the gun is more of a general purpose strafing weapon than a dedicated tank killer.
The principal weapons of Su-25 are carried on its eight underwing pylons, which have a total capacity of 9,700 lbs. (seldom carried operationally). Whereas the most common ordnance carried by the A-10 (AGM-65 Maverick missiles and Mk.20 Rockeye cluster bombs) are primarily oriented towards the anti-armor mission, the Su-25 generally carries a more general-purpose load. Most commonly carried stores include:
• FAB-100 220-lb general purpose bomb
• FAB-250 550-lb general purpose bomb
• ZAB-100 220-lb incendiary bomb
• ZAB-250 550-lb incendiary bomb
• RBK-180 & RBK-250 submunition dispensers (similar to the Mk.20 Rockeye)
• UV-16 and UV-32 57mm rocket pods
• S-24 240mm unguided rockets
The Su-25 is also cleared to carry the Kh-66 (AS-7 Kerry) air-to-surface missile, an command-guided weapon similar to the U.S. AGM-12 Bullpup; it is no longer in front-line service with the Russian air force, but may be used elsewhere. Note that none of these can be considered precision, standoff tank-killers in the same league as Maverick. Rather, they are general purpose weapons intended to deal with the broad range of materiel and personnel targets found in the area 5-50 km behind the FEBA.
Su-25 / A-10 Performance Comparison
The performance envelopes of the A-10 and the Su-25 differ substantially, a further reflection of their different design philosophies. The Su-25 is substantially lighter than the A-10, and has nearly 2,000 lbs more thrust, in addition to being aerodynamically "cleaner". No surprise, then, that the Su-25 is very much the faster, with a maximum speed (clean) of 527 kts. (606 mph), as compared to 397 kts (456 mph) for the A-10A. Clean speed, however, is a rather meaningless. Far more relevant are basic attack speeds: 372 kts (428 mph) for the Su-25, and about 300 kts (345 mph) for the A-10A. This indicates that the Su-25 is far closer in design to a conventional strike fighter than the A-10; the latter is far better optimized for the CAS mission as commonly defined in the West.
Though exact performance comparisons are not available, it is possible to say that the A-10, with a wing loading of only 99 lbs/sq ft vs. 107 lbs/sq ft (assisted by very large decelerons and a high-lift wing), has superior instantaneous turn performance. On the other hand, with its higher power loading (0.61 vs. 0.45), the Su-25 has better sustained turning performance, as well as much better rate of climb, and better overall performance in hot-and/or-high environments (like Afghanistan and Kuwait).
Variants
Though production of the Su-25 ended in 1989-90, further development of the type has continued. The first variant was the Su-25K (for Kommercheskiy), an export derivative generally similar to the basic Su-25, with certain Soviet systems deleted. The Su-25UB (Frogfoot-B) is a 2-seat operational trainer with full combat capability. It features a raised rear seat (displacing some fuel and/or avionics) under an enlarged canopy. To compensate for increased keel area forward, the vertical stabilizer has been greatly enlarged, but otherwise the airframe is similar to Frogfoot A; the Su-25UBK is the export version. The Su-25UT is an primary trainer lacking combat systems, but otherwise similar to the UB. The Su-25UB was navalized as the Su-25UTG, with a tail hook, to serve as a carrier-based trainer and possible attack aircraft for the Admiral Kuznetsev class full-deck carrier. Approximately 12 were produced, but at present it appears that the Kuznetsev air group will be limited to Su-27K Flanker multi-role fighters.
As a private venture, Sukhoi developed the Su-25T (for Tank), a dedicated anti-armor Shturmovik similar in concept and mission to the A-10A. Based on the Frogfoot-B airframe, the Su-25T replaces the rear seat with an enlarged dorsal spine for additional fuel and the avionics associated with the Shkval electro-optical sight system. Ordnance options have been expanded to include a number of modern tactical standoff missiles, including the TV-guided Kh-25ML (AS-10 Karen), laser-guided Kh-29L (AS-14 Kedge), and the anti-radiation Kh-58 (AS-11 Kilter) and Kh-31R (AS-17 Krypton), and KAB-500 laser guided bombs. However, the primary weapon appears to be the laser beam-riding AT-12 Vikhr anti-tank missile, of which upwards of 16 can be carried. According to US sources, these have an effective range of some 8km (probably more), and, like the AGM-114 Hellfire, can penetrate all known tank armor. Thus the Su-25 has an standoff anti-tank capability roughly comparable to the A-10A.
Because of its higher speed and inferior maneuverability, its tactics would probably require somewhat higher pop-up approaches, with concommitantly longer periods of exposure. This may be acceptable, however, because of the paucity of forward area air defenses in Western armies. The Su-25T would not have to face the redundant, interlocking, and mutually supportive layered system used by the Soviet Army. Its main threat would be the FIM-92 Stinger, a man-portable shoulder-fired IR missile with a maximum range of around 6 km, or similar missiles such as the French Mistral or British Javelin. Longer-range systems positioned further back, such as the German Roland, British Rapier, or French Crotale, lack the range to overwatch units in the forward area. In addition, with its E-O sight system, the Su-25T can acquire targets at much longer ranges than A-10s relying on visual acquisition. It can, therefore, exploit the longer ranges of missiles like the AS-14 (not to mention ARMs like the AS-11 and AS-17) to avoid or destroy longer-range air defense systems. Working in conjunction with the latest Russian attack helicopters (Mi-28 Havoc and Ka-50 Hokum), the Su-25T could become part of a Russian JAAT concept that at least in theory , can be as effective as the A-10A/AH-64 Apache combination.
As of 1995, the Su-25T has been offered for sale to several countries, but none have been exported to date. A limited production batch have been accepted by the Russian air force for evaluation purposes (and to underwrite the development of the aircraft).
