Alexander Velovich/MOSCOW
WHEN the SUKHOI DESIGN bureau's project to upgrade its Su-25 Frogfoot design stopped, following the collapse of the Soviet Union, the programme appeared to be going the same way as many other air force developments - nowhere.
This has not proved to be the end of the line for the Frogfoot, however. The Russian air force's frontal-aviation ground-attack units still need an all-weather attack aircraft, fulfilling the roles carried out by the Sukhoi Su-17 Fitter and Mikoyan MiG-27 Flogger.
Sukhoi, with funding from the air force, followed the T-8M with work on the T-8TM. (The Su-25TM, now referred to as the Su-39, was previously known as the Su-34. The Su-34 designation is now given to the Su-27IB strike variant of the Flanker.) Beyond the impish sense of humour exhibited by Sukhoi chief Mikhail Simonov, the numerical designator reveals little. The aircraft will be given an "official" Sukhoi number only if, and when, it enters air force service.
The T-8TM modification, is intended to further advance the Frogfoot's modernisation, by providing a day/night, all-weather, attack capability, using radar and imaging infra-red (IIR) sensors, as well as incorporating new air-to-surface and air-to-air weapons.
Sukhoi chief designer Vladimir Babak is confident that the air force will continue to support the Su-25TM. "We have modest financial needs because we had completed the bulk of the flight tests before money became a problem [on the Su-25T], and everybody was working at full strength," he says.
The Su-25T development effort seems to have focused on improving the basic Frogfoot's ground-attack capability, with a dedicated anti-armour system through the Shkval (Squall) nose-mounted television-sighting system and the Vikhr (Whirlwind) laser-guided anti-tank missile.
Sensor pods, intended to improve the aircraft's all-weather capability, were included as part of the programme, but development of some of the sensor equipment encountered difficulties. Only the Mercury low-light-level TV pod was successfully produced.
A pod mounted 8mm-band radar, developed by Leninets in St Petersburg, and an imaging-infra-red pod were also under development. The IIR pod has been referred to as Khod in some Polish publications.
The Mercury pod works by using electronic enhancement of a TV picture, allowing identification of a bridge-sized structure in a clear, almost moonless, night at 6-8km (3-4nm) or a boat at 6-7km, while a tank can be identified at a range of 3km. This performance is said to be adequate, in providing a 24h attack capability, against some classes of targets, with guided and unguided weapons.
The Su-25T was marketed with the Mercury pod when it was first shown at an international air show in Dubai in 1991.
Experiments with the IIR system proved to be less successful. Babak says that its performance depended largely on atmospheric humidity, but it did not meet specification, so development efforts were dropped.
Babak claims that Sukhoi has finally found an indigenous Russian manufacturer of an IIR system based on new-generation components, and a system meeting the requirements is promised to be ready for flight tests in 1997.
He reveals that the fate of the 8mm-waveband radar was also determined by the collapse of the Soviet Union because the manufacturers of its major components are based in Ukraine, and the Russian air force felt that it "...could not proceed with development with a foreign component-supplier". St Petersburg-based Leninets said at the time of the Soviet collapse that it would take another two years to develop a system from Russian-built components. Babak estimated that, even with a new digital computer and new software, it would take at least four or five years to develop.
Sukhoi needed a quicker solution and so approached Russian radar manufacturer Phazotron, which was developing the Kopyo (Spear) radar for Mikoyan MiG-21 Fishbed upgrades.
The Kopyo could provide an all-weather attack capability with a set of mapping modes, including Doppler beam-sharpening to 0.45° (1:10) and synthetic-aperture radar (SAR). In the SAR mode, with a resolution of 30 x 30m in azimuth the mapping range provided is several dozen kilometres. A group of tanks can be detected at 25km and a port crane or a dock at around 100km.
An important addition is the capability to detect naval targets such as missile boats (at 75km) and destroyers at the maximum range of 200km - in the latter case the range is limited mostly by the radar horizon.
The radar is mounted in a pod on the fuselage centreline station. It has a 500mm-diameter flat antenna with scan of +40° in azimuth and +20° to -60° in elevation.
Babak says that four sets of Kopyo radars have been produced: one for the test stand at Moscow's GosNIIAS avionics and weapons-integration research institute, two destined for the MiG-21 upgrade and one which is being fitted into a container developed for the Su-25TM.
KOPYO FLIGHT TESTS
Flight tests of the pod-mounted Kopyo will begin in May. Phazotron chief designer Yuriy Guskov believes that these will not take long, as the design incorporates components, technology and software already proven in the N-010 Zhuk radar developed and tested for the MiG-29M.
The Kopyo, is a radar developed for a multi-purpose fighter, and it brings a new dimension of air-to-air and anti-ship utility, to the Su-25TM. Detection range for a fighter-size target is 57km in head-on conditions and 25km in tail-on circumstances. Multiple-target track-while-scan mode and a load of four Vympel R-77 (AA-12 Adder) active-radar air-to-air missiles (AAM) would provide the Su-25TM with considerable anti-aircraft capability.
A pair of extended-range Vympel R-27ER (AA-10 Alamo) semi-active AAMs may help the aircraft to win a duel by offering higher average speed and longer engagement range than that of standard Western Hughes/ Raytheon AIM-7 Sparrow medium-range missiles. Four R-27R missiles may also be carried under the Su-25TM's wing.
For close-range engagements, the Su-25TM may carry a pair of infra-red-guided Vympel R-73s (AA-11 Archers) or Molniya R-60s (AA-8 Aphids).
At 5,000ft (1,500m) and 250kt (460km/h) indicated airspeed the Su-25TM, even with a 1.5t bomb load and 50% of fuel reserves, has a turn radius of 570m, making it a slippery foe in a turning fight. Naval pilots flying the Su-27K (Flanker D) have gained experience of the Frogfoot's turning ability in dissimilar combat exercises against Su-25UTG naval trainers.
Integration of the Kopyo radar will also enable the Zhvezda Kh-31A (AS-17 Krypton) and Kh-35 (AS-X-20 Kayak) anti-ship missiles to be employed. Both weapons have active-radar seekers and carry 90kg and 145kg warheads, respectively. While the ramjet-powered Kh-31A offers a higher average speed of 1,360-1,550kt (2,500-2,900km/h) and a range of 50km, the turbofan-powered Kh-35A can be launched at 130km range, but has a subsonic speed of 470-520kt.
After production of the Su-25 in Tbilisi, Georgia, had stopped, Sukhoi arranged co-operation with the Ulan-Ude plant in Siberia. In 1995, the first Su-25TM assembled there was exhibited at the Moscow International Air Show. This year, another two or three aircraft will join the flight test programme.
The Su-25TM builds on the considerable work put into the Su-25T programme. Flight tests of the Su-25T (T for tank-killer) began as far back as 1984. Combat experience gained in missions over Afghanistan prompted several design refinements. The first was to enhance combat survivability. To complement the polyurethane foam in the fuel tanks, adjacent fuselage compartments were filled with elastic porous filler. This outside filler was intended to prevent the impulse splash of fuel out of the tanks if hit by a bullet or shell.
A gap between the fuel tanks and air intakes was also introduced, to reduce the possibility of fuel getting into the engine inlets following combat damage. The central part of the fuselage was strengthened and, in addition to a cockpit welded from titanium plates, more armour was added to protect the avionics bay, fuel-feed tank and fuel pipes.
The design modifications, which were intended to improve the aircraft's combat survivability, accounted for 7.5% of the standard take-off weight. The weight increase is justified by the design bureau's view that it enhances the aircraft's survivability by a factor of four to six.
This latter figure has been proved, not only by tests and modeling but by combat experience, claims Babak. The aircraft is intended to be able to be flown after having been hit by a burst of cannon shells, or a Stinger shoulder-launched surface-to-air missile.
The Su-25T was developed from the two-seat Su-25UB trainer airframe, substituting the rear cockpit with another equipment compartment and adding 1,000kg of fuel capacity in the central fuselage tank. The four inner-wing pylons are wet and can accommodate 800litres of fuel or 1,150litres in external fuel tanks.
Low-altitude combat-mission radius, with a standard bomb load of 2t, is 400km. At cruise altitude, the mission radius with the same bomb load is increased to 630km.
To compensate for the increase of 2t in maximum take-off weight, the R-195Sh engines were up-rated by 10%, to 44kN (9,900lb) thrust each. The take-off run and landing roll, even on unpaved airstrips (for which the Su-25T is fully cleared), do not exceed 600-700m.
While a Su-25 pilot, can use only his own "MkI Eyeball" for detecting and identifying a target, the Su-25T was designed to have the Shkval TV-sighting system with a 10° field of view and 23x magnification. The Shkval I-251 was developed by Krasnogorsk OMZ, a manufacturer of Zenit cameras. Images from the scanning optical head are displayed on the IT-23VM cathode-ray tube in the right upper corner of the instrument panel.
On average, the Shkval offers a threefold increase in identification range of ground targets, compared with pure visual conditions. A house can be identified at 15km range, a tank at 8-10km and an Apache-class helicopter at 6km. An automatic image-correlator ensures tracking of a target against ground, sea or sky background. The optical system has three-axis stabilisation and tracking angles of +15° to -80° in elevation and +35° in azimuth. A laser-range finder/designator follows the target with a laser beam through the same optical system, providing range for weapon firing and target-illumination missile guidance.
According to Babak, automatic procedures for attacking a target illuminated by laser from a ground-based fire controller have been developed, tested and proved to be very efficient. A portable laser illuminator, compatible with the Shkval has been developed by NPO Polyus, the leading Russian laser manufacturer.
The major weapon for the Su-25T is the Vikhr laser-guided beam-riding anti-tank missile. Two loads of eight missiles, are normally intended to be carried. Vikhr engagements start from a range of 8-10km, allowing several targets to be designated in a single pass. The missile's tandem warhead is designed to defeat 1,000mm of armour.
VIKHR EFFECTIVENESS
Although the Su-25T can carry and use ordinary semi-active laser-guided missiles such as the Zhvezda Kh-25ML (AS-10 Karen), Molniya Kh-29L (AS-14 Kedge) and S-25L guided rocket against hardened targets, the Vikhr is more effective in engaging armour.
The Vikhr missile can also be used to engage helicopters and aircraft. During tests, the missiles proved to be capable of destroying even a Tupolev Tu-16 Badger drone.
Su-25T navigation consists of an air-data system; twin inertial-navigation systems; the A-312 RSBN radio-navigation system, combining TACAN and instrument-landing system functions; the A-723 long-range radio-navigation Loran/Omega system; ShO-13A Doppler ground-speed sensor; and RV-21 radar altimeter.
For the Su-25TM, it is planned to add a satellite-navigation system, further improving accuracy of the navigation system to some 10m from the current 100m.
To reduce pilot workload, the auto-pilot has several modes of automatic trajectory-control, providing altitude and heading stabilisation, automatic route navigation through programmed way-points and approach to target area, repeated approach to a designated target and automatic landing.
Considerable work also went into improving the aircraft's defensive aids. Babak says that the highest priority was put on countering the threat from portable surface-to-air missiles such as the US Stinger or Russian Strela and Igla.
The aircraft has an UV-26 dispenser with 192 chaff or flare cartridges, but even this stock of flares can protect the aircraft only for a limited time. In addition, the aircraft has an electro-optical jammer at the base of its fin.
The jammer is based on a powerful cesium lamp, which has an energy consumption of 6kW and creates amplitude-modulated infra-red emissions for use as a decoy. To improve the jammer's operational effectiveness, attempts were made to reduce the aircraft's infra-red signature by a factor of three to four.
Additional air intakes were added on the upper surface of the aft section of the engine nacelles, ducting cool air to the nozzles, reducing their temperature threefold.
A circular centrebody was introduced in the engine nozzle, to shade the turbine blades and reduce the infra-red signature even more. Babak says that the price paid for these is not high, raising fuel consumption by only 2-3%, while the result is extremely effective.
The radar-warning receiver (RWR) on the Su-25T is a new design with digital signal processing. It covers the 1.2-18GHz waveband, with +30° elevation and 360° azimuth coverage. When analysing radar threats, the RWR indicates their priority and advises a pilot on defensive manoeuvres. The RWR is also used for cueing the seekers of anti-radiation Raduga Kh-58 (AS -11 Kilter) missiles, four of which can be carried. This allows the Su-25T to be used in the defence-suppression role, as well.
A pod-mounted active-radar jammer may also be carried under the outer wing pylons covering +60° in azimuth forward and rearward and +30 in elevation. A wide variety of jamming techniques includes high-frequency noise, and spurious range signals can be generated .
Export opportunities for the Su-25TM are related mostly to those countries, which already operate Russian-built aircraft. The Su-25 has been exported to Bulgaria, Czechoslovakia, Hungary, Iraq and North Korea.
Priced at about $15 million, the Su-25TM presents a highly cost-competitive attack aircraft - on paper, at least. It remains to be seen whether Sukhoi can replicate its recent export successes with the Su-27 Flanker with its uglier sibling.
Additional reporting by Douglas Barrie
Source: Flight International
