So it seems that the 14 ex-Bulgarian air force Su-25 Frogfoots donated to Ukraine has underwent a modernization very recently.
AN IN-DEPTH LOOK AT BULGARIA'S MODERNISED FROGFOOT FLEET
By
Alexander Mladenov 21st June 2021
FEATURE
Alexander Mladenov looks at the recently refurbished and upgraded Su-25 attack aircraft that are earmarked to continue in Bulgarian service through to at least 2028.
The Su-25’s new pixelated camouflage blends in well with the autumn terrain around Bezmer air base in Bulgaria. Alexander Mladenov
The
Frogfoot, widely known as an ugly, sturdy aircraft for hauling heavy war loads, has been seriously underrated in Bulgarian service over the last two decades. That is all now changing with the type being given a new lease of life after a comprehensive refurbishment an life-extension program. Combined with a substantial flight/navigation and mission avionics upgrade, it will be kept relevant as per the needs of the Bulgarian Air Force (BuAF - Bulgarski Voennovazdushni Sili).
Today, Bulgaria is the only NATO member fielding the Soviet-era armor-protected twin-engine attack aircraft, and the BuAF fleet development plans call for continuing the operations with the type into the late 2020s. This is something no one would have imagined when the Cold War ended in 1991.
This Su-25 has a warload of five UB-32A rocket packs, accommodating 32 57mm rockets of the S-5-series in addition to an SPS-141MVG radar jammer pod and a pair of R-60MK air-to-air missiles. Alexander Mladenov
35 years in service
Bulgaria was among the early export customers for the
Frogfoot, taking on a fleet of 36 Su-25Ks and four twin-seat Su-25UBKs between 1986 and 1988. The heavily armored attack aircraft were used for equipping the two squadrons of the 22nd ShtAB (Attack Aviation Regiment) at Bezmer, with each of these provided with a fleet of 18 single-seaters and a pair of two-seaters. One of the single seaters was lost in a training accident in 1989 and another was damaged beyond repair in 1995.
In the 2000s, no fewer than 14 single-seat aircraft were sold out by the Bulgarian MoD to local intermediary companies, to be subsequently re-sold abroad. Six more are still stored in Bulgaria, as their new owner has proved unable to find customers outside Bulgaria so far.
Centered around the integration of the all-new SOI-25 flight display system are two MFI-10 6in x 8in color multifunctional displays, an IRP-5 back-up display and ILS-31ZhK HUD. Alexander Mladenov
In 1994, following a major organizational reform of the BuAF, the Su-25-equipped combat unit at Bezmer was transformed into the 22th ShtAB, with a new structure consisting of headquarters (with various sections and services), two Su-25 flight squadrons (staffed by pilots only) in addition to a flight-line maintenance squadron (the ‘owner’ of the base’s fleet, comprising 39 aircraft at the time), a scheduled maintenance/field repair squadron, plus airfield servicing and logistics support squadrons.
The BuAF’s next major structural reform, undertaken in 2008, sharply reduced the size of the resident attack unit at Bezmer, as it lost its long-time number plate and continued with only one flight squadron. The unit got its new Forward Deployment Base (FDB) name and had an authorized numerical strength of 14
Frogfoots – ten single-seaters and four two-seaters. A handful of additional Su-25s are also kept in long-term storage at Bezmer, to be used as spare parts donors, while another example is on static display at Graf Ignatievo air base.
Majors Vladislav Todorov and Radostin Lyutskanchev. Major Vladislav Todorov (left) was the first Bezmer FDB pilot to retire, but in 2020, he opted to return to military service and continue flying the refurbished and upgraded Frogfoot. Alexander Mladenov
The one and only
In the early 2000s, the Su-25’s mission set was gradually shifted towards a wide variety of secondary combat support missions, to serve all of Bulgaria’s military branches, following the withdrawal from use of both the MiG-23BN and Su-22M4. It remains the only dedicated strike type in the inventory, with the active fleet comprising two Su-25UB two-seaters, built in 1988 at the Ulan-Ude Aviation Plant in Russia, plus six more Su-25K single-seaters, built in 1987 at the Tbilisi Aviation Production Enterprise, Georgia.
These
Frogfoots have now been cycled through a comprehensive airframe and engine overhaul at the 558 ARZ maintenance, repair and overhaul (MRO) facility in Baranovichi, Belarus, in a bid to extend their service life by another eight years and 800 flights hours. Following this latest life-extension program, the total service life of the BuAF
Frogfoot fleet has been increased to 40 years, while its flight hours have been boosted to 2,000-2,370 (this varies between different airframes).
By comparison, the original service life for the Su-25K and Su-25UBK, as set in the late 1980s by Sukhoi OKB, the type’s design authority, was 20 years and 2,000 flight hours, whichever was first. The time between overhauls (TBO) was originally set at 800 flight hours and ten years.
Colonel Milen Dimitrov is the Bezmer FDB Commanding Officer. Alexander Mladenov
Despite their old age, the
Frogfoots have been used very little, with the single-seaters cycled through the overhaul and life-extension logging between 741 and 1,053 flight hours each. Not bad for aircraft that are more than 30 years old. Meanwhile the two-seaters are known to have amassed between 1,244 and 1,570 hours, according to official Bulgarian MoD data released in August 2018.
Among the main advantages of the high-wing
Frogfoot (as experienced Bulgarian pilots and technicians will tell you) is its rugged and reliable structure, while the aerodynamic configuration, using a straight-wing layout, makes it a very good and stable platform for weapons delivery. The R-95Sh turbojet, featuring a TBO of 500 hours, is a rather old and fuel-thirsty technology, but, over the years, it proved extremely reliable and easy to maintain – very unusual for such old powerplants which obviously do the job.
Su-25UBK ‘White 002’ has seen the most intense use since its re-delivery, with some 70 flight hours amassed in little more than four months of operation. Alexander Mladenov
Bound for Belarus
The Bulgarian MoD released an open tender for the Su-25 overhaul and life-extension in August 2018 and Belarus company 558 ARZ was the only bidder. Bulgaria’s defense minister at the time, Krasimir Karakachanov, was the most influential supporter of the program. He was the main political force behind the funding being made available. Requests to tender were issued very quickly after the decision to go ahead with the upgrade, with a contract signed a mere four months later.
The deal was signed off in December 2018, and the first
Frogfoots were transported (disassembled) to Belarus in July 2019. Initially, when launching the open tender procedure in August 2018, the BuAF required to cycle through the program as many as 12 aircraft, but it eventually turned out that the budget of €41.92 million ($49.20 million) would be sufficient for just eight Su-25s.
This Frogfoot comes armed with four S-25OFM rockets with powerful fragmentation-blast warheads complemented by a pair of BETAB-500 bombs and a dualpod Satellite-M2 jammer system. Alexander Mladenov
The first two of the completed
Frogfoots – single-seater ‘White 246’ and two-seater ‘White 002’ – were eventually returned to Bulgaria, transported by Il-76 airlifters on September 21 and 22, 2020, respectively. Their acceptance by the BuAF, including check flights, took place during the first half of October that year.
The last Su-25, single-seater ‘White 254’, was returned to Bulgaria on February 11, 2021. Despite the substantial avionics upgrade, the type has retained its original designation: Su-25K/UBK. Together with the overhaul and the life extension, the eight
Frogfoots received substantial upgrades, mainly required to deal with the numerous obsolescence issues of the aircraft’s 1970s analogue avionics suite.
All eight refurbished and upgraded Su-25s lined-up on Bezmer FDBs main apron for a display to the Bulgarian defense minister, Krasimir Karakachanov, on February 26 this year. Alexander Mladenov
Key upgrades
The upgrade work centered around the integration of the all-new SOI-25 flight display system, representing a glass cockpit with two MFI-10 6in x 8in color multi-functional displays (MFDs). They provide the increased situational awareness (displaying flight/navigation and tactical information) called for in these modern times. An IRP-5 back-up electronic display and the ILS-31ZhK head-up display (HUD) replaced the conventional analogue flight and navigation instruments as well as the ASP-17BTs electro-optical sight.
The all-new SN-25 navigation system is another substantial component of the upgrade package, incorporating a BTsVM-MVS digital computer and a SNS satellite navigation receiver with a 14-channel dual GPS/GLONASS capability (said to be able to provide positioning accuracy within 16ft) in addition to Western-supplied KNR-643A VOR/ILS and AN/ARN-154(V) TACAN receivers.
After the deep refurbishment, the Bulgarian Su-25 fleet has been certified as good for a further 800 flight hours and at least eight more years of service. Alexander Mladenov
These modern-day
Frogfoots also sport the all-new PS-25 weapons control system, to ensure weapons functionality and much-improved accuracy for the delivery of unguided weapons. This means the Su-25’s existing Soviet-era arsenal is more relevant in addition to the newly added S-13 122mm rockets (fired from up to eight B13L five-round packs) and the R-73E (two) air-to-air missiles useful for self-defense and intercepts of slow-movers.
Furthermore, the PS-25 features a newly introduced navigation bombing mode – to drop free-fall bombs on unseen targets at known position. This becomes possible thanks to the greatly improved accuracy derived from the aircraft’s new navigation system. The maximum bomb drop altitude has been increased to 16,400ft (compared to 6,600ft for the non-upgraded
Frogfoot), and this capability enables the pilots to keep the aircraft out of reach of a variety of short-range surface-to-air missile (SAM) and anti-aircraft artillery (AAA) threats.
The first two upgraded Bulgarian Frogfoots were redelivered in September 2020, followed by two more in October 2020. This is the first single-seater, ‘White 246’, introduced into regular service in October, after completion of the acceptance testing procedure. Alexander Mladenov
The dual-pod Satellite-M2 jammer system, manufactured by the 558 ARZ, is set to improve the aircraft’s survivability when facing modern radar threats – both airborne and ground/ship-based ones. The Bulgarian requirements called for a newly integrated jammer pod system capable of providing self-protection against radar-guided short- and medium-range SAM systems.
The Satellite-M2, covering a frequency range of 4-18GHz, is capable of creating a wide variety of deception jamming signals to disrupt the range-finding and tracking functionality of ground-based and airborne weapons control radars and missile radar seekers – both semi-active and active-radar types. The jammer consists of two pods to provide head-on and tail-on protection and operates in a fully automatic mode, without the need for pilot involvement.
The maximum bomb delivery altitude for the Frogfoot has been increased to 16,000ft compared to 6,600ft for the non-upgraded aircraft. Alexander Mladenov
The list of the new mission equipment integrated in the upgraded Bulgarian
Frogfoots also includes the SVR-2T video/audio recorder for recording the information displayed on the HUD and the two MFDs in the cockpit. An upgraded Tester-U3-2 crash-resistant digital flight data recorder is also included in the upgrade package, provided with a new memory module and delivered together with the Dvina ground-based flight data analysis system.
The upgraded Su-25K/UBKs also received somewhat improved capability to integrate with other fast-jet types, due to the improved communications capability on board, achieved by adding the second comms radio – a long-time request of Bulgarian pilots flying the Soviet-era attack aircraft.
In their upgraded form, the BuAF
Frogfoots come equipped with two Russian-made Prima-DMV VHF/UHF radios with an 8.33kHz channel spacing, replacing the old-generation R-862 and R-828 transceivers. This new addition is deemed as a useful improvement for enabling participation in international exercises – in Bulgaria and abroad – but has nothing to do with the aircraft’s use in real-world coalition operations.
Bomb trolleys loaded with hard-hitting ordinance carried by the BuAF Frogfoots – including a pair of BETAB-500 concrete-piercing bombs and a FAB-250M-62 high-explosive bomb seen on the rearmost cart. Alexander Mladenov
Upgraded
Frogfoots also received an all-new color scheme, comprising of a pixelated camouflage pattern with a base olive color and pixel blocks in brown and green, combined with a white-painted underside, applied at the 558 ARZ before delivery.
Flight operations in Bulgaria have shown that the new pattern, which, at first glance, seems to be too multi-colored, is highly effective for hiding low-flying Su-25s on the terrain background with prevailing forest and vegetation cover in most of the seasons, rendering the visual detection from the air more difficult.
Back in the game
The success of the return-to-service program for the Su-25 fleet was appreciated by the Bulgarian Chief of Defense Staff, Admiral Emil Eftimov, during his visit to the BuAF’s Forward Deployment Base (FDB) at Bezmer airfield, in the southeastern part of the country, on December 10, 2020.
Portraying all its power, this Frogfoot climbs with its wing-tip brakes extended, revealing its landing lights. Alexander Mladenov
The Defense Minister, Krasimir Karakachanov, then visited Bezmer on February 26, 2021, to accept all eight rejuvenated
Frogfoots and commission them into service. He also expressed his satisfaction with the quality of the job done by 558 ARZ but was reluctant to promise that the remaining six or so Su-25swill be cycled through the program.
Currently, 558 ARZ has a warranty servicing team and a stock of spare parts and consumables at Bezmer to meet its two-year warranty servicing commitment. The list of the primary missions assigned to Bezmer FDB includes provision of close air support (CAS) to the Land Forces and the Special Operations Forces and air interdiction, in addition to support to Bulgarian Navy operations in the littoral zone. Visual reconnaissance is also among the list of the front-line missions assigned to the
Frogfoot force, as well as participation in combat search and rescue (SAR) operations.
The list of secondary missions includes support of the BuAF, Land Forces and Navy in their day-to-day training and also during various national and international exercises. For the Air Force and Navy, this kind of support involves flying as adversaries – for training fighter pilots and ground-based SAM and AAA crews for countering air threats.
The BuAF has carried out regular flight training operations with the first two re-delivered Su-25K/UBKs, following the deep overhaul and upgrade performed at the 558 ARZ company in Baranovichi, Belarus, in late October 2020. Alexander Mladenov
In the SAM training missions with live firings – conducted annually at Shabla Range on the Black Sea coast – Su-25s are regular participants, dropping heat-emitting SPM-100 flare bombs, slowly descending on parachutes, as practice targets for SAMs and fighters. This job has also been performed for foreign nations – who send their air defense units for live-fire practice in Bulgaria – and it is expected to continue in the future.
Frogfoot's arsenal
Today, only unguided ordinance is cleared for use by the Bulgarian
Frogfoots, including a wide range of free-fall bombs, rockets and guns. In the past, the fleet was also capable of firing the Kh-25ML (AS-12 Kegler) and Kh-29L (AS-14 Kedge) laser-guided missiles.
The maximum Su-25 warload on ten external stores, including ordinance and external fuel tanks, is 4.6 tons, with the biggest single bomb that can be carried by the non-upgraded
Frogfoot weighing 1,102lb.
The two-seater Frogfoot retains the full targeting suite and weapons capability of its single-seater counterpart. Alexander Mladenov
Up to eight of these, of high-explosive type, designated FAB-500M-62 or FAB-500M-54, can be suspended on eight hardpoints. Some other heavy bomb load variants comprise of ten FAB-250-120 551lb high-explosive bombs or 32 OFAB-100-120 220lb fragmentation/high-explosive bombs on eight multiple bomb racks.
The rocket warload is represented by up to eight UB-32A packs, each for 32 57mm S-5 rockets or eight B8M1 packs for 80mm S-8-series rockets, offering increased range and lethality, compared to the rather antiquated S-5. Alternative weapon loads include up to eight 240mm S-24 rockets or four of the more-powerful tube-launched S-25OFM rockets, as well as KMGU-2 bomblet/landmine dispensers. The PS-25 weapons control system also added the capability to deliver S-13 122mm rockets fired from B13L five-round packs, but these are not available in the BuAF inventory.
The effective range to deliver forward-firing weapons when using the Klen-PS later rangefinder-designator is between 0.2 and 3 miles. The upgraded
Frogfoot also retained the GSh-30 30mm twin-barrel cannon in the VPU-17A pack provided with 250 rounds, built into the port side of the forward nose, under the pilot’s cockpit. Unleashing highly destructive projectiles weighting 0.86lb each, at a muzzle velocity of 870m/s, the cannon sports a rate of fire of 3,000rpm and its effective firing range is between 0.5 and 0.9 miles.
The new PS-25 weapons control system allows Frogfoot pilots to use the Su-25’s existing air-to-surface arsenal in addition to the newly added S-13 122mm rockets, fired from B13L five-round packs (up to eight), and R-73E air-to-air missiles for self-defense and intercepts of slow-speed air targets. Here, an Su-25K is seen armed with four UB-32A rocket packs, each accommodating 32 S-5 57mm rockets. Alexander Mladenov
The R-73E (AA-11 Archer) is the only guided weapon currently cleared for use by the upgraded BuAF
Frogfoots. It is an agile short-range air-to-air missile, fitted with a highly sensitive infrared seeker. The R-73E visual cuing and aiming is facilitated by the newly added PS-25 weapons control system, displaying the relevant aiming and lock-on symbology in the air-to-air mode on the ILS-31ZhK HUD.
In fact, the maximum weapons load, when toting a pair of R-73Es, is now limited to six 0.5 tons, or 550lb bombs (or six missile launch rails, rocket packs or multiple bomb racks), or 24 220lb bombs, as the newly added air-to-air missiles are now carried on launch rails suspended on the outermost pair of main pylons.
The auxiliary underwing hardpoints, used in the past for the carriage of R-60 air-to-air missiles on the non-upgraded Su-25, are now being utilized for the suspension of the Satellite-M2 jammer pods.
The Satellite-M2, manufactured at 558 ARZ in Belarus, is a dual-pod jammer for disrupting air-, land- and sea-based radars used for target detection, tracking and weapons control. Alexander Mladenov
Pilot impressions
Major Radostin ‘Wizard’ Lyutskanchev, who is among the most experienced Bulgarian
Frogfoot pilots, told Combat Aircraft Journal about the advantages offered by the upgraded avionics: “The new avionics brought much-improved new capabilities in the attack role. The pilot workload has been greatly reduced, because the upgraded aircraft now boasts an excellent navigation capability. It has satellite-aided (GPS/GLONASS) navigation and the MFDs provide us with a wealth of information, allowing us to fly on a pre-planned route in bad weather and, at the same time, allowing a search for targets on the ground, commencing the attack maneuver at the right spot. When in navigation mode, the HUD shows cuing information to the waypoint to which you are flying (a diamond with a dot inside it).
“When flying on a pre-planned route, the system constantly calculates the distance and time to the next waypoint or time on target, which depends on the speed. There are also newly introduced navigation modes for flying an instrument landing approach while returning to the airfield from a pilot-selected position. The Su-25 does not have an autopilot and therefore the pilot is constantly in control. In each of the modes, he is required to follow the cues displayed on the HUD.
The BETAB-500 is among the hardest-hitting pieces of ordinance carried by the Su-25. Weighing 1,051lb, it is advertised as capable of piercing 3ft-thick steel-reinforced concrete under a 9ft thick ground cover. Alexander Mladenov
“The upgrade brought a brand-new weapons delivery mode, the so-called ‘navigation bombing’ that allows us to drop bombs outside the lethal range of the low-altitude air defenses, such as MANPADS [man-portable air defense system], small-caliber antiaircraft artillery and even the Osa SAM system (SA-8 Gecko).
“Navigation bombing can be performed from an altitude of up to 16,000ft. This can be done in two ways – either in straight-and-level flight, or while in a turn, with 15-, 30- or 45-degree bank angles. The Belarusians tended to comment that the bomb delivery accuracy in the navigation-bombing mode should be the same as that in the visual aiming bombs mode, somewhere between 20-50m. 558 ARZ representatives also told us that, with minimal modifications, new precision-guided weapons could be integrated into the Su-25’s arsenal.”
Frogfoot pilots have tended to note that their upgraded mount is also provided with a comprehensive flight data recording system, which records the HUD picture in addition to the video on each of the displays and also has cockpit voice-recording capability.
In the upgraded Bulgarian twin-stick aircraft, the Frogfoot instructor also enjoys a HUD repeater mode on one of the cockpit displays. Alexander Mladenov
Among the most useful features of the Bulgarian Su-25s cycled through 558 ARZ, as Major Lyutskanchev shared with CAJ, is the deeply refurbished Klen-PS laser rangefinder/target-designator. In the past, the worn-out device used to measure the distance to target resulted in serious mistakes, leading to significant deviations of the bombs and rockets. Now the distance measuring is precise, enabling accurate aiming and weapons delivery. The bomb delivery accuracy when using visual aiming, utilizing the range information derived from the Klen-PS, is claimed to be within 20m.
We look at the recently refurbished and upgraded Su-25 attack aircraft that are earmarked to continue in Bulgarian service through to at least 2028
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