Soko J-21 Jastreb: Attacker by Nature

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Soko J-21 Jastreb, Yugoslav Air Force, 1968-1996
Part of the Yugoslav Air Tree suggestion

Introduction:
The Soko J-21 Jastreb was a Yugoslav light attack jet aircraft developed in the 1960s to provide air support against invading columns with little preparation. It was a single-seat development of the G-2 Galeb trainer with a stronger engine and greater armament. The J-21 would make for a well-rounded Yugoslav strike aircraft in the early jet ranks.

Specifications:
Crew: 1

Dimensions
Length: 10.88 m
Wingspan: 11.68 m (10.56 m without wingtip tanks)
Height: 3.64 m
Wing area: 19 m²

Mass
Empty: 2,804 kg
Max take-off: 4,915 kg (when loaded with 250kg bombs and four HVAR)

Propulsion
Engine: Rolls Royce Viper Mk 531
Thrust: 13.33 kN

JATO: 2x SR-1 14AS-1000 rockets, each provides 4.45 kN of thrust

Performance
Maximum speed: 820 km/h at 6,000 m
Cruise speed: 740 km/h at 5,000 m
Climb rate: 21 m/s (1,260 m/min)
Range: 1,520 km with wingtip tanks
Flight ceiling: 12,000 m

Armament
3x 12.7mm M3 Browning machine guns (135 rpg)

2 inner hardpoints able to carry:

  • 2x 250kg FAB-250 bombs

  • 2x SN-3-50 carriers for three 50kg bombs each

  • 2x 150lt PLAB-150 napalm tanks

  • 2x 200lt PLAB-200 napalm tanks

  • 2x L-128-04 rocket launchers

    • 4x domestic 128mm NRZ-128 “Munja” rockets
      • M74 HE warhead
      • M80 HEAT warhead
  • 2x L-12-57 rocket launchers (present since early production)

    • 12x 57mm BR-1-57 (Yugoslav equivalent of the S-5M) rockets or
    • 12x 57mm BR-2-57 (S-5K) rockets
  • 2x L-16-57 rocket launchers (in late production planes)

    • 16x 57mm BR-1-57 (S-5M) rockets or
    • 16x 57mm BR-2-57 (S-5K) rockets
  • 2x KPT-150 cluster bomb dispensers [if they’re added to WT]

6 outer hardpoints able to carry:

  • 6x 127mm HVAR rockets

Countermeasures:

  • Two POJ-264 containers, each has 40 flares (IC-3) and 8 chaff (PA-1)
    • Installed in limited numbers of Jastrebs for combat missions in the Yugoslav Wars

History:
The Soko J-21 Jastreb originates from the Yugoslav Air Force’s assessment in the early 1960s for a future light attack aircraft. It was considered that given the proximity of most airfields to the border, they would be vulnerable to attack from the get-go and an aircraft capable of take-off from unprepared airfields was needed. Its role would be to stop armored spearheads advancing on the JNA’s rear, though not with a large payload as it would run only one sortie at a time. As foreign aircraft were expensive, the domestic G-2 Galeb two-seater trainer was chosen as the basis for the future single-seat attacker with minimal modifications.

The decision to design the “Jastreb” was taken on October 7, 1961, when the first Galeb prototype had already flown. The first J-21 prototype flew on July 19, 1965. Compared to the G-2, one seat was removed and the wing structure was reinforced to allow for heavier suspended weapons. However, the most important change was the engine: the Jastreb used a Viper Mk 531 engine, belonging in the same family as that of its trainer predecessor but with greater thrust (13.3 kN). A third nose-mounted Browning was also added.

The J-21 entered service with the Yugoslav Air Force on the 31st of December, 1968, where it gradually replaced the American-supplied F-84G Thunderjets. However, Jastreb procurement was considered a stopgap measure until the twin-engine “Orao” attacker could arrive. The Soko factory in Mostar produced 119 Jastrebs from the single-seat attack version, until the last was delivered to the JRV in 1977. Another 38 reconnaissance aircraft, the IJ-21 variant, were produced in 1970-77, and 18 NJ-21 two-seat trainers were made in 1974-77.

Though it was being phased out in favor of the J-22 Orao by the 1980s, the Jastreb still played a role in the hostilities of the 1990s. 10 of them were shot down in combat missions over Croatia and Bosnia, making the JRV consider protection for their “hawks”. To counter anti-air missiles, a number of aircraft used in combat squadrons received flare dispensers. To counter small arms fire, in 1991 No. 24122 became the prototype for an armored J-21, receiving armor plates designed by VTI on the cockpit sides and seat. Despite the 113.8 kg weight increase, a flight demonstration on January 3rd, 1992, showed its flight performance wasn’t hampered. A contract was signed for the upgrade but it was soon abandoned.

The J-21’s role in the new Yugoslav Air Force was mostly redundant thanks to the more capable J-22 Orao and G-4 Super Galeb. With the Agreement on Sub-Regional Arms Control, it was retired from JRV service in 1996. However, it remained in service with the Republika Srpska, where in 1994 four Jastrebs had been shot down by F-16s with air-to-air missiles as part of a no-fly zone enforcement near Banja Luka. It was retired from the Republika Srpska Air Force in 2006. J-21s were also exported to Zambia and Libya, while three of them fought for the Zaire government in the First Congo War in 1997.

J21 3
Trainer NJ-21s in flight.

Gallery:

Gallery

J21 5

113999_53145902_lk7121SokoJastrebHVAR
J-21s were displayed in air shows with 2 HVARs attached on each outer hardpoint, but it was only a marketing trick as they could only carry 1 in flight.

J21 6

J21 10

J 21 cockpit

Sources:

Sources

https://www.airwar.ru/enc/attack/j1.html

Soko J-1 Jastreb

SOKO J-21 Jastreb: Yugoslavia’s Advanced Single-Engine Jet Aircraft

A Compendium of Armaments and Military Hardware (Routledge Revivals), p.467 [available on Google Books A Compendium of Armaments and Military Hardware (Routledge Revivals) - Christopher Chant - Google Books]

Glasnik RV i PVO magazine (1983 November-December issue, can be downloaded here Download Glasnik RV i PVO 1983 - 06 - PDF Magazine but don’t expect anything more than the datasheet attached above)

Odbrana magazine (168th issue, available here https://www.odbrana.mod.gov.rs/odbrana/168/168%20Odbrana.pdf)

Mamci i Panciri (available here Mamci I Panciri | PDF)

57 mm Rockets:

krusik.rs - Aircraft rocket BR-1-57

www.mbnamenska.com/download/DoubleBaseRocketPropAndPropCharges.pdf

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+1 for Yugoslav tree

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+1 Would love to see it in a future Yugo tech tree

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