Songrim SR-8

The Songrim SR-8 is a twin-engine, all-weather multirole strike fighter based on the Glasic Iolar air superiority fighter. It is produced under license in Menghe by the Songrim Aviation Design Bureau. In a nod to its original designation, it is also known as the Gŭmdoksuri, or "Golden Eagle," making it the first Menghean combat aircraft to bear an official nickname.

Though it originated as a foreign derivative, the original SR-8G incorporated a number of unique changes to suit Menghe's needs, including wingtip missile rails and a refueling probe. During the 2000s and 2010s, Menghe also developed its own domestic improvements to the SR-8 airframe, driving further divergence with other Tripartite models. Over 460 SR-8 airframes were produced between 1999 and 2019, making Menghe the third-largest operator of the Iolar family after Tír Glas. Menghe is set to surpass Dayashina as second-largest operator in 2021.

Licensing and development

Import competition

The Menghean Ministry of National Defense began examining candidates for a twin-engine heavyweight fighter in the early 1990s, seeking a platform that would fit between the DS-5's poor range and the SR-7's poor maneuverability. As sanctions on Menghe had been lifted following its regime change and the nuclear disarmament, foreign imports or license deals were once again on the table, and the MoND viewed them as a practical way to cut development costs and speed up availability.

Four foreign aircraft were selected for evaluation in 1993: the Letnian Or-27, the Glasic Iolar, the Sieuxerrian Super-Mirage Export Model, and the Ostish Greif. The Greif, in competition with fighters well outside its weight class, was quickly ruled out, though not before Daesŭngri's engineers could thoroughly look it over. The Mirage was also eliminated, though Sieuxerrian engineers refused to hand over the airframe after trials, concerned about the risk of reverse-engineering. This left the Or-27 and Iolar, both outstanding in speed and maneuverability, as the finalists.

The decision between the two became a high-stakes one, not only because of the planes' capabilities, but because it could affect Menghe's geopolitical alignment for years to come. For much of 1994 the Or-27 seemed to be the preferred option, but the Letnian government pressured Orlov to export it with downgraded radar systems, angering the Menghean representatives. Tír Glas, hoping to exploit this break, offered to the Iolar-F with its APG-70 radar. As a further guarantee, GAC exported APR-70 kits for use on SR-7 upgrades, and held out the possibility of technology transfers for future domestic Iolar improvements. These promises won Menghe over, and in 1995 the MoD ordered 40 Iolar airframes for training and evaluation, with a production license under negotiation. The OR-27 was still held out as an option if the Iolar did poorly, but the deal nevertheless marked a key milestone in Menghe's transition away from Letnian military equipment.

Iolar-M

The forty airframes delivered to Menghe in 1995 and 1996 were manufactured in Tír Glas under the designation "Iolar-M," with M denoting Menghe. They were based on the Iolar-F, and came with the still-new APG-70 radar system, but incorporated some downgrades to protect sensitive technology. The ECM system and radar warning receivers were both last-generation models, but otherwise the onboard systems were up-to-date. Some custom changes were applied to the hardpoints, allowing compatibility with the YGG-5 missile and Menghean GP-series bombs. The basic airframe was entirely original.

Menghe's Iolar-Ms were assigned to the 56th Operational Testing Squadron, which compared their capabilities against those of the SR-7 and a single Or-27 purchased for testing. Pilots trained on the SR-7 roundly praised the new aircraft's thrust and agility, as well as its impressive radar suite. The Or-27 was found to have better agility, but the difference was deemed minor, and the Iolar's high thrust-to-weight ratio and full multirole capability easily counterbalanced it.

After 18 months of flight testing, the commanders of the 56th Operational Testing Squadron formally approved the Iolar-M, but presented Songrim with a list of desired changes for the licensed version. Songrim engineers, who had broken down one airframe for study, concurred.

Domestic production changes

License production of the Menghean domestic variant began in 1999, with deliveries starting in 2000. In line with previous aircraft of foreign origin - like the DS-1 and SR-3 - it was given a domestic manufacturer designation, Songrim SR-8G.

Based on feedback from flight trials with the Iolar-M, the Songrim design team made a number of changes to the airframe, some of them based on features of the Or-27. To protect the engines from foreign-object ingestion on takeoffs and landings, variable-angle grated screens were added on the intake floors. An IRST scanner was added just forward of the canopy, with both air-search and ground-mapping modes. Some other changes were made to the avionics, navigation lights, and ECM system.

The question of how to change the refueling system stirred greater debate. No other Menghean combat aircraft refueled through flying-boom receptacles like those on the Iolar, so conversion to a probe-and-drogue system was necessary for compatibility. The Ministry of Defense required that the probe be retractable to reduce drag, and that it be part of the core airframe, usable when no drop tanks or conformal fuel tanks are fitted. Disturbance to existing fuel space, complexity, and visibility of the probe from the cockpit were also factored into comparisons. An Orlov-style probe in the nose was deemed ideal for space and visibility, but ruled out due to the lack of nose space, especially with the addition of an IRST system. This left two options: a telescoping probe which retracted into the right wing root, where the original receptacle had been, and a hinge-up probe which would wrap around the right side of the forward fuselage when not in use. The latter option was eventually adopted, as it was lighter and less mechanically complex.

Design

Performance

Due to the combined effect of many small changes, such as the added wingtip hardpoints and sturdier landing gear, the SR-8G is slightly heavier than the Iolar E, and has slightly more drag. Nevertheless, its powerful engines give it excellent acceleration, including the ability to conduct a vertical climb. Its large wing area gives it a low wing loading, allowing it to pull sharp turns without bleeding too much velocity - a persistent problem on the DS-5 and SR-7.

Early-production SR-8s used the Glasic TF-530 turbojet. Under a memorandum of understanding signed in 1997, the first 120 engines were manufactured in Tír Glas by Morris Foley Aero Engines, and the next 120 were shipped in knock-down kits for local assembly. Subsequent engines would be built under license by Donghae Heavy Industries. Locally built engines bore the designation Donghae Type 74-124.

Like the Iolar C and E, the SR-8 can mount conformal fuel tanks (CFTs) on either side of the fuselage beneath the wings, each carrying 2,270 kilograms of fuel. Menghean Army SR-8s generally fly air-superiority missions without CFTs, which cannot be jettisoned mid-air, in a bid to maximize maneuverability on contact with the enemy. CFT use is nearly universal in Navy squadrons, which emphasize range and payload.

Armament

In its "clean" configuration, with no CFTs attached, the SR-8 has 13 hardpoints:

• 1 on each wingtip (YGG-5 only)
• 3 under each wing, in a combined unit (center: 2050 kg; sides, 2 air-to-air missile rails)
• 2 under each lower fuselage corner (YGG-6/7 only)
• 1 centered under the fuselage (2050 kg).

With conformal fuel tanks attached, the four corner under-fuselage hardpoints are obstructed, but six new hardpoints become available. These can be fitted with bombs, bomb racks, or air-to-air missiles, though air-to-air missiles can only be mounted to the front and end hardpoints and obstruct the center one.

Gun armament consists of a six-barreled rotary autocannon in the right wing root, carrying 400 rounds of 23×133mm ammunition. As Menghe already operates 23×115mm ammunition in some fighters - notably the DS-5 and SR-7 - standard Army and Navy practice is to designate the SR-8's gun as 24mm and its ammunition as 24×133mm, in order to avoid errors in supply shipments and the arming of planes.

Sensors and electronics

The SR-8G uses the AN/APG-70 radar, which has both air search and ground search modes. The designers also added a terrain-following mode which, in combination with a radio altimeter on the underside of the fuselage, allows the SR-8 to conduct low-level flight in poor-visibility conditions.

Another sensor change comes in the form of a Sieuxerrian IRST system mounted above the nose, offset slightly to the left. In air-search mode, it can detect aircraft and cue missile launches, allowing the SR-8 to engage enemy aircraft without triggering their radar warning systems. Menghean publications claim that the SR-8's IRST has a range of 50 kilometers against a fighter-size target, though actual detection range depends heavily on humidity, altitude, and whether the target is using afterburner. The IRST sensor also has a ground-search mode, which can either track individual targets for ground-attack missions or project a view of the landscape ahead onto the pilot's HUD for low-visibility flying.

Due to the addition of integral terrain-following capability and IRST imaging, the SR-8G no longer needs the separate features of the AN/AAQ-13 navigation pod. As Menghe had already purchased ATLIS-II and PDL-CT laser targeting pods from Sieuxerr, these were used in place of the AN/AAQ-14. Domestic sensor pods replaced both of these in the 2000s. Owing to these changes, Menghean SR-8s never carried the LANTIRN targeting pods which had been ubiquitous on Glasic and Dayashinese Iolars until the introduction of the Litening system.

Differences with Iolar

A condensed summary of the differences between the SR-8G and Iolar E is reproduced below, in approximate order of prominence:

• Wingtip hardpoints for YGG-5 air-to-air missiles
• IRST sensor ahead of cockpit, offset to the left
• Large, squared-off ECM antennas on top of the vertical stabilizers
• Folding grates on the intake lower surfaces
• Refueling probe on the right side of the nose, folds flush with the airframe when not in use
• Original refueling receptacle is absent
• Slightly reinforced tires and landing gear
• Different datalink and VHF antennas on upper and lower fuselage

Subsequent variants of both aircraft introduced further changes, some of which were functionally similar, but as design work was conducted independently, implementation differs. The Iolar Fíréan CAT.3 features an IRST sensor, but it is smaller and further forward, and it adds two-dimensional thrust vectoring nozzles, but these are squared off rather than gimballed as on the SR-8N.

Variants

Iolar M:

Special variant of the Iolar E downgraded and adapted for export to Menghe. Manufactured in Tír Glas and delivered in 1995 and 1996. Not technically part of the SR-8 family, as it lacked the SR-8G's changes, but closely related.

SR-8G:

Initial production variant. These were exclusively twin-seater multirole aircraft; no single-seat version was produced. Production started in 1999.

SR-8G1:

Software update of the SR-8G to support the YGG-7 Hwasal air-to-air missile. All existing airframes had been converted by 2005. The G1 designation was also applied to SR-8Gs produced after 2003 with built-in YGG-7 compatibility.

SR-8N:

New variant of the SR-8 introduced in 2006. Though externally identical to the SR-8G and G1, it featured greatly improved ECM equipment underneath its antenna fairings, and its radar reportedly had greater resistance to jamming. It also carried new engines with 137 kN wet thrust and an extra pair of under-wing hardpoints, supported by an improved fly-by-wire system to maintain maneuverability.

SR-8G2:

Designation applied to SR-8G1 airframes refitted with the SR-8N's ECM equipment, radar modules, and extra hardpoints.

SR-8D:

This is a dedicated air superiority variant introduced in 2013 to compete with supermaneuverable Or-27 derivatives in Maverican service. It features thrust-vectoring engine nozzles, which pivot around a canted axis to produce roll, pitch, and yaw depending on combination. It also came with a greatly improved phased-array radar, with extended range and improved frequency hopping to improve resistance to jamming and detection. The SR-8D is exclusively single-seat, as its features were deemed less useful on an attack aircraft, and it was produced in tandem with the SR-8D after its introduction.

SR-8R:

Unveiled in 2017, the SR-8R is a low-observable variant of the SR-8, built with radar-absorbent materials and fitted with the 8D's radar (though not its engines). The vertical stabilizers are canted outward and the wingtips once again lack launch rails. Its improved engines make it supercruise-capable. Though less stealthy than a dedicated fifth-generation fighter like the Huntress or SR-12, it still has a greatly reduced radar cross-section, especially over the frontal aspect.

For maximum stealth, the SR-8R can be flown with its under-wing hardpoints removed, and four air-to-air missiles carried in special enclosed weapons bays on the conformal fuel tank positions. Alternatively, it can be fitted with the baseline CFTs and external hardpoints, giving it the same range and payload options as previous SR-8 models with a still appreciable reduction in radar cross section. Reduced-RCS drop tanks and hardpoint-mounted enclosed missile bays were displayed at a 2019 expo.