Songrim SR-7

Songrim SR-7
SR-7D at Hansŏl-li airbase, 1998
Role	Interceptor (SR-7G, D) Reconnaissance aircraft (SR-7N)
National origin	DPRM
Manufacturer	Songrim Aircraft Design Bureau
First flight	1977
Introduction	1981
Status	in service
Primary user	Menghean Army
Produced	1981-1997
Number built	346

The Songrim SR-7 (Formal designation: 송림 6호 전투기 / 松林六號戰鬪機, Songrim Chil-ho Jŏntugi, "Songrim No.7 Fighter;" Short designation 송림-7 Songrim-chil "Songrim-5") is a supersonic, high-altitude fighter-interceptor designed in the Democratic People's Republic of Menghe during the 1970s and early 1980s. It was developed and built in parallel with the more successful Daesŭngri DS-5.

Development

Origins

During the early 1970s, when the DPRM's main fighter aircraft was the Daesŭngri DS-2, the Menghean Ministry of National Defense expressed an interest in acquiring a more modern "third-generation" fighter. The program requirements called for a speed of over Mach 2 in level, high-altitude flight, a service ceiling of over 20,000 meters, and a nose-mounted radar capable of tracking aircraft and targeting air-to-air missiles.

Menghe's two main combat aircraft design bureaus, Songrim and Daesŭngri, both began independent work on their own prototypes. As the Daesŭngri team favored a fast, agile, low-level fighter, Songrim's designers drew up plans for a high-altitude interceptor to complement it. In light of past experience during the Pan-Septentrion War, Menghean military planners viewed bomber aircraft based out of Dayashina as a major threat, and the DS-2 was only able to conduct "point-defense" interception around a small area due to its limited range and speed.

Songrim initially planned to procure a production license for the Letnian Orlov Or-15. Its only previous aircraft, the SR-3, was also an Orlov derivative, and license production would allow for faster entry to service. But Sim Jin-hwan, who came to power in 1971, pushed both bureaus to complete a fully domestic design as a demonstration of Menghe's technological capability. This news came as a boon to Daesŭngri's designers, who were worried that the Army would instead procure the MiG-23, but the Songrim team had little experience with independent design work and initially struggled to keep up.

In an effort to close the expertise with Daesŭngri, which thus far had the most experienced design team, Songrim hired former aviation engineers from Letnia. It is possible that project documentation relating to the Or-15 was also transferred to Menghe, and Western intelligence sources would later erroneously report that the Songrim prototype was a direct descendant of the "Flagon," but Songrim ultimately kept its promise of developing a domestic airframe.

Design phase

To fit the interceptor role, the designers sought a large airframe with high thrust and a long patrol range. The favored layout carried twin R-11 engines, which had the advantage of already being produced in Menghe as the Gi-7, for use in the widely produced DS-2. One paper project in 1974 did call for a single Tumansky R-15, the high-altitude engine used in the MiG-25, but Letnia never approved licensing and the twin-R-11 scheme produced higher thrust.

Even given this powerplant type, there was extensive variation in layout. S-63, the most unconventional proposal, had a chin intake with its twin engines staggered in an over-under configuration. S-65, another, had a single tailless delta wing. Preliminary work eventually settled on the more conservative S-62, which had a tailed delta with small canards on either side of the nose. Two other under-nose-intake configurations were considered, but the Army favored side intakes because they were less likely to suck up debris when operating off of rough airstrips.

The first prototype airframe, S-62-1, conducted its maiden flight in April 1976. All its parts functioned as expected, but at high speeds the canards interfered with the airflow into the intakes, especially during maneuvers. Canard problems were also blamed for the loss of airframe S-62-2, which abruptly banked right and crashed during its first landing approach, killing the test pilot. Test flights of the S-62 were suspended while Songrim worked on a solution; S-64, which had an under-nose intake to avoid canard interference, was flown in its place, but the Army still disapproved of its configuration.

For the next two years, it appeared that the Songrim interceptor project was in danger of cancellation. DS-5 prototypes also suffered their share of crashes, but they were performing well, and some Ministry of Defense officials considered the DS-5 adequately fast to fulfill the interceptor role. The DS-5 did suffer from a highly inadequate radar, but Songrim was no better off, as Letnia was growing hesitant to share engineering secrets. According to rumor, Songrim engineers pressured the Daesŭngri team to constrain the DS-5's high-altitude performance by trimming fuel weight and switching to fixed-angle intakes; a more far-fetched story holds that they pressured Rajland to deploy more bombers in Nukkumaa. What is known is that Songrim's leadership relentlessly lobbied the Menghean Socialist Party to save their interceptor program, even blocking a MiG-25 export deal when one was floated.

Airframe S-66-1 took flight in 1978, and flight tests were resumed. This prototype resembled the S-62, but removed the canards to improve airflow, resulting in a more conventional tailed delta wing plan. Because the deletion of the canards had shifted the center of lift, the leading edges of the delta wings were moved further forward, as were the intakes and the entire wing plan itself. A new radar nosecone design, still ballasted with concrete in prototypes, was built to accommodate the Sapfir-23D radar of the Letnian MiG-23, which had been approved for export. S-66-1 and S-66-2 performed well in testing, and the Ministry of Defense accepted it for service in 1980, with production beginning later that year.