Editing Saab 37 Viggen (section)

=== Avionics ===
[[File:LA2-Datasaab-CK37-full.jpg|thumb|upright|The CK 37 computer]]
In the early 1960s, it was decided that the Viggen should be a single seat aircraft, Saab having recognized that advanced avionics such as a [[Computer#Digital computers|digital central computer]] and a [[head-up display]] could perform the workload of a human navigator and entirely replace the need for a second crew member.<ref name = "bomber 244" /> The use of a digital computer would reduce or entirely replace [[Analogue electronics|analogue]] systems, which had proven to be expensive to maintain and alter, as had been the case of the earlier Draken, in addition to accuracy issues.<ref name = "data saab" /> The computer, called ''{{ill|CK 37|sv|Centralkalkylator 37}}'' (short for ''Centralkalkylator 37'', "central calculator 37"), was the world's first airborne computer to use [[integrated circuit]]s. Developed by [[Datasaab]], the CK 37 was the integrating unit for all electronic equipment to support the pilot, performing functions such as navigation, flight control, and weapon-aiming calculations.<ref name = "bomber 245" /><ref name="data saab">{{Citation|title=Central Computer for aircraft Saab 37, Viggen|url=http://www.datasaab.se/Papers/Articles/Viggenck37.pdf|place=Sweden|publisher=Data Saab|language=EN|trans-title=ViggenCK37 with photos|access-date=1 December 2007|archive-url=https://web.archive.org/web/20081030040312/http://www.datasaab.se/Papers/Articles/Viggenck37.pdf|archive-date=30 October 2008 |url-status=dead}}</ref><ref>[https://www.flightglobal.com/pdfarchive/view/1969/1969%20-%201463.html "INDUSTRY International."] ''Flight International'', 13 February 1969. p. 262.</ref> In practice, the CK 37 proved to be more reliable than predicted.<ref name = "data saab" />

On later variants of the Viggen, from the JA37 onwards, it was decided to adopt a newer and more powerful [[Kearfott Guidance & Navigation|Singer-Kearfott]] SKC-2037 digital central processor, license-manufactured and further developed by Saab as the CD 107.<ref name = "data saab" /><ref name= Goebel>{{Cite web |last=Goebel |first=Greg |url=https://www.airvectors.net/avvig.html |title=SAAB 37 Viggen |date=1 December 2021|quote="The rest of the JA 37's avionics suite included...[a] more powerful Singer-Kearfott SKC-2037 digital central processor, built by SAAB as the CD 107." |access-date= 26 June 2023}}</ref><ref name=globalaircraft>{{Cite web |url=https://www.globalaircraft.org/planes/saab_37_viggen.pl | quote="The avionics suite of the JA was a major improvement over the other variants designed a decade earlier. The onboard computer was a Singer-Kearfott SKC-2037 built under license by Saab as CD 107...." |publisher=Global Aircraft|title=Saab 37 Viggen |access-date=26 June 2023}}</ref> The computing techniques and concepts, such as [[distributed computing]], went beyond use of the Viggen, in addition to civil-orientated derivatives, it directly contributed to the computers used on board the Viggen's replacement, the Saab JAS 39 Gripen.<ref name = "data saab" /><ref name = "Eliasson 38">Eliasson 2010, p. 38.</ref> Various [[electronic countermeasure]]s (ECM) were installed upon the Viggen, these were typically provided by Satt Elektronik.<ref name = "bomber 245" /> The ECM systems consisted of a Satt Elektronik [[radar warning receiver]] system in the wings and the tail,<ref>{{Citation | title = ECM contract for MSDS | format = PDF | url = http://www.flightglobal.com/pdfarchive/view/1973/1973%20-%202723.html?search=Satt%20Elektronik | newspaper = Flight International | date = 1 November 1973 | publisher = Flight global | page = 762 | quote = Satt Elektronik in Sweden provides active and passive equipment for the Saab 105XT, Viggen and Lansen.}}</ref> an optional Ericsson Erijammer pod and [[BOZ counter-measures pod|BOZ-100]] [[Chaff (countermeasure)|chaff]]/[[Flare (countermeasure)|flare]] pod. [[Missile approach warning system#Infrared-based MAW|Infrared warning receivers]] were also later installed. In total, the electronics weighed 600&nbsp;kg, a substantial amount for a single-engine fighter of the era.<ref name = "bomber 245" />

The aircraft's principal sensor was an [[Ericsson]] PS 37 X-band [[monopulse radar]], which used a mechanically steered [[parabolic reflector]] housed in a [[radome]].<ref name = "bomber 245" /> This radar performed several functions, including air-to-ground and air-to-air [[telemetry]], [[radar configurations and types#Search|search]], [[Radar configurations and types#Targeting radars|track]], [[Terrain-following radar|terrain-avoidance]] and [[cartography]].<ref name = "ford 617" /> On the JA 37 fighter-interceptor model, the PS 37 radar was replaced by the more capable Ericsson PS 46 X-band [[pulse-doppler radar]], which had an all-weather [[look-down/shoot-down]] capability reportedly in excess of 50 kilometers and [[Semi-active radar homing#Continuous-wave|continuous-wave]] illumination for the [[Skyflash]] missiles as well as the [[Track while scan|ability to track two targets while scanning]].<ref name = "warwick 1261" /> According to Ericsson, it had a 50 percent chance of spotting a low-flying [[McDonnell Douglas F-4 Phantom II]] within a single scan and possessed a high level of resistance to interference from ECM.<ref name = "warwick 1261" />

Saab and [[Honeywell]] co-developed an automatic digital [[Aircraft flight control system|flight control system]] for the JA 37 Viggen, which has been claimed to be the first such system in a production aircraft.<ref name = "warwick 1261" /> To assist low altitude flight, a Honeywell [[radar altimeter]] with transmitter and receiver in the canard wings was used.<ref name = "bomber 245" /> The aircraft was also fitted with a Decca Type 72 [[Doppler radar#navigation|Doppler navigation radar]]. TILS (Tactical [[Instrument landing system|Instrument Landing System]]), a landing-aid system made by Cutler-Hammer AIL, improved landing accuracy to 30&nbsp;m from the threshold on the short highway airbase system.<ref>Battle, EH et al. "Some Early Achievements in Landing Guidance using Mechanically Scanned Pulse-encoded Beams", ''IEEE Transactions on Aerospace and Electronic Systems'', Vol. 25, no. 5, 1989, pp. 775–81.</ref> In order to effectively enforce Sweden's air space, the Viggen was integrated with [[STRIL|STRIL 60]] national defence system.<ref name = "bomber 243" /> The JA 37 Viggen was also equipped with a [[Garrett AiResearch]] digital [[Central Air Data Computer]], modified from the unit used upon the [[Grumman F-14 Tomcat]].<ref name = "warwick 1261" />

Initially, only a single reconnaissance (S) variant was considered, but fitting cameras as well as a radar proved to be impossible. The SH 37 maritime strike and reconnaissance variant was very similar to the AJ 37 and differed mainly in a maritime-optimized PS 371/A radar with longer range, a cockpit air-data camera and tape recorder for mission analysis. "Red Baron" and a SKa 24D 600&nbsp;mm LOROP camera pods were usually carried on the fuselage pylons.<ref name = "chant 458" /> The centreline fuel tank was converted for a short period of time to a camera pod with two Recon/Optical CA-200 1676&nbsp;mm cameras. In addition to the reconnaissance equipment, the SH 37 could also use all weapons for the AJ 37.{{Citation needed |date= January 2013}} For the photographic SF version, the radar in the nose was omitted in favour of four SKa 24C 120&nbsp;mm and two SKa 31 570&nbsp;mm photographic cameras as well as one 57&nbsp;mm VKa 702 [[Thermographic camera|Infrared linescan camera]] and air-data camera; all of which were integrated with and controlled by the aircraft's central computer.<ref name = "chant 458" /> Additional equipment, such as more camera pods, fuel tanks, ECM pods, and self-defense air-to-air missiles could also be carried upon the fuselage pylons.<ref name = "chant 458" />

The fighter-interceptor version of the Viggen, the JA 37, featured various avionics changes, including the extensive use of digital electronics alongside mechanical technology.<ref name = "Eliasson 115">Eliasson 2010, p. 115.</ref> In 1985, the "fighter link" entered service, permitting encrypted data communication between up to four fighters; this enabled one fighter to "paint" an airborne enemy with guidance radar for the [[Skyflash]] missiles of the three other fighters in a group while they had their own search and guidance radars switched off. This system was operational ten years before any other country's.<ref>{{Citation | date = April 2001 | url = http://www.militartekniska.se/mtt/include/archive/200104/MTT401_Viggen.pdf | title = Viggen | place = [[Sweden|SE]] | publisher = Militar tekniska | url-status=dead | archive-url = https://web.archive.org/web/20070926193720/http://www.militartekniska.se/mtt/include/archive/200104/MTT401_Viggen.pdf | archive-date = 26 September 2007 | df = dmy-all}}</ref> The autopilot was also slaved to the radar control to obtain better precision firing the cannon.<ref>Forsling, G. and Järmark, B. "Optimal Fuselage Aiming." ''AIAA Paper 85-1961''.</ref> Once in service, the Viggen's [[software]] was regularly updated every 18 months.<ref name = "Eliasson 125">Eliasson 2010, p. 125.</ref> In 1983, the [[mean time between failures]] (MTBF) was reported as 100 hours, a very high reliability level for the generation of avionics systems involved.<ref>Gunston, Bill ''Modern Combat Aircraft: From Fighters to Battlefield Helicopters''. Hong Kong: Hennerwood Publications, 1983. {{ISBN|978-0-86273-074-1}}.</ref>