Saab 37 Viggen
The digital central computer was the first of its kind in the world, automating and taking over tasks previously requiring a navigator/copilot, facilitating handling in tactical situations where, among other things, high speeds and short decision times determined whether attacks would be successful or not, a system not surpassed until the introduction of the Panavia Tornado into operational service in 1981.In November 2005, the last Viggens were withdrawn from service by the Swedish Air Force, its only operator; by this point, it had been replaced by the newer and more advanced Saab JAS 39 Gripen.Vigg is also åskvigg, or "thunderbolt" (thunder wedge), stemming from the thunderstones of Nordic folklore, called "åskviggar", said to come from the lightning strikes of Norse god Thor when he hunted giants with his war hammer, Mjölnir.[18] Enabling such operations imposed several critical demands upon the design, including a modest landing speed, no-flare touchdown, powerful post-landing deceleration, accurate steering even in crosswinds on icy surfaces, and high acceleration on take-off.[21] In 1963, Saab finalized the aerodynamic design of the aircraft; the aerodynamic configuration was radical: it combined an aft-mounted double delta wing with a small, high-set canard foreplane, equipped with powered trailing flaps mounted ahead of and slightly above the main wing; this would be judged to be the best means to satisfy the conflicting demands for STOL performance, supersonic speed, low turbulence sensitivity at low level flight, and efficient lift for subsonic flight.[12][23] Further aerodynamic refinements during the later stage of development included the addition of dog-tooth patterns upon the main wing to generate vortices, allowing for the elimination of blown flaps from the canard.[25][26][27] This first flight, which lasted for 43 minutes, was flown by Erik Dahlström, Saab's chief test pilot, who reported the prototype to have been easy to handle throughout.[31] A total of five prototypes would be produced, four of which being modified AJ 37s and one being a sole pre-production JA 37 model, to test the control systems, engine, avionics, and armaments respectively.Amongst the changes involved, interchangeable armaments and sensor payloads were implemented in addition to the adoption of new mission planning and threat analysis computer systems.[45] In 1996, according to Swedish air force material-department chief General Steffan Nasstrom, the various upgrades performed to the Viggen since its introduction had "doubled the effectiveness of the overall system".This was essentially a heavily modified licence-built variant of the Pratt & Whitney JT8D engine that powered commercial airliners of the 1960s, with an afterburner added for the Viggen.[citation needed] Mechanical simplicity was also favoured, so the air intakes were simple D-section types with boundary layer splitter plates, while the fixed inlet had no adjustable geometry for improved pressure recovery.[48] For the JA 37, the RM8A was developed into the RM8B, achieved by adding a third low-pressure compressor stage over the preceding model, increasing the turbine inlet temperature and fuel diffusion within the combustion chamber.In the event of an in-flight engine failure, emergency power was provided by an automatically deploying ram air turbine (RAT), capable of generating 6 kVA.[28] 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 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.[22] The use of a digital computer would reduce or entirely replace 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.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.[50] On later variants of the Viggen, from the JA37 onwards, it was decided to adopt a newer and more powerful Singer-Kearfott SKC-2037 digital central processor, license-manufactured and further developed by Saab as the CD 107.[28] 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.[29] According to Ericsson, it had a 50 per cent 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.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.[62] Unusually for a 1970s fighter, the JA 37 variant of the Viggen featured three multi-purpose cathode-ray tube (CRT) display screens fitted within the cockpit, in a system called AP-12, developed by Saab and Ericsson.[71][page needed] A consequence of a tailless delta design, such as in the Viggen, is that the elevons, which replace more conventional control surfaces, operate with a small effective moment arm; their use adds substantial weight to the aircraft at takeoff and landing.[73] To withstand the stresses of no-flare landings, Saab made extensive use of aluminium in the airframe of the Viggen, which was constructed using a bonded metal honeycomb structure; the entire rear section of the fuselage, downstream of the engine nozzle, formed a heat-resistant ring composed of titanium.[74][75] The main landing gear, manufactured by Motala Verkstad, was highly strengthened as well; each leg held two small wheels fitted with anti-skid brakes placed in a tandem arrangement.[78] Ground crew would enter the munitions fitted into the aircraft's central computer using a load-selector panel, which would automatically choose the correct values for fire control, fuel consumption, and other calculations.It fired the same cartridge as the GAU-8, reportedly 50% heavier shells at a higher velocity than the ADEN cannon, resulting in six and a half times the kinetic energy on impact, and was effective up to 2,000 meters.[92] In practice, one of the most significant issues encountered with the Viggen during low-level flight, as extensively performed during a typical attack mission profile, was the threat posed by birds; thus, the Swedish Air Force paid close attention to their migratory patterns.The 37E Eurofighter competed against Dassault-Breguet's proposed Mirage F1M-53, the SEPECAT Jaguar, Northrop's P-530 Cobra (on which the YF-17 was based), and General Dynamics's YF-16;[104][105] on 13 January 1975, United States Secretary of the Air Force John L. McLucas announced the YF-16 had been selected as the winner of the ACF competition.[109] According to leaked United States diplomatic cables, India's interest in the Viggen was reported to be entirely due to Rajiv Gandhi's influence, and had alleged have been without any input from the Indian Air Force.
Multirole combat aircraftFighter bomberPhoto reconnaissanceMaritime patrolStrike fighterTrainer aircraftManufacturerSaab ABSwedish Air ForceTufted DuckThunderboltcanardintegrated circuitscombat aircraftPanavia TornadoSaab 32 LansenSaab 35 Drakendelta wingaeronauticalmaiden flightaerial reconnaissanceanti-surfacetwo-seat trainerinterceptorexportSaab JAS 39 Gripendefinite formSwedishdiving duckthunderstonesNordic folkloreNorse godgiantswar hammerMjölnirAarne Lakomaacanard wingssupersonicBas 60force dispersalroad runwaysBas 90National Security CouncilEisenhowerSwedish National Defence CollegePolarisBill GunstonEurofighter TyphoonDassault RafaleIAI Kfirvorticesblown flapsthrust reverserSwedish Air Force MuseumLinköpingturbofanRolls-Royce Medwayafterburnerde Havilland TridentPratt & Whitney JT8DVolvo RM8prototypeaerospaceFlight InternationalMcDonnell Douglas F-4 Phantom IIParis Air ShowRoyal International Air TattooinflationmicroprocessorMIL-STD-1553serialdata busAIM-120 AMRAAMlicence-builtpneumaticturbojetsplitter platesTumansky R-15ram air turbinehead-up displayanalogueDatasaabSinger-Kearfottdistributed computingelectronic countermeasuresradar warning receiverBOZ-100Ericssonmonopulse radarparabolic reflectorradometelemetryterrain-avoidancecartographypulse-doppler radarlook-down/shoot-downSkyflashability to track two targets while scanningHoneywellflight control systemradar altimeterInstrument Landing SystemSTRIL 60Garrett AiResearchCentral Air Data ComputerGrumman F-14 TomcatInfrared linescan camerasoftwaremean time between failurescathode-ray tubeliquid-crystal displaySaab 105fuselagearea rulemoment armaluminiumhoneycomb structuretitaniumanti-skid brakesvertical stabilizeractuatorhardened aircraft sheltersunderground hangarshardpointsanti-ship missilescruise missile