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Thor's New Hammer - the Saab A37 Viggen Article & Plans
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Thor's New Hammer Here's Yer Bird, All You Ducted Fan Enthusiastsby Patricia T. Groves In days of yore, when governments first began assembling their air forces, aeronautic one-upmanship depended on a wood and wire technology. Designer/ builders knew that the few thousand dollars (pounds, rubles or drachmas) required to produce a military aircraft wouldn't bust the national economy1 It was a simplistic era during which the major concern was to find an engine any engine, of almost any acceptable horsepower-that would run for 60 minutes in succession.  Saab 37 Viggen multi-purpose Mach 2 STOL combat aircraft.  Removal of some electronic gear and the forward fuel tank provided the second seat for the Viggen trainers. Belly tank contains additional fuel.  In order to retract smoothly into the thin wing, the extra strong main landing gear units are tandem. During 1640 ft. "no flare" type landings, the tandem arrangement provides an added shock absorber. The thrust reverser, triggered by switches on the landing gear, can be preselected in the air.  To reduce scramble time, the Viggen can stand at continuous alert, supported by a single electrical power and air conditioning unit which is ejected during start-up sequence. If no ground unit is available, the Viggen can start on its own.  Capable of a 1310 ft. takeoff run, a Swedish aluminum overcast departs one of their Air Force's strategically located road bases.  From brakes off to 36,000 ft. takes two minutes. Landing speed is about 137 mph.  Cockpit of Saab 37 Viggen. As the technology that supplied those first little scout rolled merrily along, development and production costs took off - jet-propelled. Until the advent of the Korean War it was still possible (although not always practical) for most nations to "keep up with the Joneses." And, conceivably, individual aircraft companies could independently develop an airplane from scratch on a (relative) shoestring. Since then, however, military aviation has been at the sufferance of each nation's budget considerations and individual national priorities. Because of the sheer complexity of today's military aircraft, the old-time day- or night fighters and the specialized bombers (per se) are giving way to the military aircraft "system." Sweden, long a neutral nation, alert to its own defenses and historically sympathetic to less technically developed countries, has produced such a system in its Aircraft 37. Nicknamed Viggen (Thunderbolt in English), it's basically a flying platform that is adaptable to various primary and secondary mission requirements2. Both the AJ 37 Viggen (a fighter/ bomber whose primary mission is that of attack and secondary mission is as a fighter), and the SK 37 Viggen (a two seat trainer that is also combat adaptable), are currently operational. In the prototype test or developmental stages are two strike/recche versions. Their differences are mainly internal, and both the SF 37 (intended for land reconnaissance), and the SH 37 (destined for sea surveillance duties), will carry the appropriate punch. Scheduled for delivery in early 1975 is the JA 37 fighter/interceptor, a planned follow-on to the current AJ 37. The JA 37, with a more powerful engine and additional avionics, will differ little from the present model, except for an internally mounted 30 mm Oerlikon KCA cannon. (On other models, all armament is external to the aircraft.) Basically an all-weather aircraft, the Viggen is scheduled to phase-out Sweden's Lansen and Draken airplanes in the attack and reconnaissance roles. As a progression of the delta-wing Draken, the Viggen has a tandem-delta wing which is flap-equipped on the canard surface. This bold and attractive configuration gives it the high speed characteristics of a delta wing while the foreplane gives it that added "plus" of an STOL's short field performance. As a manned weapon system, the Royal Swedish Air Force's proposed System 37 began in 1958 when development work on the Draken was peaking out. Included in System 37's overall requirements were the aircraft with power plant, avionics, ordnance, photo equipment, special ground-handling equipment and testing and training equipment (including simulators). Because the Viggen represented a bigger, more technically integrated pro-duct, it amounted to a whole "new aircraft, new engine and new electronics based on new technical principles3. For the Swedes it constituted a major national undertaking. The project, under constant review with the constant threat of economic cutoff, is the result of a vast team work effort between the Swedish Air Force, Saab-Scania (the prime contractor), and numerous Swedish and foreign (mostly American) sub-contractors. In the fall of 1961 general specifications for a multi-purpose, single-engine, single-seat aircraft with STOL capabilities were approved. In December it was decided that the aircraft should be powered by a military version of Pratt & Whitney's JT8D turbofan engine. Built under license by Volvo and fitted with a Swedish-built after-burner, the engine allows the Viggen to cruise economically at low altitudes, yet provides high reheat thrust when it has to get up 'n scat. It can operate at Mach 2 at high altitudes or Mach 1.1 as low as 330 ft. off the deck. Actual design, begun in October 1962, was frozen in May 1963. Including the probe, overall length of the Viggen is 53 ft. 5 in. Span of the main wing is 34 ft. 9 in. Height overall is 18 ft. 4 in. Since the airplane operates out of Sweden's network of underground hangars, the main fin folds to reduce overall height to 13 ft. 1 in. Wherever possible, integration of "off the shelf" items into the Viggen resulted in considerable savings in overall development costs. These items were fitted into existing aircraft and subjected to thorough testing in order to establish their compatibility with other new or existing systems. All systems tie into a digital computer. In order to control a potential Mach 2 airplane, it was necessary to come up with a computer system that would get the pilot's workload down to tolerance level and present understandable information without turning him into a blithering idiot drowned in facts. Simulators were used to design placement of instruments and to determine how much a man can absorb and still make decisions. A sophisticated airplane with sophisticated innards can wind up a pretty "heavy" proposition. From the beginning, Saab engineers had the Viggen on a strict diet to reduce all possible weight without endangering aircraft integrity. They sweated over every pound. With nearly 25% of the skin area made up of inspection hatches, its fuselage (built along conventional lines) is of high strength aluminum alloy composed, as much as possible, of bonded honey-combed panels. (All control surfaces are honey-combed.) Because of its high cost, titanium is used only in hot areas and in all standard bolts. Still and all, maximum takeoff weight for the AJ 37 with standard armament loads is about 35,275 lb. In September 1964, the first of seven prototypes - each built for specific systems-test purposes-was begun. It made its maiden flight on February 8, 1967 with the other six prototypes following between then and July 2, 1970. By February 13, 1971 the first flight of a production AJ 37 was accomplished, and delivered into Air Force service in June of that year. Of the 175 Viggens ordered (157 AJs and 18 trainers), 30 were in service as of March 1973. One independent expert has called the Viggen "incomparably the best constructed aircraft this writer has ever seen."4 Now with thousands of research, development and test flying hours behind it, and with the inevitable bugs inevitably working out, production is scheduled to go into the 1980s. Presented such possibilities in a ready-made machine, Australia, the Netherlands and Switzerland are interested. Notes 1 The first use of the specific term "Military Type" aircraft was on March 13, 1911 when the Curtiss Company received a $6000.00 order from the U.S. Government. Robert B. Casari, (U.S. Military Aircraft 1908 to April 6, 1917), p. 1. 2 Except as especially noted, all data supplied by Saab-Scania. 3 Schroder, Olsson and Ljungkvist, "Viggen" Astronautics and Aeronau,tics, December 1969, p. 26. See also: Canadian Aeronautics and Space Journal (Vol. 18, No.6), June 1972, pp. l67ff. 4 Roy M. Braybrook, "The Fight for the Skys," Air Enthusiast (Vol. 4 No.6) June 1973, pp. 281.  <click for larger version>  <click for larger version> Notice: The AMA Plans Service offers a full-size version of many of the plans show here at a very reasonable cost. They will scale the plans any size for you. It is always best to buy printed plans because my scanner versions often have distortions that can cause parts to fit poorly. Purchasing plans also help to support the operation of the Academy of Model Aeronautics - the #1 advocate for model aviation throughout the world. If the AMA no longer has this plan on file, I will be glad to send you my higher resolution version. Try my Scale Calculator for Model Airplane Plans.
Posted November 27, 2010 |
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