Thor's New Hammer - the Saab A37 Viggen Article & Plans
January 1974 American Aircraft Modeler
article on the Saab 37 Viggen was scanned and OCRed from my purchased
copy of the January American Aircraft Modeler. Patricia Groves wrote
the article and Björn Karlström added his trademark perfection to
a set of 4-view drawings. You can make a set of plans from the 4-view
since fuselage and airfoil cross-sections are shown.
Thor's New Hammer
Here's Yer Bird, All You Ducted Fan Enthusiasts
by Patricia T.
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.
When the call to war sounded, the world's first military aviators
had but one mission-to scout. Aboard the state of the art, gentlemen
pilots plied their gentlemanly trade while waving at one another
in the clean, fresh air above the littered trenches. Then came the
moment one saluted, not with his hand but with a side arm.
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
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
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."
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).
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
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
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.
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
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Posted November 27, 2010