Saab 37 Viggen

https://en.wikipedia.org/wiki/Saab_37_Viggen

The Saab 37 Viggen ("Thunderbolt") is a retired Swedish single-seat,
single-engine, short-medium range combat aircraft. Development work on the type
was initiated at Saab in 1952 and, following the selection of a radical delta
wing configuration, the resulting aircraft performed its first flight on 8
February 1967 and entered service in 21 June 1971. The Viggen holds the
distinction of being the first canard design to be produced in quantity. The
Viggen was also the most advanced fighter jet in Europe until the introduction
of the Panavia Tornado into operational service in 1981.

Several distinct variants of the Viggen were produced to perform the roles of
strike fighter (AJ 37), aerial reconnaissance (SF 37), maritime patrol aircraft
(SH 37) and a two-seat trainer (SK 37). In the late 1970s, the all-weather
fighter-interceptor aircraft JA 37 variant was introduced. In November 2005, the
Viggen was retired from service by the Swedish Air Force, the only operator,
having been replaced by the newer Saab JAS 39 Gripen.

From the onset, the Viggen was planned as an integrated weapon system, to be
operated in conjunction with the newest revision of Sweden's national electronic
air defense system, STRIL-60. It was used as the nation's standard platform,
capable of being efficiently adapted to perform all tactical mission roles.
Other requirements included supersonic ability at low level, Mach?2 performance
at altitude, and the ability to make short landings at low angles of attack (to
avoid damaging improvised runways). The aircraft was also designed from the
beginning to be easy to repair and service, even for personnel without much
training.

One radical requirement of the proposed aircraft was the ability for it to be
operated from short runways only 500 meters long; this was part of the Bas 60
air base system that had been introduced by the Swedish Air Force in the late
1950s. Bas 60 revolved around force dispersal of aircraft across many wartime
air bases, including road runways acting as backup runways. Utilizing partially
destroyed runways was another factor that motivated STOL capability. Bas 60 was
developed into Bas 90 in the 1970s and 1980s, and included short runways only
800 meters in length. 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.

During 1964, construction of the first prototype aircraft commenced; on 8
February 1967, the first of an eventual seven prototypes conducted its maiden
flight, which had occurred as per the established development schedule. 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. Writing at the time, aerospace publication Flight International
described the flight as having been "Sweden's astonishing unilateral stand in
the front rank of advanced aircraft-building nations..."

Each of the seven prototypes were assigned different roles, although the initial
aircraft were focused on supporting the development of the initial production
variant, the AJ37. In 1967, the Swedish Government concluded that the
in-development AJ 37 Viggen would be both cheaper than and superior to the
McDonnell Douglas F-4 Phantom II. In April 1968, the Swedish government formally
issued the authorization for manufacturing of the Viggen to proceed, issuing an
order for 175 Viggens that year. Also in 1968, Saab began work on the Viggen's
maritime reconnaissance and photo reconnaissance variants. In May 1969, the
Viggen made its first public appearance outside of Sweden at the Paris Air Show.
On 23 February 1971, the first production aircraft, an AJ37 model, conducted its
first flight. In July 1971, the first production aircraft was delivered to the
Swedish Air.

With the performance requirements to a large extent dictating the choice of the
engine, the airframe turned out to be quite bulky compared to contemporary
slimmer designs with turbojet engines. The first prototypes had a straight
midsection fuselage that was later improved with a "hump" on the dorsal spine
for reduced drag according to the area rule. The wing had the shape of a double
delta with a dogtooth added to improve longitudinal stability at high incidence
angles.

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. Hinged leading edge surfaces can help counteract this, but
an even more effective tool is the canard. The canard surfaces were positioned
behind the inlets and placed slightly higher than the main wing, with a higher
stall angle than the wing, and were equipped with flaps. The lifting canard
surfaces act as a vortex generator for the main wing and therefore provide more
lift. An added benefit was that they also improved roll stability in the
transonic region. The canard flaps were deployed in conjunction with the landing
gear to provide even more lift for takeoff and landing.

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. 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. The design requirements imposed by the large anti-ship
missiles employed upon the Viggen necessitated that both the undercarriage and
vertical stabilizer be quite tall. To accommodate this, and to allow the main
landing gear to be stowed outside of the wing root, the undercarriage legs
shortened during retraction. The vertical stabilizer could also be folded via an
actuator in order that the aircraft could be stored in smaller hangars, hardened
aircraft shelters, and underground hangars, the latter of which were employed by
the Swedish military to limit the damage of preemptive attacks.

Role
Attack, fighter, reconnaissance

National origin
Sweden

Manufacturer
Saab AB

First flight
8 February 1967

Introduction
21 June 1971

Retired
25 November 2005

Primary user
Swedish Air Force

Produced
1970–1990

Number built
329

Unit cost

$2,000,000 (1967)

In July 1971, the first production AJ 37 Viggen was delivered to the Swedish Air
Force. The Skaraborg Air Force Wing (F 7) became the first wing to receive
deliveries of both the single-seat AJ 37 attack model and the twin-seat SK 37
training model of the Viggen, where upon the type began to replace their
existing Lansen aircraft. Conversion training to pilot the Viggen involved a
minimum of 450 flight hours performed on an initial mixture of the Saab 105, the
Lansen, and finally the Viggen itself; dedicated Viggen simulators were also
used, the latter of which was seen as a decisive factor in the ease of
conversion to the type.

The Viggen was designed to be simple to maintain, even by conscripted flight
line mechanics with limited technical training. A single Viggen could be
maintained by a team of five conscripts under the supervision of a single chief
mechanic. Standard turnaround, including refueling and rearming, took less than
ten minutes to perform; while an engine replacement took four hours. Over the
long term, the Viggen required 22 man hours per flight hour of maintenance work
at the depot level, and nine man hours per flight hour at the front line.

By the mid-1980s, Swedish Viggen fighter pilots, using the predictable patterns
of Lockheed SR-71 Blackbird routine flights over the Baltic Sea, had managed to
achieve radar lock-on with radar on the SR-71 on numerous occasions. Despite
heavy jamming from the SR-71, target illumination was maintained by feeding
target location from ground-based radars to the fire-control computer in the
Viggen. The most common site for the lock-on to occur was the thin stretch of
international airspace between Öland and Gotland that the SR-71 used on the
return flight. The Viggen is the only aircraft to get an acknowledged radar lock
on the SR-71.

Retirement

By 1994, the replacement of the Viggen by the later and more advanced Saab JAS
39 Gripen was in progress, the type being progressively phased out as greater
numbers of Gripen aircraft were delivered. On 25 November 2005, the last front
line Viggen was formally retired by the Swedish Air Force. A few aircraft were
kept in an operational condition for electronic warfare training against the
Gripen at F 17M in Linköping; the last of these Viggen flights took place in
June 2007.

Specifications (JA 37 Viggen)

General characteristics
Crew: One
Length: 16.4 m (53 ft 9 in)
Wingspan: 10.6 m (34 ft 9 in)
Height: 5.9 m (19 ft 4 in)
Wing area: 46 m² (500 ft²)
Empty weight: 9,500 kg (21,000 lb)
Loaded weight: AJ 16,000 kg; JA 17,000 kg (AJ 35,273 lb; JA 37,478 lb)
Max. takeoff weight: 20,000 kg (44,000 lb)
Powerplant: 1 × Volvo RM8B afterburning turbofan, 72.1 kN / 125.0 kN
afterburning (16,200 lbf dry, 28,110 lbf afterburning)

Performance
Maximum speed: Mach 2.1, 2,231 km/h (1,386 mph) at 11,000 m (1,386 mph at 36,100
ft (11,003 m))
Range: 2,000 km internal fuel only (1242 mi)
Service ceiling: 18,000 m (59,100 ft)
Rate of climb: 203 m/s (12,200 m/min) (40,026 ft/min)

Armament

1x 30 mm Oerlikon KCA cannon with 150 rounds
Six missile stations for two RB71 Skyflash (only JA37), four AIM-120 AMRAAM (JA
37D), or six AIM-9 Sidewinder or four 135 mm (5.4 in) rocket pods.
U95 ECM pod (JA 37D)




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