Issue 16 - Saab: Twin jet trainer - The Saab 105
By: Tim Callaway
It served as a jet trainer, light ground attack aircraft, reconnaissance platform and four seat communications aircraft, yet the Saab 105 began life as a concept for a business jet.
Towards the end of the 1950s, Saab began considering the civilian market again, this time with a view to building a small, high speed business jet. There were a number of concepts studied, including a very advanced delta winged five seat aircraft. At the same time, towards the end of 1958, the Swedish Air Force began considering a replacement for the de Havilland Vampire J 28C trainers then in service.
With the J 35 Draken beginning to enter service, the Vampires were no longer adequate trainers to introduce pilots to flying supersonic jets. The Swedish Air Force was evaluating a number of foreign designs, such as the British Hunting Jet Provost and the Canadair Tutor to fulfil the requirement, but was keen to buy a domestically produced aircraft.
Saab was well aware that the military market was far larger than any potential civil sales of a light jet, so it modified the light jet concept to a more conventional design, launching the Saab 105 in April 1960. Under project manager Ragnar Härdmark, the design evolved to become a high winged, twin engined aircraft with the instructor and pupil seated side by side under a large, single piece canopy.
The new trainer was to be powered by a pair of Turboméca Aubisque low bypass turbofans of 1635lb (7.49kN) thrust each, given the designation of RM9 in Swedish Air Force service in line with previous engines. On December 16, 1961, the Air Board approved the continuance of the design project, with the proviso that the trainer could also act as a ground attack aircraft. This was followed in April 1962 with a preliminary contract for the purchase of 130 aircraft should the design meet the performance requirements.
Construction of two prototypes began immediately after this, with the first flight taking place on July 1, 1963, with test pilot Karl-Erik Fernberg at the controls. Early test flights revealed a number of aerodynamic problems with the air intakes and engine exhausts, both of which required extensive modification. This also affected the wing root design, beneath which the engines, intakes and exhausts were situated, so it was not until June 17, 1964, that the second prototype made its maiden flight.
However, the modifications to the first aircraft had proved satisfactory prior to this, so in March 1964 the Government had approved the purchase order for the aircraft now designated SK 60. The original order was increased to 150 aircraft in August 1965, the same month that the first production aircraft flew for the first time.
The Swedish Air Force Flying School at Ljungbyhed, also known as F 5, received its first SK 60As in April 1966. Initial problems were experienced with engine reliability, but these were corrected through an extensive modification programme. On July 17, 1968, the first student pilots began training on the aircraft, with all 149 production versions of the type delivered by 1968. Once the type was in service, a series of modification programmes were carried out on the aircraft, resulting in four sub types.
The first of these was the SK 60B, a ground attack version of the trainer which was fitted with up to six underwing pylons for weapons and a Ferranti F-105 integrated strike and interception system (ISIS) multifunction sight in front of the port seat. Around 60 aircraft were modified to this standard from 1970 onwards and their pylons could carry a pair of pod mounted 30mm Aden cannons, two 12.7mm machine gun pods for gunnery training, bombs up to 550lb (250kg), 12 5.3in (13.5cm) rockets or six 5.7in (14.5cm) rockets. None of the pylons could carry external fuel tanks.
A single prototype of the next version of the Saab 105 was built, flying for the first time on January 18, 1967. This was the SK 60C, which was intended to be an enhanced light strike version which could also perform reconnaissance and forward air control missions.
These aircraft had an extended nose which housed a Fairchild KB-18 panoramic camera and an infrared search unit. The SK 60C could also carry a photoflash pod on one of the wing pylons to carry out night photography. Including the prototype, which was the 150th and last Saab 105 delivered to the Swedish Air Force, 30 aircraft were converted to SK 60Cs from both A and B variants. A number of SK 60Cs later had the camera port faired over as the reconnaissance role was taken over by other types.
Saab had also designed the 105 from the outset to be capable of operating as a four seat liaison and communications aircraft, a feature harking back to the design’s origins as a light business jet. The two Saab ejection seats could be quickly removed and replaced with four airliner type seats which had no provision for wearing parachutes but were at least comfortable, or four rather more military seats which did allow for the wearing of parachutes. During the mid-1970s, 10 aircraft were permanently modified as four seat transports and designated as SK 60Ds.
A small number of four seat Saab 105s were equipped with commercial civilian instruments and an instrument landing system (ILS). These were known as SK 60Es, and were used to train Air Force Reserve pilots in flying commercial aircraft. All of the E versions were eventually used in the same role as the SK 60Ds, as light transport and liaison aircraft. All of these modification programmes were carried out by the air force’s central maintenance and repair centre, the CVM.
Saab had been working on a replacement for the Saab 105, the B3LA, but this project was cancelled in 1979. In 1988, a structural upgrade programme was carried out on the 142 SK 60s of all versions still in service, to keep the aircraft in service for as long as possible. This included new wings and other structural strengthening and modified ejection seats. This structural programme was extended still further in 1993, when 115 SK 60As, Bs and Cs were fitted with a pair of the Williams Rolls FJ44 turbofans.
These engines produced 1900lb (8.45kN) of thrust each, but were not only more powerful, they were also quieter, cleaner, burned less fuel and were much easier to maintain. The aircraft were also fitted with a fully automatic digital engine control (FADEC) system which enhanced the fuel efficiency of the engines and gave them what is known as ‘carefree’ handling.
The four seat SK 60D and E models were not given this upgrade, instead these aircraft were grounded and used as spares for the remainder of the fleet. The SK 60 is still in service today as an advanced pilot trainer, a remarkable record of service for this type of aircraft. That so many of the original fleet of 150 were still available for upgrade 27 years after their introduction is nothing short of amazing. Military trainers and ground attack aircraft are very hard used machines, so this record speaks volumes about the 105’s inherent toughness and reliability.
Aside from the Swedish Air Force, the Austrian Air Force also acquired the Saab 105, but a much modified variant. On April 29, 1967, Saab made the first flight of the 105XT, an export version modified from the second prototype. This was fitted with the much more powerful General Electric J85-GE-17B turbojets which produced 2845lb (12.6kN) of thrust. These engines meant the 105XT could carry a much heavier load of external stores, 4410lb (2000kg).
The internal fuel tanks were increased in size from 308 gallons (1400 litres) to 450 gallons (2050 litres), and provision was made for the carriage of two 110 gallon (500 litre) drop tanks on the inner wing pylons. The XT could also carry the AIM-9J Sidewinder air to air missile. The wing was strengthened to accommodate this greater weight, and to absorb the increased performance stresses the engines also gave the aircraft.
In 1968, the Austrian Air Force ordered 20 of these modified aircraft, designated Saab 105Ö, and followed this with an order for 20 more the following year. These 40 aircraft were all delivered between 1970 and 1972, replacing the Saab J 29 Tunnans still in service in Austria. The 105Ös were used to fill the training, reconnaissance, close air support and air defence roles, being fitted with a specially designed Vinten camera pod under one wing and a photoflash pod under the other to fly day and night reconnaissance missions.
In 2010, 12 of these aircraft underwent a life extension programme aimed at keeping them in service until at least 2020. Both Switzerland and Finland were offered modified export versions of the Saab 105, but both sought solutions in other aircraft types. The second prototype was modified once again in 1972 to become the sole example of the Saab 105G. This was fitted with a comprehensive navigation and attack system, but it attracted no orders. However, the second prototype remained in service as a flying testbed and trials aircraft until 1992 when it was retired to a museum.
The Saab 105 did not attract the same attention as the supersonic fighters and other types that Saab produced, but it was no less an impressive aircraft for that, reliable and enduring. It also earned a special place in the hearts of the Swedish and Austrian people as the mount of their national aerobatic teams, the Swedish ‘Team 60’ and Austrian ‘Karo As’ and ‘Silver Birds’.
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