5 Looking into the Future on JAS Gripen Spillovers
5.5 Manufacturing Lightweight Technology (Case 16)
5.5.1 Lightweight Aircraft Structures: Saab and Gripen
To accomplish the lightweight design of JAS 39 Gripen demanded by the Government customer the Saab design team adopted a holistic approach to optimize the choices made. This approach involved an evaluation of the weight reductions to be achieved through
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1. The use of new and light materials, for instance carbon fiber composites.
2. The design of special framework constructions (lattices) that allowed lighter panels to be used.
3. The development of special machining techniques, for instance the high-speed machining tool of Modig (see Case immediately below) that made it possible to cut the weight of metal structures without weakening its load-carrying capacity.
4. The use of electric control systems on the aircraft (for instance fly-by-wire) instead of hydraulic or mechanical.
5. The development of simulation technology to optimize the localization of new lightweight structures.
6. To optimize the use of the complementary weight saving that came with other new design features of the Gripen aircraft.
The wing of the Gripen was built in carbon fiber composites together with British Aerospace. Twenty to twenty-five percent of the weight of the airframe was to be made of carbon fiber composite components giving together a weight reduction of some 25%.
Thanks to the new miniaturized electronics, composite materials, and software development, it was possible to reduce the volume significantly and consequently also the weight. Compared to its predecessor Viggen, Gripen is roughly half the volume and weighs half as much, but it still has the same or superior performance in all respects, and notably in systems functionality. Its range is much longer, and it carries the same weapons load.
To achieve the aerodynamic “instability” properties of the JAS 39 Gripen aircraft it was necessary to use an electrically directed fly-by-wire control system, rather than the earlier and much too slow mechanical and hydraulic systems. The fly-by-wire system required much less space and was much lighter and therefore also contributed to the desired lightweight features of the aircraft. Electrical (fly-by-wire) controls and the densely compacted electronic circuits designed by Saab reduced weight further.
One could say that the design of compact, lightweight, and robust systems products is a special competence of modern military aircraft and weapons industry.
The fly-by-wire control system introduced on the JAS 39 Gripen was not only necessary to achieve the speed of controls and maneuverability (immediate func-tional flexibility) necessary on a statically unstable aircraft. Weight was signifi-cantly reduced (as were space requirements) when the mechanical and hydraulic transmission of signals was replaced by electrical wire. Considerable flexibility for future functional modifications of the aircraft also came with the fly-by-wire con-trol system. One example is the in-flight swing-role capacity, the integrated cockpit displays and the “joy stick” to make maneuvering of the aircraft easier and free time and attention for the combat role of the pilot. The swing-role capacity was achieved by combining the design of the avionics with sophisticated software and the fly-by-wire control system. Safety was achieved by having two or more parallel systems and constant electronic monitoring of functions.
The lightweight construction technologies pioneered on the JAS 39 Gripen aircraft have come in handy on the civilian side. Saab is currently manufacturing
the Tactical Management System for the new European lightweight helicopter NH 90 for Eurocopter (Ny Teknik, No. 4, Jan 26, 2005). Saab’s military lightweight technology was also transferred, to the extent it was economical, to the parallel development of Saab’s civilian passenger aircraft, the 340 and 2000 models. On the choice of material, civil aircraft is sensitive to costs, while performance is the prime concern of military aircraft. The military aircraft pioneered the early use of expensive carbon fiber and composites. Their higher costs, however, are to a con-siderable extent a matter of the small volumes of their production. The new envi-ronmental and fuel economy concerns of today and the rush for lightweight structures in many industries mean that volumes are now going up and that Saab’s experience from lightweight construction both from the JAS 39 Gripen and its civilian aircraft development has become the foundation of its systems contracting work for both Boeing and Airbus.
5.5.1.1 Case: Modig Machine Tools in Virserum
A high-speed metal machining technology was first developed as Saab Gripen engineers cooperated with a machine tool manufacturer in a remote district in Sweden (Modig Machine Tool in Virserum). Modig had a long history as a devel-oper and manufacturer of machine tools. It was founded in 1948. The quality of the Modig machine tools had already taken the company to both the North and South American markets and to Australia.13
In 1985, Modig had started experimenting with a high-speed machine tool to raise process productivity. But the method did not work because temperature increased rapidly as the speed of machining increased. Both the tool and the metal being cut melted. By accident, however, the high-quality Modig machine tools had caught the attention of Saab, which now asked Modig if it could develop an intrusion machine for long aluminum profiles. It did.
Saab engineers, however, also understood the problem with high-speed machin-ing that had halted Modig’s experiments. They understood that as the speed was increased further temperature would go down since the heat would then be removed with the waste material created. The first test center in the world for high-speed machining was established in 1987 at the Modig Virserum location where experi-ments were performed together with Saab and the Linköping Technical Institute.
Saab understood that this machine tool could manufacture (lightweight) compo-nents that had not been possible to manufacture before and acquired its first Modig high-speed machine tool in 1989. Processing precision could now be raised which made it possible to process metal components for Gripen with very thin walls for structures that were very light but could still carry the needed loads.
Saab was also very generous to Modig and allowed Modig’s customers to visit and inspect the machine in use in its Linköping facilities. Saab’s support raised the quality reputation of Modig and very soon the Modig high-speed machines were used by most air craft manufacturers in the world, including Boeing. Modig has even become a quality supplier of tool development for Boeing.
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Before “September 11” Modig had 130 employees. After September 11 it received no order for 16 months and went bankrupt. The managing director and owner Percy Modig, however repurchased the bankrupt company, which is now again a global supplier of high-speed machine tools, albeit no longer the only one. The number of employees is much smaller, but Modig uses a large number of its former employees as subcontractors. Modig has developed a method to distribute development work geographically in a fashion that was unthinkable before the mid-1990s when the Internet began to become a practical industrial tool.
During my interview visit, the Modig and Boeing people had an Internet-based video conference with online live presentation of CAD designs to discuss the progress of work on, and technical details of a machine tool Modig was designing for Boeing.