Developments in adhesively bonding the wings of the SAAB 340 and 2000 aircraft

Abstract

The development of the adhesive bonding of the wing of the SAAB 340 and 2000 aircraft is traced from the development of the technology during the Primary Adhesively Bonded Structure Technology (PABST) research programme performed at Douglas Aircraft under contract to the US Air Force Wright Laboratories in the late 1970s through initial fabrication by Fairchild in America in the early 1980s to series production by SAAB in Sweden and, today, also by CASA in Spain. The saga of solving a processing problem encountered in America before the first aircraft was delivered is recounted as an object lesson in how to approach problems and in the benefits derived by doing so promptly and thoroughly. Every aspect of the problem was identified and replicated in the laboratory where, because it was understood properly, it could be duplicated and prevented at will. The lessons learned about bonding tool designs from this investigation and during the manufacture of the PABST fuselage were implemented during the transfer of production of the wing from America to Sweden. The use of a floating caul plate, rather than a traditional rigid bonding tool, is explained. The justification for doing so is the virtual elimination of all fit problems and the production of a far more uniform void-free bond line. In addition, the evolution of progressively simpler, yet more effective, bagging procedures is also described, culminating in a refinement of a technique pioneered by Fokker in Holland. Today, all breather and bleeder layers have been eliminated. This reduces costs and the need for disposal of costly expendable materials and also permits a positive check of the fit of the details by visual examination through the transparent bag once the vacuum is drawn before the assembly is inserted into the autoclave, giving an opportunity to correct any misfits while it is still possible to do so. Consequently, there is also no need for traditional verifilm operations. The tooling technology developed during the PABST programme did not die when the contract was completed with no follow-on production programme for large transport aircraft in the United States. It is alive and flourishing in Sweden. In addition, as the paper describes, the transfer of the technology was so complete that it has since been improved upon. Today, the bonding of the stiffened wing skins for these two aircraft is probably the most advanced and simultaneously the most forgiving production application of large-scale metal bonding the world has yet seen.