DEVELOPMENTS IN ADHESIVELY BONDING THE WINGS OF THE SAAB-340 AND SAAB-2000 AIRCRAFT

The development of the adhesive bonding of the wing of the SAAB 340 an d 2000 aircraft is traced from the development of the technology durin g the Primary Adhesively Bonded Structure Technology (PABST) research programme performed at Douglas Aircraft under contract to the US Air F orce Wright Laboratories in the late 1970s through initial fabrication by Fairchild in America in the early 1980s to series production by SA AB in Sweden and, today, also by CASA in Spain. The saga of solving a processing problem encountered in America before the first aircraft wa s delivered is recounted as an object lesson in how to approach proble ms and in the benefits derived by doing so promptly and thoroughly. Ev ery aspect of the problem was identified and replicated in the laborat ory 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 fusela ge were implemented during the transfer of production of the wing from America to Sweden. The use of a floating caul plate, rather than a tr aditional rigid bonding tool, is explained. The justification for doin g 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 a lso described, culminating in a refinement of a technique pioneered by Fokker in Holland. Today, all breather and bleeder layers have been e liminated. This reduces costs and the need for disposal of costly expe ndable materials and also permits a positive check of the fit of the d etails by visual examination through the transparent bag once the vacu um is drawn before the assembly is inserted into the autoclave, giving an opportunity to correct any misfits while it is still possible to d o so. Consequently, there is also no need for traditional verifilm ope rations. The tooling technology developed during the PABST programme d id not die when the contract was completed with no follow-on productio n programme for large transport aircraft in the United States. It is a live and flourishing in Sweden. In addition, as the paper describes, t he transfer of the technology was so complete that it has since been i mproved upon. Today, the bonding of the stiffened wing skins for these two aircraft is probably the most advanced and simultaneously the mos t forgiving production application of large-scale metal bonding the wo rld has yet seen.