Adhesive Bonding of Aircraft Primary Structures

The Primary Adhesively Bonded Structures Technology (PABST) program conducted by McDonnell Douglas for the USAF Plight Dynamics Laboratory has broadened the horizons for future applications of adhesive bonding to aerospace structures. A major portion of this program was concerned with the use of new environmentally-resistant adhesives and primers, and an improved surface preparation involving the use of phosphoric acid anodize. This portion has been well publicized and explains past service failures and how to avoid their recurrence. This paper emphasises structural considerations. These include (1) a comparison between the performance of bonded and riveted construction, (2) an explanation of why the bonding was found to be superior in most situations, (3) the techniques for identifying where not to use adhesive bonding because its misapplication could lead to a reduction in damage tolerance just as significant as the improvements associated with the judicious elimination of mechanical fasteners, (4) an outline of the procedures used in PABST to size the bonded joints, (5) a description of the bonded joints, and (6) a summary of the significant findings of the structural testing of panels and the Full-Scale Demonstration Component, a 42-foot long by 216-inch diameter approximation of the forward fuselage of a wide-body transport aircraft. Manufacturing considerations are also included, along with a discussion of the need to integrate the tooling and design concepts. This massive amount of work, with such a strongly positive result, inspires much confidence in the more widespread use of structural adhesive bonding in all new aircraft.