Development of a Bonded Repair for the F-16 FS479 Bulkhead Vertical Tail Attach Bosses

Abstract

A bonded repair has been developed to repair cracked FS479 bulkheads on the F-16 aircraft. The cracking occurs at the vertical tail to aft fuselage interface in a sharp fillet between the vertical tail attach boss and the top flange of the bulkhead. The repair approach entails machining off the attach bosses along with any existing cracks, and bonding on a replacement 'saddle' with an optimized contour that eliminates the stress concentration caused by the fillet. As a final step the saddle is reinforced with boron doublers to optimize the load transfer. This repair is a cost effective alternative to bulkhead replacement because it can be applied in the field and does not require the removal of the bulkhead from the aircraft. To date, the repair has successfully completed proof of concept static testing over a temperature range of − 65^○F to 200^○F and durability testing at room temperature to 1.5 lifetimes. This paper details the repair design and summarizes the results obtained in the proof of concept program.