Any person who takes up the task of building an airplane has to decide just how good is good enough. In many cases, there are generally accepted rules that define tolerances that can be measured to determine if a part is good or bad. Edge distance, hole spacing, and many other things have been determined by experts. In some cases, however, there are cases where the builder is left to determine if the quality is good enough. A weld that is perfectly acceptable to one builder may not suit another.
Many times the work required to correct a deficiency may introduce more problems than the issue itself. The FAA created advisory circular AC43.13-1B Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair as guidance for maintenance and construction of an aircraft. This guide, and our own personal standards, serve as a guide to determine when a repair is needed and how it should be done.
On my RV-10 project, I recently came across a situation where some poorly driven rivets needed to be removed. In this case the two pieces were not held tight together, and the riveted joint was clinched. Removing a clinched rivet can be rather difficult as the rivet expands to fill the space between the parts, making it nearly impossible to drive the rivet out of the hole. This rivet proved to be particularly nasty, and during the removal process the hole was severely enlarged.
My first inclination was to drill for the next size rivet and just hope it would hold. However, better judgement prevailed, and I decided to step away and find a better course of action.
The damaged part was one of the bulkheads in the aft end of the tail cone. My error occurred as part of the process of riveting the tail cone assembly together, and it was no longer practical to remove and replace the assembly without doing more harm than good.
I weighed my options for a few days and referred to AC43.13-1b for guidance on how to best repair the part. I determined that my best, and safest, course of action would be to fabricate a part to be placed over the enlarged hole and reinforce that area.
I started the repair process by cleaning up the parts, ensuring that any remnants of the bad rivet were removed. Then I cleaned up the hole removing any burrs before drilling the hole for the next size rivet. Next, I used a set of dimple dies and a pop rivet gun to re-set the skin dimples to ensure the two pieces nested together properly.
The next step is to ensure that I can properly set a rivet in the damaged area. My solution was to fabricate a reinforcement plate that would fit over the bad rivet and also be captured by rivets adjacent to the repair.
I used a scrap bulkhead as a template to trace the outline of the flange onto a small piece of aluminum. I cut out the piece and filed and shaped it to match the flange it would sit on. I clamped the part into place, drilled the holes to match, then dimpled the holes. A couple shots of primer, and the part was ready to be riveted into place. I riveted everything into place, using a NAS 1097 rivet in the enlarged hole. These rivets are sometimes referred to as "oops rivets" since they have the shank of a 1/8" rivet with the head of a 3/32" rivet.
As builder’s we each have to determine if our work meats industry standards. More important is our own personal standard for quality and workmanship. These personal standards are driven by desires for safety, quality of work, or expedience. In the end, beauty is in the eye of the beholder, but quality is in the eye of the builder.
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