RPM the A&P wrote:
Hi,



I'm looking for input on the best way to layout a repair of some "hangar
rash" on the tail boom of my Taylor Coot amphibian project.



The damaged area is on a 10in diameter .065in 6061 T6 tube that serves as
the tail boom on this aircraft. The part was dropped and sustained a crease
roughly perpendicular (but not quite) to the length of the tube.



I have removed the displaced material and now have an opening 4.1in long and
1.1in wide.



Since I'll be joining two sheets of .065, I've selected -6 rivets. I also
realize that I'll need to slip roll the patch.



I'm now trying to apply the guidance for stressed skin repairs found in AC
4313-1B around paragraph 4-58 figure 4-16 and tables 4-9 through 4-11 (note
that there is apparently no table for 6061 T6).



Here is a link to an image showing the current state to the repair:



http://rilinterface.com/Cootnest/Ima...e/DSCN0997.jpg



I'd love to get folks' input on how best to lay out the repair for this.



Thanks!



Russ

http://rilinterface.com/cootnest


I recommend using 2024-T3 for the repair doubler, putting it inside, and putting a filler on the outside. This is not because the 2024
is stronger, but because it will be much easier to buck large, hard rivets against a harder material than 6061. The heads go against
the 6061 outer skin, you'll need a 5x rivet gun and a really heavy bucking bar. You can also use fresh icebox rivets (-D, -DD) or heat
treat AD rivets, (if you're daring enough). The most important thing is to thoroughly prime and seal the skin and repair doublers
before riveting them together. Rivet spacing in 43-13 seems really close to me, compared with actual rivet spacing in aircraft or in
aircraft structural manuals. I'm too lazy myself, but MIL-HDBK-5 will give you FAA acceptable numbers for calculating the number and
size of rivets needed for the repair.

Your photo really sucks, by the way. Without knowing the location of the damage on the aircraft, there's no way to determine the load
path. With digital cameras and unlimited web space, there's no reason not to upload a couple hundred photos of the aircraft to a
Google photo album.

--
John Kimmel


I think it will be quiet around here now. So long.