Scott Royall's Comments about Bulkhead Cracks
This is Scott Royall's response to Tom Neeb's request for suggestions about repairing bulkhead cracks in David Hutton's N4051.
Hi Dave and Tom: My rear bulkhead looked about like yours when I took the tail off of N4172 (see Photo 1). It is an indicator of serious water damage throughout the lower section of the fuselage and wing. The plywood skin can become brittle from being wet and dry too often or soft from dry rot. I also found rot at the forward end of the lower longerons, and the shear web had delaminated from the center section of the main spar on the front and the back. Be careful to make sure you find all the bad stuff and get it fixed.
I decided to remove and replace the rear bulkhead using it as a pattern to build a new one. I removed the hardware and used a thin knife blade to separate the plywood skin from the bulkhead. It wasn't very hard and there was no damage caused to the fuselage skin by this process. Remember that the glue used on these planes is water soluble. When I pulled the bulkhead out it came apart in about 6 pieces (Photo 2). The two plywood pieces were totally delaminated from the spruce, and the spruce was weather cracked all the way through. The metal reinforcing plates that were bolted to both sides of the the bulkhead are shown in Photo 3. I have two sets of these parts. The duplicate parts are extra. Photo 4 shows the bracket that is used to bolt the reinforced bulkhead assembly to the upper longeron. (You will probably notice that the left hand bracket is turned around backwards). The last photo shows my finished job. I used a lot of fiberglass to reinforce and waterproof so I didn't use the metal brackets. I'm sure I ended up with a stronger end product for a little less weight.
My rebuilding process was a little different than what you will probably do. My wing was so bad that I am using an amateur built wing and completely rebuilding the rest of the airplane. I invited the local FAA guys over to my house to see what I am doing and they wrote me a letter giving me permission to certify my Mite as experimental homebuilt. I chose to do that because of the serious damage to the original wing.
[Click to enlarge images]