Keith Mackey's Suggestions about Bulkhead Cracks
Great pictures. Now I understand the problem. I'm hopeful we can find a way to share information on fixes to common problems with detailed photos as a means of helping those with little wood aircraft experience from some of the "experts" who have owned and rebuilt Mite's for many years. The Mite Site is the perfect place for that information to be archived.
When I rebuilt my aircraft, there were no cracks in the area where you found them on yours, hence I am not experienced in the best solution. I would suggest the following:
Remove the plates that are described in SB 17 to better examine the structure. Attached are two "before" photos I took of my airplane during restoration showing the area with the plates removed. You will have to make a determination of how to repair the cracks that are clearly visible in the photos. I would suggest you seek the advice of Advisory Circular (AC) 43.13-1B Chapter 1. Wood Structure, and someone like Dick Rank who has completely replaced the bulkhead. I know that Gil Gilbert is a master woodworker and would probably also be willing to give advice.
The steel parts in the photos are looking pretty rough. While you have things apart, It would be a good idea to refinish them. Attached are photos of what I did. I bead-blasted the steel and examined them carefully with a 10x magnifying glass, powder coated them and reinstalled with new hardware. Make sure you clean up the elevator torque tubes also. Make sure the heim bearings in the ends are in good shape and turn freely with out much wear (lateral movement).
The bulkhead in question is one of the most critical parts of the airplane and its proper attachment to the plywood structure of the tail cone is very important. The bulkhead is attached to the two top stringers that run the length of the tailcone by the metal plates and angles. Note the crack discovered in the angle in picture 1838. The angle was replaced. Check these carefully also with a 10x glass after removing paint and rust. I coated the entire tailcone with the plates and fabric removed with the PolyFiber brand 2-part epoxy varnish which provides a waterproof seal of the wood. In the last picture, you will note the shiny appearance of the wood after the varnish is applied.
Carefully explore the information links from the maintenance page. A repair for the vertical fin spar is described here.
Dick Rank wrote a series of articles about the structure of the airplane that are very relevant to your situation. Here's the one on the rear bulkhead.
Hope this info helps,
[click to enlarge]