Champ Fuselage bulkheads; 4 or 5 ?

[Eric Brown]

Is anyone knowledgeable on the addition of the 5th fuselage former / bulkhead ? Apparently a 5th fuselage plywood bulkhead was added to the 7 series starting with the 1950's 7EC model. Bulkhead p/n 5-10000 / 5-393 became the 2nd of 5 bulkheads, placed between the original #1 and #2 bulkheads.

In my 7AC / CCM / EC conv. project, I was wondering if there a good reason or an advantage to install the 5th bulkhead. The only reason I can think of to leave it out, is to save a little weight. Whadda you guys think ?

 

[Big Ed]

I can't speak to your plane, but in my 78 Decathlon, the 2nd and 3rd bulkheads provide the mounting points for the comms antenna plane on the dorsal fuselage. That is an aluminum plate corresponding to the rectangular patch shown below. That might have something to do with the design change.

I will also note that the #2 and #3 bulkheads warp easily, and the factory has substantially beefed up those components over the years. The current design has 3/4" bracing strips screwed and glued to the plywood formers to add rigidity. So it also could be that the added bulkhead was to better support the stringers in that area, and the radio plane was a matter of convenience.

Adding a bulkhead would entail welding tabs onto the frame, no?

 

[Eric Brown]

Yes. Adding 3 tabs would be necessary, but not a problem.