The International Cessna^® 170 Association

Hello gentlemen and ladies.
I need some advice, and will appreciate all responses.
My mechanic found, at annual, that the aft bulkhead, P/N 0512108-3, figure 22-87 for those with a schematic, is cracked.
The aft bulkhead assembly is P/N 0512108, figure 22-86.
This is where the tailwheel springs attach.
I need a replacement, new or used.
Or perhaps a hint about an approved repair process.
It appears that a lot of skin needs to be removed to get to the defective part.
N1361D Serial # 20107
Thanks, in advance.
Jim Heidere

Discount Aircraft Salvage is listing a 0512108 "170A/B bulkhead", in new surplus condition. There number is 509-276-2849

I had the same problem with my 1950 170A. I believe my A&P purchased one and manufactured another – he may have manufactured both but I saw the jig he used for one. He manufactured the new one by first building a wooden form that fit perfectly inside the cracked bulkhead. He then flattened the cracked bulkhead and used it as a pattern for the replacement bulkhead. The new one was then bent using the form he had made earlier. I would never have guessed he made the part from looking at it.

wingnut wrote:Discount Aircraft Salvage is listing a 0512108 "170A/B bulkhead", in new surplus condition. There number is 509-276-2849

Thank you, very much.
Jim

markeg1964 wrote:I had the same problem with my 1950 170A. I believe my A&P purchased one and manufactured another – he may have manufactured both but I saw the jig he used for one. He manufactured the new one by first building a wooden form that fit perfectly inside the cracked bulkhead. He then flattened the cracked bulkhead and used it as a pattern for the replacement bulkhead. The new one was then bent using the form he had made earlier. I would never have guessed he made the part from looking at it.

Thanks you, very much
Jim Heidere

markeg1964 wrote:I had the same problem with my 1950 170A. I believe my A&P purchased one and manufactured another – he may have manufactured both but I saw the jig he used for one. He manufactured the new one by first building a wooden form that fit perfectly inside the cracked bulkhead. He then flattened the cracked bulkhead and used it as a pattern for the replacement bulkhead. The new one was then bent using the form he had made earlier. I would never have guessed he made the part from looking at it.

Hi Mark,
I would regularly inspect that bulkhead for cracks. The method of fabrication you mention is possible in the field, using 2024-O (soft) material and then heat treating to T42. This would be legal, and considered an owner produced part. This bulkhead is 2024 alloy, .071" thick (an odd size) and is a very important part. I know there is no way to fabricate this part from T3, and doubt good results could even be obtained using soft material and form blocks as you described. I've made some complicated parts before and I do not believe this part could be made without stretch forming method which requires equipment most of us dont have. The factory bulkhead has an angle, bent forward around it's perimeter, is especially tight radius at the bottom, without flutes or notches. The lack of flutes and/or notches on this tight radius, and considering the thickness of the material, is a good indication that the factory used a method of stretch forming. I'm not trying to discredit, nor be critical of your mechanic fabricating the part. If he successfully duplicated this part, that's very very impressive. If he used a different alloy or thickness, or incorporated flutes or notches to effect fabrication, the part would not be legal, and considering the fact that it is primary structure could be a dangerous situation.
My point is, I think you should study on this, and regularly inspect. The flange of the bulkhead turns forward, so a boroscope or videoscope would be the ideal methods, but a small mirror and flashlight could be placed through the holes where the rudder cables exit the skin.

Here is an illustration of the part being discussed: Item 87 in the pic:

Thanks for the illustration George.

I would like to clarify something for ark and others. As these aircraft get older and special parts become scarce, more people will take advantage of FAR 21.303(b)(2) owner produced part. It's important for owners and maintenance personnel to understand the benefits and risk of fabricating a part.
The bulkhead discussed in this thread has a formed angle around it's perimeter. The lower portion has a radius about the same as a snuff can. Try bending some paper around a snuff can and you'll see what happens. With aluminum, the same thing happens, that extra material has to go somewhere. And you can't fold it back onto itself like the paper because 2024 work hardens with every move, and will crack before you get anywhere near this radius.
This particular part is stress loaded in ground and air operations; basically functions as a landing gear mount structure and tail feather mount structure.
I just hope the mechanic that "made" this part really didn't. Maybe said he could/would, found out he couldn't, bought one and never said different.

Here's a pic of one I have that gives a better view of the radius Del is discussing:
Del, you should quit that snuff. It'll rot your lower jaw and mouth off with cancer.

It looks like I give some miss information. I was going through the pile of parts from several annuals ago and it turns out my A&P didn’t manufacture one of the bulkheads as I had remembered but several smaller parts. In addition to the one pictured, he made a similar part that was a little smaller.
After looking at my old bulkheads I would have to agree with Del, the curves required would be next to impossible to recreate without proper tooling. The aluminum used in the bulkhead is much thicker than what is used in the above part.