The International Cessna 170 Association

So I get a text from Jim Wildharber asking be if I have a good part p/n 0512108-5 Bulkhead Assembly Angle - Stabilizer attachment. I say that's really strange whats wrong with it. He says the holes are worn (slotted or egged out). I say that is really strange cause this is the second time in less than a month I have a member contact me for the same part for the same reason, egged out holes. What are the chances the same wild man with a file attacked the holes in two airplanes, and they be discovered within a month.

I tell Jim there is probably more to the story and that he should have Del figure out why someone would do this.

Well it turns out the Association also owns a part with egged out holes. The mad man with a file is starting to get around. Or maybe, just maybe Cessna made the parts this way.

I believe the consensus of Del and George Horn, who has the Associations part in hand, is yes, Cessna slotted the parts.

So how about we get everyone to go look at their parts and lets see how many slotted parts are in the field. Here are some pictures of slotted and unslotted brackets.

Those slotted holes sure look to be machined that way. There is even peeling paint on the inside of the slot in the close-up.

Might be interesting to know if the ones with slotted holes are found on 170's made toward the end of production.
It does seem like a slot would make a low-stress mounting more likely, minimizing stress on the bulkhead that the front of the stabilizer attaches to.

On both of the Cessna 170A's that I have rebuilt the Tail cones on they were round holes. But those slotted holes sure look factory to me.
Jim

Jim's plane is a '55 and the other Showboatsix has a '56 172 conversion. Bet this is a late model production change.

Well huh. Thinking this might have been a late production change to the part I looked at the A model IPC and compared it to the B model. Same part number including the -5. That is not conclusive but generally Cessna changed the dash number when a part changed at all.

Next I looked at the '56 IPC. Started to think ah huh, this was probably a change to accommodate both the old elevator and the new 172 design. But I can't find a figure that shows clearly how the rear elevator attaches in a early 172. What I found looks like this part or anything like it did not exist in a 172. Yet Showboatsix asked specifically about pn 0512108-5 in his '56.

The mystery takes a strange twist. I've now got to find an early 172 and look to see how they were built.

Bruce Fenstermacher wrote:Well huh. Thinking this might have been a late production change to the part I looked at the A model IPC and compared it to the B model. Same part number including the -5. That is not conclusive but generally Cessna changed the dash number when a part changed at all.

Next I looked at the '56 IPC. Started to think ah huh, this was probably a change to accommodate both the old elevator and the new 172 design. But I can't find a figure that shows clearly how the rear elevator attaches in a early 172. What I found looks like this part or anything like it did not exist in a 172. Yet Showboatsix asked specifically about pn 0512108-5 in his '56.

The mystery takes a strange twist. I've now got to find an early 172 and look to see how they were built.

My buddies 1956 172TD does not have a part like this at all, it is a casting the same as later 172's and the bolts that attache the stabilizer rear spar are installed fore and aft or longitudinally. Where as the 170's all have vertical attachment bolts. I have always found this interesting because the prototype 170C was converted back into a 170B after the project was completed. And I presume as there is no documentation that I know of showing how the Horizontal was attached on that airplane. I suppose it could have been either way. But would have required Cessna to convert the rear bulkhead after going back to the rounded empennage if it had been a casting.
I now have a mission to look at every 170 I see to see how it is configured holes or slots.

Just checked my 170 A serial number 19006 and it's only has round holes for attachment. As I have recently refitted my tail feathers due to SIDS inspection it was a very smug fitting all round .

[oops, smug means very tight . Aussie translation ]

I looked this morning 53B model 25501 has holes no slots.

Well, here's another data point. I was at the airport today so I crawled under and checked the attachment on my plane (a '52). All four holes are slotted the same way. See below which is the best photo showing the elongation. It's just one of the bolts/holes. The others are similarly slotted. Note that in Bruce's photo above showing the two different attachments (one with round holes and one with slotted holes), you can see that the holes of the one with round holes are located near the edge. On the one with the slotted holes, the elongation starts at this same location and projects inward from the edge. On my plane, the bolts are located in the side of the slot closest to the edge -- where they would be located if the version of the attachment without slots was used. They are not located in the elongated portion, which I think you would expect if the elongation was caused by the bolt. One other thing: when I first crawled under the plane, there was loose paint around the nut in the attached photo covering the elongation. I carefully looked at it to see if I could detect any evidence of movement and didn't see any. I used my finger nail to remove the paint (some of which was over the elongation) to reveal and better see the elongation. (The photo was taken after the paint was removed.) If the elongation were caused by the bolt, I would not expect to see paint around the nut in that area, especially over the elongation. The plane was last painted in the 1980's, so I'm guessing that the attachment has been that way since at least that time. (Yes, repainting my plane is on my list.) (If you are wondering about the unpainted nut on the left in the photo, according to my log, it was installed during the 2012 annual when some corroded hardware in that area was replaced. I choose the nut I photographed because it appeared to be original. In other words, the paint on it was not disturbed -- until I disturbed it).

1955 sn 26541:

Here you go Bruce, My 1953 P/N0512108-5 Stab Blkhd fitting has holes not slots.

Dennis

170B SN25400 - holes no slots.

As a base point, my 1955 170b is serial no. 26958. Pictures, posted by Bruce of the slotted holes, were taken by Del when he started maintenance work.

53 S/N 25656 holes,
Obviously bolts are in tension, so I wonder if it's a Cessna fix for a build variance between the stabilizer and the distance to the aft bulkhead forward of the stab ?