Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle - Stab

How to keep the Cessna 170 flying and airworthy.

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c170b53
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by c170b53 »

Canav8; I did not see your last post when I last posted but readin your post I'm thinking the engineers were likely amongst the workers. The mod would not be stealth work IMHO but like my last post, that is just my pitch.
Jim McIntosh..
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by Showboatsix »

What makes the slotted holes unairworthy? That should always be the question. Is there insufficient edge distance? A close eyeball would easily tell whether the holes were milled. Hand drilling would not produce identical smooth holes with straight walls.

ANSWER:
It does not conform to "new part" factory standards. That would be like putting the wrong propeller on the engine, where is your approved data for that repair/installation?
Or installing the wrong spark plugs, or setting the engine timing to something other than published specs, I could list a hundred examples of what if's, but in this case we have a part that does NOT fit or conform to Cessna Factory specs, so without factory authorization, or an STC, a Service Bulletin to make the modified part legal, I would have to say that this part is in an UN-AIRWORTHY condition.

When Cessna says they have no record of this modification, and their NEW part comes with 4 holes drilled "round", I really doubt that some misguided well intending Cessna assembly worker took it upon himself to auger out the holes on the assembly line to make his job easier to install the stabilizer is highly unlikely!

So as the Cessna 170 Club has been confronted with this issue, and with your organization's influence with Cessna, I would think that they (elected officers) would get the straight facts from Cessna through their contacts and solve this issue, is it legal or not!

Since I was the one who brought this forum question up back in March, and the only information I have received is from my Contacts back at Cessna, which says the part does not conform to a new part standard, then I have no other choice but to flag this part as an UN-AIRWORTHY item and install a correct new Cessna part.

Unless proper documentation is provided that says this is an acceptable part.
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c170b53
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by c170b53 »

Sure, I mean if we only had one report of only one instance of this part not conforming to what Cessna NOW says is not in spec (although they likely may not have data from the build) I think your reasoning would be sound. But what answer from Cessna might be an easier, no liability answer, in lieu of doing non revenue producing research?
There's more than one report of this part having slots and the part seems to be surviving just fine. I guess if a person is concerned that a part that has years of inservice use might fail in the next 50 hours before the usual annual because Cessna now says ..er...that's not how we would make a new part, O.K. That's their call.
Personally I try fix problems or things that show they have performance issues. How do I know if there's a problem; inspection, reports of failure rates and AD's. This part seems to have slipped through the cracks or maybe it has been crack free? Performance has been good or we would have tons of posts on the subject. Remember we care about this plane whereas Cessna really doesn't produce parts for it anymore. No Ad's and I'm not aware of any sb's although I think Gary would be the in know for those.
Again SBS it's your call and you have seemed to have made it (which is better than sitting on the fence). But to be clear I'm not nor have I suggested that standard practices are ignored as suggested by SBS with his examples.
If we can get a poll of all the tails with this phnomena and tally the numbers of combined hours would that sway SBS's thinking?
In my aviation career I'm of the belief that In aviation, Its risk tolerance doctored with regulation, proof is in the time in service and performance. Today a simple version of that might be called flight testing.
Just curious how long have you been a test pilot with this unbeknownst issue with your plane :D ?
Jim McIntosh..
1953 C170B S/N 25656
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by wingnut »

Jim,
Your aircraft was the first one I had noticed the slotted holes. After having received the photos of the that the association owns, that made 2 out of 3 slotted. I had 3 other 170's and a Bird Dog in the hangar at the time. 2 of 4 were slotted. Since I noticed yours, that makes 4 out of 7 slotted (observed just since you were here). I like the slots.
All the slots are machined, and the same dimensions. These were not "slotted" in the field. They were slotted by Cessna. Why? I don't know for sure, but if anyone has ever noticed the gross misalignment of the rudder hinges, it makes a perfect common sense solution.
I can't buy into the idea that these slotted parts should be culled. Consider the loading; it is primarily in tension with pitch, and with yaw the load is first transferred thru the 4 aft vertical to stab attachment bolts/fittings which fasten to the upper flange of the horizontal aft spar. These slotted holes are where the 4 bolts fasten the lower flange of aft spar to the fuselage aft bulkhead. I could imagine a problem if the slots were sideways (left to right), but zero problems fore/aft.

We have lost a tremendous amount of information in the past generation about the how, what, when, and why certain things happened on the assembly line. Manufacturers were/are not required to get FAA (or in this case CAA) approval for minor changes to the type design. Just because a tech support employee now, (who was likely not even an itch when these planes were built) says he can't find documentation today doesn't mean it did not exist; more importantly, that said documentation needed to exist for this minor change at all, ever.
When I first noticed the slotted holes in Jim's plane, I was concerned only that it might be a field alteration attempt to accommodate an improper repair or installation. Even so, the machined holes looked nicely machined. So, before condemning or praising the idea, I did research. There is no problem unless you require a permission letter from Textron, or lack the ability to properly align all 3 rudder hinges as you torque the bolts, and shim the forward spar as required.
Del Lehmann
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by c170b53 »

Del is commenting on Jim Wildharber's plane, which is a very fine plane.
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by ghostflyer »

Wing nut has my total support on the concept and the events of past with Cessna . When I was rebuilding my Cessna the factory techno,s often told me about production changes that were not documented as they considered them to be minor . I was told about some 170b , the last one s on the assembly line having 2. Gearboxs fitted ???? There are aircraft with different rear windows . I have seen a 170a with a very heavy rear fuselage frame ,it looks original and nothing in the log books . So I keep,a open mind .
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by Bruce Fenstermacher »

And I should mention that Cessna is not the only company who's current employees don't have all the answers as to how they built their product.

Continental tried to tell a member by his serial number, he had a engine he didn't. They insisted they could not reissue a data tag. Wasn't until our Association toured Continental at convention and George found and talked to a person at Continental on our members behalf. I'm not sure if the person George talked with at Continental knew how to decipher their own serial numbers or George educated them, but our member got the correct data plate from Continental after being told they wouldn't issue it.
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by hilltop170 »

I checked 1715D yesterday and the holes are round. 1951 C-170A s/n 20158. This part has never been replaced according to the logbooks.

It was not uncommon for Cessna to make changes and not document them. The 195 assembly line was moved late in the production run. The jigs were re-positioned with the horizontal stabilizer angle of attack several degrees different than before. The leading edge of the horizontal of later s/n planes is 5/8" higher than the older planes.

Mort Brown, Production Test pilot told me it was because the floor in the new location was not exactly the same elevation as the old location and the millwrights who set the jigs just bolted them down to the new floor without surveying-in the exact elevation like they should have. Mort said they determined what had happened only after the production test pilots noticed a performance difference with the later planes.

Cessna made the decision to NOT correct the problem (probably because they knew production would soon cease) and it was never documented in the records.

So if the 170 vertical stabilizer bracket holes were modified to slots by Cessna to make things easier to assemble, it is easy to imagine. Who knows, maybe the 170 assembly line was also moved at the same time and the 170 jigs might have been set-up incorrectly (like the 195) building-in an error that was never corrected. If slotting those bracket holes was the easiest solution, it's also not hard to imagine why Cessna did it and never documented it.
Last edited by hilltop170 on Fri Oct 14, 2016 5:52 pm, edited 2 times in total.
Richard Pulley
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by bat443 »

N9174A, 1949 170A serial # 18935 has the bracket with the slotted holes, no record of ever being changed and appears original.

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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by hilltop170 »

Well, that blows my theory!
Richard Pulley
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1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by c170b53 »

I like Del's theory (heck I liked Richard's as well :D ). :D
Jim McIntosh..
1953 C170B S/N 25656
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by c170b53 »

Looking at the rudder, (my thought/theory/just wondering :D ) like a slow-mo accident, look away if you're MX squeamish) you'd think you could shim out a misalignment either way between the lower rudder hinge and upper hinges. The holes appear to allow the HS to be moved forward provided there's sufficient space between the HS forward spar and the fuselage bulkhead. There's shims to allow adjustment / movement and the shims as well take up the gaps but if the stab was brought Fwd, wouldn't that change the amount of elevator throw? There's blocks to adjust the throw limit but what would increase the throw ?
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by wingnut »

c170b53 wrote:Looking at the rudder, (my thought/theory/just wondering :D ) like a slow-mo accident, look away if you're MX squeamish) you'd think you could shim out a misalignment either way between the lower rudder hinge and upper hinges. The holes appear to allow the HS to be moved forward provided there's sufficient space between the HS forward spar and the fuselage bulkhead. There's shims to allow adjustment / movement and the shims as well take up the gaps but if the stab was brought Fwd, wouldn't that change the amount of elevator throw? There's blocks to adjust the throw limit but what would increase the throw ?
Jim, you nailed it! Yes, the fore/aft position of the tail feathers will change the symmetry. I've not personally observed this myself, but I did have several phone conversations with a fellow a few months ago. I think he was in Alaska or Canada. He could not get proper elevator travel, and I suspect the symmetry of the the horizontal stab in relation to the fuselage was a factor. It could have been something else. I ask him to call me back when he figured it out, but thus far no info.
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by c170b53 »

Del, You understand what I'm thinking but gee wouldn't there be an easier way to make this adjustment.? So as much as I like my theory, I don't understand why the fitting can be found on various s/n 's in a somewhat sporadic fashion. We might find it easier to determine the why if we could create a map of the serial numbers and the type of holes in this fitting from a majority of members. With that info we might better understand the why and if the change meant some other form of change that goes hand in hand with each hole type.
My tail is apart right now, I might try playing with it to see what the real world results are of moving the horizontal stab forward. Anyone have dimension's of the slot?
Jim McIntosh..
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Re: Need Fig.25-24, p/n 0512108-5 Bulkhead Assembly Angle -

Post by c170b53 »

Digging in and digging out :D ( Yes Gary I might have to yell for a smaller shovel :oops: )
Back to this post http://www.cessna170.org/forums/viewtop ... tor+travel
Swixtt could you have a look at your rear horizontal stab 's lower aft attachment point and advise whether those (your) attachment holes are elongated ? In trying to solve the mystery of some holes elongated and some not, I tried moving my stab fore and aft and as Del and I thought it's obvious it changes the pivot point of the elevator aft bellcrank in a big way and thus will affect the elevator travel.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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