1948 170 Rebuild

[Stick.Back.Aviation]

I do like the idea of being able to see the rivet and know what a good smooshed tail looks like. Likely if it looks good no one will ever know the difference. I am waiting for some paycheck money to buy a bunch of aluminum. That is my hang up for the wing. Any of you guys ever had to reskin a door? it looks like they shot all the rivets around the perimeter of the door and then folded of a thin strip of metal that the seal fit in to. Only problem there is it covers the rivet tails. I can take all that off but going back together I can't figure out how to replace that door seal holder strip around the whole door. Any ideas there?

[GAHorn]

I’ve rec’d an email from a trusted source which informed me that Cessna considers the skins beneath the fuel tanks to be a highly-stressed area and recommended counter-sunk rivets in that area.

[c170b53]

Any of you guys ever had to reskin a door

Yes,I have as likely those who have had to replace the upper hinge. My doors (53B) did not have seal retainers, the seal is just glued in place. The door skin is easy, if I could do it

[ghostflyer]

We had to do a repair on the undersurface skin of a wing of a cessna 172 C [I think it was a C ]. It had a gouge of about 10 to 12 ins in its undersurface and about 1 in deep . This was due to some one trying to jack the aircraft using the tie down ring on the strut. The jack went for a walk. The damage was then bondo filled and painted . It was during a 100hrly it was picked up. Cessna was contacted for advice [paid]. The recommendation was made using a single sheet of aluminium from wing root to the strut. Due to corrosion prone area in the hat section it was suggested we use 6061-T6 and go to the next size thickness. [can’t remember the thickness. ] . The rib on the outboard side of the tank had to be replaced with new . The original rib was badly dented and had started to crack also. What surprised me was the price of the new rib was less expensive than I expected . Cessna was totally clear that the hat sections could not be glued ,screwed,or nailed, or bolted . Countersunk rivets had to be used. The hat sections are part of the stress structure of the wing. THEN another panel of aluminium is then riveted on top of the hat section and this panel having edges riveted to the inboard rib and the out board rib of the tank. Cherry max rivets[countersunk] were used to attach it to the hat sections . It’s my belief this mod was incorporated in later production models . New hat sections were used [PMA] ,some company in Texas made them. All areas were zinc chromated .
DISCLAIMER. The above advice was for entertainment and interest purposes only . Please comply with all information in FAA and aircraft manuals and seek the services of a A/P and a IA when carrying out repairs and modifications .

PS. All the paper work and drawings have been lost due to floods,I am only relying on memory

[ghostflyer]

Just come from a meeting of a number of aerospace engineers and some i have worked with for many years . We were discussing Cessna repairs and drawings from Cessna . It appears that Cessna paid advice from engineering isn’t consistent with their structural repair manuals . [This is the reason of the meeting due to a job being completed now with major corrosion in the fuel cell area and main spar of a 172. ] I mentioned about the repair that we did on the L/H wing of a Cessna 172 about 15 years ago. . This was the aircraft that some clown tried to jack up a 172 using the tie down ring as a jack point . I was hoping my colleague that was working with me at that time might have some of the drawings . He even remarked he recalled that counter sunk rivets had to be used on the undersurface of the wing holding the hat sections in place. It took 3 persons to counter sink the undersurface of the wing panel. There was a section of information highlighting what fasteners to use and specifications on the drawings .
There was five of us now looking at another undersurface wing of a 172 in my hangar and they had used normal mushroom rivets . So I looked at my 170a and it has mushroom rivets . we can’t use the corroded wing as an example as it’s been repaired so many times and no documentation . There was a 2000 year 172 on the flight line and the undersurface is smooth with no rivets heads showing.
I didn’t go out to mislead any body ,i was just recalling what we did on that job.

[n2582d]

I’ve rec’d an email from a trusted source which informed me that Cessna considers the skins beneath the fuel tanks to be a highly-stressed area and recommended counter-sunk rivets in that area.

George, Was this "trusted source" referring specifically to the 1948 C-170? I would think the loads on that skin would vary a lot depending if we're talking about a fabric wing, a metal strut-braced wing or a full cantilever wing like the C-195. Wouldn't the primary load on that '48 C-170 skin be the weight of the 12.5 gallon fuel tank? Here's a back of the napkin calculation of how much that skin should support (I'd appreciate if the engineers out there would correct me if this is total BS): 12.5 gallons X 6 = 75 lbs. + 10 lbs. ??? tank weight = 85 lbs. X 4.4 g load limit for utility category = 374 lbs. X 1.5 g safety factor = 561 lbs. ultimate load. My other question is why countersunk rivets? I've always been under the impression that universal head rivets are stronger than equivalent size flush rivets -- at least when the skin has been countersunk. The C-170B uses four hat sections under its larger tank. They are fastened with AN470AD3 universal head rivets spaced 4" apart on each flange. One reason to replace the spot welds with flush rivets might be so that, when sanding the silver coat(s), one doesn't sand through the fabric over the head of a universal head rivet. How thick is the lower skin, under the tank of a '48 C-170? On the C-170B it's 0.020" -- too thin to countersink. The skin and the corresponding hat section would have to be dimpled if replacing the spot welds with flush rivets. What size and spacing would one use if installing flush AN426AD rivets in place of spot welds? I don't think one can assume a rivet has the same strength as the spot weld it replaces. One would have to use the tables found in section 8.2.2.3 "Spot and Seam Welding" of MIL-HDBK-5J to figure that out. My opinion is that one would have to get DER approval for such an alteration. Probably easier to try and duplicate the original structure with spot welds assuming you could find some place to do that.

Here's some additional trivia on the subject of replacing spot welds with rivets.

[cessnut]

AC43.13-1B tells us not to weld 2024.

[GAHorn]

Gary, your question is a good one if confined to the thread topic….but this thread has “drifted” to other models than the ‘48…(and your own response addresses other models)… witness Miles post in which he recommends a shop with a “jig”….that will not be applicable to a ‘48….owned by a shop who will not work on any “ragwing” Cessna. Did you question Miles post?
My “trusted source” is an aeronautical engineer who read this thread and privately offered his experience as opposed to my recommendation of structural adhesive. I imagine he was concerned that my comment might be considered on subsequent models and he indicated he’d received contradictory information directly from Cessna, so I posted his thought on the matter, expecting anyone working on this repair might investigate further than this discussion thread.
Frankly, on a ‘48 ragwing, if it were mine, I’d still consider modifying with adhesive.

[n2582d]

AC43.13-1B tells us not to weld 2024.

I was wondering if that only applied to gas welding but paragraph 4-89 (d) seems to be more of a blanket policy. It says not to weld 2024 and 7075 aluminum alloys "because the heat from the welding process will cause severe cracking." It's interesting, in the section of AC43.13-1B about spot welding, it says, "Refer to MIL HDBK-5 for joint construction and strength data". Here's a table from MIL HDBK-5J which shows that it is ok to spot weld cladded 2024 but not bare 2024:

Click to Enlarge

Cessna spot welded aluminum on numerous parts. I have no idea if these parts -- including the skin under the fuel tank in the '48 and the associated hat sections -- are 2024 or some other aluminum alloy.

[n2582d]

Gary, your question is a good one if confined to the thread topic….but this thread has “drifted” to other models than the ‘48…(and your own response addresses other models)… witness Miles post in which he recommends a shop with a “jig”….that will not be applicable to a ‘48….owned by a shop who will not work on any “ragwing” Cessna. Did you question Miles post?

As I read it, the thread drifted from discussion about replacing the gearbox in a '48 to corrosion on the skin and hat section under the fuel tank of a '48 C-170. The topic was gearbox replacement, not wing skin corrosion, when the suggestion of a fuselage jig came up. I had no idea Del "will not work on any 'ragwing' Cessna," but I did see that Miles said the jig was a Cessna factory jig. Are you saying Del doesn't do fuselage work on aircraft with aluminum fuselages which have fabric wings or that Del doesn't do fabric work? I'm surprised Del doesn't have the ability to fabricate the "Blue and white striped attachments ... used with the '48 Cessna 170" as seen in figure 5 of Service Kit SK 8053-1.

Click to twice Enlarge

[GAHorn]

Gary, your question is a good one if confined to the thread topic….but this thread has “drifted” to other models than the ‘48…(and your own response addresses other models)… witness Miles post in which he recommends a shop with a “jig”….that will not be applicable to a ‘48….owned by a shop who will not work on any “ragwing” Cessna. Did you question Miles post?

As I read it, the thread drifted from discussion about replacing the gearbox in a '48 to corrosion on the skin and hat section under the fuel tank of a '48 C-170. The topic was gearbox replacement, not wing skin corrosion, when the suggestion of a fuselage jig came up. I had no idea Del "will not work on any 'ragwing' Cessna," but I did see that Miles said the jig was a Cessna factory jig. Are you saying Del doesn't do fuselage work on aircraft with aluminum fuselages which have fabric wings or that Del doesn't do fabric work? I'm surprised Del doesn't have the ability to fabricate the "Blue and white striped attachments ... used with the '48 Cessna 170" as seen in figure 5 of Service Kit SK 8053-1.

Cessna Fuselage Jig.png

The thread is Titled “1948 170 Rebuild” Not restricted to geabox, wing, fuselage, wing tanks or any other specific item I don’t believe. I thought my comment was pretty clearly in regard to wing/fuel-tank area repair and didn’t think my comment would be misinterpreted so I mentioned that Del does not work or ragwing airplanes because he specifically has told me so. If you want to know if he’ll work on a fuselage of a ragwing I guess you’ll have to ask him directly. I see your point that it (the fuselage) might not be something he’d refuse.

[Stick.Back.Aviation]

Still monitoring all transmissions very closely. Traveling a lot for work = less time to work on plane but more money (soon) to buy parts. Liberated the door skin from the door frame and am desperately trying to find .032 locally to avoid the $120 shipping, although at this point I may just pull the trigger and get a couple sheets to soften the shipping blow. I am going to need wing ribs as well and have been halfassedly searching for replacement wings. Another conundrum in this very involved rebuild.

Does anyone know why Cessna loves flathead rivets? They seemed to be used in critical areas... cant find anything in the IPC or online about them other than they may just be the rivets they used. Does not seem like a good answer. Planning to move the fuselage inside this Friday. That will definitely warrant another picture.

Thank you gentlemen for staying interested this long!

[cessnut]

That is interesting about the bare vs. clad. It might relate to corrosion. Cessna did spot weld 2024, and in some critical areas like vertical fin spars. I have looked into this in the past and was informed by people much more knowledgeable than me that to do it properly requires equipment not accessible to most of us.
I don't know why they used those flat rivets. AN470AD rivets should constitute a suitable replacement. Also watch out for rivets that appear to have a #4 head but have a 3/32 shank.

[ghostflyer]

While there was a heap of thread drift [I am guilty ] the subject matter i was referring to was about the repair of the undersurface of a 172 C wing, We were using 6061 T6 alloy . But the next size up from standard and dimpled with a press. Our instructions came from Cessna engineering. why Cessna wanted counter sunk rivets used ??. The hat sections are not only to support the fuel tank but stiffen the box section of the fuel tank enclosure. The structure around the fuel tank is a heavily stressed due to wing loading. Please note the modifications that Cessna has done over the years to this area and the trailing edge spar also. With regard to the recent corrosion issue that was mentioned in my second post [another aircraft ] of the hat section and skin ,spars being corroded that wing was scrapped .
Personally I will not think about or look at a Cessna 170 rag wing . I do not have the knowledge or experience on that sort of structure .

[Stick.Back.Aviation]

I was finally able to get everything inside! Now I will really be able to roll my sleeves up and make some progress. Thinking the fastest way to get this project done is to start buying scratch off tickets ...

~Tyler Z