I am having the side panels remade for my '57 C180 due to cracks and general ugliness. I have a local metal shaper that is a wizard with sheet metal but I know 2024T3 is tough to work with on complex curves. He is working on them know using T3 and they are coming along but they are proving to be a bit difficult.

My question is this: Does anyone know what Cessna used for the cowlings? 5052? 3003? Did they use 2024-0 and heat treat it after forming? Or is is 2024T3? Anyone know?

Most likely not 2024. After looking through some reference material, 2024's elongation to failure is about 8% and 5052 is closer to 25%. I don' t know for sure but I think 5052 is more likely to be your material.

I've talked to a couple others and they believe it is most likely 5052 also.

Darinh wrote:I've talked to a couple others and they believe it is most likely 5052 also.

6061-0 formed and heat treated to 6061-6 . Repairs or replacement will be done by at least a appropriated airframe mechanic =A&P .What part are you trying to repair ? Selkirk has the cowling in Fiberglas from nose to firewall . They ALL crack around the forward edge . There are service Bulletins about cracking on other sections -DO NOT WELD !!!! I realize they are expensive but that's how it is.

Repairs or replacement will be done by at least a appropriated airframe mechanic =A&P .What part are you trying to repair ? Selkirk has the cowling in Fiberglas from nose to firewall . They ALL crack around the forward edge . There are service Bulletins about cracking on other sections -DO NOT WELD !!!! I realize they are expensive but that's how it is.

Thanks Bill,
The repairs will be done by me under the careful watch and approval of my A&P/IA. The repairs are just flush panels to replace small areas that have cracked. And yes I know Selkirk sells fiberglass cowlings but I don't have $8000 to spend for a one when I can repair mine for less than $200. Maybe sometime down the road but not now.

So here's the question: Why is 6061-0 used (heat treated to 6061-6 after forming) and not 2024-0 (which could also be treated to the T3 condition)? I am not a metallugist but aren't the characteristics of 2024 superior to 6061?

Darinh wrote:Why is 6061-0 used (heat treated to 6061-6 after forming) and not 2024-0 (which could also be treated to the T3 condition)? I am not a metallugist but aren't the characteristics of 2024 superior to 6061?

2024 corrodes significantly easier than 6061- it is really noticeable. 5052 is better than either for corrosion resistance. 2024 in any temper is more crack prone, but it is quite a bit stronger (50% more, roughly) than 6061-T6. 5052-H38 is workable, is as strong as 6061-T6, but you definitely cannot anneal or heat treat it, and if you draw or bend it, you need to watch it closely.

If I were designing it from scratch, I'd design it with 6061 (for corrosion and fatigue). I'd simply use a thicker gauge to beef it up. That being said, 2024 or 6061-T6 or 2024-T3 or 4 would work fine, but I might alodine the part or just the holes to help out on corrosion if I used 2024 (it's generally al1000 clad to prevent corrosion).

6061 also buffs up really nicely-2024 corrodes/dulls pretty fast. 6061 holds alodine, while 2024 can be a challenge. Both paint well, of course. All of them have similar elasticity and mass for all intensive purposes, so you don't have to worry about that.