Suitable steel for all brackets etc.

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misterpeter

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Hi everyone out there! I have a question :) is 1.4301 austenitic stainless steel usable for the hundreds of brackets and connections in a wooden aircraft construction - in this case a cub? The reason I ask is that I can find specs for the chrome-moly tubing everywhere, but not a mention of the ‘requirements’ for these parts. My job involves this material almost exclusively and since I’m running the 4kw laser-cutter at the moment and can use a 70-ton brake for the bending; I’m otherwise actually employed as a TIG-welder, so it would be very ‘convenient’ for me if this material is allowed in aircraft construction… just a thought!
Look forward to your expert opinions! Peter
 

pjphilli

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My short answer... YES. This link includes some basic properties, other equivalent names (e.g.: 304 stainless), scroll down and get to properties you can compare with chrome-moly.

 

misterpeter

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Hi and thanks for the reply :) I am aware of the broad properties of this material, but since it is not strictly used as a structural steel, I am concerned that it might not be allowed by the FAA (or whoever lays down the regulations!) for this purpose, We all know how ‘particular’ they are about details like this! That thin-walled 4130 is the standard for tubular framework is well known, but as I said before, I haven’t been able to find directives or specs regarding requires grades of steel for fittings. Is there a list somewhere of what is allowed for aviation purposes?? Believe me, here in Germany, a list or table would be necessary! :)
 

pjphilli

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As an example, reference the Fleetwings Sea-Bird from the 1930's made of stainless steel. Perfect for an amphibian flying boat hull design. First nuclear power plant I played with was 304 austenitic stainless for the reactor shell... as an experimental aircraft, you can use what you chose that best meets your design criteria, or comfort level. You should be able to easily determine by evaluating the properties of the metals any differences. I suspect you'll find they are insignificant for fittings in a wood framed aircraft.

 

TFF

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I’m saying it’s not a good material. It tends to crack. Good for a firewall or heavy gas tank.
 

proppastie

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Might want to check your local German inspection authority.....but I believe the original Cubs did not use 4130 ....not sure exactly what (1025 ?)......of course the original Cub only had 40 or 65 hp.
 

pjphilli

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Aft fuse is 1030 mild steel tube, cockpit FWD was fuse was only 4130. Think all misc fittings and brackets are 1030 with OEM. In my J5 could hang the airplane from a rafter by a single wing tank hold down strap :)
 

Dan Thomas

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Most homebuilts use 4130 sheet for the fittings. It has a 97,200 PSI ultimate and 63,100 yield.

The tensile strengths I find for 304 stainless are 73,200 ultimate and 31,200 yield. I sure wouldn't use it in place of 4130.
 

TFF

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There are similar European steels to 4130. We do not have access to them here so there is no way to ever figure out what is close. Is this “Cub” built like a Sopwith Camel or a Pietenpol?
 

misterpeter

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Well, that’s what I call a discussion! Firstly, to clear one thing up: I have no intention of substituting 4130 with 304 - that would be dangerous, I agree, especially for the tubing! However, I have never found it stated that 4130 should be used for the fittings! That is the main point of the question here.
The tendency to crack, I had not come across before, I must admit; I thought that being a metal that does not work-harden, that cracking would be unlikely? Keep the ideas coming, please and I will try to get to the bottom of this with the German powers that be and post my findings here, of course.
 

misterpeter

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Regarding how it will be built, I am not conversant with the differences in construction between the Pietenpol and Camel, so can’t comment on that. It will be built like a Super Cub!
 

misterpeter

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I must admit that I had not as yet considered aluminium of any kind for fittings and attachments, though I will be making the tanks and other non-stressed items in ally. Interesting idea, which would offset the weight disadvantage of a wood versus steel build, but I don’t think that it would work, especially where high tension and elongation and compression of bolt holes are concerned? I could be wrong, of course, so please correct me!
 

TFF

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I lifted this

Austenitic stainless steels can be produced to be very soft with a yield strength of about 200 MPa and they can be strengthened by cold working, which can raise the yield strength by up to a factor of ten. Unlike ferritic alloys, they can retain their ductility at cryogenic temperatures and their strength at high temperatures. Their corrosion resistance can range from regular everyday use to highly specified use such as in boiling seawater. Despite their superiority among stainless steels, austenitic steels have inferior resistance to cyclic oxidation compared to ferritic alloys and they are also susceptible to stress corrosion cracking. The endurance limit of austenitic steels is lower (~30% of their tensile strength) than ferritic steels (~50 - 60% of their tensile strength) which means they are more prone to fatigue failure.


Except for reading pre WW2 plans, I have never seen a regular homebuilt not specify 4130 for sheet. ULs sure, but not heavy planes. But what you are asking is really a simple engineering problem. Figuring out the stresses and matching the size of material you picked to pull it off. If it needs to be 1/2” thick, it’s probably not the best choice.
 

BBerson

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However, I have never found it stated that 4130 should be used for the fittings! That is the main point of the question here.
The steel is listed on the plans or factory approved drawings. Normalized or annealed 4130 or 1025 sheet usually.
Much easier to drill, saw, and weld and purchase in all sizes than stainless.
 

misterpeter

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I do have the choice to build as original in ‘metal’, and the welding is not a problem for me. I have not yet decided, but despite the weight and cost disadvantage of wood, it has other properties that make it more attractive to me: It is a lot ‘softer’ to fly and absorbs sound, vibration and shock a great deal better… regarding the stainless, I get it for scrap price and can cut, bend and weld at work, which would be ‘convenient’. My boss would kill me if I brought 4130 in to cut or work on!
 

Mad MAC

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The only issue with using stainless is that if it is welded, the region of the heat effected zone loses the strengthening gained by being cold worked. That issue can be accounted for in the part detail design. What hardness grades are you using, Aerospace 304 can come in annealed, 1/4 hard, 1/2 hard, 3/4 hard and full hard.

There are other European near equivalents to 4130, a couple i dealt with are 25CD4 and 15CDV6 (1.7734), the later being superior to 4130 but doesn't appear to be used in aerospace without heat treatment, post welding.
 

misterpeter

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If I were to build in steel, I would of course be welding the nearest equivalent… That I can do where I’m going to be building (not found a suitable workshop yet :( ) When I get the chance for a good going through the drawings, I will find out all about the fittings and which ones are needed for the chosen main construction.
My biggest problem, being now in Germany will be sourcing all the parts that I cannot make myself without special equipment… I am also an apprenticed foundry patternmaker, but I don’t want to go to those lengths - yet!
 

TFF

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What special equipment is needed to make a Cub? If there is some class of airplane that makes sense to do it in wood, that would be a good reason.

Once done, the traditional made one will always be worth more. You also can’t be as hard on a wood as a steel one. I have some internet Bucker Jungmann plans in wood. It’s uninspiring. Lots of show and no go. No Bucker for sure.

What wood would you build it from? The price of airplane wood is crazy and hard to get. I’m a wood fan for the right things, not for everything.
 
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