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Stainless steel tubing for giant scale PA18 SuperCub

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Old 01-08-2012, 10:34 AM
  #1
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Default Stainless steel tubing for giant scale PA18 SuperCub

Hi all,

I started a giant scale (1/3) PA18 project with the fuselage build from stainless steel tubing. Like planes from Graeme Mears and Paolo Severin. I already did my own plans using the original Piper drawings as a source. And I also did a first "test frame", (1/3.85) but it turned out that there are no good engine options and for scale build it would be better to go with 1/3.
Anyhow, my problem right now is to find a supplyer for the thin walled (outer diameter sizes 0,118” to 0,354”, wall thickness 0,01” or 0,02” for the most stressed out parts) stainless steel tubes. The ones for my testframe came from Paolo Severin but this is not a good (because to expensive) solution for a complete and bigger frame.
It is easy to find stainless steel tubing (MacMasterCarr e.g.) but they don't offer tubes with the thin wall, some industrial supplyer only wanna sell 100 feet or more, which is a little bit to much....

So maybe somebody here can help with some information or knows a shop where I can get thin walled stainless steel tubing ?

I am thankfull for any advice or help.

Chris


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Old 01-08-2012, 10:45 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Nice workmanship.

Rafeek
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Old 01-08-2012, 10:47 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Beautiful work, Cris
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Old 01-08-2012, 10:52 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Very nice work[8D]

How about buying the 100 foot lengths and then sell the excess to other RC builders at your cost plus a little for your time and effort? Win - win?
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Old 01-08-2012, 10:57 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Check out www.onlinemetals.com
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Old 01-08-2012, 11:04 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Suggest that you check with Aircraft Spruce or perhaps other homebuilt aircraft suppliers.  They have quite a bit of tubing available, although very limited in the sizes that you are looking for.  I would also seriously recommend that you consider using 4130 or even 1030 steel as opposed to stainless because of cost, availability, and ease of fabrication.
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Old 01-09-2012, 05:46 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Thanks for your input guys,
I already checked Onlinemetals and Aircraft Spruce without success. Yesterday I found Eagle Stainless, the have all the stainless steel tubing I need. Let's see, if they are willing to do smaller trades.

Chris
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Old 01-09-2012, 06:00 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub


Quote:
ORIGINAL: pilotarix

Thanks for your input guys,
I already checked Onlinemetals and Aircraft Spruce without success. Yesterday I found Eagle Stainless, the have all the stainless steel tubing I need. Let's see, if they are willing to do smaller trades.

Chris
Just curious. Why stainless? FS AC use 4130 which I understand is much easier to use. Sincerely, Richard
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Old 01-10-2012, 03:45 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

@Richard

I do not have the best answer to your question because regarding the material I only follow what others have done before me.
I do belive that you do not get 4130 alloy in the size you will need for an RC fuselage. It is very difficult to weld such thin material, so we use brazing with silver solder (56%), instead of welding. Remaining flux in the tubes (you can not avoid that) from the soldering process would cause rust in "normal" steel tubes, not so in stainless steel. I am not sure, but stainlees steel might also be lighter than normal steel.
Check also http://www.paoloseverin.it/techno/index.html and http://www.hvrcf.org/Misc%20Documents/Mears.pdf for further information.

Chris
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Old 01-10-2012, 04:52 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Good answers. I guess I was thinking of the articulated Cub landing gear made by Robart, et al, that I think are 4130. But I am just speculating. Good luck.

Sincerely, ichard
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Old 01-10-2012, 06:46 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

@Richard

that is exactly right, the Robart landing gear is made from 4130 alloy "aircraft steel" and it is welded, not brazed. I checked the possibilities for welding stainless steel instead brazing. In areas like engine mount wing hinges or other connections I would feel much more comfortable with real welding than brazing. Unfortunately it is not that easy to weld thin stainles steel, which does not mean that it is impossible. I already talked to some people who are experienced welders and they all agreed that you will need a lot of experience and high quality technology. For further information check google "micro TIG welding".
So it is easy for a company like Robart to have the technology and experienced people, but I would also asume that the tubes of their 1/3 landing gear are not so thin walled.

Anyhow, another problem is the material, the actual reason for this thread. I have never seen 4130 alloy tubing with the size of 13/32 or below, which would be the largest diameter used in 1/3 aircraft. BTW the original tubing for the full scale landing gear is 1.25". Certainly you can get every material you want, unfortunately sometimes it is unaffordable because you must buy 1000 feet or more at once.

I still appreciate every hint for a stainless steel tubing supplyer in the size mentioned above, who is willing to make smaller trades also.

Chris
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Old 01-10-2012, 09:18 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

I do have some 4130 in my garage that is 3/16X.028 and some 1/4X.035 that I have used in fabricating aircraft stuff.  I have welded 4130 with both oxy-acetylene and gtaw processes.  Stainless steels will require gtaw only.  If you braze the structure, you will not be able to take advantage of the full strength of the steel alloys at the joints.  If you are trying to learn, I would suggest oxy-acetylene because the equipment cost is a little cheaper.  I admire your desire to be perfectly scale, but 3/16" converts to a little over 1/2" in 1/3 scale.  I have built several full size airplanes and have rarely used any tubing as a structural member that is less than 5/8".  Once covered, it will be almost impossible to tell the difference anyway without a micrometer. 

It seems as if the major road block to using stainless is the availability in less than 1000 ft purchases.  I once needed some 2.5mm GL-2 plywood.  The minimum order quantity was significantly greater than my needs.  I asked the supplier who some of his customers were and then contacted one of them and asked if he would sell me a few sheets of his GL-2 plywood.  Turns out that this customer was more than willing to share a few sheets with me and only charged me what he had paid for the material.  I got lucky by running into this guy.  Good luck to your pursuit as well.
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Old 01-12-2012, 08:30 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Chris,

Have you checked smallparts.com?

I'm just getting ready to start myself on Graeme's Super Cub, but wanted to use the Nelitz construction to minimize some of the welding.

I notice you're in Hummelstown, I'm in Easton....

Gordon
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Old 01-12-2012, 03:11 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Hi,

Quote:
Have you checked smallparts.com?
never before, but now I did, thanks for the info.
Interesting, a lot of stuff, a good source if one or two pieces of tubing are needed. Even though I can't find the perfect sizes (wall thickness) for the small tubes 0,2" OD. Unfortunately, compared with Eagle stainless more expensive, therefore not a solution for a whole project, but as mentioned above, definetely a solution to get some pieces quickly.

I have never heard about the "Nelitz construction" do you have a picture ? Is that the construction without a "turtle deck" ? Please post some infos about the Graeme's Super Cub, do you got the plans or is there a kit ?
Have you seen the kit from Paolo Severin (http://www.paoloseverin.it/page72/page72.html), maybe not that nice like the Graeme's Cub, but close.

Chris
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Old 01-13-2012, 06:21 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Hey Chris,

I should have been more specific. The Bob Nelitz 1/3 scale J-3 plan was issued in either 1981 or 1982 and is recognized as the most accurate of the J-3 plans. Construction uses a welded cage to carry the wings, and through the cabin. Construction is traditional model construction using dowels to simulate tubing. There are a few build threads going at the moment using the Nelitz plan set.

Fast forward to Graeme's magnificant Super Cub. His construction replicates the full scale using stainless steel tubing, silver brazed the same way you did. What I mentioned earlier was that I wanted to use Graeme's outline, but use the traditional construction as indicated on the Nelitz plan to minimize the welding. On Graeme's plan he references tubing size and wall thickness, available from either McMaster Carr or Smallparts.

How heavy is your airframe? Beautiful work....How did you radius the tubing before brazing?

Hope this helps.

Gordon
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Old 02-09-2012, 10:54 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

I recently finished gas welding a 1/3 scale J3 Kitten. I redrew the original factory plans in autocad and then printed at 1/3 scale. Nickel bronze welding rod was used to weld 3/16" and 1/4" mild steel brake line, about .028 wall. Complete steel fuselage with all tail surfaces, tube motor mount and landing gear weighs about 8 lbs.
Jim
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Old 02-09-2012, 11:48 AM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Quote:
ORIGINAL: pilotarix

Hi all,

I started a giant scale (1/3) PA18 project with the fuselage build from stainless steel tubing. Like planes from Graeme Mears and Paolo Severin. I already did my own plans using the original Piper drawings as a source. And I also did a first ''test frame'', (1/3.85) but it turned out that there are no good engine options and for scale build it would be better to go with 1/3.
Anyhow, my problem right now is to find a supplyer for the thin walled (outer diameter sizes 0,118” to 0,354”, wall thickness 0,01” or 0,02” for the most stressed out parts) stainless steel tubes. The ones for my testframe came from Paolo Severin but this is not a good (because to expensive) solution for a complete and bigger frame.
It is easy to find stainless steel tubing (MacMasterCarr e.g.) but they don't offer tubes with the thin wall, some industrial supplyer only wanna sell 100 feet or more, which is a little bit to much....

So maybe somebody here can help with some information or knows a shop where I can get thin walled stainless steel tubing ?

I am thankfull for any advice or help.

Chris
Chris,

Try Ray's Dies at http://www.raven-ind.com/tubing.htm.

Look under Tubing to see a table of stock sizes they carry. They might be able to make a specific size you seek...but custom will be pricy

These are formed and welded from flat stock. But they also make seamless
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Old 02-09-2012, 01:25 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub


Quote:
ORIGINAL: motorhd

I recently finished gas welding a 1/3 scale J3 Kitten. I redrew the the original factory plans in autocad and then printed at 1/3 scale. Nickel bronze welding rod was used to weld 3/16'' and 1/4'' mild steel brake line, about .028 wall. Complete steel fuselage with all tail surfaces, tube motor mount and landing gear weighs about 8 lbs.
Jim

How about some pictures? Thanks.
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Old 02-09-2012, 06:54 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Hi,

@Jim
If you really talking about welding and not about brazing, this must have been a tremendous amount of work. Brazing those tubes is easy and quick but welding.....
Anyhow, I would really appreciate more information, especially about the welding rod you used (diameter), and some pictures, that would be perfect.

@Mattk
thanks for the very interesting link, I think I will get a quote for scale "Piper channel" and some other stuff I will need for the horizontal and vertcal stabilizer.


Chris
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Old 02-09-2012, 10:11 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

I stand corrected, it is brazing. I made fillet brazed joints using 3/32" dia. 10% nickel bronze 130,000 psi hi strength brazing rod. The melting point is about 1800 degrees. Harris stay silv white brazing flux was used. This is the same type of rod used to weld bicycles and British race car frames like the Lotus. I fish mouthed the tube ends with a small round file the same size as the tube. The joints look good and should be strong because fillet has such a hi tensile strength, probably almost as strong as the mild steel tube . I will try to post some pictures.
I mig welded 2 full size J3 kittens in the late 80's, I have more time in building this 1/3 replica then I did the real ones.
I obtained the rod from n.juppenlatz company inc. in Portland, Oregon toll free 866-839-8585
type FC-1800 Hitensile brazing rod 3/32"

P.S there is some discussion about this type of brazing on vintage race car and bicycle forums. You might notice that some times it referred to as nickel bronze welding.
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Old 02-10-2012, 03:28 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Here's some pics.



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Old 02-10-2012, 03:49 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub


@Jim
Thanks for all the information, I used basically the same technic, but I used 56% silver brazing rod instead the nickel bronze rod, but I also used Harris Stay-Silv white brazing flux. I am wondering if this nickel bronze brazed joints have more strength than those with silver? My fear is that brazed joints for the engine mount may not have enough strength to withstand the engine vibration.
I tried to get this nickel bronze rod at AirGas today, but the don't have that in stock and I was wondering if the guy behind the counter did understand what I was talking about. They had some bronze welding rod with silicone, but those seems to be more for welding. Anyhow, I hope I can order some online to test it.
What torch did you used, I use a Smith jewelers torch with oxygen and MAP pro gas, unfortunately there is no MAPP gas anymore. I look forward to see your pictures.

Chris
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Old 02-10-2012, 04:58 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Hi Chris,
It looks like the nickel bronze has about twice the tensile strength of the 56% silver rod. The nickel bronze has a much larger plastic range,meaning it is easier to control and makes better fillet welds. I use a small set of B tanks, oxygen- acetylene, the type the refrigeration guys use.
The torch says victor c1000
I just talked to Neal at the number in the previous post, and he still has the brazing rod mentioned.
Jim
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Old 02-10-2012, 07:53 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Jim,
weird, I wrote my posting, send it and went for dinner, I could swear that your post with the pictures wasn't there at this point of time. We must have sent our postings at the same time.
I really like what I see, your brazed joints looking great, and your engine mount is exactly what I also wanna do .... scale. Great job. I would asume the firewal is from aluminum, what kind of engine is that, gasoline 4 stroke?
I will call the "n.juppenlatz company inc." company on Monday maybe I can order some there.

Many thanks for the pictures and the information!

Chris

P.S. I bet, that a lot people here would appreciate it, if you keep us posted about your great project, like I will do with my project, thanks.


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Old 02-10-2012, 08:22 PM
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Default RE: Stainless steel tubing for giant scale PA18 SuperCub

Thanks Chris,
The engine is a OS FT300 twin. It is an almost exact 1/3 replica of a 1/2 Volkswagon engine which is what the original J3 Kitten used. It runs great on 15% glow fuel cut with 50% methanal and spark ignition.
I wonder if we should share this thread or start a new one?
Jim
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