4130 vs 1020

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builderwannabe
Posts: 9
Joined: Mon May 13, 2019 8:05 pm

4130 vs 1020

Post by builderwannabe » Sat Sep 28, 2019 6:11 am

Gents, more seemingly simple questions here. The plans seem to call for a lot of 1020 steel for the metal parts of the plane(i.e. landing gear, cables, fittings,...) but it appears that now folks are using 4130. While I understand that material science has progressed a lot since the 1930s, is there a reason for the added strength in the 4130, other than the added safety margin( and wouldn’t Mr. Pietenpol have designed the parts with a safety margin). The reason I ask is 4130 must be TIG welded while other forms of carbon steel could be stick or wire welded. I really can’t drop 2k into a TIG setup when I promised my wife the plane would cost less than 15k.

Sean

tom kreiner
Posts: 35
Joined: Sat Feb 25, 2017 9:49 am

Re: 4130 vs 1020

Post by tom kreiner » Sat Sep 28, 2019 7:08 am

Sean,

While you are free to build your plane with anything you prefer, you may, at some future time, decide to sell that craft, and build some other plane. When you go to sell the plane, the pool of buyers may be limited if you’ve used non aircraft materials.

Answering your specific question about the two materials, 4130 has roughly: Double the Ultimate strength, Double the Yield strength, and about 2.5x the FATIGUE strength of 1020.

On the surface this may not seem important, but when flying in light turbulence - a condition hard to avoid - all of the lift, cabana, engine mount, and empennage fittings will be subject to cyclic stresses. These are the stresses that produce fatigue...

After some amount of cyclic stress exposure, a fitting will fail. Would you prefer to use a non aircraft material in that application, or a something that was designed specifically to withstand those stresses?

All that said, to the best of my knowledge, there has never been a structural failure of a Pietenpol.

As for welding, newer Tig machines, or even used ones are available at pretty reasonable costs. I picked up a Miller 200A Tig machine for $350. Including a full tank of argon. They’re out there, just look. Also, don’t dismiss gas welding, as over twenty thousand J3 cubs were welded with gas torches.

Hope this helps...

EAB4
Posts: 61
Joined: Mon Mar 06, 2017 2:08 pm

Re: 4130 vs 1020

Post by EAB4 » Sat Sep 28, 2019 7:15 am

pretty sure 4130 has been gas (oxy-acetylene) welded for many years...

builderwannabe
Posts: 9
Joined: Mon May 13, 2019 8:05 pm

Re: 4130 vs 1020

Post by builderwannabe » Sat Sep 28, 2019 7:03 pm

Tom and EAB4, thanks for the reply and info, sounds like i best buy a TIG welder or learn to gas weld.

Sean

Bill Church
Posts: 7
Joined: Fri Feb 24, 2017 8:48 am

Re: 4130 vs 1020

Post by Bill Church » Sat Sep 28, 2019 10:54 pm

Non-aircraft material? 1020/1025 steel tubing actually has a good deal of history in aircraft structures, such as J3 Cub and Aeronca Champ/Chief.
There's nothing wrong with using 1020 steel where called for in the plans.
Finding 1020 steel tubing in the specific sizes called for, in small quantities, however, may prove to be a challenge. 4130 is much more readily available in all of the various sizes needed.
If using 4130 steel, the most important things to keep in mind are:
1) use the proper filler rods
2) allow the welds to cool slowly in still air.

Bill C.

ArthurD
Posts: 19
Joined: Tue Jun 26, 2018 2:00 pm

Re: 4130 vs 1020

Post by ArthurD » Sun Sep 29, 2019 2:44 pm

There isn't that big a difference between 1020 and 4130. 4130 has 80 KSI ultimate and 52 KSI yield in the annealed state. 1020 has 57 KSI ultimate and 43 KSI yield annealed. So it's a little weaker but it's also more ductile and it absorbs twice as much energy on the Izod Impact test. I'd argue that that the 1020 frame is certainly strong enough for normal flying, I don't think one has ever failed in flight, and if you were to crash it then it would absorb more energy.

Brian Amato
Posts: 106
Joined: Fri Aug 31, 2018 9:23 am

Re: 4130 vs 1020

Post by Brian Amato » Tue Oct 08, 2019 3:53 pm

4130 is very easy to gas weld. I built my entire Corben Jr. Ace fuselage out of 4130 and it welds like a dream. I know....that probably sounds like a smart a## thing to say if you're just starting to weld but, really, it's pretty easy after you've done a little practicing.
Use mild steel rod.

Cbear
Posts: 1
Joined: Wed Feb 06, 2019 10:32 am

Re: 4130 vs 1020

Post by Cbear » Fri Nov 15, 2019 8:32 am

If you don't mind gas welding, you can usually find a good deal on a setup on craigslist or Facebook marketplace. Around here in Detroit I see sets come up almost daily for about $400 for large tanks/torch.

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Terry Hand
Posts: 58
Joined: Thu May 18, 2017 2:37 pm

Re: 4130 vs 1020

Post by Terry Hand » Mon Nov 25, 2019 8:56 am

ArthurD, I am curious as to why 4130 was created then and used in aviation if there was little difference between it and 1020. Not trying to smart or argumentative - I am really curious.
Semper Fi,

Terry Hand
Athens GA

ArthurD
Posts: 19
Joined: Tue Jun 26, 2018 2:00 pm

Re: 4130 vs 1020

Post by ArthurD » Mon Nov 25, 2019 12:40 pm

I don't know enough about the history of steel tube airframes to say for certain why manufacturers favored 4130, but I can think of two good reasons why they might. One would be that they probably did a normalizing heat treatment which gives 4130 even more of a strength advantage. The other reason would be that (depending on the failure mode) a 1020 tube has to be larger and heavier to carry the same load and the small advantage in crash survivability probably wasn't worth the extra weight.

So if you're an aircraft engineer in the 1920s trying to design the lightest airframe possible and you have access to a heat treatment oven then 4130 probably makes a lot of sense.

My argument is that if you're building a pietenpol in your garage without access to a heat treatment oven and you know that the 1020 airframe is strong enough and you're not going to resize the tubes to take advantage of the extra strength of 4130 anyways then I believe you're better off going with 1020.

That being said I do happen to have access to a heat treatment oven and I am deviating from the plans to make a long version steel fuselage that's also a little deeper and wider. So in my case I do actually prefer to have the extra strength over the ductility of 1020.

Bill Church
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Joined: Fri Feb 24, 2017 8:48 am

Re: 4130 vs 1020

Post by Bill Church » Sat Dec 07, 2019 7:52 pm

4130 tubing is typically sold in the normalized state (4130N). For thicknesses of 1/8" (.125") or less, when welded (using either Oxy/Acetylene or TIG) it will return to the normalized state, provided it is allowed to cool slowly, in still air. Colder ambient air, or even a slight breeze will cause the weld affected zone to cool too quickly, and will result in a more brittle weld, which will be more likely to fail, when stressed. As long as the welds are done under the appropriate conditions (warmer ambient air, slow cooling in still air), there is no need for heat treatment of welds on lighter gauge 4130 steel.

Bill C

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