Re: 4130?

Please correct me where I am wrong, and I am sure that I must be as all of this is new to me. My understanding is that 4130 is 2.5 times as strong as the same size piece in mild steel, so I shoould be able to build a frame out of it using the same O.D. tubing and wall thickness with an increase in strength of 2.5 times. Another option would be to use thinner walls in some areas and reduce weight as well. Does this sound logical to you?

Compare aluminum to steel by weight and aluminum is stronger. Compare aluminum to steel by size and steel is stronger. Aluminum is lighter (less dense) and therefore when compared pound for pound will be much larger than the equivalent weight piece of steel. This is intuitive by life experience if you think about it and you will find you already knew this. Squish a beer can and then squish a (steel) V-8 can.

Reply to
Zorro
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Yes 4130 will make a stronger lighter frame. To weld it you are better off getting a TIG welder, but you will have a learning curve on TIG.

The best TIG filler metal is ER80S-B2, which can be bought from

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If you use ER80S-B2 you do not need to post-weld heat treat the frame.

You can MIG weld 4130. You will need to buy some 4130 MIG wire to fit your machine, and you will have to use a oxy-acetylene torch to do your post weld heat treat. You have to warm the joints to about 800 deg F then let them cool.

Use a Tempilstik to verify your temperature.

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Reply to
Ernie Leimkuhler

Ernie,

Thanks for the reply. This info mirrors what I had heard from others on the street. I was unsure about the MIG welding of 4130 though and I had heard conflicting information about the post welding heat treatment. If I MIG it I can do it myself and already have the equipment, I think. Do you use the same shielding gas for 4130, 75/25? From what I have seen, TIG machines are pretty expensive plus I would need to buy two gas bottles for it? There is a local welder that says he can weld the frame for me using a torch and rod, but I imagine that taking a long time at $hop rate$. :)

Building one of these airframes from scratch is a pretty time intensive project and envolves a lot of customization of parts dimensions in small degrees so it would be hard to cut and bend all of the pieces in advance making the use of a professional welder that much harder to get done a little at a time. I am not above welding it myself with a MIG welder if I can get it at least as well as my mild steel frame is. Is there any special techniques or tips that you might share for using a MIG to weld 4130?

My current torch setup uses propane and oxygen. Would that work to heat the joints if I bought a rosebud tip for it? Do you heat the joints after the entire frame is assembled or do you heat them as you go along?

Thanks again!

Steve

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Reply to
Steve Thomas

Zorro,

I understand that about the wight and strength. I do not want a welded aluminnum airframe however. I have come to appreciate the durability and safety of a steel airframe over the years. :) I spent years flying bolted together aluminum frames and the difference is like night and day. Weight aside, the same diameter and wall thickness piece of tubing made of 4130 or mild steel weighs about the same as each other, right?

Steve

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Reply to
Steve Thomas

yes

It is difficult to see any difference between MIG welding mild steel or

4130.

That should be sufficient for your heat treating. Buy the Tempilsticks though.

Tack the whole frame together before you weld any of it.

TACK EVERYTHING BEFORE YOU WELD ANYTHING!!!!!

That way all the pieces keep the others from distorting as much.

After you have it all tacked, start welding, but don't weld too much in one area. Try to spread the heat out so it is more dispursed around the frame.

Once the whole frame is welded, then start tempering your welds.

after you have brought all the welds up to the proper heat, drop a heavy wool blanket over it and let it cool slowly.

Reply to
Ernie Leimkuhler

Steve, I think you better look at your design and determine what failed and why before determining that you simply need to build stronger. If you are attempting aerobatics in a ppc you have bigger issues than frame design. Many race cars and aircraft are built to crumple and absorb the energy of the crash instead of transmitting it to the weakest member - the human. You might be doing yourself a favor staying with mild steel.

Jerry

Steve Thomas wrote:

Reply to
jerry rausch

I'd like to hear from someone more expert but I have heard that an advantage of mild steel is that it will bend when 4130 might crack and fail catastrophically.

Ted

Reply to
Ted Edwards

Jerry,

Yes, I know that the aerobatics distorted one set of tubes and the other distortion was from a few hard slams to earth. :) The design is sound under normal conditions and will be under extreme conditions with 4130. I flew the original airframe tonight and just got in. I usuallly fly at least once a day when the weather permits and sometimes 2 or 3 times a day. The slight distortion from the hard landings was due to using smaller diameter material on the main root tube to save weight over some of the other tougher desiigns. The tubes that distorted from the aerobatics was due to the high "G" forces coming out of full power spirals, again from using lighter material than some of the tougher designs. If I use close to the same wall thickness tubing in these areas in the 4130 it should be perfect and I will use thinner stuff in the rest of the frame where it is not as critical. The main reason for building with 4130 instead of mild steel again is to save precious weight. In mild steel the airframe's empty weight is 440 pounds. :) Maybe I can get that down to 400 pounds and be stronger at the same time.

Have a good one!

Steve americanspiritppc.com

Reply to
Steve Thomas

Could be, but there sure are a lot of airframes made with 4130. One way to find out! :)

Steve

Reply to
Steve Thomas

Remember that the frame will not be any stiffer than mild steel. The difference will be that it will not take a permanent bend as soon as mild steel. Randy

Yes, I know that the aerobatics distorted one set of tubes and the other distortion was from a few hard slams to earth. :) The design is sound under normal conditions and will be under extreme conditions with 4130. I flew the original airframe tonight and just got in. I usuallly fly at least once a day when the weather permits and sometimes 2 or 3 times a day. The slight distortion from the hard landings was due to using smaller diameter material on the main root tube to save weight over some of the other tougher desiigns. The tubes that distorted from the aerobatics was due to the high "G" forces coming out of full power spirals, again from using lighter material than some of the tougher designs. If I use close to the same wall thickness tubing in these areas in the 4130 it should be perfect and I will use thinner stuff in the rest of the frame where it is not as critical. The main reason for building with 4130 instead of mild steel again is to save precious weight. In mild steel the airframe's empty weight is 440 pounds. :) Maybe I can get that down to 400 pounds and be stronger at the same time.

Have a good one!

Steve americanspiritppc.com

Reply to
R. Zimmerman

Nascar and a few other racing associations have moved to 1018 tube from

4130 . They were finding that in a crash the welds would fail on 4130 before the tubes would bend so you would have 4130 tubes break off on the ends and get shoved through the car, possibly piercing the driver or gas tank.

1018 would just crumple, but the welds would hold.

Reply to
Ernie Leimkuhler

What Randy is telling you is that **ALL** steels have essentially the same elastic modulus and therefore the same stiffness. If you replace a mild steel tube with a lighter 4130 tube, you *will* find the following: The frame will have more flex. The tube will be able to bend more before breaking or taking a permanent set. Even if you used the same dimensions (and therefore weight) in 4130, your airframe will *not* be stiffer. Stronger, yes. Stiffer, no.

Ted

Reply to
Ted Edwards

You don't need to post heat a migged or tigged airframe. It doesn't help a bit in the long run.

Reply to
John Thompson

If the airframe is completely triangulated then it would be stiffer with the higher-tensile material. No?

Reply to
Mike Graham

Does it hurt anything? I have always heard that you DO need to post heat airframe joints and that the FAA mandates it in AC43-13-1A. I need to go read it myself. :)

Reply to
Steve Thomas

That is exactly what I am after here too. If I save some weight in areas where the extra strength are not needed it will be a real bonus as it is an airframe. Stronger, not stiffer is just what the doctor ordered. :)

Reply to
Steve Thomas

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Reply to
jerry rausch

Thanks John,

I will try to locate one of thise books. My shop area is in my attached, insulated garage so keeping everything warm should not be a problem.

Reply to
Steve Thomas

I went on a tour of the Robinson Helicopter Plant in Torrance, CA and saw the

4130 tube frames used. They TIG with special cups allowing an inch and a half of stickout to get into those tight corners. After all the welds are done the frame gets clamped to a special jig and it all goes into the oven. It's really amazing to see how it all comes together!
Reply to
Zorro

I am about to start the finish welding on a 4130 airframe for a homebuilt biplane. Any chance you got a manufacturer or part number on that special cup you saw? What kind of gas flow were they using?

Ebby

Reply to
Ebby

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