Seamless drawn versus DOM Tubing

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

DaveK

Well-Known Member
Joined
Apr 21, 2007
Messages
382
Location
Northern California
I know most (all?) aircraft built with steel tube these days use seamless drawn tubing. There is also hot rolled drawn over mandrel (DOM) tubing that the racing community uses a bunch. Does anyone know if there are differences in strength, buckling resistence, etc. between the two differenct styles of 4130 tubing? I know Bob Hoover suggests using the DOM to save money, but I haven't found much engineering data for this type of tubing.

Any help appreciated.
 

djschwartz

Well-Known Member
Joined
Jun 21, 2008
Messages
982
Location
Portland, Oregon
I would not substitute materials in this way unless you're willing and able to do a LOT of destructive life testing. As expensive as seamless CrMo 4130 is, you really won't save that much in the overall cost of the aircraft and I expect you will pay a weight penalty to ensure that you do not have problems from the seam.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,485
Location
Port Townsend WA
I called around for quotes on mild steel tubing and found it was always more expensive than 4130 in small quantity. So I gave up and just use 4130. What is the price of the tubing used by racers?
BB
 

PTAirco

Well-Known Member
Joined
Sep 20, 2003
Messages
3,667
Location
Corona CA
I have heard the same thing about the use of DOM tubing by the racing crowd. Since you can get it in 4130 too, I would think it has its uses if the price is substantially lower than seamless. It is very straight and dimensionally accurate (except after welding tubing of any kind, nothing is all that straight anyway). If used in tension or compression, I can't see it making a whole lot of difference and if used in bending, such as tail surfaces, you could always orientate the tube so the welded seam is on the neutral axis.

A lot of airplanes in the 30's used fabricated tubing made of high strength steel, that was rolled or folded into shape and riveted at the seams or had clever folded locked joints. I would probably use it if the price was a lot lower than seamless and I needed an awful lot of it. And maybe throw in a "what-if-factor"...
 

DaveK

Well-Known Member
Joined
Apr 21, 2007
Messages
382
Location
Northern California
Thanks for the input. I'm not at all serious about using it, but I am curious since it can be obtained locally quite easily. In compression buckling is the controlling factor and that shouldn't be affected much by rolled and welded versus seamless. Same in tension if the material is normalized. But bending may have an issue. But if this material could be used and doesn't present any significant issues then why does no one use it. It is sort of like using douglas fir instead of spruce that many people do. You don't save that much, but it does work. Again I'm just curious if someone has done this and if it works out or if there is a fatal flaw to its use (e.g. it splits down its length, etc.)

BBerson you are right the price in small quanities doesn't save you anything, but in large lengths it actually can save a substantial amount. In full 20 ft lengths the tubes were significantly cheaper then seamless in this area. For a fuselage I would end up with a bunch of extra tubing if I went that route and it wouldn't be optimized because of having to buy only a limited number of different thicknesses to keep from having to order short pieces.

PTAirco mentioned the use of high strength steel in the 30's and I remember reading that there was problems with its use, though I don't remember what those problems were. Since many of the tubes are limited by buckling, which isn't affected much by going to a higher strength steel you likely wouldn't gain much if any strength in the resulting structure. I think these couldn't be welded either.
 

djschwartz

Well-Known Member
Joined
Jun 21, 2008
Messages
982
Location
Portland, Oregon
Douglas Fir is being used increasingly due to the increasing expense of acquiring spruce. Fir is about 25% stronger and also about 25% heavier. It is also more variable in quality than old growth Sitka Spruce. Making the best use of Fir requires some structural engineering to achieve a structure with the same strength and weight as the original spruce. Some antique biplane restorers are using fir and leaving the dimensions the same since the added weight is relatively small compared to the overall weight of the aircraft. If I build a new wing for my Stephen's Akro I will use fir as I need the spar to be stronger and I am limited in the amount I can increase the dimensions based on the way the wing mounts in the fuselage. The biggest challenge in using Fir is finding aircraft quality wood. There is no regular source of certified aircraft quality Fir so you need to know how to select it yourself. With patience you can find suitable wood at your local home store or lumber yard; though, it might take quite a few trips over time and a willingness to cut away unsuitable material to get what you need.
 

PTAirco

Well-Known Member
Joined
Sep 20, 2003
Messages
3,667
Location
Corona CA
PTAirco mentioned the use of high strength steel in the 30's and I remember reading that there was problems with its use, though I don't remember what those problems were. Since many of the tubes are limited by buckling, which isn't affected much by going to a higher strength steel you likely wouldn't gain much if any strength in the resulting structure. I think these couldn't be welded either.

The problem was mainly one of longevity - the high strength steels were brittle and prone to fatigue cracks around rivet and bolt holes. In an era when a front line fighter was obsolete in a matter of two or three years, this wasn't much of a concern. The other problems of buckling stability when using such very thin material was solved by intricate curving and fluting of the section.

Neither of those two problems really comes into the use of DOM material and I only mentioned it to show that fabricated tubing can have its uses as well as seamless.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
10,310
Location
CT, USA
Interestingly (and equally irrelevant to the original subject, but since somebody brought up alloys...) the prewar Taylorcrafts had fuselages made of 1020 tubing, while the postwar planes used 4130. They were completely interchangeable... the logs for my 1941 T-Craft showed a damaged fuselage being replaced in the late 1940's with a "new factory fuselage" (and later, the wings with a set of "good used wings").

-Dana

"If you're not a liberal at 20, you have no heart.
If you are not a conservative when you're 30, you have no head."
-- Winston Churchill
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,485
Location
Port Townsend WA
My Piper Supercub manual lists all the fuselage tube sizes and most of the tubes are 1025 steel.
1025 seamless would be better than DOM if you can find it.

I have a race car book that recommends 1020 seamless for rollbars.... the authors says 4130 is not recommended because 4130 is not as "tough" in a collision, tends to crack instead of bending and absorbing the crash energy.
BB
 

DaveK

Well-Known Member
Joined
Apr 21, 2007
Messages
382
Location
Northern California
But back to the original question. Is this stuff actually inferior in practice? Saying you're better off getting seamless doesn't really answer that question. If no one has any experience with it then say so!
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,485
Location
Port Townsend WA
I have tested some welded seam tubing. It split at the weld when bent.
So no, I have not built any airplane parts with anything but seamless 4130 and I don't know of anybody else that does.

BB
 

Midniteoyl

Well-Known Member
Joined
Sep 3, 2003
Messages
2,406
Location
Indiana
I think people are confusing standard Electric Resistance Welded (ERW) pipe with Drawn Over Mandrel (DOM) tube. Seamless (CDS) and DOM of the same grade alloy, hardness and temper should be the same strength, with DOM actually getting the nod in terms of consistency.

Seamless tubes that are cold drawn are always refered to as "CDS" for cold drawn seamless. Note that many companies that purchase tubing for machining applications have gone to DOM over the past 20 years or so because the tube production process (that is, taking flat strip, forming it round and welding it) produces a much more concentric tube than the conventional seamless process (Mannesmann piercing of a hot bar). As a result, the machining customer purchases a slightly thinner DOM wall thickness than they would in a CDS tube. There is less machining required to completely "clean-up" the DOM tube versus the CDS tube.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,485
Location
Port Townsend WA
I think you are referring to thick tubing. Is it available in thin wall? (.028, .035)

One of the main reasons for using 4130 is the fact that much of the strength remains after welding. 4130 is unique in that it "air hardens" after welding to about the same strength as the original air hardened tube.

Cold rolled tube can be almost as strong because of work hardening from the mill, but welding destroys this and the joint area is much softer from what I found.

DOM might be suitable for some parts, it depends on the part, as always.
I just don't think it is readily available in thin wall. If it is available, I would like to test some.
BB
 

Midniteoyl

Well-Known Member
Joined
Sep 3, 2003
Messages
2,406
Location
Indiana
You could be right, BB, my experience in this is the thicker tubing sizes. My main point is that with the type of welding used, and then being drawn, there really is no difference in the strengh between the too. Finding DOM in a thinner wall is a different matter :)
 

DaveK

Well-Known Member
Joined
Apr 21, 2007
Messages
382
Location
Northern California
Bob Hoover on his blog mentioned using the DOM and also mentioned having to pay a weight penalty of a few pounds. Maybe that is why; he couldn't get the thinner gauges.
 
S

shengshida

The DOM tubing use the Electric Resistance Welded (ERW) pipe, however, the seamless use the cold process.
 

Joe Fisher

Well-Known Member
Joined
Feb 10, 2007
Messages
1,379
Location
Galesburg, KS South east Kansas
For me 4130 is easier to weld than 1025. As far as I know the 1940 and earlier airplanes are made out of 1025. I think of it as like the difference in working with grade "A" and Ceconite fabric.
 
Top