# Equivalent Tubes in Steel, Aluminum, Graphite Fiber, and Fiberglass

Discussion in 'Composites' started by wsimpso1, Nov 3, 2019.

1. Nov 3, 2019

### wsimpso1

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Hmm, the last thread on this topic must gotten rude fast to be locked after 3 responses... Let's keep it civil guys.

Is there any interest in setting a standard steel tube and then showing other tubes with equivalent resistance to some specified loading modes? A weight comparison could be useful to some folks...

Tell you what - IFF there is enough interest (my judgement as I will be doing the work), I will do one standard round thinwall steel tube at two lengths. I will tell you what load it will carry with appropriate FOS. I will follow with the lightest standard aluminum tube that will carry the same loads. When I have some time, I will design the lightest glass and graphite composite tubes using COTS braided tubes over mandrels to stand the same loading, and post the results.

Any interest? What size steel tube? What type of loadings do you want to see? I have data on 4130, standard aluminum tubes, E-Glass, and one Graphite fiber. If there is interest in other fibers, you have to supply all elasticities and strengths before I will run it.

Billski

2. Nov 3, 2019

### Vigilant1

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Yes, I am interested. A very generous offer.The numbers would be good to see, but if you've got time to briefly step through the process that would be especially useful. I would think flat sided tubing would be of greatest interest to someone considering some kind of CF tube structure (better surface availability for gussets), but if you show us how "I" is applied, we could use the round tube example you show for any shape of interest (square, round, rectangular, etc) etc.

I'll let others weigh in on desired loadings and sizes since some may have a specific requirement. I'd say make it convenient for yourself using data you have on hand.

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3. Nov 3, 2019

### cheapracer

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I think it's time that people take an interest in it as prices slowly come down for CF, albeit still a bit expensive. I buy 6061 at $1.00, Vs CF at$2.50 currently. Better than the \$25.00 10 years ago.

I second the square tube, 1" i guess, I believe gussets for composite tubes are going to be far easier for the flat surfaces, as well as glue'ing the skins to those same flat surfaces.

I have no problem with "black aluminium" as some do, meaning using the same 2 dimensional, flat panel techniques using CF as you would with aluminium, rather than moulding coumpound curves etc.

if I could build a Morgan'ish plane in exactly the same techinique knowing that the CF was say 60% to 70% the weight (whatever, just example) I would be interested, as others might be.

Less weight and glueing rather than all those holes and rivets ...

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4. Nov 3, 2019

### pictsidhe

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If you do the figures for one fixed size and specify the layup, scaling can be done to get first approximation properties for other sizes. Yes, I'm interested. Now, if someone tells me how to reliably and easily rivet CF tube, I'm really interested!

5. Nov 3, 2019

### cheapracer

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Shirley the point is to glue it rather than all the fuss of holes and rivets?

Fiberglass is successfuly riveted, the way it protests while you're riveting you wouldn't think so, but it's fine, never done carbon myself though so I don't know.

6. Nov 3, 2019

### TFF

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I will be very interesting.

Let’s say you pick 1in 4130 tube let’s say .035 or .049.
Are you going to make the other materials be 1in diameter and let the thickest end up where it may, or are you going to match the same characteristics as the 4130 and let the diameter and thickness end up where it may?

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7. Nov 3, 2019

### pictsidhe

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I thought I was anonymous on here, how the hell did you find out that I'm really called Shirley?

The complex fittings needed for glue is offputting for a truss. Could work for mass production, though.

8. Nov 3, 2019

### ScaleBirdsScott

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If it was square tubes of CF with flat plate gussets you could probably get a decent glue area, maybe even a sammich where permitted. One could even go in and wet dab in some tapes to really lock it all in, no?

I'm not about to jump on the idea but I could see a case where it makes some sense.

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9. Nov 3, 2019

### Vigilant1

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I think the way billski described it in the OP is the most intuitive: Make the performance characteristic (Max compressive loading in service?) the common factor and then see how the options compare. The designer probably doesn't much care to prescribe a wall thickness or even a diameter -- it takes whatever it takes. With common compressive loadings across all examples we can compare weight, cost, maybe discuss issues related to joining and fabrication, etc.

Last edited: Nov 4, 2019
10. Nov 3, 2019

### TFF

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I know it takes what it takes. I’m for designing what you want. My hope is if there is some sort of crazy size to match would be good proof that black aluminum or is that black chrome moly is not the way to go.

11. Nov 3, 2019

### wanttobuild

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Yes Sir Mr. Bill
any size tube you desire, Carbon, S glass, 3/4 .035 would be great
I really have an interest in this topic.
Ideally a baby ace with a fiberglass tube fuselage.
Btw, thank you very much for taking an interest in this topic.
You da Man!
Ben

Last edited: Nov 3, 2019
12. Nov 4, 2019

### proppastie

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somewhat confused......its the joints/trusses that matter the strength/weight of the tube should easily favor CF but with weak,heavy,or difficult to manufacture joints it goes out the window ....or not? So if you are going to pick a type of loading...to compare, one has welding/steel, rivets and gussets/aluminum, Op pick for composite.

13. Nov 4, 2019

### Vigilant1

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Sure, but the weight and size of the tubing of similar strength is a good start. Then we can add cost information--right there some folks might lose interest in CF tubes. Then maybe we can make some estimates of weight/cost/time of various joining methods using a sample fuselage section, types/weights/costs of appropriate skins, etc (there's a good chance that point is where the advantages of conventional composite sandwich skin will show up-- just a guess).

It would be nice if we could make tables with this Xenforo software. Well, Excel it will probably be.

14. Nov 4, 2019

### litespeed

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Great idea.

I would push for a representative truss section be designed and then use the different types of tubes to calculate. Then its apples vs different apples, And simpler to compare for us mugs.

My preference is for Square tubes even if you use round for the steel version.

15. Nov 4, 2019

### Geraldc

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I agree.
I learned a long time ago to calculate trusses by sections etc.Only ever needed to know this to pass the exam.I have never done one in the real world and don't want to start now.

16. Nov 4, 2019

### cheapracer

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I think that might be too much to ask of the OP?

A simple 2 ft long 1" square tube, lets go for 0.080" (25 x 2mm) wall in aluminium 6061 T6, as it's a common material to us, and compare to that.

A lot can be built knowing those comparisons.

17. Nov 4, 2019

### litespeed

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Yes I agree it is much more.

Having the tube comparison will be great.

I was jumping ahead to allow gussets to come into play.

18. Nov 4, 2019

### GeeZee

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I’m assuming this generous offer is in response to the “Aluminum tube and gusset Airbike/Legal Eagle/Parasol” thread. If so then the idea of that thread is to create something inexpensive/quick to build in the ultra light or just a bit heavier class of aircraft. My vote would be to select 4130 tube sizes that are used in these class of aircraft.

19. Nov 5, 2019

### wsimpso1

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I have started the tube comparison I the Tube and Fabric forum. Only have steel and aluminum. Composites will find their way in over the next few days.

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20. Nov 5, 2019

### stanislavz

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Ok. After this topic - i became a supporter of this forum.

But... As i go deeper and deeper to this flying "hobby" - methods how to construct are build from material property. If trying to do vice versa - it wont be nice or good. You wont rivet fiberglass, or structurally glue aluminum.

Like in this mine pure rule of thumb post https://www.homebuiltairplanes.com/...onventional-welding.27418/page-13#post-500148

Sometimes we stick borders in our brain, and going round..

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