Author Topic: Aluminum Tubing  (Read 536 times)

danieldorgan

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Aluminum Tubing
« on: Dec 27, 2017 »
I have owned a few mountain bikes and they exclusively use aluminum or carbon fiber. Steel tubing while heavy is the norm for rag and tube aircraft. I am wondering why no one uses aluminum tubing to construct the fuselage? Is it cost or durability? I've never cracked a bike frame in spite of some ham fisted handling. Bike tubes are of however of a shorter length. Could that be the issue? Disclaimer - I do not have the planning ability, knowledge, budget etc. to go the aluminum route. Just trying to absorb as much as possible.

kennyw

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Re: Aluminum Tubing
« Reply #1 on: Dec 27, 2017 »
Not an engineer.  But, I'll post this link: https://sciencing.com/strength-tubing-vs-steel-tubing-7811536.html

Some ultralights do use aluminum tubing.  But, with slower speeds and lower weights, the energy potential is much lower.

Bil438

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Re: Aluminum Tubing
« Reply #2 on: Dec 28, 2017 »
Well, while the best allow aluminum 7075-T6 is as hard as mild steel it Ultimate Tensile strength is less that 100,000 psi. If my memory is right then about 70,000 psi. 4130 Chromoly when brought to full strength is 385,000 psil. Thus 4130 can be more than 5 times as strong as 7075. True, 4130 after welding is nowhere near full strength...
Also 4130 lends itself very nicely to oxy-acetylene welding where like TIG only, the parent metal is melted into small pools and filler rod is added to the molten pool. Thus there are no cold welds in Oxy/act welding. In my experience aluminum alloys cannot be Oxy-act welded. 
Most homebuilders can work up their technique to be able to produce acceptable welds with oxy-acetylene, whereas it's a much bigger deal to produce an acceptable weld in TIG and the initial setup is much more expensive. You also usually need to have 220V available and most shops ,garages and hangars do not.
Finally the homebuilt aircraft suppliers are set up to sell tubing kits with all the material you need to weld up a fuselage. rarely so with aluminum tubing.
BillE

TejasNW

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Re: Aluminum Tubing
« Reply #3 on: Jan 24, 2018 »
I am wondering why no one uses aluminum tubing to construct the fuselage? .

I had the same question.  Doing some research it comes down to the temper of the aluminum.  Only 6061 T6 (and a few more expensive grades) are considered structural.  However, the T6 temper is a heat treatment.  The energy absorbed by the welding process anneals (softens) the alloy to a state that it no longer has the strength to be structural.

Aluminum can be returned to a T6 temper, but it is an industrial process that requires the entire work piece to be heated to a high temperature (1000+F) and quick quenched (whole piece within 7 seconds.), and then reheated to intermediate temperature for a period of time; so the process for an entire fuselage would be expensive and beyond the scope of a home builder.


oahupilot

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Re: Aluminum Tubing
« Reply #4 on: Jan 28, 2018 »
4130 Chromoly when brought to full strength is 385,000 psil. Thus 4130 can be more than 5 times as strong as 7075. True, 4130 after welding is nowhere near full strength...

This is not true, tubing is sold "normalized" with no hardening at all, hence you can cut and shape it for fitment. Welding with OA so long as the weld is not quenched will result in about the same mechanical properties.

Also 4130 lends itself very nicely to oxy-acetylene welding where like TIG only, the parent metal is melted into small pools and filler rod is added to the molten pool. Thus there are no cold welds in Oxy/act welding. In my experience aluminum alloys cannot be Oxy-act welded. 

You can weld aluminum with gas it just requires a flux to remove the Aluminum Oxide Surface.

Most homebuilders can work up their technique to be able to produce acceptable welds with oxy-acetylene, whereas it's a much bigger deal to produce an acceptable weld in TIG and the initial setup is much more expensive. You also usually need to have 220V available and most shops ,garages and hangars do not.

I found learning to weld with TIG to be not any more difficult then welding with gas. Your basically doing the same thing with your hands with difference being that the heat is from gas or electric arc.  Also there are plenty of 110 tig machince now a day at good prices. In fact I bought a ac/dc tig that will take either 110 or 220 so the old 220 problem is less of an issue. It use to be that OA was so much cheaper it was a great place to start, but the prices on tigs have really come down and the cost of Acetylene has really climbed last time I checked. I think OA is less convincing these days based on economy alone.


Finally the homebuilt aircraft suppliers are set up to sell tubing kits with all the material you need to weld up a fuselage. rarely so with aluminum tubing.
BillE

Wicks sell plenty of Aluminum tube along with steel.


danieldorgan

You can engineer a plane to be built out of either material, however Aluminium is considerably more expensive and prone to long term cyclical fatigue. Your Mountain bike will never vibrate (millions of cycles)enough to suffer cyclical fatigue and its probably much stronger then the loads it will ever see. Airplanes on the other hand suffer lots of vibration from the prop and generally the loads are higher. Having worked as helicopter mechanic in a previous life I have seen lots of cracks in aluminum, so fatigue is something that aircraft designers do need to keep in mind.

 

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