Welded aluminum frame

[wolfix]

I'm obsessed with having a frame mad out of welded aluminum square tube. I know it would be expensive. But the weight issue is what i am confused on. How does a person determine weight of a piece of aluminum tube 3/3 x3/4 x 8' ???????

[kerryd]

Wolfix , Are you saying 3" sq. tube 3/4" side walls ? Kerry

[bobhenry]

WWW.luminum.com

3x3x1/8 1.69 lbs / lft

3 1/2 x 3 1/2 x 1/8 2.026 lbs / lft

3 x 4 x 1/4 3.9 lbs / lft

better find a real good commercial welder !

[wolfix]

Wolfix , Are you saying 3" sq. tube 3/4" side walls ? Kerry

I' m sorry , I was trying top hurry and get back to work......3/4 x 3/4 ....

yeah, I know a good commercial welder is needed..... I know the welding instructor at the local community college. I thought maybe he could do what I have to have done for cost of materials...... He did some steel work for me in the past..........

[kerryd]

wolix , go to www.easternmetal.com .They'll have the lbs/ft. Kerry

[asianflava]

Aluminum frames have been beat to death here. The consensus is that it isn't worth the trouble. You have to use thicker material which negates the weight savings, it costs more, and it is more difficult to weld. You also have to take preventative measures for dissimilar metals (galavnic) corrosion. Things like the coupler and axles can only be had in steel.

A lightly constructed steel frame goes a long way in weight savings.

[TRAIL-OF-TEARS]

Yes, a steel frame can be made lite. I could pick up my frame, with wheels, to turn it over.

[wolfix]

I'm bad....... I wrote my post in a hurry. I meant to say "using aluminum tubing for the side walls." And trailer. I know most TD's use wood, but I'm not a fan of wood.

[bobhenry]

3/4 x 3/4 x 1/8 wall .368 lbs / ft

[dovaka]

Yes, a steel frame can be made lite. I could pick up my frame, with wheels, to turn it over.

right now all i have built is my frame and i can stand in the middle of it pick it up and walk around with it and it really isnt that hard
p.s. its made of steel with short torsion axles

[kennyrayandersen]

dovaka
Where did you get your torsion axles, and did you weigh them before installation? My trailer should be 500# loaded up and I'm looking for some very light-weight axles. Did you use the half torsion type?

A note on Al vs. Fe Aluminum is lighter but costlier. Even though I'm shooting for a completely crazy light weight, I haven't signed on to aluminum because it is quite expensive. I haven't completely given up, but I think I'd have to find some surplus at a really cheap price before considering it.

Here is part of the problem. If it's good aluminum -- high-strength aerospace alloy (7075, 7050, 2024 etc.) then the ultimate stress can run as high as 70+ Ksi (kips per square inch), which is double what mild steel is run up to (high-strength steel is another story, but it is really expensive as well). Aluminum is one third the weight, so it's not hard to see why we build airplanes out of aluminum rather than steel (for the most part). However this type of aluminum generally welds very poorly. The stuff that welds well, isn't as high strength (6061, 5052 etc). So the building techniques have to be specially taylored to the material.

The advantage of using low-strength steel, is that is is very cheap, and it can be readily welded. If you are careful about where and how you put the metal, you can save some of the weight by using proper design priciples.

[angib]

Kenny,

As you're an aircraft engineer, you should know all about fatigue strength, which is why aluminium isn't as attractive for a trailer as it might first seem. Most trailers don't get a crack inspection every year, which is the minimum you'd need to keep it safe. Aluminium was used briefly for the frame on a fiberglass trailer and they now display the cracking problem that you'd expect.

But if you're intending to make a sandwich composite bodyshell, why do you want a frame at all? John (?) at Tiny Tears has built a frame-less composite teardrop (though he foolishly overlooked the peel strength of the suspension mounts!) and we've discussed this idea for a wood body before. Here is my design for a frame-less Ultralight:



The red bits are the metal used to transfer the loads from the coupler and suspension into the body - but with composite construction it would be easy to chuck a bit of carbon in at these points and have no metal at all.

Andrew

[dovaka]

dovaka
Where did you get your torsion axles, and did you weigh them before installation? My trailer should be 500# loaded up and I'm looking for some very light-weight axles. Did you use the half torsion type?

A note on Al vs. Fe Aluminum is lighter but costlier. Even though I'm shooting for a completely crazy light weight, I haven't signed on to aluminum because it is quite expensive. I haven't completely given up, but I think I'd have to find some surplus at a really cheap price before considering it.

Here is part of the problem. If it's good aluminum -- high-strength aerospace alloy (7075, 7050, 2024 etc.) then the ultimate stress can run as high as 70+ Ksi (kips per square inch), which is double what mild steel is run up to (high-strength steel is another story, but it is really expensive as well). Aluminum is one third the weight, so it's not hard to see why we build airplanes out of aluminum rather than steel (for the most part). However this type of aluminum generally welds very poorly. The stuff that welds well, isn't as high strength (6061, 5052 etc). So the building techniques have to be specially taylored to the material.

The advantage of using low-strength steel, is that is is very cheap, and it can be readily welded. If you are careful about where and how you put the metal, you can save some of the weight by using proper design priciples.

i actually found a extremely small popup camper that was destroyed but the frame was solid so we just ripped the body off if it and resized it to fit our needs so the axles were allready there but they are the stubby kind that are only about a foot long and they cant weight to much right now hte frame is complete minus tounge and i bet it weighs around 100 pounds with tires on it

[kennyrayandersen]

Kenny,

As you're an aircraft engineer, you should know all about fatigue strength, which is why aluminium isn't as attractive for a trailer as it might first seem. Most trailers don't get a crack inspection every year, which is the minimum you'd need to keep it safe. Aluminium was used briefly for the frame on a fiberglass trailer and they now display the cracking problem that you'd expect.

But if you're intending to make a sandwich composite bodyshell, why do you want a frame at all? John (?) at Tiny Tears has built a frame-less composite teardrop (though he foolishly overlooked the peel strength of the suspension mounts!) and we've discussed this idea for a wood body before. Here is my design for a frame-less Ultralight:



The red bits are the metal used to transfer the loads from the coupler and suspension into the body - but with composite construction it would be easy to chuck a bit of carbon in at these points and have no metal at all.

Andrew

Other than it doesn't look quite so traditional, that might work, There may be a couple of issues. One is how you have the tounge intersecting the front part of the tear in the middle rather than going all the way to the side to transfer the load. By doing that, there won't be any 'punch loads' into the front of the tear. I think it's possible, though I'll have to chew on the asthetics a bit...

The other concern is the half torsion (if I"m reading your picture correctly) axle, which when loaded creates an overturning moment about the fore/aft axis. Perhaps the cross member you are showing would prevent this rotation. If it is done right, there shouldn't be any 'peel'-type loads. I think a small light-weight frame between these half shafts might be the easiest way of dealing with them. The one nice thing about putting an A-frame in the front is that I think the half torsion axle angles can be welded to the end of the A-frame and the piching moment, and with a cross brace the roll moment could be reacted easily.

food for thought anyway, and I'm a chewin'