Riveted Aluminum Frame

[RandyG]

Since I don't have access to a welding equipment and trying to keep the weight to a minimum, I was thinking of making my trailer frame from aluminum riveted together. I work on aircraft so I know how to plan out rivet patterns and how to rivet very well. C-channel on the sides and supports with sheet Al. in the corners. I will use a piece of steel square tubing to attach the hitch as that may be too much stress for a single Al. piece. What problems can I run into doing this and what advise does anyone have?

[RandyG]

I have been looking on good ole' Google for hours with no luck!

[KCStudly]

Thanks for breaking this out as a separate topic.

The steel to aluminum joint could result in bi-metallic corrosion, so if you go that way you may want to consider some type of barrier layer.

I tend to favor box tubing over channel. Not sure if it is 100% valid, but it seems to me that it should be lighter and stronger in both directions than channel. Channel may be stronger in one direction, but is heavier for its strength in the other direction. Look at the moment of inertia in both the x and y axis vs. weight per foot before choosing any structural form.

[RandyG]

I know the steel on aluminum will cause corr. so I decided to prime the hell out of everything before I put it together. On the C-channel vs. Box note, you don't think with the deck of the flooring it will have enough strength? C-channel will allow me to use solid rivets through-out the entire frame. If I use box, I will not have access to the inside to form the shop head so blind rivets will be needed... I trust solids much more.

[KCStudly]

Good point. If channel then probably channel formed from sheet with uniform thickness, rather than tapered flanges?

There has been a big movement in hot rods in recent years going with aircraft theme and lots of riveted sheet aluminum. Old bomber style with nose art and brown leather trim, etc. Go with the theme and carry it through. Just be careful to isolate any interior aluminum from the exterior so that the cold does not transmit through. Jeff P.'s brother commented on this on his(military?) ambulance conversion; wished he had pulled all of the interior skin off and isolated it from the box stiffeners.

Sounds like you have the talent and understand the design elements necessary for success. Go for it!

[Shadow Catcher]

If you have worked on aircraft then you are headed in the right direction and yes the C channel will work just fine. This is stress panel construction and can be very strong.
Our trailer is all aluminum frame including the tongue. The first version of the Mega Mini had a catastrophic frame failure in the tongue and I had ours reinforced to prevent that.
If it were me I would bolt the steel tongue to the frame using gold anodized bolts with a thin piece of rubber or plastic between the steel and aluminum. You will be using steel bolts and screws and when I was looking for ways to prevent/delay galvanic action and there are four approaches that I could find, stainless steel bolts and screws, galvanized, anodized, and using PTFE pipe dope. I am using all of them and monitoring what happens.

[RandyG]

Thanks for the input, but after talking to some guys at work, an all aluminum frame would be plenty strong (tongue and all). I will cut some .090" - .125" strips standing up to beef up the tongue area. The leaf srping attach point is what I'm worried about though. But I will get strips stacked side by side in the c-cannel and bolt a plate to each side of the channel to extend below it to attach the springs. Not sure if that makes sense.
I did bend a piece of .063 into the channel today and it was very strong on each axis but twisted very easily. Not an issue once it's all together though.

[angib]

There's no problem in building from aluminium. The tongue will always be the most highly loaded part, much more than the axle mounts, but there are plenty of all-aluminium trailers (eg, for snowmobiles) out there and some forum members have built teardrops on them. You will need to apply a bit of thought to the area of the body front immediately above the tongue, as that will be carrying quite a bit of the tongue load. I would recommend an A-frame design, like the Ultralight chassis below, rather than a single tongue as the A-frame spreads the loads out better into the body. You could even use the two bits of ready-made angle section shown in blue to spread the axle load.



Don't you want to use Z-shaped frames, to make it easy to get at the back of the rivet?

Even if you go all-aluminium construction, you will have to bolt steel parts to the frame, so you have the possibility of galvanic corrosion. In practice, if you don't intend to park your trailer in salt spray, I don't believe that will be any problem - galvanic corrosion requires the circuit to be completed so unless you immerse the frame in sea water, or just maybe continuous salt spray from a salted road, it won't occur.

If you want to be obsessive, coat the joints between steel and aluminium with zinc chromate jointing compound such as Duralac. This works fine on stainless steel fittings riveted to aluminium boat masts, which is a much more severe environment. If you have aircraft contacts, you should be able to get zinc chromate paste (it's a MIL-spec item) - if not, you will need to buy it from a marine supplier.

[KCStudly]

Not sure about POHMie land, but here in the northeast and across the "Rust Belt" of America, they use a lot of road salt in the winter. They are starting to switch to a liquid melter, and say that it is better for the cars and roadways, but salt corrosion is a problem if you expose your stuff to winter driving. Rover Mike's Rover body has a lot of aluminum panels and there are signs of galvanic corrosion around some of the bolt holes on the lower lying sections of the bed behind the rear wheels, presumably from road salt being kicked up.

[RandyG]

Corr. is a main concern of mine, not from rock salt (we don't use it here in the south) but from the high humidity here in La. I think with a good coat of primer then as nice coat of paint it should be fine. But I will probably put a layer of Corrosion Preventative Compound on there as well. CPC just dusts on the top coat and protects from corr. but it will wear off over time so it will need to be reapplied every couple of years. Do you think .090" 2024T-3 will be strong enough on the connection points for the leaf springs?

[Shadow Catcher]

You might want to consider 5086 or 6061 marine grade. The problem I ran into is the finite modulus of elasticity of aluminum. There was a lot of flex/bounce at the point where the frame 2X4X.25 rectangle went under the body of the trailer. This is where #1 MM failed, Both sides snapped. These are pictures of the original construction minus the additional bracing.





You might want to check on what is used for horse trailers, not much that is more corrosive on aluminum than horse pee. Boat trailers are also made using aluminum.

[RandyG]

Yeah, I looked up your frame when you told me you had an all Al frame. Really nice work on it, too bad it failed. But a little flex it not a bad thing. If your building material doesn't flex it will either bend and not spring back or crack. That's why I want to use T-3, not too stiff but not too soft. I may start building after this other project (A surfboard plaque for a co-worker relocating).

[RandyG]

I drew up a design this week but not enough time to work on it. I'm thinking with the amount of material I'm using the frame will weight less then 40 lbs or so. That's without the plywood panel on the top to tie in the rest of my build. I will use extruded c-channel to attach the leaf springs and square tubing to the tongue.

[rowerwet]

Corr. is a main concern of mine, not from rock salt (we don't use it here in the south) but from the high humidity here in La. I think with a good coat of primer then as nice coat of paint it should be fine. But I will probably put a layer of Corrosion Preventative Compound on there as well. CPC just dusts on the top coat and protects from corr. but it will wear off over time so it will need to be reapplied every couple of years. Do you think .090" 2024T-3 will be strong enough on the connection points for the leaf springs?

as and aircraft mechanic and someone who spends a good deal of time smashing rivets in aircraft, I would follow the procedure used to rivet naval helicopters as told to me by the man who taught me riveting,( he worked on the Kaman Helicopter assembly line making sea sprite helicopters.)
all panels, plates, frames, stringers and rivets were coated in zinc chromate, every hole that was drilled had zinc sprayed into it, the rivets were shot wet, that means they were dipped in zinc chromate and then pushed into the hole, then they were bucked, and the head and tail were painted with zinc chromate again. any scratches were also touched up with zinc as well.
When blockhead... oops... McNamara decided the navy needed to buy Hueys instead, Bell sent people to see how Kaman built navy helicopters, then ignored everything they saw and took Hueys off the end of the assembly line, and sprayed them all over with zinc chromate. After one cruise they "navalized" Hueys looked like swiss cheese...
there isn't much of a harder climate than the ocean, zinc chromate dipping every part should do the trick, if not, find a place to annodize everything, Soviet aircraft use that instead. more expensive to manufacture, but more durable.

[RandyG]

Build thread here ---> http://www.tnttt.com/viewtopic.php?f=50&t=54126