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Thread: Aluminium Caravan Question
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2nd Dec 2018, 08:59 PM #1Member
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Aluminium Caravan Question
Hi All,
I have been toying with the idea of building a small light weight camping caravan.
The idea has been developing in my mind for the last decade or more, and revolves around the stagnant designs that I see in caravans currently. Effectively, they are boxes on wheels and heavy. Many years ago we had a small Topagee which had two (2) double beds, hard top and when loaded with water weighed in at 420 Kg. We used this for 4x4 (Wonnangatta, Fraser Island, Kangaroo Island etc) for our family of four (4). It was light enough to be dragged over any obstacle.
Recently I have noticed some European caravans have an Aluminium frame construction (drawbar) - so it can be done. Whilst I realise that 4x4 driving is much more demanding than bitumen driving, with a lower weight component, it may be feasible.
To that end I would like to build a circa 1:1.5 scale model to prove (or disprove) the concept.
So I have a couple of questions for the brainstrust of the forum as follows:
1. How can a traditional steel coupling be attached to an Aluminium drawbar?
2. The same question applies for the suspension system, or can Titanium be used inlieu of steel components? Corrosion between two (2) dis-similar metals is the concern here.
3. In mocking up a scale model (and as I am lousy at Aluminium welding) is there any suitable glue that can be used to bond Aluminium to Aluminium?
4. What grade Aluminium section and sheet should be used?
Thanks All.
George
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2nd Dec 2018, 10:10 PM #2Most Valued Member
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Hi George, the coupling would be bolted to the frame as would the suspension. Without knowing the type of suspension that you're thinking of using, makes it hard to suggest a mounting system.
We use Timbren Suspensions, they're a bolt on arrangement and can be wheel aligned fairly easily.
Timbren suspensios.png
What are you wanting to glue, square tube to square tube, square tube to sheet??? I'd use Sikaflex to glue the sheet to the tube.
I'd be inclined to use a marine grade aluminium. There are several types that could be used. Have found a link to the grades recomendation, of course it's at the bottom of the list under transport.
https://www.metalsupermarkets.com/wh...-should-i-use/
You could make a steel chassis, and bolt the caravan framing to it.
KrynTo grow old is mandatory, growing up is optional.
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2nd Dec 2018, 10:43 PM #3Member: Blue and white apron brigade
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2nd Dec 2018, 11:02 PM #4Member
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Hi Kryn,
Looking at attaching square tube to square tube, so possibly Sikaflex could be the go - it is afterall for a prototype proof of concept thing.
Ideally I wanted to avoid doing a steel chassis for weight considerations and I am concerned about the corrosion aspects of puting Al with Steel. Maybe a rubber gasket perhaps?
Some more thinking I think!
George
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3rd Dec 2018, 12:14 AM #5Most Valued Member
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As a general rule, plywood sheeting is laid on top of the chassis, then the side frames are attached on top, then bolted with Huck fasteners, they won't pop like a POP rivet but work on a similar principle.
I'd think twice before discounting the steel chassis, modern vans are using a product similar to the Lysaght C channel. The beauty is that should something let go when you're out bush, you can weld it up, even in the middle of nowhere, using Car batteries, BTDT.
I don't think that'll work with aluminium.
Have you looked around the caravan yards to see how they're constructed?
KrynTo grow old is mandatory, growing up is optional.
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3rd Dec 2018, 07:53 AM #6Golden Member
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George
galvanic corrosion is what you are concerned about. Titanium and aluminium would be a bad combo. Here is a chart showing how it works.
SSINA: Stainless Steel: Corrosion
Eric
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3rd Dec 2018, 10:21 AM #7Member
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3rd Dec 2018, 10:38 AM #8Member
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Hi Kryn,
If I go this route, will the Huck Fasteners promote a Galvanic effect ie connecting the Aluminium to the Steel Chassis? Hmm, I wonder if there are non-metallic options available that could connect the two (2) dissimilar metals?
I have looked at some caravans in various stages of construction, but not an indepth look.
Next time I have the opportunity, I will. that stated, from what I have noticed most are using what I would term as old school construction methods ie tried and proven. What I am looking at are lighter and more innovative options. It may not work, but it is worth exploring...
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3rd Dec 2018, 01:25 PM #9Diamond Member
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There's plant trailers that are aluminium, the idea being to maximise what can be towed within the 2t limit. It might be worth dropping past a hire place like Kennards or Coates and checking out the trailers they use for their mini excavators.
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3rd Dec 2018, 03:21 PM #10New Member
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George,
The coupling can be separated from the ali by a UHMW gasket and just bolted on. You can make the entire chassis and frame from ali and avoid galvanic corrosion. The frame can be made from any of the 60 series aluminium RHS.
Cheers
Pete
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3rd Dec 2018, 03:42 PM #11Member: Blue and white apron brigade
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My experience is that UHMWPE is a poor material for gasket as over time under vibration and pressure as it will squish and flow allowing bolts to loosen.
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3rd Dec 2018, 07:22 PM #12Member
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3rd Dec 2018, 08:22 PM #13Member: Blue and white apron brigade
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PTFE is used in some stationary structures but once again I think it would fail under vibration.
Shellac is an old time favourite and was used on the Statue of Liberty.
You might be better off with a couple of coats of epoxy enamel.
Using bolts means electrically isolating the bolts as well which becomes a right PITA.
If you completely electrically isolate your hitch from the rest of the trailer you need to run an additional wire for lighting etc.
SWMBO's Al horse trailer just uses a Galv hitch - it's parked outside and there doesn't seem to be much corrosion at the junction although the last time I saw it there was a plastic drum over the hitch.
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4th Dec 2018, 08:16 PM #14Most Valued Member
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Landrovers for many years used aluminium panels, and a steel chassis and frames. Corrosion isn't as much of an issue as you'd suspect.
On one of mine the door skins have corroded a bit where they sit against the steel frames, but its 35 years old, sat out in the weather and has poorly designed door drains etc. You'd see worse corrosion on an all-steel vehicle.
I may be wrong but suspect that a well painted coupling on an aluminium frame wouldn't be a major problem. More likely a bigger issue on a boat trailer.
If you really wanted to isolate it then something like suspension mount bushes might be an option. Would obviously need to be designed in such a way that if the bush fails the coupling doesn't separate.
Or use something like a Tregg hitch style coupling and build a aluminium "block" for it to go through (attached to the chassis), and again use suspension bushes to achieve the isolation between the steel part of the coupling and and the block/chassis.
For me, the major issues with an aluminium chassis is fatigue life and repair-ability. Particularly when talking about an off-road type van.
If you're looking for a light/strong chassis - have you considered a steel truss design? Not commercially viable due to the labour involved (if that's where you were heading), but they give light/rigid/strong structures that are relatively easy to fabricate and very repairable. Some examples are race car space frames and light aircraft engine frames.
I spent quite a few years doing aircraft structural/sheetmetal work, but have also built a few small ~4m sailing dinghies using foam/fibreglass composite construction.
If I was building a van (and its an idea I've toyed with) it would definitely be a composite body. Built in insulation, repairable, incredibly light and stiff, easy to paint and its built as a shell rather than sheets that need to be attached, joined and sealed and provide natural places for leaks etc.
You can easily make your own composite panels by laying up glass cloth on both sides of a sheet of foam, or buy pre-made panels if you don't want the hassle of that step. 2D and 3D shapes are also relatively easy to achieve.
To answer another of your questions regarding bonding of aluminium to aluminium, sealant/adhesives such as Sikaflex work well, but if you're talking rigid structural bonds there are special epoxies designed for doing it.
Keep in mind that welding aluminium is only one way of joining it. In the case of aircraft where the high strength alloys used aren't weldable, it was traditionally riveted/bolted joints but much has moved to more composite construction and bonded joints.
Great project and I'll be very keen to see what you come up with.
Steve
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6th Dec 2018, 09:54 PM #15Member
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