chelseaz27 wrote:Thanks Fred! I really like your teardrop. I am wondering about making the width of the trailer as wide as the tires. Is there an advantage to having the wheel wells outside of the trailer? Also with a width of 45.5 inside, is it comfortable with two?
Four wide is good for me, but that may depend on the size & sleeping habits of the occupants. Try sleeping together in a box at home. A five wide with enclosed wheel wells still leaves a four foot bed, more involved construction & weight.
He is even considering using aluminum as not only the trailer frame but for the mainframe as well. He would like it to weigh as little as possible. Shooting for less than #650.
My concern about an aluminum chassis is fatigue failure of the tongue & axle mounting, Andrew explains it in this thread:
viewtopic.php?f=35&t=65130&p=1157563&hilit=aluminum+fatigue#p1157563Aluminium is a fine material - if you have years of experience of building trailers from it, or you have a team of aeronautical stressers to design it. For everyone else, it is a bit of a gamble.
Most trailers don't fail on one-cycle strength (one enormous load) but on fatigue strength (many little jiggles) when cracking starts. Most aluminium alloys have the disadvantage, compared to steel, that they do not have a fatigue (or endurance) limit, so even if the jiggles are tiny, if it is jiggled for long enough, in the end the aluminium will fracture. This graph from Wikipedia shows the effect:
Image (couldn't get the image to copy & paste, but you can look it up on Wikipedia or Goggle).
So in steel as long as the jiggles are less than about half the maximum strength, it doesn't matter if there are one million or one billion of them, the steel won't start cracking. But with aluminium alloys, there is no such limit.
DC3s were built before the much stronger age-hardening aluminium alloys (Duralumin was the first, I think) had been discovered, which is why many DC3s are still flying when younger planes aren't. It says diddly squat about the long term strength of an aluminium trailer frame.
Welders often like to quote the 'stronger than the parent metal' claim, but they rarely say 'failure will occur in the parent material in the heat-affected zone right next to the weld', as that isn't such good advertising. And they are talking about one-cycle strength, not fatigue strength, which is often much lower for welds.
The Australian trailer rules go so far as to recommend that tongues/A-frames are not welded to the front cross member of the trailer at the point where they cross it, so that the lower fatigue strength of the welds do not start cracking - and the Aussies have a lot of washboard roads, which are the ideal 'jiggler' to cause fatigue failure, so they have more experience of this than most.
Clearly, it is possible to build a strong, long-lasting trailer frame from aluminium, but it isn't guaranteed.