When I started shopping for a boat trailer, I needed to find one which would be long enough to support the length of the longest piece of the plane (the fuselage, at 14.5 feet). I didn't yet know how I was going to mount the wings, so I wanted to find a trailer at least as wide as one wing (5.5 feet) to give me maximum flexibility as I worked out my design for the support structure.
I looked around at my local craigslist and found a half-dozen candidate trailers over the course of a week. After corresponding with the sellers who helped me measure and provided pictures of the critical bits, I narrowed it down to one trailer -- a mid-90's Calkins trailer designed to carry boats up to 16 feet long.
The owner knew I wasn't interested in carrying a boat, so knocked $50 off of his asking price in order to keep the ratcheting winch to use on another project. That, combined with the current registration and working position lights made for an easy decision to buy. $375 and one DMV form later, I drove it home.
One of the nice things about the trailer is that the boat-mounting hardware was all bolted in place, meaning that I could unbolt it and have a minimalist structure on which to build my "airplane rack." I spent several hours with a hammer, wrenches, penetrating oil, and a significant amount of elbow grease. Some of those old bolts were really rusted in place!
The trailer had an interesting feature -- the horizontal cross-members pivot along their long axis in order to distribute the weight of a boat as it is loaded onto the trailer. I wanted the trailer to be a bit more rigid, so I removed the large three-quarter mounting inch bolts. I then enlisted the aid of my friend Dan to help me mount and weld them in place. (Dan is a fellow home-restorer -- check out his blog.)
That done, I went back to the drawing-board and sketched a few designs for the trailer's superstructure.
In the end, I decided to mount the wings vertically rather than horizontally. That allowed me to have an enclosed space in the "center" of the trailer, into which I could place all of the other parts of the plane: engine, landing gear, panel, etc.
I built a long, narrow box. Here's the beginning of one side:
I bolted the side to the horizontal cross-members with some brackets I salvaged from the boat-carrying hardware.
I connected the sides with some horizontal members, on which I planned to set the fuselage:
I then extended the sides of the boxes to be a full 14 feet long. Near the tongue of the trailer, I bolted the box to the frame with two U-bolts. I also built a platform across the low, steel, horizontal members, centered on the trailer's axle, to which the heavy stuff (like the engine) could be strapped.
I left the vertical pieces long, planning to cut them to the appropriate length once the fuselage was on the trailer (it would be lousy to drive across the country and realize that the structure was too short). Gussets were added at the various corners to add rigidity to the structure.
As you can see, most of the 2x8's are installed in their best weight-bearing configuration: horizontally with the narrow edge up. The vertical members are not, but I'm not overly worried because they only need to support the wings. The wings are are relatively light (a bit over 100 lbs each), and they contain a rigid internal structure which will help them stay in place and add structural stability to the vertical members when they are hung in place.
Now to get on the road...