I'll say right off the bat that this has precious little to do with airplanes.
I've been considering the construction of a small travel trailer ("caravan" to those across the pond). The commercially available fiberglass trailers (Scamp, Casita, etc) have a lot to recommend them over the conventional stick-built wood-and-tin trailers (or newer cousins with a thin fiberglass material affixed to a wood frame). They have very few seams to leak, generally don't fall apart from rot if they do leak, and are fairly aerodynamic. But, they are made with chopper guns and polyester resins shot into molds, then the two halves screwed together, so not a good approach for a one-off. I can't find a floorplan that I think is ideal, and, anyway, this could be fun.
I've been thinking of making a simple body to go on a standard steel frame utility trailer chassis. All major portions would be flat vacuum-bagged XPS core panels (for rigidity and insulation value). The front wall might be curved to the top and maybe the sides would "boat tail" in slightly as a concession to aerodynamics, but probably no compound curves. Weight/specific strength isn't nearly as important as in an airplane, but I'd still like the thing to be relatively light (e.g a 6.5' x 13' body on a steel trailer with an all-up empty weight of about 1800 lbs). Cost is a consideration. Edges of the panels would have reinforced cores (foam replaced with?) and the structure temporarily screwed together, then all seams covered by FG tapes and resin, so it becomes a single-piece hull (spray or roll some thick, rubbery colorful coating over the lapped/taped areas and call it "trim" to avoid having to fair/fill/sand the areas where the tapes are used to bond the panels).
So, some questions:
- Would the construction method above likely work, or would the corners need to be beefed up with metal fittings, gussets, etc? Better ideas?
- The resin: While I'd thought vinylester might be the preferred choice (cost), I'm coming back to epoxy just due to a reduced likelihood of stress cracks and easier/safer working properties. Smart? Dumb?
- The reinforcement: Would standard e-glass be the best cost/strength candidate?
- The skins:
-- Outside skin: A trailer is likely to get bumps and whacks. A 1/4" skin of plywood on the outside of the foam (topped with FG/epoxy, and paint) would seem to offer a good ability to reduce the needed thickness of cloth/resin, spread the pressure of local impacts to a larger area of the core, and handle abuse, but I'd really like to avoid the use of anything that is susceptible to water damage and rot. So, any other suggested (cheap/lightweight) material that can provide local reinforcement and also be bonded to foam and epoxy? Or, would you just skip the sheet goods and go with a thicker glass layer? Suggested weight of glass (e.g. would a single layer of 7.5 oz do it, or would you use something thicker? BIAX?
-- Inner skin: Same considerations as above. I had thought the fiberglass reinforced plastic (FRP) sheets available at home centers (for building shower stalls, etc) might be a good standalone answer for the interior skin--they are not very light, but they are fire-resistant, look okay wihtout any other finish, and readily available. If I could get them to bond well to the foam, I might save a lot of time and expense by avoiding the need for any FG or epoxy layups on the interior. I've heard they expand/contract a lot with temperature, that's another thing I'd need to check out.
-- Attaching cabinets, walls, etc: It would be easy to incorporate wood in strips/strategic places in place of the XPS core material to provide a hardpoint for screws, but as mentioned above I'd like to avoid wood. I've seen phenolic sheet as the normal way of making hardpoints in aircraft--I'm wondering whether to stick with that or find something "good enough" that is more economical. Aircraft Spruce wants $20/sf for 1/4" thick phenolic, though I'm sure an industrial supplier could beat that price for large quantities. I might need quite a bit of it,
Thanks for any ideas, links, stifling your laughter.
I've been considering the construction of a small travel trailer ("caravan" to those across the pond). The commercially available fiberglass trailers (Scamp, Casita, etc) have a lot to recommend them over the conventional stick-built wood-and-tin trailers (or newer cousins with a thin fiberglass material affixed to a wood frame). They have very few seams to leak, generally don't fall apart from rot if they do leak, and are fairly aerodynamic. But, they are made with chopper guns and polyester resins shot into molds, then the two halves screwed together, so not a good approach for a one-off. I can't find a floorplan that I think is ideal, and, anyway, this could be fun.
I've been thinking of making a simple body to go on a standard steel frame utility trailer chassis. All major portions would be flat vacuum-bagged XPS core panels (for rigidity and insulation value). The front wall might be curved to the top and maybe the sides would "boat tail" in slightly as a concession to aerodynamics, but probably no compound curves. Weight/specific strength isn't nearly as important as in an airplane, but I'd still like the thing to be relatively light (e.g a 6.5' x 13' body on a steel trailer with an all-up empty weight of about 1800 lbs). Cost is a consideration. Edges of the panels would have reinforced cores (foam replaced with?) and the structure temporarily screwed together, then all seams covered by FG tapes and resin, so it becomes a single-piece hull (spray or roll some thick, rubbery colorful coating over the lapped/taped areas and call it "trim" to avoid having to fair/fill/sand the areas where the tapes are used to bond the panels).
So, some questions:
- Would the construction method above likely work, or would the corners need to be beefed up with metal fittings, gussets, etc? Better ideas?
- The resin: While I'd thought vinylester might be the preferred choice (cost), I'm coming back to epoxy just due to a reduced likelihood of stress cracks and easier/safer working properties. Smart? Dumb?
- The reinforcement: Would standard e-glass be the best cost/strength candidate?
- The skins:
-- Outside skin: A trailer is likely to get bumps and whacks. A 1/4" skin of plywood on the outside of the foam (topped with FG/epoxy, and paint) would seem to offer a good ability to reduce the needed thickness of cloth/resin, spread the pressure of local impacts to a larger area of the core, and handle abuse, but I'd really like to avoid the use of anything that is susceptible to water damage and rot. So, any other suggested (cheap/lightweight) material that can provide local reinforcement and also be bonded to foam and epoxy? Or, would you just skip the sheet goods and go with a thicker glass layer? Suggested weight of glass (e.g. would a single layer of 7.5 oz do it, or would you use something thicker? BIAX?
-- Inner skin: Same considerations as above. I had thought the fiberglass reinforced plastic (FRP) sheets available at home centers (for building shower stalls, etc) might be a good standalone answer for the interior skin--they are not very light, but they are fire-resistant, look okay wihtout any other finish, and readily available. If I could get them to bond well to the foam, I might save a lot of time and expense by avoiding the need for any FG or epoxy layups on the interior. I've heard they expand/contract a lot with temperature, that's another thing I'd need to check out.
-- Attaching cabinets, walls, etc: It would be easy to incorporate wood in strips/strategic places in place of the XPS core material to provide a hardpoint for screws, but as mentioned above I'd like to avoid wood. I've seen phenolic sheet as the normal way of making hardpoints in aircraft--I'm wondering whether to stick with that or find something "good enough" that is more economical. Aircraft Spruce wants $20/sf for 1/4" thick phenolic, though I'm sure an industrial supplier could beat that price for large quantities. I might need quite a bit of it,
Thanks for any ideas, links, stifling your laughter.
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