Teardrops n Tiny Travel Trailers

I found this toy trailer on ebay and thought it would make a neat looking stretched teardrop, maybe 12' long?. It has that 30's era design from the original Aero trailer
The current bid is $41, Danny

Danny:

How would a builder make the top rounded off from the center?

Would it be annealed and molded down to the sides from the center top beam?

Looks like it would be more work but surely would be an artistic endeavor.

Have you thought of making the beast for your next attempt?

There are a few on the forum that like stretching the envelop and this design
would do that. Maybe Andrew or others with talent could give some insight
and thoughts that might help in design and decision making.

I think that is nice!!! I just don't have the skills to build it. Thanks for sharing!!!

sdtripper2 wrote:Danny:

How would a builder make the top rounded off from the center?

Would it be annealed and molded down to the sides from the center top beam?

Looks like it would be more work but surely would be an artistic endeavor.

Have you thought of making the beast for your next attempt?

There are a few on the forum that like stretching the envelop and this design
would do that. Maybe Andrew or others with talent could give some insight
and thoughts that might help in design and decision making.

Steve, No that won't be my next tear. Jane thinks it's ugly and it poses so many problems with all the curves, but if Airstream can do it someone may be able to do a take off on part of that design. I just thought it was interesting & worth posting. Some may find part of it's elements attractive enough to include in their build. Danny

Isn't that a miniature rocketeer..of course minus a few things-Doug originals

rbeemer wrote:Isn't that a miniature rocketeer..of course minus a few things-Doug originals

My thoughts exactly.
I've been tossing around the thoughts of a curved top front to back. You'd have to go with curved spars like in the hatch, and Fiberglass. I don't think you could get wood to work. The hatch would be real interesting to build.
Scott

Someone needs to buy that and reverse engineer it. I tried a while back using those photos, and the result was far from ideal.

Mike...

OK, here comes today's lesson!

There are two sorts of curvature (of a surface) - single curvature and double curvature.

In single curvature, the surface is curved in only one direction - at right angles to that direction, the surface is flat. Examples of single curvature surfaces are cylinders, cones and teardrop trailer top skins. A flat sheet can be bent into single curvature - if you let go of the sheet, it will spring back, or can be bent back, into a flat sheet.

In double curvature, the surface is curved in both directions and there is no direction in which it is flat. Examples of double curvature are spheres, old car fenders and (horse) saddles - note that in the saddle, the curves go in opposite directions, one inwards, one outwards. A flat sheet cannot be bent into double curvature without stretching and/or shrinking it in places - if you let go of a double curvature sheet, it may spring back a bit but it will not go, or be bent, back to being flat.

Now that trailer model requires lots of double curvature and you just can't bend plywood to do that. You can't even bend an aluminium skin to do that, unless you've either got a big press and dies (and a spare million dollars or two....), or you can shape sheet metal on an English* wheel.

The two materials/construction techniques that come to mind for low volume, thin double-curvature are fiberglass and cold-moulded plywood. Fiberglass is only a way of reproducing a double-curvature shape - you still need to make the original plug or mould.

Cold-moulded plywood involves laying hundreds of strips of plywood, many of them tapered in width, over a mould in two (or more) layers. When both layers are completed, the whole skin can be lifted off the mould.

I'm sure I've shown some of these photos here before, but they are so stunningly beautiful, that they bear being repeated. This is a one-off cold-moulded wood monocoque (=unibody, =frameless) three-wheeler car body. The last photo shows the mould over which the body was laminated.




Like building a one-off in fiberglass, this is no more than ten times the work of building a normal teardrop shape in plywood. Well, OK, maybe twenty times but, anyway, a lot less than a hundred times......

So now you're going to ask how an Airstream can have double curvature.... and I'm going to say that it doesn't (mostly). If you look closely you'll see that most of it is just single curvature within each piece - like a football, the pieces are stitched together to make something that looks like it has double curvature.



The one exception is those quarter panels under the front marker lights - those may be pressed into double curvature, but actually I doubt they are - I think Airstream has just carefully worked out how far they can go with distorting single curvature panels.

Andrew

* Strangely, we don't call them English wheels - but then we don't have anything like an English muffin, either!

Juneaudave wrote:I think that is nice!!! I just don't have the skills to build it. Thanks for sharing!!!

Daaaa-ve!!!???
Canoe forms, bead and cove wood strip construction... stapleless method of course.

Dean in Eureka, CA wrote:Canoe forms, bead and cove wood strip construction... stapleless method of course.

You have a balloon..... but I have a pin.

Bead and cove systems work on gentle curvature that is nearly single - canoe and yacht hulls being good examples. But they are not good at doing full double curvature, like a sphere, because they normally use constant width strips.

To do full double curvature you really have to go to a strip plank system, like carvel hull planking, where each strip is tapered in width and individually fitted in place. To make an eight-of-a-sphere like the top front corner of that trailer model, you would need planks that taper to zero width.

Andrew

Andrew,
Mathematician I am NOT, as all gods will testify (some no doubt with snickering) but couldn't you adapt (a la Buckminster Fuller's lovely geodesic dome) a series of ever-smaller triangles to do that?

I wonder if someone were to frame it out in lumber first, then stretch heavy canvas or whatever over it tightly (It worked for antique airplanes) and then apply layers of fiberglass on top. Then go back inside to seal the canvas against mold & mildew and fill it with insulation. The finished interior doesn't have to follow the exterior exactly and could be angled segments or right angles vs curves. It could be a nightmare too. Danny
Something like Roly did on this box lid.

Danny...I gave some serious thought to a cold molded trailer, one thing to consider is how to do the interior so that it looks good in wood. but you could frame it up like a boat hull and make the interior pieces less curved. This would add a lot of dead space between the interior and the exterior surface. Another approach would be to make it up like a boat hull, skin the inside and fill the rest of the area between the interior skin and the exterior with laminated foam...shape it and then glass it with cloth...It'd be a lot of glass work and bondo to get it looking good, but it would be well insulated. Or with the interior skin done and the framing and a few chines put in like on a boat, you could have it shot with spray foam...after it cures, shape it and then glass it. I'm still thinking about a compound curved trailer...but there are a ton of details to work out and it's not a couple of month build. There is a program out there for cold molding and I think Rasp mentioned it in an earlier thread.

I wonder about that toy on E-Bay...looks like a repaint on it to me.. Doug
PS I think you should do it....save me a lot of mistakes!!!

doug hodder wrote:I wonder about that toy on E-Bay...looks like a repaint on it to me.. Doug
PS I think you should do it....save me a lot of mistakes!!!

Doug, it mentioned is was repainted, someones bad. I wouldn't mind having that toy just to study and play around with ideas but I'm sure it will skyrock in price at the end of the auction. I'm not interested in building it as is. I think the roof and walls would be quite heavy anyway unless a plug was made to glass over. Danny

If someone on the forum wins this, please take lots of nice orthographics photos of it so we can make some drawings...

Mike...