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Old 08-02-2013, 11:14 PM   #1 (permalink)
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Trailer thread! Teardrop builders wanted.

Were I to build this myself, it would necessarily come after the full Coanda-effect kit on my panel van and turning my '58 Beetle into a redwood Zeppelin. So I release this under Creative Commons Attribution 3.0 Unported* for anyone who wants to build a teardrop, but doesn't know how to get outside the 'box'.

What defines a teardrop? I would suggest
•simple-curved aerodynamic shape
•one-sheet floor
•no standing room
•side hatch entry
•body narrower than the wheels
•rear kitchen

What I propose
•simple-curved approximation of The Template
•since I'm cutting the sheet, I cheat with a 4x12 or 5x10 sheet
•I propose to stretch the template in the Yth direction — 150 to 200%
•move the entry to the truncated boattail
•tandem wheels on a single axle
•5 out of 6 ain't bad, integrated water storage

I've worked with geodesic domes so I'm used to approximating curves with straight lines. The template could be rendered as a low frequency triangular faceted asymmetrical dome, as I did with the wooden motorhome design. In this case I start with a hexagon base and curved vertical edges. The 60° angles become 45° in front to accommodate jack-knifing and 22.5° in the rear to give a good closing angle. The tail is truncated to the size of the door. The various possible [straight or] curved edges mean the shape goes all wiggly-wobbly compared to a geodesic shape. Straight edges result in a Template semicircular arc, a 5' wide body would have 2 1/2' of headroom. A deep curve would result in a Conestoga-like wide body.


One thing I once owned that went down the road to an hopeful new owner was a 1952 Silver Streak Clipper. I don't have the trailer today, but I do have a measured drawing.

The quarter-spherical end caps use tightly gored material, narrow strips in simple curves and lots of seams. The thing I like about the construction of that trailer was that the frame was a 5" diameter center spine with 6" C-channel crossmembers. And that was it—each crossmember terminated in a carriage bolt through the plywood deck An aluminum C-channel the same thickness as the skin material was screwed to the upper surface of the deck to carry the inner and outer wall skins. The outer skin was aluminum and the inner was steel.


A second influence is the Bowlus Papoose. I saw a 20-footer when I was in college, and they sell 35-foot Bowlus Road Chief replicas for $100,000 (or try to). The Papoose is 16 feet long, that's getting into teardrop territory. It's one of those cases where it would go faster backward.

Another influence is these pictures I found of a trailer called The Roswell.


What this suggests to me is to use the hexagonal-pod construction (a design that goes back at least to Domebook 1, if your interested) to get a low-resolution highly-streamlined shape that because it uses the simple curves and has one flat wall is IMHO technically a teardrop!

So using the construction of the Silverstreak frame and extrapolating from the single-trailing-arm suspension on my Westphalia utility trailer, this design extends the Roswell concept in three ways:
•The door and it's associated framing is moved from the thin-walled side, to a flat truncation of the Template shape.
•The Stretched hexagon plan of the Roswell is made asymmetrical. The front angle is 90° to allow jack-knifing, and the rear angle is 45° to get the 22 1/2° optimum taper in the rear. The profile is level from the center [skylight] to the top of the door.
•The suspension consists of a dog-bone arm (sort of like a double-ended front motorcycle fork) that pivots on an axle stub and carries a wheel and tire on each side. The design scales from a 4x8 on 4ea 8" wheels to a 5x10 on 10" wheels or even a 5x16 on 12" wheels.

Small versions might be unsprung. More advanced version would have rubber in torsion and disk brakes or kinetic recovery that dampens the ride by charging a battery.


The center tube could double as a water tank, with the weight carried low in the center. 3 to 14 gallons by my calculation. The back of the Buck-Rogers-fin-like flat Trophenwagen-style fender top would flip out into a seat on either side of the door or a bench along the side. The rear bumper folds down into a step beneath the door. Kitchen (if any) would be over the hitch, the reverse of normal teardrop practice.

Cross section could be anything from the 5x2.5 aerodynamic optimum to 4x4 or as big as 5x6, and it could be squircular! I think once you widen the body and enclose the wheels it's not really a teardrop, although 4/5x6 would look something like an horse trailer. If the wheels were at the center section, half wheelwells could fit in pretty neatly, making shelves in the interior.

This leaves a lot unsaid, construction materials (PolyMetal vs corrugated vs burlap/hoops), center of balance, central skylight bubble vs trolley roof, & etc,. & etc. I choose to stop here.

'What do you think, Sirs?'



*This work is licensed under a Creative Commons Attribution 3.0 Unported License. Creative Commons — Attribution 3.0 Unported — CC BY 3.0


Last edited by freebeard; 08-02-2013 at 11:19 PM..
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Old 08-03-2013, 01:35 PM   #2 (permalink)
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think

I'd like to see a road-going version trekking down the highway for a real-life experience.It would ask the RV'er for less sacrifice than some of the stuff I'm cobbling together.
The upper curvature looks real yummy after seeing You-Tube of square-edged travel trailers blowing completely over in a crosswind!
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Old 08-03-2013, 08:31 PM   #3 (permalink)
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aerohead! Tag, you're it. As you say you have a history with this sort of thing. I have a history of having trouble getting other people to build my ideas.

On that first model the edges are 4', 3' and 5' front to back. I started with the center section 3' long and the center at 18" to get the 135°/2 and 157.5°/2 angles to the center. The result is a short 'thorax' and a long 'abdomen'.

I'm currently making a 2nd model, same scale, same 10' length but on a 4x10 sheet. The edge lengths will be arbitrarily 4',4', and 4'. Also the wheels were pushed back so they could be tucked inside the max width; but I think teardrops are like that because of the weight of the kitchen in back. So the new model has the wheels in the (newly longer) center section with semi-enclosed wheelwells and half-fender/spats. And it will be skinned with corrugated material.

If someone was building one, I might go back to the 3D modeling and compare squircles at 45° to each other.

If I did build one myself, it probably would be based on my Westy utility trailer. I have a source for the (thoroughly thrashed) suspension parts via thesamba.com. It's a 4'x3'x1.5 box. Some redwood bows with temp bracing, with burlap shrunk to fit and sprayed with clear polyurethane would get me in the game.
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Old 08-09-2013, 11:43 AM   #4 (permalink)
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Have you thrown together a model WITH the tow vehicle to look at airflow? Maybe you could fit in more interior space on the front if it's within the template. Of course you'd want to accomodate about 15* of yaw in the air flow as well.

I was imagining a boat hull type construction with longitudinal wood slats. That would look fantastic.



Another thing to think about would be integrating the wheel pods into the body. I was thinking you make the standard 40's style wheel and skirt, but then extrude it into the body. Kind of like this Topolino dragster I saw a couple years ago, but with skirts.

It would eliminate the aero uncertainty of the "tunnel" between wheel and body. Of course, you'd want to make a legitimate teardrop instead of this stylized mud guard.

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Old 08-12-2013, 04:20 AM   #5 (permalink)
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Thanks for thinking about it. I basically threw together a few ideas—the shell, the frame and the suspension—that are really independent. Hanging two wheels on a single suspended pivot is probably the least viable. It's intended to reduce the frontal area for the wheel and tire, and *might* work retrofitted on any teardrop.

Likewise the Silver Streak frame detail could be applied to any teardrop.

The compound curve wood strip construction is optimal, but I was trying to work within the stated teardrop parameters. Your suggestion could work on this frame and suspension.

Here's how Bowlus handled the fenders:

But I like the idea of a flat-topped fender that folds out into a bench or table.

I'm back from a road trip so maybe I'll make progress on the 2nd iteration. On the other hand, I have a design for a teardrop that would scale down to bicycle or motorcycle size that is the traditional flat-sided shape. I'm not sure where people's interests lie.
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Old 08-12-2013, 10:43 PM   #6 (permalink)
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Old 08-13-2013, 02:43 AM   #7 (permalink)
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dremd -- Darn—now I gots to get off my butt.

Quote:
Have you thrown together a model WITH the tow vehicle to look at airflow? Maybe you could fit in more interior space on the front if it's within the template. Of course you'd want to accomodate about 15* of yaw in the air flow as well.
I didn't address this. It intended to be generic, but it's 1"=1". I'll look for a Barbie doll.

The three straight segments are distributed along the teardrop curve. That's really low resolution. Overlaid in 2D the two corners overlap about as much as a circle overlaps a square of equal perimeter. The Classical problem; squaring the circle, via eyeball engineering.

Adjusting the relative side lengths changes the angles.It happens that with ~3, 4, and 5ft sides the front angle is ~45° and the middle side are parallel. If you sharpen the nose the middle sides taper to the rear, for instance.

Cross section at yaw angles is less, is it not? OMG
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Old 08-15-2013, 02:03 PM   #8 (permalink)
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I've thought of similar, starting with a ~$200 cheapo 4 X 8 open flatbed trailer from Northern Tools or Harbor Freight, the kind that folds and stands on end to take up less garage space.

Replace the cheap Chinese bearings and wheels/tires on day one, because they're worthless.Use Coroplast for the Conestoga wagon sides and roof, to act as wheel skirts and partly enclose the wheels for better streamlining. No point in wasting that space and having the wheels make extra drag. Insert fiberglass or aluminum tent poles into the flutes for stiffness. Extend the floor forwards to cover the folding tongue of the trailer, no reason to waste that space. Extend the floor aft to act as a loading ramp and to be the base floor for the teardrop tail. Use Coroplast for all skins, essentially shaped per your model shown above. Make a fairing to cover the axle below, turning it into essentially an airfoil shape to reduce drag.

This would be a sorta mini-horse trailer, with teardrop rear. Great for hauling motorcycles, and/or as a camper trailer.

Could probably do this project for less than ~$500 if all new stuff, considerably less if you can find the basic trailer on Craigslist or similar.
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Old 08-15-2013, 06:33 PM   #9 (permalink)
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Otto -- Thanks for taking the time.*

...but, I've thought about all that, like you, and I'm trying to move beyond that. For instance:

•the frame. A central spine and a few crossmembers, one doubled up to make an axle inside the shell, incorporating a water tank and step/bumper. It's a sub-frame inside a monocoque shell. Added windows would be like in Burt Rutan's airplanes.

•aerodynamics of the wheels? I choose to reduce the frontal area of the wheel/tire and create a low frontal area dual-use fender. The tandem wheels could have a connecting fillet and Moon disks.

•Coroplast. I was intentionally vague. Alumacorr is aluminum skinned coroplast, but it still doesn't take abrasion as well as PolyMetal, for similar weight. Grimco MaxMetal has thicker skins. (Links on request)

Hey, plywood ribs, stringers and cedar shingles laid longitudinally and lapped vertically, with the ends bandsawed like fish scales.

In coroplast's favor, the stiffen ribs could also pin the curved sections together. Welding rod tack welded end to end 12' long and bent twice.

If/when I get back to model #2 it will be 3-3.5' tall with a 'trolley top' of 8-10" to get away from that horse-trailer look.

*Had I gotten vanity plates for my Notchback Type III, they would have read OTTOBON.
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Old 08-29-2013, 06:29 AM   #10 (permalink)
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I have had one of the 1720# HF trailers for 10 years without bearing failure hauling all sorts of things. I DO repack the bearings at the beginning of each season. I also had one of the lighter 4x8 trailers with 10" wheels for 25+ years with no failures there either.

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