Teardrops n Tiny Travel Trailers

Hope that name isn't taken already...

OK -- here is a rough sketch of the idea in my head. It is 12' long, 6'high, and 5'wide. Subtract two inches of width and one inch of height for interior dimensions.


The idea is to build it from 1" foam, covered in some sort of fabric. The curved profile should provide ample strength at a significant weight savings compared to 2". The floor would also be 1" foam, with a fabric skin below, and a lauan skin above. I figure about 16 sheets of foam will be required, so at, what -- 8 lbs per sheet? -- that would be under 120 lb by the time I subtract waste. Add fabric and paint and lauan and hardware, and I think I could bring the whole thing in at under 700lbs, trailer included. I'm shooting for 600 lbs or so.

I'm curious to hear any feedback -- this is early in the design phase. Critical elements to me are a permanent bed, a place to sit, and a place to stand. I envision two small desk chairs by the table.

The bed is double-size, minus the rounded corners. It would be mounted 18" or so above the floor, so there is a generous basement below, accessible from outside. The bed platform is structural. The table would have a half-height bulkhead, and the galley a full-height one, to lend additional rigidity to the fuselage. The footlocker would also strengthen the front profile.

It will fit on a somewhat modified 4x8 trailer. The back needs to be narrowed and lengthened to support the back end, and the tongue need to be lengthened. Haven't worked out all the trailer details yet. I think that the profile should produce minimal drag, so that even a small car could tow it without issues. I intend to put on trailer brakes, nonetheless.

I love the fact that the bed is permanent, rather than doubling as the table. I also like the nose area. The only thing that might concern me is the axle seems too far forward?

I will enjoy watching this come together.

MBob ... The only part that I see that would be difficult would be the front transition off the roof to the round Nose ... How are you gonna' do that ???

I am wondering about the axle placement, as well. That drawing is just approximate. My thinking, however, was that the bed and basement will carry a fair amount of weight, which would be somewhat balanced by the galley in the rear. But, if the cargo is loaded towards the front (in the basement), I am guessing it would still have a tongue-weight bias. However, I haven't actually done a lot of math yet on it. The tapering tail removes about 50% of the volume of the space behind the axle. Additionally, on a trailer this light, putting a deep-cycle battery on the tongue should make a big difference in the weight distribution.

As far as how to put the roof on... I don't know if it is clear in the pictures or not, but the walls are perpendicular (as in straight up and down). My thought is to just build the thing 6' tall, front to back, to facilitate getting the curvature right on the nose. Then, I can come back and cut the top curve on, being careful to get it the same on both sides. Once that is cut, the roof panel should just lie in place, with a notch cut at the front wall to blend the two surfaces. I anticipate it would take a bit of build-up and forming to get it smooth. Did that make any sense?

Well, sorta ' ... You may want to make a small model first just to test the design ... 1/4" Foam makes a great material for this ... even old foam meat trays ... I built a model long before I attempted the big one ... just to see if it would work ...

I like it better the other way- with the V forward.

One thing that isn't clear in my drawing -- the roof will not curve smoothly into the front wall in a compound curvature. There will be a joint there where it transitions between the two surfaces, and there will be a small angle there. The goal is just to make it as smooth as possible.

I don't anticipate launching into this one right away. I already have a LittleGuy 4-wide that we love, and with a kiddo in college, I don't need more things to spend my money on. I am thinking that once she is out of college in three or eight more years, then I can start in on a project, with the goal of having it ready before retirement...

jimqpublic wrote:I like it better the other way- with the V forward.

The V forward doesn't give the best aerodynamic advantage. As I understand it, the closer you can come to the shape of a drop of water falling, the better off you are. So, that was my starting point. I am trying to make a trailer that can easily and safely be towed within the tow limits of a small-ish car, such as a Toyota Corolla -- considering weight and also drag. I will tweak some more long before I build, and I'm not an engineer, so I'm open to input.

Hi Mojave Bob,

I think you have a really good design going there. A couple-three
tweaks I'd like to offer for consideration would be:

1- I'd move the door a little sideways toward the wheels/front so that
you could have a counter or closet from the tail's point to the area you've
labeled the galley. If the door would need a little curve in it there, that
shouldn't be too hard to do in foam - but it could be positioned on the tail
wall before the tighter curve where the sidewall starts to curve into the
tail wall. A 10" to 12" deep counter or side hanging closet could be very
useful. Even an 8" deep space would give useful storage as closet or
counter with a cupboard below or even open shelves below for shoes
[especially when wet] or what-not. That 8 or 10 or 12" [or wider as
possible] distance from the tail point to the door should give much more
strength and rigidity to the tail point construction as the two meeting tail
walls would be bracing each other and would have wider and therefore
stronger sections meeting to do the bracing.

2- I wouldn't worry about any compound curves in the front where the
down sloping roof meets the curving [semicircular shaped] front wall area.
I'd just measure/approximate the height of the tow vehicle and have the
front wallcenter rise to that height, or a little below, to meet the downward
curving roof. I'd then radius the roof and wall joint for the whole trailer
body. From what I've read on the subject so far it seems that 'radiusing'
a nominally 90 degree joint is very beneficial aero-wise and not as difficult
as compound curves. even a 1/2 -1" 'radiusing' would help. All you'd
need to reinforce the roof&wall joint would be to glue either @ a 2" strip of
wall thickness foam against the top of the wall at the ceiling/roof joint and
then glue a 1" strip of foam on top of that at the joint for a 'stepped crown
molding' effect that would then allow you to round over the outside
to a 1-2" radius on the outside of the joint. If you don't like the stepped
crown molding look at the joint you could alternatively bevel some foam
strips to fit into the side & roof interior joint. You could then reinforce both
the exterior and interior side & roof joint areas with some of the fiberglass
cloth tape and whatever you are using as glue or coating - epoxy or
TBII-III or paint etc. before you cover the whole with fabric and coating.

3-Also don't forget to include some appropriate wood or aluminum or such
reinforcements around openings and attachments of walls to floor and
floor to frame etc.. Also remember the "sock effect" in the overall
scheme of things.

It'll be interesting to see your design evolve and the build begin!

Cheers,
Norm/mezmo

P.S. Here are a couple links to web sites that may be of help.

This outstanding foam and fiberglass Swedish build has good info very
pertinent to your proposed build.

http://www.goldbrand.info/index.html

Here's a FYI type thing for you. Again, I'm pretty sure it's Swedish,
that shows an inspired craftsman's efforts. First, he did a custom car
and then a steel TTT he named the "Dreamliner" as well.

http://hem.bredband.net/heavy1/index.htm

http://hem.bredband.net/heavy1/dreamliner/page_01.htm

Mez, after seeing your links , see now how MBobs could succeed ...

I just changed a construction line for visualization (mine ) and it works !!! Maybe just rounding some edges later ... ??? http://www.tnttt.com/gallery/image.php?image_id=81741

Norm -- some great suggestions.

I am continually reworking this design in my mind. I like the idea of moving the door forward a bit, but my intention is to use a stock aluminum framed RV door, which will require a flat section of wall. (They are surprisingly light, foam cored, seal well, and have a built-in screen door). I could achieve that if I changed the shape a bit into more of a true water droplet. I might need to stretch the overall length a bit to get the desired interior space, though. Fortunately, that isn't a problem in foam! It might end up requiring a custom trailer, but that won't stop me. I'll have to try some new drawings. I wish I had the patience to figure out SketchUP.

You and GPW hit it exactly right on my front end design. That is what I had pictured in my mind, but blended a bit more than what GPW drew for clarity. Basically just a bent lid on a round box.

Do we have any fluid-aero dynamics engineers lurking this thread? What is the relative drag co-efficient difference between two identical optimized water-droplet shapes, one 5' wide, and the other 6' wide? And, how long should the tail be relative to the "head" of the droplet?

Simple thought : the more surface area presented to the "relative wind" the more drag ... easy to experience by "flying" your hand out the car window ... Rounded edges are better , creating less vortices ...

Ok -- My research so far has indicated that for best aerodynamics, it would be pointed at the front and the rear, but that can introduce some very strange towing dynamics at speed. The best profile to combine aerodynamics and towability would be rounded front with a long, pointed tail -- the longer the better.

So, I have re-drawn the profile to move the door forward, as suggested by Mezmo. The axle is actually now forward of center, but the square footage of trailer forward and behind the axle is equal. With the tongue added out the front, the axle ends up being centered between the hitch ball and the tail. The roof profile at the front should provide some down pressure on the tongue as well, so I think from a weight distribution perspective, I am ok.

What I'm not sure about is the effect of that long tail in a crosswind. Would that introduce instability at speed, or would the smooth slipstream keep it balanced? The air pressure around the nose should give it quite a bit of grab, but enough to overcome the sail effect of the tail? What do you guys think? I could add airfoils at the rear if I could come up with a suitable design.

Anyway, here for your consideration and comment is Dreamliner2:

Gee Whiz!!! Now your axle placement is WORSE

Sometimes a little less streamlining and more practicality is a "Good thing" ...

GPW wrote:Gee Whiz!!! Now your axle placement is WORSE

Sometimes a little less streamlining and more practicality is a "Good thing" ...

Why do you say it is worse? Yes, it is forward of center on the trailer body, but is centered from ball to tail, and the trailer volume is distributed equally ahead of and behind the axle, with the primary cargo area forward of the axle to provide a forward weight bias.

I disagree that too much efficiency is a bad thing. This is a brainstorming process to provide maximum efficiency. I want to be able to safely tow with a minimal tow vehicle. If I bunch up the trailer shorter and "boxier", sure, I can achieve the amenities in a shorter package at the same overall weight, but my wind loading would put too much strain on my transmission, and would have a far greater impact on my towing gas mileage.

No, this does not represent a final buildable design. I just think we need to think "outside the box". On another small trailer forum, somebody was surprised at how much their mileage dropped between towing a molded fiberglass trailer to towing a T@B. The are similar size and weight. The differences are in frontal area and profiles. The squarish "shoulders" and
"hips" of the T@B reduced their towing mileage by several mpg. I want to have as little impact on mileage as possible.