Aerodynamics - One Hundred Years of Missed Opportunities

[twisted lines]

Now the warnings
I was cutting my side walls down while you posted that!
2" in 8'
Ill be ok I am going for the tapered rear as well as a top drop the last 12"-13"
My deal on #2 was mileage; drop with #1

 

[kd8cgo]

Oh my! Well we can't bake any cakes without breaking a few eggs! I think it will turn out

 

[StaceyK]

Has anyone seen this Safari Alto A2124? They’re saying the shape reduces drag by 15% (47% of their other models) and the shape looks like it might be a little easier to replicate…sort of! They changed the frame so that it’s smooth underneath….

Sent from my iPad using Tapatalk

 

[kd8cgo]

First I've seen that model, but I know that other Alto models have some really nice design elements. It looks like it follows many recommendations for aerodynamic improvements, I like it! I've seen their teardrop-shaped pop up roof Safari Condo model before, also cool!

 

[Rustic313]

Just kicking this around, and looking at the shape plus the polydrop...

Rather than a rather difficult to build curved shape, I think you could probably just use straight angles and get 80% of the way there. Keeping everything straight opens up the use of easy to source and work with construction materials too like sheet plywood, aluminum panels, roof panels, etc.

DESIGN ONE (SIMPLEST)
- Front: Straight vertical up until you get to the window height of the tow vehicle, then a slanted piece at approximately a 45 degree angle to get to the roof peak of the trailer.
- Slightly sloped long roof back to the vertical line marked "15 degrees."
- Rear: Chop it off straight down at that point. "Kammback."

That is basically what the polydrop does with their smaller trailer, except instead of going straight up at the front and back they have a slope. For a DIY home build "KISS" seems to just call for going straight up and down.

This is pretty simple: You have two straight vertical walls, and a roof with two different angles on it. Water runoff is not an issue.

Eyeballing it with the help of a CAD sketch of a basic steel trailer on the ecomodder tool, if you are 4' high at the peak of your interior box space (4x8 sheet of plywood... and keeping the total height shorter than a sedan or CUV height), I think you can go about 10' long if you chop it down at the 15 degree mark. If you're 52" high at the peak of your interior box space, it looks like you can go about 14' long.

DESIGN TWO (HARDER)
For a longer trailer you could put a "bend" in the roof piece, effectively having a fairly long gently sloping roof, and then a bend to a steeper roof segment towards the back. Exact placement depends on the length of the trailer vs. the airfoil template, but the slope clearly gets steeper the further back you go.

Looking at the CAD drawing of the steel trailer, I think I'd probably go with a gently sloping roof to the fourth line (between those marked 25 and 15 degrees -- can't quite read it), then a steeper roof to the 22 degree mark. This lets your design be about a third longer.

This is remarkably similar to what Polydrops does with their longer trailer.

Depending on how you do this you could also have that second "bend" be hinged for a kitchen space. From a practical point of view, honestly most of the space aft of the line marked 15 degrees seems pretty marginal in utility. The headroom is getting really quite short. And as interesting as having the rear galley is, adding that hinge adds more water intrusion problems (just google "teardrop galley leaking" -- seems a common issue).

I guess it could also be useful if you had something with extremely low height, but I can't imagine going much shorter than 4' tall.

I also honestly don't know how practical this is. I would certainly consider building a 5x10 DIY trailer, but a 5x20 seems like a lot.

 

[FischAutoTechGarten]

I suspect the Chesapeake Light Craft Tear Drop Camper is highly optimized aerodynamically. It isn't simply slab sided and has the proper taper at the rear to reduce drag.

https://clcboats.com/teardrop

 

[kd8cgo]

I suspect the Chesapeake Light Craft Tear Drop Camper is highly optimized aerodynamically. It isn't simply slab sided and has the proper taper at the rear to reduce drag.

https://clcboats.com/teardrop

It has some good aero features, particularly the taper at the top roof interface with the sides which is great for crosswind drag performance, and the added hitch box fills in the area between the tow vehicle and the trailer nicely, but it has the same problem with a very poor profile shape as most traditional teardrops, R-pod, VW beetle, etc - the rear roof/hatch area drops way too steeply to be aerodynamic and instead functions as an air brake:

 

[Melvin-TNT]

Sketchup 3D examples of an approximate "fully streamlined half-body" on top of a Harbor Freight 4x8 trailer, behind a basic model of my tow vehicle. This is not intended to showcase an actual build design, but simply what applying the streamlining template in 3 dimensions (with no other shape constraints or considerations) would look like. I scaled the body shape to the width and roof height of the tow vehicle, it ends up 5 1/2 ft. wide, and ~4' tall above the trailer deck at the roof peak. The body length in this example, coming to almost a point at the rear - is just over 11 1/2 ft. long. I thought this might help visualize what the curvature of a streamline looks like next to "real components" like the car and the trailer frame.

View attachment 1143755
View attachment 1143754
View attachment 1143753

 

[Melvin-TNT]

Instead of putting the galley cross ways this design has enough length you could have a longitudinal galley.

Use a split hood like on a lot of pre war (WWI) cars and trucks. For example the Pilot house Dodge truck design with a wide center band would be strong and easy (for this design) to fabricate.

You wouldn't get as much shelter from the weather but you wouldn't be dealing with a 16" galley either.