Aerodynamic trailer design

[Ecky]

Thanks Frank. I'll probably stick with the stock length too, given that info.

Got my hitch installed:






Will probably purchase a trailer and begin construction after the new year.

[euromodder]

Originally Posted by Ecky

The tail lights are only 4.7ft apart edge to edge, and the further the trailer sits back, the narrower it needs to be.

but then, closing the gap with the towing vehicle gets harder - and that's where a lot of mpg's are lost pulling a trailer.

[Ecky]

Updated designs:










Design two has less volume and less turning radius, but would be easier to construct and will likely have more aero benefit. It also has a wonderful symmetry to it: 6' x 4', 12" in the rear and 18" in the front, 24" from the ball, 30 cubic feet, which effectively triples what I can bring with me. I would likely split the top with hinges on either side, so I can open it and carry large items such as appliances.

[Ecky]

The more I think about it, the more I like your CRX trailer and find my design converging on it, aerohead. It's an elegant solution.

This is what I'm up to now:




I decided it would be possible to keep the rounded nose so long as I didn't slope it at the top, which would require that I cut two fitting ovals. Turning angle is down to 65° if I don't set the nose back, but I'm thinking of constructing the trailer with a plywood frame, bottom, and lid, and siding that you'd use in an RV shower which would give and return to shape if it hits the bumper; plus it's waterproof. 7' length keeps the slope shallow enough that I should hopefully have reattachment of air before the tail end, and lets me cut it from two 4x8 sheets of plywood. I don't think I'll be able to easily round the top edges like you did.

What I haven't decided on yet is what to do about the fenders and underside. As I understand, extending the fenders down to cover the front of the tires should provide aero benefit, but that might be a bit ambitious for my first iteration.

EDIT: I miscalculated the volume of my design #2 in post #33, it should have been 22.5 cubic feet. Volume of this design is ~32 cubic feet.

EDIT2: Should I lower the front an inch or two, do you think? The leading edge of the cylindrical nose is within the template, but moving back, it's not.

[skyking]

Here are some inexpensive torsion half axles from Northern tool. These are probably the same cheap axles from amazon.
Reliable Rubber Torsion Axle Suspension Units | Rubber Torsion Axle Suspension Units| Northern Tool + Equipment
I have towed torsion axles before, and the ride is far better than the typical spring setup.
If you fab your own and put a telescoping tongue on it for storage, you can make a couple of intermediate length holes for testing purposes.

[MetroMPG]

Originally Posted by aardvarcus

Ecky,

I rescind my former statement, you are using the tool correctly. However the tool that you are using is using an older version of the Aerodynamic Streamlining Template. There is a newer version which is slightly more aggressive, the AST-II.

I will admit I didn't follow the streamlining template revision discussion closely. Should should I update the tool with a revised image?

[aerohead]

Originally Posted by Ecky

The more I think about it, the more I like your CRX trailer and find my design converging on it, aerohead. It's an elegant solution.

This is what I'm up to now:




I decided it would be possible to keep the rounded nose so long as I didn't slope it at the top, which would require that I cut two fitting ovals. Turning angle is down to 65° if I don't set the nose back, but I'm thinking of constructing the trailer with a plywood frame, bottom, and lid, and siding that you'd use in an RV shower which would give and return to shape if it hits the bumper; plus it's waterproof. 7' length keeps the slope shallow enough that I should hopefully have reattachment of air before the tail end, and lets me cut it from two 4x8 sheets of plywood. I don't think I'll be able to easily round the top edges like you did.

What I haven't decided on yet is what to do about the fenders and underside. As I understand, extending the fenders down to cover the front of the tires should provide aero benefit, but that might be a bit ambitious for my first iteration.

EDIT: I miscalculated the volume of my design #2 in post #33, it should have been 22.5 cubic feet. Volume of this design is ~32 cubic feet.

EDIT2: Should I lower the front an inch or two, do you think? The leading edge of the cylindrical nose is within the template, but moving back, it's not.

I like the idea of efficient use of materials,and I think your nose will basically slip into the wake area as you've drawn it.There'll be turbulence due to the gap but I think you'll have reattachment everywhere except the belly.

With enough length,even a sharp-edged box will regain attached flow.

The front of the trailer will be embedded within the Insight's wake.Here's a shot of a 1st-gen Golf/Rabbit wake.

The gap-drag is an unknown quantity.Here you can see the drag of a Clark-Y airfoil as a function of gap location,etc..

As to the fenders and bottom,I've gone ahead and enclosed mine,with full sides,complete belly pan,and I'm about half-way with complete wheel fairings.
You might just do simple skirts down to where a belly pan with diffuser might be,and some simple fairings before and after the wheels.
Or just skip it,get a baseline for whatever you do,then later,if you add the bottom cleanup,you can compare performance to see what difference the bottom made.
On low-drag cars,the wheel drag alone can constitute half of the overall drag,so the 'cleaner' you get,these naughty bits become more and more important.

[Ecky]

Originally Posted by MetroMPG

I will admit I didn't follow the streamlining template revision discussion closely. Should should I update the tool with a revised image?

This is the template aardvarcus linked, and the one I've been using:

[Ecky]

Trailer frame assembled. Here's a very rough (not to scale) sketch:




Down the road I'm hoping it'll look a bit more like this:




When I asked my father his opinion on what color I should paint it, he said that because black is the fastest color, it's probably also the most aerodynamic. Thinking of just extending the car's color scheme, though I might add a stripe somewhere.

EDIT: Top view, without the addition of fenders

[nemo]

Originally Posted by MetroMPG

I will admit I didn't follow the streamlining template revision discussion closely. Should should I update the tool with a revised image?

Would there be a way to have it switchable in the tool or 2 versions of the tool (one with each version). It would be interesting for comparison.