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Ed-in-Maine 02-23-2012 02:13 PM

Which Trailer shape is better??
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Hi All,
I've scrounged up some power tools and will start building my truck Duck Tail and a small "Teardrop" camping trailer. I can easily build either trailer type and both strike the right cord as to style to my eye, so my question is which shape would be better aerodynamically? The car in the scene is a Toyota Matrix which is the real tow car.

The trailer is built on a Harbor Freight 4'x8' trailer kit. Basic dimensions are set at 4' wide, 4' high and 8'-10' long(could go a little longer if that helps).
Thanks for any input.
Ed :turtle:

Oh and much thanks to someone who mentioned Google SketchUP. What a fantastic free tool. I worked AutoCad a long time ago and this free tool would have cost a few grand back then. Computers and programers are simply amazing:thumbup:

Cd 02-23-2012 02:58 PM

I'm no aero expert, but I would guess that the trailer with the wedge shaped front end would be better due to the fact that its front end will be closer to the airflow coming off the vehicle in front. It also has more storage space.
I notice you have too steep of an angle on the rooflines of both designs.

Rather than have a pointed front to the design, you will most likely see more benefit if you flip your design backwards and have it boattail at the rear.

Cd 02-23-2012 03:01 PM

Edit : sorry . Didn't open the thumbnail ( waiting at dentist )
I would go with the rounded ( I thought it was a wedge ) from end for sure.

(The one farthest from the car )

jakobnev 02-23-2012 04:59 PM

Would you consider something that was basically shaped like a boat tail extension to the car?

Sven7 02-23-2012 05:07 PM

Lay this shape over the side of your blueprint. Scale it so the ground on the drawing is at the ground position for your trailer, and the top of the car in the drawing is at the top of your trailer (4'?).

Choose how long you want to make your trailer and cut off the rear end of the drawing at that point. The longer you make it, the better the aero. If possible apply the second drawing to the plan view so the thing tapers in both directions. If you're really adventurous, generous radii on the edges will also help.

*Make sure you cover the bottom of the trailer so it is smooth. If you can, build the body of the trailer out to cover the wheels.

Frank Lee 02-23-2012 05:16 PM

The answer is (c), none of the above.

The closer you can keep the front of the trailer to the back of the tow vehicle, the better. If the back of the tow vehicle is large and flat (pickup and cap), (a) would be best, but put radii on all the leading edges. If the tow vehicle is a small sedan or some such, (b) might be better if the flat trailer front largely matches up with the rear of the trunk. Many, many trailers, especially the teardrops, have sharp junctions from sides to front/top/rear. It is expedient for construction but hurts aero. Then, teardropping more sharp than template leads to the rear being in turbulence... probably just as well off making a squareback then and enjoying the extra interior space.

Also, think in 3-D; boattail it in plan view as well.

Sven7 02-23-2012 05:30 PM

Frank, won't the trailer be too far back for any real benefit if he doesn't have skirts to fill in the huge gap that will inevitably be there?

Sven7 02-23-2012 05:36 PM

Here's my design in Alias. It combines space efficiency with aero efficiency and complicated surfaces with ease of construction.

Frank Lee 02-23-2012 05:36 PM

I forget, is it 36"+ where the gap really starts to hurt aero?

It's a tough situation, making it as close as possible without risking hitting the trailer when backing up, going over bumps and dips, etc. Perhaps the best solution is some sort of flexy fairing that can close or at least partially close the gap without damaging anything... I seen some attempts at that on tractor/trailers but not at the consumer level.

I'd call Sven's proposal (c)- it looks quite good... now put radii on the leading and upper edges.

Sven7 02-23-2012 05:40 PM

Depends what Ed wants to make- an aero pull-behind that also hauls cargo, or a trailer that is also aerodynamic. Yours, Frank, is the former, and mine is the latter. Two different ways to approach the same problem.

I don't know how big the gap would need to be to really hurt the mileage but it'll probably be a meter or so from the get-go.

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