Improving a box cargo trailer
 

First post from a lurker.
I searched around, but if another thread answered my questions, please point me to it.

I tow a Haulmark Transport 5x8 enclosed cargo trailer (haulmark dot com/bumper-pull_cargo-trailer/Haulmark-TS-5wide/Haulmark Trailers - Cargo Trailers - Bumper Pull Trailers - Transport 5' Wide) with a 2013 Lexus RX450h.

It's a tall box with airbrakes for fenders, and it kills the hybrid's mileage (17mpg loaded, 18 empty, vs 27 wo trailer). Its only attempts at aero are a gently rounded front and radiused front corners.

I know there are many things I could try, but I'm looking for quick improvements.

A NoseCone is too expensive and requires customization for the 5' wide trailer.

A v-nose is too much work for my available time.

A full belly pan doesn't look too hard.

These vortex strake devices (ecomodder dot com/forum/showthread.php/vortex-strake-device-reducing-aerodynamic-drag-26123.html) would be simple with some aluminum angle, but I'd just be guessing at size, and it's debatable whether they work anyway.

Some sort of trailertail device (atdynamics dot com/aero.htm]Aerodynamics 101 - Tractor Trailer Aerodynamics | ATDynamics) would probably be the biggest bang for the buck but it'd take me a while and it would all be custom.

So those fenders are killing me, sticking right out in the way. I was thinking of fairing the fenders back into the body at their rear, from the top and outside of the fender down to the lower corner, with the side and bottom of the fairiing closed. Thinking there's more to be gained at the back of the fender than the front, if one were to choose. The top of my imagined fairing would be about at the same angle as the vortex strake devices above!
I'd do the front of the fenders differently (and later), with the top of the fairing remaining level with the top of the fender to the front corner of the trailer.

Moon discs (probably not pizza pans) on the outside of the wheels, stationary pizza pans inside the wheels (attached where the brakes would be if there were any).

Can't do a flat fender skirt because the tires, surprisingly, stick out beyond the big fenders.

Mods to the tow vehicle are. not. allowed .

Thoughts on which would give the most benefit for time spent?

Thanks,
Jonas

thread
 

You might do a Search EcoModder.com for the thread 'Full-Boat-tail trailer with gap-fillers for T-100'.
There are a lot of visual drag tables sprinkled in there which might help.
Also,if you can find the thread for the VW Jetta trailer thread and see how they addressed the car/trailer gap.

Yes, thanks for the links. There is a lot of useful info in those threads, and I'm familiar with the basic concepts and drag tables. But there's not much for practical application to my cargo trailer.

Jonas

This will ease things a bit :

Haulmark Trailers - Cargo Trailers - Bumper Pull Trailers - Transport 5' Wide

The front and sides seem to be radiused already, which is good.


You can buy "dust" plates that go between the wheel hub and the rims.


It'd be about the best mod you can do however ...

A crossflow plate on the centreline - or a series of smaller plates - on the front of the trailer would also help.
These prevent or reduce crossflow between the towing vehicle and the trailer, reducing drag.
Just don't put them too close to the sides.
http://www.freepatentsonline.com/6986544-0-large.jpg


Anything that smooths out the squarishly protruding wheel fenders would be OK - best in 3D, but even angled flat plates would help, and can cover the wheel arc in one go while you're at it.


Don't add any cylindrical shapes to the rear of a trailer.
They add drag and reduce stability - google "coanda effect" to see why.
A sharp cut-off line at the rear is OK.


Higher tyre pressure, as long as it doesn't make the trailer bounce.
Higher tyre pressure can also be applied to the tow vehicle as an invisible mod.
You might like the sharper handling ;)

Thanks, Aeromodder -

As you might know, I can't post URL's yet, so thanks for adding that.

I've seen those "crossflow vortex trap devices" in the same article as the "vortex strake devices." Same inventor, if I'm not mistaken. I also saw an add or a post for one in the middle rather than multiples - the one seems it would be simple to accomplish.

Those squarish fenders just bother me. In addition to the frontal area, I'd like it better if they were semicircular from the side view, not so much gap between the tire and fender. I could replace them with the round ones, but ...

Unfortunately from an improvement perspective, my focus is on using the trailer, not spending (more) time and money on it. If I can sneak on some simple things for now I'll be happy. With multiple 1000 mile round trips coming, improvements would be welcome.

I'm at the trailer tire max sidewall and trailer recommended pressure - 50psi on new tires, and I put a couple extra in the TV.

And I hadn't seen the term "coanda effect," I'll check it out.

Aerohead -

I wasn't paying attention to who it was sending me to the T100 thread - I read your whole thread, awesome work. Hope I didn't come across dismissively in my reply.

Jonas

How much of a penalty from ideal airflow would a triangular trailer tail extract?
(ok- found it here http://ecomodder.com/forum/showthrea...tml#post294074
with a similar example dropping Cd from 0.25 to 0.214)

My enclosed car hauling trailer has a drop-down ramp, but I use long extensions to get the low-riding car in and out. I'd rather rebuild the ramp to be longer, and extend the roofline down at approx 12 degrees till they meet, forming a 'triangular prism' tailcone. Not a pyramid, as the apex will be just as wide as the base. This approach maintains overhead clearance while coming up the ramp and entering the trailer. Actually, I could make the end of the ramp about 20" narrower than the hinged end, to match the floor width between the wheelwells. That would provide perhaps 10-15 degrees of taper on the tailcone sidewalls.

Enclosed trailer aero kammback thread
 

and I found this thread http://ecomodder.com/forum/showthrea...+aero+kammback.

Don't know why that didn't turn up in my original search, but very helpful in understanding the possibilities, and of course includes posts from Aerohead and Aeromodder!

I was trying to find some tall plastic wastebaskets with rounded edges as material for fender fairings, but the tall-enough ones are pretty pricey. Maybe I'll cobble a couple together. I've found the material of the Rubbermaid or other quality brands to be excellent for shaping, in that they already have useful radii and can be cut and manipulated easily. Easier that buying and forming aluminum.

Jonas

Rubbermaid
 

In the masonry section of The Home Depot,they have a $7 black ABS mixing pan with pretty good radii all around it.Weighs maybe a pound.The long axis sides might be long enough for fender lead edges.
At Tractor Supply they have a black ABS feeding trough with very generous edge radii,along with steel support structure complete for around $119.This trough is large enough to make leading edge radii for the vertical trailer sides in the long axis,and maybe enough material at each end for the fender leading edges.Very lightweight for its size also.
If you GOOGLE semi-trailer fuel economy you'll see where at least one manufacturer is offering a 'kit' to soften these squarish edges.

prism
 

In 1933 Walter Lay,at University of Michigan did wind tunnel research on a car model with a prismatic tail.
*The roofline curved as with Mair's boat tail,then descending into a constant 18-degree slope out to a point.
*The sides had initial curvature as above,blending into a constant 12-degree angle.
*The side/roof intersection was radius'd with the minimum,around 5% of the vehicles width.
*There was no up-swept 'diffuser.'
Lay measured Cd 0.12 for the smooth model.Kamm and Fachsenfeld reproduced the model and got the same results in the late '30s.
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A tail based upon something like this would be a lot easier to fabricate than the ideal compound curves.
As with Kamm and Fachsenfeld,you'd just decide how much length you could live with,and then just slice off the rest so to speak.
*It's extremely important to have the initial curvature,as NASA did with their Dryden Research Center truck studies.

Well, it all boils down to how much time / money you want to put into it - and what the return in fuel savings off these modifications is over the upcoming trips.

One of the folks on here had a semi-cylindrical tail as that was quick & easy to construct ... it didn't bring better MPG and it decreased his trailer's stability.

Out on the road, you never have a perfectly straight headwind, so the wind / Coanda effect is pulling differently on either side, inducing instability.


If you were to use some sort of tube or to go in front of the fenders, those can be used to store stuff in them as well.