Minimizing Aerodynamic Effect for Trailer Towing
 

Everything has trade-offs . . . efficiency / utility / aesthetics / availability / cost / storage ...

This is the project, and the goal is to improve towabiltiy and economy. The constraints are the usual (cost, time, availability of pieces, ...) then, add aesthetics and functionality.


http://www.synthx.com/i/ProjectConflict-00.jpg


Background: For work I sometimes attend events that require a lot of "stuff". I've outgrown the truck, so added a trailer. Couldn't find what I wanted, couldn't afford custom, don't have time to build it, so finally opted for this. Got a good deal, so this is where I start.

Now I'm thinking mods just for fun to see what it can become, but I'm constrained --- have to face realities --- aesthetics are important because it's part of the company presentation (outdoor events and will have company logos), and functionality (must be easy to use). I'd love to tape it all up, unfortunately, a lot of people are quick to judge . . .

I appreciate suggestions -- with a focus on practicality (see above constraints). Boat tails, for instance, though good for drag reduction, have practicality issues when long enough to be effective. I'd like your help thinking through mods that can look nice as well as be functional, practical, cost effective and efficient.

I'd love to see any examples of what you've done too. I have a bunch of ideas, but I'll insert them later.

Thank you, in advance, for your suggestions. This should be fun ... not just with the discussion, but also in the doing!

Additional research from another discussion
 

Yes, Thank you. I have read that thread and love the idea of a completely streamlined trailer, unfortunately not in the time or financial budget. I love much of what was in that thread and especially some of the posts from aerohead and skyking.


Off the bat, the hit for towing the trailer home (empty just after I purchased it) was around -2 MPG. Not huge, all things considered, and not very scientific (based on a one-way trip of 50 miles).

I'll post more about the first "real" trip when I get the info complied. Driving along gave me lots of time to think, and the mods are stewing in my head.

I suspect simply radiusing the front of the trailer and adding a box cavity to the rear of it, would give the most bang for the buck.

trailer mods
 

If you have an awning company nearby,they could roll-form square aluminum tubing and heli-arc it into a skeleton framework for an aerodynamic nose which would resemble an Airstream or W-W 2-horse stock trailer.
This framework could have aluminum skin riveted on and painted to match the trailer.
The same company could also make you skeletons for the wheel fenders,to create lower drag fairings.
Short of composites,I can't think of a more direct route to drag reduction which also addressed your aesthetic considerations.

Welcome to Ecomodder!

http://ecomodder.com/forum/member-fr...01-2-04-41.png

I posted this picture a while back and someone actually implemented it on a travel trailer. I think he used 4" stovepipe, the split kind, unrolled and attached to the front edges of the trailer. It's a way to get the radiused edge without intruding into the box.

Beyond that, race car wide-body fenders over the stainless steel ones. And see if you can channel the air from under the tow vehicle to under the trailer, or at least divert it to the sides.

Aerohead, I love the idea with the awning company. I love it particularly because I've already been to a local company to discuss exactly that. I have not decided yet on what direction to go, but that is high on the list.

I had not considered also having them do something over the wheels and fenders. Thank you for that addition. I think that's a pretty cool idea.

Also, Freebeard, the half pipe thing sounds interesting. Do you know of anyone who has actually done that? And, what was the result?

OK, here's the info. First "real" trip was 199.2 miles. The only mod done for the first trip was to lower the hitch (level out the trailer and reduce frontal area).

The drawbar in the first post photo above has a 2" drop, this one has a 4" drop. It needs a touch more, and I have an 8" drop, but that seems a little too much.

http://www.synthx.com/i/ProjectConflict-02.jpg

The total for the first trip was down 2.2 MPG from normal, but that's not the whole story. The truck is a 4.6L manual trans and generally very capable. By itself, loaded, it holds 75+ MPH on the highway for this route without a problem.

This is Colorado, so there are lots of hills (and satisfying descents), of course, but with the trailer, there were several times climbing it struggled to hold even 65. Certainly added weight is a factor (+900#), but I think the aerodynamic load is killer. (I have a long flat bed trailer I've pulled with a lot more weight and it doesn't have nearly the drag of this sail.)

OK, the understatement is "Go slower." I understand the V^2 contingent -- which is, one of the conflicts because time is also important. Anyway, next step is to try a few aero mods. I've got one in mind that I think you'll like.

Trailer wheel covers, aftermarket folding trailer wind deflectors and box trailer nose cones. DIY boxed-in trailer wheel fenders and mod your own folding trailer boattail panels.

Interesting front nose cone or gap fairing. http://www.freightwing.com/common/im...ap_fairing.jpg

http://cdn2.bigcommerce.com/server90...0.1280.jpg?c=2

http://www.nosecone.com/images/home_r4_c3.jpg

http://www.surfbus78.pwp.blueyonder....images/TT1.jpg

http://www.ewals.com/media/480028/Tr...-5_450x338.jpg

Two posts 12 minutes apart? If no-one else has posted, just click Edit and add to the first one.

I was hoping someone else would chime in, but since you ask I made the effort. Searching on 'trailer front edge radius' for instance didn't work. Searching on the picture title turned up zero (doesn't search inside HTML tags?) Believe it or not, I finally hit pay dirt with 'Wurlitzer juke box'.

http://i59.tinypic.com/k9dqhu.jpg
http://ecomodder.com/forum/showthrea...tml#post481517

If you can't sort out the details, PM Hersbird, it's his trailer.

The second picture does seem to show the front vertical edges are rounded a bit? The corners only need a small radius, 4% of the width, like 3", to get smooth flow.

Looks like it could use some rounding on the top though.

Something like this:
http://graphics.fansonly.com/photos/...0828201037.jpg

Is shrinking the gap something you'd consider? Shortening the tongue might make it harder to maneuver, but might help. Phil has posted some graphics about the gap distance.

Found one:
http://i1271.photobucket.com/albums/...Untitled-6.jpg

That's actually hilarious on the jukebox part. I also have taped up and added some aluminum straps to the Styrofoam domes. I don't have good before and after testing, especially on just one part of the mods I did. I do know the last trip home with the camper I got over 16 mpg. That's with a tow vehicle I have a hard time getting 20 without towing. I loaned it out for a month and the family using it averaged 12 mpg! Probably 100% city with lots of prewarming as they have a newborn and no garage.

Here is what the front looks like today, and the rear.
http://ecomodder.com/forum/member-he...117-154543.jpg
http://ecomodder.com/forum/member-he...117-154624.jpg

Thank you, everyone. The above info and photos (especially the camp trailer corners) are cool. Yes, I agree, the top edge needs something for sure.
_____

OK, on with the project. Violated my own requirement for aestetics because I couldn't resist testing the concept. Yea, Yea, YKYAEM if .....

Mods:
1) put on the 8" drop receiver (lowering the front of the trailer "sail" another 3"). It is now slightly tilted down forward on level ground -- not sure if that's better or worse for aerodynamics. Maybe I'll just need to buy a 6" drop.

2) filled the void between vehicle and trailer as much as practical. Drempt this up and just had to try it.

3) used the cap rear window as a deflector. Not sure how much this helps, but it sits down nicely against the tarp at speeds over 40 mph. Makes a slight deflector over the tubes and introduction of the trailer.

The problem with most fillers between the tow vehicle and the trailer is they don't accommodate turning. I loved the spandex idea used with the VW towing the trike trailer, but they also had an issue with turning and took it off when exiting the highway.

So, stacked 5 truck tire inner tubes on the tongue. They fit pretty close against the truck, but "move" when turning. I then wrapped it with a tarp and taped it to the trailer sides for better streamlining to the trailer. It looks totally red-neck.

http://www.synthx.com/i/ProjectConflict-04.jpg

http://www.synthx.com/i/ProjectConflict-05.jpg

Amazingly, the way I tied the inner tubes at the back keeps them in place beautifully. So well, in fact, it is hard to move them enough to access the hitch -- and impossible to use the tongue jack. Had to lift in on and off via strong back.

Anyway, I'm jazzed to try it. Any bets?

I like your stack o' tubes :thumbup: as long as the tarp doesn't flap in the wind.

:thumbup: :thumbup:

This beats any of our suggestions. I understand there was only a 2.2mpg difference, so even if you gain back half that it might be hard to measure.

I agree with Frank Lee on the tarp (as most things). It would be interesting to see it without, if only to see the lashings. Perhaps fins of coroplast on piano hinges the front corners, with the front halves of the inner tubes exposed? For questions on the excessive hitch drop, I'd PM slowmover. Or just go to his profile and search out everything he's written.

One thing I'd wondered about: Does it need vinyl signage to represent at events, or will it be blank to keep it on the down low out on the highways. The blue tarp doesn't help either case.

I like looking things up. Thanks.

gap
 

http://i1271.photobucket.com/albums/...head2/Gaps.jpg
http://i1271.photobucket.com/albums/...Untitled-1.jpg
http://i1271.photobucket.com/albums/...ead2/Gaps2.jpg
http://i1271.photobucket.com/albums/...ead2/Scan3.jpg
http://i1271.photobucket.com/albums/...ead2/Scan2.jpg
http://i1271.photobucket.com/albums/...ad2/image1.jpg
http://i1271.photobucket.com/albums/...ad2/image5.jpg
http://i1271.photobucket.com/albums/...Untitled37.jpg
http://i1271.photobucket.com/albums/...titled15_7.jpg
http://i1271.photobucket.com/albums/...titled7_10.jpg
http://i1271.photobucket.com/albums/...titled8_10.jpg
http://i1271.photobucket.com/albums/...titled17_6.jpg

http://ecomodder.com/forum/attachmen...1&d=1448071064

It looks like the window sticks up too high; maybe you could design something smaller that attaches to the hinges.

Second trip. 166.2 miles. Without even looking at the fuel numbers, I could tell it made a difference. On trip #1 I had a hard time holding speed, and 80 mph was pushing it. With this (except going up a few of the hills) I was able to cruise at 75 mph. I sped up to test it at one point and did 90 on the flat without much trouble.

The tape held on the way there, but came undone at the bottom on the trip back (some loss of effect for sure). This photo, taken out the back window driving at dusk shows the tarp being pulled by the wind (note the lower corner where the black trailer is visible). Interesting, because it's the wind from below causing much of the turbulence -- more perhaps than from the sides.

http://www.synthx.com/i/ProjectConflict-06.jpg

This photo shows the trailer the next morning with the tarp loose.

http://www.synthx.com/i/ProjectConflict-07.jpg

Final fuel numbers gave minus 1.5 MPG for the trip over normal driving without the trailer -- 0.7 MPG improvement over the trailer by itself. Interesting mod, but not very practical (limited access to the truck, really hard to use the tongue jack) though nice for security since the hitch and tongue jack are near impossible to access and popping a tube would make a huge noise! Anyway the Ghetto look has to go and I need the functionality.

The fuel economy numbers are not scientific. Conditions were similar, but not exact. Secondly, we traveled faster (7 mph faster average) on trip #2 than on trip #1 (because we could), so that distorts the values.

The take away: substantially filling much of the void changed fuel use ~5%. I'd guess if the top of the tubes had been covered, including a proper slope up to the trailer top along with better accommodation near the bottom, (and real tests at the same speed) that number would rise to something closer to 7 or 8% -- in line with the numbers Aerohead has posted from books about tractor-trailer combos. Cool.

By the Way, Thanks to Aerohead for the above images. Most of them I've seen posted in other threads, but a couple were new to me. Thanks for posting.

Another interesting point -- not one comment or question from any observers about it. I can't believe it looks normal, but .... I didn't have a black tarp, and the blue is obnoxious. I was ready for criticism and weird questions.

Finally, it will get decals. I've been slow, but got some quotes. It's more fun to mod than to decorate.

2nd trip
 

Thanks for doin' the experiment.It's valuable information and will become part of a growing database.:thumbup:

Trip #3. No mods, but slower speeds. OK, so it's a feeble attempt, but I' like to understand the relationship of speed and fuel consumption as it relates to pulling the trailer. Trip #3 was 189.6 miles on 14.1 gallons. 13.4 MPG. That's down 1.4 MPG from the baseline no trailer, and a 1.2 MPG better than the first trip with the trailer.

Interestingly, this is better fuel economy than with the gap filled.

The difference is speed. Don't have exact numbers, but the average speed on this trip was down something in the neighborhood of 10 mph from the first trip. Meaning, spending 20-25 minutes extra each way saved about the same in fuel as adding the gap filler inner tubes.

Of course, better aerodynamics makes more difference at higher speed, so the effect is diminishing, but with 3 people in the vehicle (that's an hour of man pay extra for the journey). Interesting balance to deal with on time v. savings v. cost.

I like the idea of time being irrelevant and just riding my bike. I'd have a hard time pulling said trailer, but aside from that, riding, even all day long, uses less gasoline than even the best of hybrids. :)

Please, someone invent a hitch that extends at low speeds and retracts (shortening the gap) at highway speeds...

I am amazed at the low mpg hit you are seeing. I have a 6x12 covered trailer like that, also one axle, and it kills the mpg on my Ram 1500. Not sure about freeway numbers though.

But you want the shortest hitch-to-rear axle distance when backing up.

Maybe if it racked in and out based on the angle. You might could do it with a Watts linkage.

There's 5th wheel hitches that do this, most manually slide, but some do it automatically while turning. I've often wondered why I've never seen such an arrangement for semi-trucks. Small gap on the highway, larger for turning.

Here's an automatic one.

http://www.pplmotorhomes.com/parts/r...ubm-sml250.jpg

(Not a 5th wheel guy myself, maybe someone who tows a 5th wheel can add some details?)

speed vs mpg
 

*the power required to overcome wind resistance varies as the cube of the velocity.
* the power to overcome rolling resistance is more linear.
* mpg will track engine power basically,but won't necessarily have a linear relationship as its brake specific fuel consumption (which determines mpg) can vary as a function of engine load.
* every vehicle combination will have a sweet spot speed for highest mpg,but these best MPGs may occur at a velocity which is completely unacceptable.
*you can get 40-mpg in a new Corvette,but you'll have to drive 40-mph to get it.

Semi-trailers
 

If Barbie and Ken squirt out in front of the big rig and it has to jackknife,it's bye-bye trailer face and tractor rear.Better just to do movable gap-fillers.

Not with the automatic type. It slides back when the trailer turns, No action from the driver required.

automatic
 

For semi-trailers?

What force would it take to 'shorten' the hitch, when it is under tension from tons of stuff being dragged down the highway? Possibly equivalent to rolling resistance?

force
 

We'd have to add the aero drag force of the trailer also.

The idea of an extend-o tongue is not bad. Forces are not that high comparatively, so something with a screw, for instance, could accomplish that easily. -- Bigger screw for a bigger trailer / load. Stopping would likely be the highest loads (depending on brake balance). Spinning it in and out is no problem with a good gearmotor because it does not have to happen quickly. Cheap GPS and such would make it pretty easy to tell how fast you were going. If the action happened progressively as speed increased from let's say 30 mph (full extension) to 50 mph (full compression) you'd get the bigger benefits at the higher speeds where it's important.

I find it pretty interesting that you mention this, because I've been contemplating the various aspects of doing this for semi trucks for a long time. There are some dynamic issues associated with changing the hitch load as the trailer comes closer, but I think most of those could be properly compensated by axle position and trailer load management (where you put the stuff in/on the trailer).

Fixed trailer frame with a nose cone on the trailer that racks in and out?

I always thought the solution would be a tow vehicle with a spherical tail centered on the hitch point. Then a convex nose on the trailer could pitch, yaw and roll without affecting the gap.

If that were my rig, I'd wrap it with Coroplast or other sheet material. It would make a bulbous extension over the tongue, as the experiment does, and flow smoothly into the sides. It would be tapered from the wheels to the roof, rather than stepped at the fender tops, to be easy to build, and to provide some extra width that would be carried to near the tail, and then curved in, winding up angled 15 degrees off the center line to minimize wake turbulence. The compound curve at the forward roof line can be done many ways, depending on what you find handy. In the truck wake, it does not have to be very smooth for the air, but the eye would prefer it.

If you add a spoiler over the back of the Pickup it would kick the air over the trailer.
2010 Ford F150 Universal Wings

Also add a tail fairing to the back of the trailer.
Northeast trucking company adds tail farings to cut fuel | ZDNet

AirTabs work too.
Airtab | Aerodynamic Fuel Savers | Welcome

truck spoilers
 

From what I've seen,it takes a wind tunnel to figure out a proper geometry for a truck spoiler.
The following is a set of very degraded TV images I photographed on pause,from a VHS recording of a series of tests conducted by Texas Tech that I was given in 1990.
Every configuration has separation or overshoot except the deep,bulbous trailer nose at bottom right.
This is a tough DIY project with a limited budget.
http://i1271.photobucket.com/albums/...titled28_5.jpg

here is a aero camper trailer I am designing for tow behind a VW Golf cheater diesel...
Attachment 19295

aero camper
 

Looks like an easy pull.And not a killer,fabrication-wise.:thumbup:

not recommended
 

Without adequate testing,there's a risk that the flow will overshoot.Some of the angles of successful fairings are counterintuitive when you see them in action.
NASA would say the rooftop spoiler would be okay if you were also going to do the gap-filler again.
http://i1271.photobucket.com/albums/...Untitled37.jpg