Project Aero Car Trailer

[aerohead]

If you could do an inter-library loan for one of Wolf Heinrich Hucho's books on 'Aerodynamics of Road Vehicles',you'd find a wealth of empirical data from testing of commercial vehicles of all kinds.
There's a lot of quanta.You could noodle various configurations,look at the numbers,see if you can get close to your target.
The Renault V.I.R.A.G.E.S. tractor trailer is Cd 0.29 with extended boat-tail.
Fluids is fluids.University-built 7,000 mpg student projects,or World Solar Challenge aerodynamic technology can all benefit a truck/trailer.
You've mentioned some good ideas.GOOGLE IMAGES is your friend!
Will wait for your sketches.

[KamperBob]

Originally Posted by mateospeed

I've become fasinated with the idea of making a super-efficient tow rig after reading some of the great info on this site and others. Y'all have some great ideas, backed up sound research and testing. That's so refreshing to see...

A little background on me: I'm a Mechanical Engineer working for Naval Air Systems Command (I rebuild helicopters). I also race Spec Miata in the southeast, at tracks like Virginia International Raceway (VIR), Carolina Motorsports Park (CMP), Roebling Road Raceway (RRR), Rockingham Speedway, Road Atlanta, and Summit Point. My wife is a budget analyst for the Navy, so she controls my money, both at work and at home! She's also very good at cost/ benefit analyses and things of that nature.

The tow rig: 2004 Chevy 2500HD with a 6.0L gas engine, 4-spd auto, and 4.10 gears. 108k miles, completely stock, and a very competent machine. I've been happy with it thus far. It get 14mpg unloaded at 60mph (2200 rpm), so I pretty much use it only for towing or hauling. I have a tonneau cover that I never use, because it prevents me from putting the ATV or motorcycle in the bed. I actually have it up for sale, so I count its use out. Otherwise, I ride a motorcycle.

The trailer: 24 ft box enclosed (box) trailer. Radiused vertical leading edges, and that's about it. It at least has drop-axels, so it rides lower than most, with about 8 inches of clearance. This isn't always the best, because it scrapes frequently coming into/ out of gas stations. And, as you can imagine, I stop for gas a LOT. Trailer estimated weight is 7,000 lb: 4300lb empty, 2300 lb car, 400 lb tools/ gear.

Current performance numbers: ranging b/w 8.5-10.5mpg (~9.5 avg.) towing at 60mph. Going faster would be really nice, since I live a minimum of 4 1/2 hours away from any track, but it sucks fuel so quickly I can't justify it. I also feel as if I have good power for what I need. Climbing hills is now problem; I could maintain 60mph up a decent hill if I really wanted to. I usually just stick it to about 1/2 to 2/3 throttle and let it slow down as it wants to. I don't feel like I need more power, which is something to say if you're a racecar driver/ sportbike rider!

The project: I think some huge improvements could be made to my setup! If an 18-wheeler, loaded with 80,000 lb can get 7mpg at 60, I'm sure I can do a whole lot better!

Ideas:
1) Streamline the transition between truck and trailer
-add a bed cap/ camper shell, hopefully one that angles up at the rear
-possibly add wings/ fairings to the bed cap to further direct airflow
-add a contoured trailer nose to guide the airflow from the truck to the sides and top of the trailer.

2) Reduce the turbulent wake behind the trailer
-a tail section that is able to be removed/ moved easily to allow ingress/ egress of the car seems like it would be very helpful. I believe what I'm envisioning is called a Kamm back. I'll post a link to a commercial product I've seen when I find it.

3) Operate the truck as close as possible to its highest efficiency range.
-difficult to determine, since I can't seem to find a BSFC chart for anything close to my engine.
-Judging by the relatively high throttle use required, the somewhat-high RPM, and the relatively small drop in mpg I'm guessing I'm pretty close as-is.

4) Change gearing as is appropriate after reducing aerodynamic drag.
-Most likely a 3.73 or 3.55 gear. This would obviously help non-towing fuel economy as well.

5) Use a more efficient drive train (most likely not happening until the current units fail).
-swap to a diesel. The OEM diesel is a 6.6L unit with WAY more power than I need. I think it'd be fun to install something not intended for this truck, like a cummins or mercedes diesel. :-) Suggestions on specific engines and where to get them?
-manual transmission. Oh, how I'd love this. Complete control, more gears, more efficient. I'd like to do this with any engine. If I could have found my truck with a manual, I would have!
-convert to E85. I'm not convinced this is a good idea, but it sure would be cool. Since E85 is cheaper, and has a higher octane rating, it might work. I've tossed around the ideas of increasing the compression ratio of the engine, and would definetly need to add a turbo. I'd also need to upgrade the fuel system to handle the extra flow rate required, and reprogram the electronics to expect the correct fuel. Also, I'd have to bring a large (100 gal?) auxiliary fuel tank, as E85 stations are few and far between. Luckily, there's one a few miles from my house, but there isn't another one for 100 miles or so. Running E85, I could potentially have more power on tap (turbocharging), plus run the engine at a more efficient zone by requiring more airflow for the same power output, and getting that airflow by turbocharged/ intercooled induction. I've heard that starting an E85 engine in the cold can be difficult as well. This one's a big investment and a big risk, with a lot of factors involved!

So why post this thread? I'd like to get y'all's comments and suggestions on improvements to be made. Keep in mind the truck has a large cooling demand, both for the brakes, and the engine/ tranny. The whole point of improvements is to save money in the long run, so without a business analysis, no projects are going to go anywhere! The queen says NO!

I need the most help finding an accurate method for estimating the fuel savings to be gained by making these modifications, so that a return-on-investment calculation can be run.

I also want to be able to share with other towing folks what I do and if it works. I searched and didn't find anyone else describing their experiences towing a large trailer, but they're out there!

Soon to come: sketches of my rough ideas for fairings and aero improvements.

Thanks!
-Matt McBride

Matt, since your trailer is so much bigger and heavier than the car you tow inside it, what are your requirements?

Just thinking out loud here... if I wanted to tow the car behind the truck and maximize fuel economy I'd consider the absolute bare minimum. Sell the trailer. Put a drawbar on the front of the car and tap its tail lights like motorhomers do, making it a 4-down toad. Put an aerocap (Bondo?) on the bed for tools and let the Miata draft in what's left of the truck wake. That would seem to minimize weight and frontal area with least harm (and possibly some improvement) to Cd. OTOH if you have interior space requirements then that idea isn't worth dirt.

As for your list of mods, I personally would not bother with any major surgery to the truck. I honestly don't think you would ever break even. I could be wrong of course; that's just my opinion.

[Fat Charlie]

Originally Posted by jamesqf

PS: Maybe this is a stupid question, but why not just drive the Miata to the track?

Because it's a track car. You can't count on being able to drive it home. Same goes for hauling it on its own wheels; you can't even count on it rolling. An enclosed trailer really is the best for this. Surgery to the trailer might make a lot of sense, but ditching it doesn't.

[jamesqf]

Originally Posted by Fat Charlie

Because it's a track car. You can't count on being able to drive it home.

Well, the same is true - though perhaps (but only perhaps :-)) to a lesser degree - when you drive on the highway.

[Frank Lee]

Originally Posted by KamperBob

Matt, since your trailer is so much bigger and heavier than the car you tow inside it, what are your requirements?

Anyone see how "The World's Fastest Indian" streamliner was towed to Bonneville?

[slowmover]

Obviously the same trailer can be towed by different vehicles with different mpg results . . but the more aero trailer can be towed by a wider variety of vehicles (think Airstream travel trailer where a 9k 34' triple axle can be pulled by a minivan with good results; see CAN AM RV and articles by owner Andy Thomson).

A 2000-2005 Dodge or GM turbodiesel will get the best fuel mileage, overall. But another TV may be even better with full-on aero work. The V8-366 GM is known for poor mpg.

Trailer towing -- with that big gap between trailer and TV -- means that aero treatment ought to be separate. Maximize the advantage for each vehicle, first. Work on obvious mechanical deficiencies: sloppy steering linkage, alignment (both vehicles), proper tire pressure, brake drag, etc. Number of steering corrections and brake applications per 10 or 100 miles is to be minimized. Also, set up hitch rigging according to weight scale readings. Set a baseline, with full record-keeping.

As for the trailer: a boat-tail makes the most sense for a single modification (with a nosecone), IMO. A sway-eliminating hitch (Pro-Pride) also maximizes any tendency to track less than true. The two will complement one another as the "natural" antisway of a barn door is reduced. This form of sway -- yaw -- is more pronounced than folks realize . . . the deadened steering of pickup trucks and driver inexperience/sensitivity mask the reality. Trailers with short suspension travel (nearly all of them) move around on the highway quite a lot over a given distance (in comparison to the tow vehicle) as the vehicle "compensates" for winds, other traffic, pavement, etc with side-to-side motions. And trailer loading should be weight-scale checked with wheel-by-wheel readings.

In example: I would do all and sundry to reduce internal tire temperatures. First, though, I need a way to monitor them [TPMS]. A windy day with ongoing steering corrections is going to show higher temps, obviously (for given terrain & climate). Centramatic balancers, shock absorbers, etc.

As to re-fuel: Trip-plan your stops in advance (MM or Exit #) and drive in stages. It's much easier on the driver which tends to help FE when all stops are known in advance. With my TT or your rig where ground clearance matters I may use GOOGLE Streetview or other to check ingress & egress at fuel stations. Most truck stop chains are accommodating in these terms, I find.

Again, the best baseline and records will best show any aero improvements . . alternately, they may mask them if not attended. Please don't assume any mechanical issues are moot due to young age or low miles. I'd check even the brand-new ones against the FSM.

Pics would also be great. Look forward to this.


.

[botsapper]

...interesting to read the confusion and disinterest from some people. The shared Photoshop contribution came from an earlier thread; the simple request for aero ideas on an large EXISTING trailer. Like I mentioned, the rendering combined many intriguing ideas. The first was a custom front deflector, when not in use could be retracted flush to the pickup cab cover. http://www.fiberglassrv.com/forums/a...1&d=1280143335
The next is a pyramidal-shaped nose cone on the top & front of the trailer, that serves as a tighter aero bow but still clears the truck rear quarters on tight turning maneuvers. NoseCone On Aerodynamics
The most controversial ideation is the re-contoured top profile. The concept retro-fits a curved top following the Don-Bur 'teardrop' case studies, that even a resulting larger frontal area with a flowing teardrop top profile still tested in savings!! Aerodynamic Teardrop Trailer
(Note: Don-Bur Teardrop design is a vigorously protected & registered design).
Requisite wheel covers & spats.
And to terminate all the flow was adding a fold-away boat tail, now existing and producing savings for 'enlightened' long-haul trucking companies.
http://www.atdynamics.com/gallery_video.htm
...nothing exotic but the 'vapor' concept does combine many proven ideas to a whole towing aero package.

[mateospeed]

Originally Posted by jamesqf

Just what I was thinking. If the trailer is specifically to haul the Miata, it doesn't need to be any bigger than the Miata, does it? (Assume gear & spares go in the truck bed.) So build it to have an aero teardrop shape going back, with clamshell top that opens up for access.

So what you have is a flat bed that carries the Miata, a vertical riser at the front edge that mounts gap seals, and two aerodynamic fairing half-shells that just pop off. (I do wish I could draw...)

PS: Maybe this is a stupid question, but why not just drive the Miata to the track?

I should have mentioned a few things: 1) the trailer carries all the gear, none of it goes in the truck as of now. This is for 2 reasons: reduced loading time (I can leave the gear in the trailer), and the fact that the bed is currently open, and offers the potential to soak everything in the bed when it rains.

We use the trailer as an RV, workshop, and headquarters while we're at the track. Its height is important, because if it were not standing-height inside, it would be essentially useless. In ideal cirumstances, yes, I'd make a trailer shape to just enclose the car. Good ideas, I wish I could use them!

The miata cannot be driven to track because A) it's a full-blown race car, and isn't street-legal, and B) I frequently crunch the bodywork (usually the front fenders) or otherwise break the car, and need to count on being able to trailer the car home. It's not, however, a stupid question. There are Spec Miata racers that build their cars street-legal and drive them to the event. They are not, however, at all competitive.

Originally Posted by aerohead

If you could do an inter-library loan for one of Wolf Heinrich Hucho's books on 'Aerodynamics of Road Vehicles',you'd find a wealth of empirical data from testing of commercial vehicles of all kinds.

I've heard a ton about Mr. Hucho, and hadn't even considered finding his book at a library. I simply wrote it off as too expensive to purchase, and didn't think it further.

Originally Posted by aerohead

Will wait for your sketches.

Whoops! Completely forgot! Will attach when I complete them.

Originally Posted by KamperBob

Matt, since your trailer is so much bigger and heavier than the car you tow inside it, what are your requirements?

Again, I forgot to mention that the 8.5x8x24 trailer is pretty much necessary for interior space. I wish it wasn't so heavy, but I got it for a steal, so it's what I've got.

Originally Posted by KamperBob

As for your list of mods, I personally would not bother with any major surgery to the truck. I honestly don't think you would ever break even. I could be wrong of course; that's just my opinion.

When you say 'major surgery', are you referring to add-on aero mods to the exterior of the truck, or transplanting engine/ transmissions into the truck. If you're talking about the powertrain, I'm going to agree. I've run a few examples, and it's WAY cheaper to trade. I'll never find an ideal vehicle, but it'll be cheaper overall.

Originally Posted by KamperBob

Just thinking out loud here... if I wanted to tow the car behind the truck and maximize fuel economy I'd consider the absolute bare minimum.

Originally Posted by Fat Charlie

Because it's a track car. You can't count on being able to drive it home. Same goes for hauling it on its own wheels; you can't even count on it rolling. An enclosed trailer really is the best for this. Surgery to the trailer might make a lot of sense, but ditching it doesn't.

Hit the nail on the head.

-Matt

[mateospeed]

Originally Posted by jamesqf

Well, the same is true - though perhaps (but only perhaps :-)) to a lesser degree - when you drive on the highway.

Indeed. However, for the sake of this project, considering the car assumed to be not able to return home under its own power. This happens frequently enough to consider it expected.

Originally Posted by slowmover

Trailer towing -- with that big gap between trailer and TV -- means that aero treatment ought to be separate. Maximize the advantage for each vehicle, first. Work on obvious mechanical deficiencies: sloppy steering linkage, alignment (both vehicles), proper tire pressure, brake drag, etc. Number of steering corrections and brake applications per 10 or 100 miles is to be minimized. Also, set up hitch rigging according to weight scale readings. Set a baseline, with full record-keeping.

Here I was thinking the best gains might be seen by working on that very gap you speak of, buy adding a deflector to the truck, and/or creating a nose-cone for the trailer.

I have taken care to make sure the truck and trailer are in as good mechanical condition as I'm mechanically capable. Tire pressures are monitored, and hubs and brakes are checked for slop and drag before every trip, as well as recieving a top-up on grease.

One thing I haven't done is weighed the trailer to ensure proper tongue weighting. I do, however, have a weight-distributing hitch with sway control. I've driven a few rigs with significant sway problems, and don't want to ever deal with it again. On the way to South Carolina 2 weekends ago, I was looking at a 25 knot steady wind at a 45-90 degree angle to head-on, and experienced no perceptible sway. It was truly wonderful. That said, a small improvement might be seen in weighting the trailer more properly. I check the tire temps whenever I stop, and they're never move than "warm," but they are getting eaten rather quickly: less than 2k miles and I'm looking at replacing them already! However, this seems to be the norm for everyone else at the track. It was also simliar with the old open trailer.

[mateospeed]

OK, I have the sketches scanned in as a pdf, but it's way too big to attach, @ 628KB. Ideas?