## Aero trailer design study from Mercedes-Benz shows 18% lower wind resistance, almost 5% reduction in fuel consumption

##### 25 November 2011
 Mercedes-Benz’ new Aero Trailer design. Click to enlarge.

Mercedes-Benz is presenting a design study at “Trailer 2011” show in Belgium for an aerodynamic trailer that shows a reduction in wind resistance by up to 18%, with an accompanying decrease in fuel consumption by almost 5%.

Numerous individual measures lower the wind resistance of the entire unit. A front airdam on the trailer reduces the distance to the tractor unit and lowers the wind resistance by 1%. Side trim panels contribute an 8% improvement—they are slightly drawn-in at the front and characterized by an opening at the rear. This steers the air in the direction of the rear diffuser. The diffuser has the shape of a parallelogram and links up with the underbody panelling. This improves the wind resistance by 1–2%.

A rear end taper measuring slightly more than 400 mm in length forms a crucial part of the aerodynamic concept. It features folding elements to facilitate access to the load compartment. The rear end taper improves wind resistance by a further 7%.

Crowdsourcing a different approach to optimizing trailers
Brad Bennett, a designer in British Columbia, is proposing a retractable trailer unit as a different approach to reducing wind resistance and fuel consumption when deadheading (returning empty).
Bennett said that his research found that semis tend to travel from 15% to 50% empty over the distance of their trips—especially short haul rigs that range around 200 miles from base.
Bennett’s plans call for the trailer walls to be made from strong composite materials so the walls will be narrower allowing the interior space to remain almost the same. The back door will roll up and the walls will ride on a electric gear track assembly. Loading-wise, it’s still basically the same trailer, Bennett says.

Photoshopped rendering of retractable trailer concept. Click to enlarge.
Bennett is welcoming comments on his concept.

Mercedes-Benz says that the 18% reduction would result in a reduction in fuel consumption amounting to almost 5% in real-life road traffic. In the case of an average mileage of 150,000 km a year this means a saving of some 2,000 liters (528 gallons US) of diesel fuel and a reduction of more than five tonnes of CO2.

The dimensions of the load compartment remain unaffected by the design. The familiar box—13.6 m in length, 2.55 m in width and with an overall height of 4 m—remains available for the freight, just as before. The aero trailer’s only restriction is the fact that its length measurement exceeds the currently permissible limit by almost half a meter, due to the tail-end extension. The handling and maneuverability are not compromised by the taper, according to Mercedes-Benz. This does highlight the need for changes to legislation, as in the case of tail lifts and transportable fork-lift trucks, for instance, where exceptions of a similar magnitude are already granted, the company suggested.

The aero trailer is the flagship of the new “Truck and Trailer 7plus” initiative being launched by Mercedes-Benz. By taking a holistic approach to the tractor unit and trailer it aims to considerably cut the fuel consumption even further than is currently the case. The basis of the “Truck and Trailer 7plus” formula is the fuel consumption of the new Mercedes-Benz Actros, which more than 7% lower than its predecessor model.

Tests in the wind tunnel and on the road prove that considerable further consumption progress is possible for semitrailer tractors. As an example, measurements taken in the wind tunnel at Mercedes-Benz have shown that a side trim panel on the trailer cuts wind resistance by 8%.

During test drives on the Record Run route this translated into a real-life consumption benefit of some 2% for a semitrailer tractor weighing 40 tonnes. In the case of an average annual mileage of 150,000 km in long-distance transport this results in a saving of around 750 liters of fuel.

In addition to this, at the instigation of Mercedes-Benz, a working group of truck and trailer manufacturers under the umbrella of the German Association of the Automotive Industry has carried out further tests on the aerodynamics of semitrailer tractors. In the framework of this study, measurements in the wind tunnel at Mercedes-Benz concluded that modifications to the cab such as a supposedly aerodynamic extension result in merely minimal improvements where wind resistance is concerned.

There is much more potential in aerodynamic measures at the tail end of the trailer; a minor extension of the tail end in the form of a “boat tail” brings significant benefits. Four flaps measuring just 400 mm in length and positioned at an angle reduce the wind resistance of the entire semitrailer tractor by nearly 10%. In arithmetical terms this corresponds to virtually 3% less fuel consumption or more than 1,000 liters of diesel a year. This is also shown by the simulations which have been carried out for the aero trailer.

As part of its “Truck and Trailer 7plus” initiative Mercedes-Benz is working on further holistic measures aimed at lowering fuel consumption. One of the projects involves the inclusion of information on the trailer’s tires in the tire pressure display in the cab of the new Actros.

The FleetBoard subsidiary is also currently developing methods of integrating the trailer in its systems. This forms the basis for concrete opportunities for increasing economy and therefore environmental compatibility to an even greater extent—for example, selecting the nearest available suitable trailer for a particular job, correctly allocating truck and trailer, and transmitting trailer data to the truck’s cockpit.

Nothing new here...they've been exploring modifications for semis to improve fuel efficiency for decades....move along....

I disagree.
They may well have been exploring this for 40 years, but now is the time to implement it.
I am surprised, however that an 18% reduction in wind resistance only generates a 5% reduction in fuel consumption.
Must be a lot of rolling resistance to deal with as well.

The point is the costs always seem to exceed the benefits for the private sector...unless you want to go the socialist/marxist route and mandate adoption & regulation of aerodynamic devices by the government. If these were such a great idea, trucking companies would have modified their trailers decades ago.

I doubt that saving $2000 per year on fuel will justify the additional cost of these new trailers. 53 ft trailers sell for about$40,000. Also, i'm surprised that no one has worked on the trailing edge of the trailer, the place where a majority of aerodynamic drag is created.

One can also reduce payroll taxes or taxes on earnings and increase gas/diesel taxes and companies will save more with such devices.

Here's one idea; http://www.atdynamics.com/trailertail.htm

53 feet may be the problem?

@ejj,
I am sure you are right here.
How do you get the tail off a container quickly and where do you put it after you have unloaded the container.

Sounds like you need something which folds down under the back of the flatbed, and can be magically erected in place when you need it (and won't rip off at 70mph).

You would have to build "Tail exchanges" where you could drop the tail and pick up another one at each port / unloading station, which would take time and organisation.
You would probably need to employ someone extra to run it.

If you were doing very long journeys, it might be worth it, like across Australia or Russia (but why not use rail in that case).

ejj & mahonj, those are are problems they were trying to solve with this idea; http://www.atdynamics.com/trailertail.htm

ai_vin / mahonj - I don't want to sound like a broken record but there are nationwide trucking companies that have been operating for decades - England, Old Dominion, etc. and they haven't adopted "trailer tails" or any other aerodynamic enhancers.

Improved, faster cargo e-trains could take 120+ fully loaded trailers across the country much faster and at much lower cost than 120 individual truck tractors.

E-tractors at each end could pick-up and deliver as many trailers as required.

Both operations would be clean, highly efficient and use at least 50% less drivers and use no liquid fuel.

Our highways and bridges would last time as long without major repairs. Driving a car on truck-free highways would be pure joy.

Saying that the private sector knows all is blind. They may not care about marginal fuel costs, but added up over millions of trucks and we import a LOT more oil than we should. Get off the private sector knows all nonsense.

Wow, there are a lot of ignoramuses on this site. I've been a truck driver and I own a website dedicated to "green" trucking. Most of you have no idea what is required of transportation/logistics and freight hauling.

First, these things aren't implemented because they cost way more than their payback would ever be. Trucking companies and owner/operators are already running on pretty slim margins as it is.

The company I drove for implemented APUs (alt power units) on all of its trucks long before it was ever a requirement in California. Those units cost about $5,000 a piece. Multiply that across 120 trucks, which were already bought at roughly$120,000 each plus $60,000 per trailer (refrigerated). Those APUs were great for us on the road, since they don't shake the truck like idling does and they provided 110v power built-in. They were, however, like Harley's and required constant repair and maintenance. The company's owner told me that those units were a net loss of$3,000 per truck per year on top of their cost to purchase and install. He was ready to throw them out when CA passed their anti-idling law.

Trailer skirts are currently readily available and add 2-3% in drag improvements, but cost about \$2,000 to purchase and install and are just one more thing on the trailer that gets broken/bent/torn off at the dock/truck stop/etc. Trailer caps (end diffusers) are also readily available, but are, again, one more thing to get broken/bent/torn off at the earliest opportunity. You'd be amazed how many drivers break stuff on their trailers on a regular basis, usually while backing into a dock or parking spot. I was personally in three wrecks in one year, all of which involved someone backing their truck into mine.

As for the asinine e-train plan someone proposed.. Great idea if you can come up with the trillion bucks to pay for it and can figure out how to get it to work on our current outmoded, outdated, overloaded rail system...

There's an American Company, ATDynamics ( ATDynamics.com ) that already has a commercial product that saves 6% fuel: The Trailertail (what Mercedes is prototyping).

Perhaps, Mercedes should team up with ATDynamics since they already have a proven commercial product already streamlining thousands of non-aerodynamic trailers?...

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