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Going with the flow

Interest is running at an all-time high when it comes to trailer aerodynamics these days. After suffering through one of the worst oil price shocks in history last summer with prices climbing to more than $147 a barrel and diesel fuel costs skyrocketing to over $5/gal. across much of the U.S., fuel efficiency became the No. 1 concern among fleets large and small. Even with oil prices plummeting back

Interest is running at an all-time high when it comes to trailer aerodynamics these days. After suffering through one of the worst oil price shocks in history last summer with prices climbing to more than $147 a barrel and diesel fuel costs skyrocketing to over $5/gal. across much of the U.S., fuel efficiency became the No. 1 concern among fleets large and small.

Even with oil prices plummeting back down to around $50 by the end of 2008 and diesel falling into the $2.50/gal. range due to a worldwide economic recession, the trucking industry's interest in fuel efficiency hasn't waned.

“As diesel prices soared to new heights in July, many [fleets] were forced to re-evaluate the way [they] did business,” noted Gov. Bill Graves, president and CEO of the American Trucking Assns., in his “State of the Industry” speech last year. “For the first time ever, fuel became the industry's leading business expense, outpacing driver compensation.”

That re-evaluation put the spotlight on trailer fuel efficiency more than ever before, says David Tate, president of Randolph, OH-based East Manufacturing Corp., which makes a variety of vocational dump and refuse trailers, plus flatbeds.

“Four or five years ago, when fleets talked fuel efficiency, they were really only talking about their tractors,” he explains. “Now they are increasingly looking at the fuel efficiency of their trailers as a way to further cut down on their operational costs.”


Yet, by the same token, that doesn't mean fleets are blindly willing to fork over extra cash for more aerodynamic trailers, says Rob Hancock, vp-product development for trailer maker Wabash National Corp., Lafayette, IN.

“Do fleets want aerodynamic improvements for their trailers? Yes,” he points out. “Are they willing to buy them despite the higher cost? There are a limited amount of fleets that are willing to incur the higher cost.”

“The major fleets are very sophisticated data-gatherers. They know [in many cases] the effect on fuel consumption down to the one-tenth of a mile per gallon of adding these types of [aerodynamic] products,” notes Stuart James, vp-sales for San Diego-based Hyundai Translead.

“They will pay for improvements to their trailers, but they will not incur higher costs. They are prepared to take a life-cycle cost view of adding aerodynamic products to their trailers but will only consider them if there is a clear, quantifiable long-term cost reduction to be had,” he explains. “I like to say these guys are all from Missouri, as in ‘trust me’ doesn't count — it's ‘show me’ that counts; give me proof, let me prove it to myself that these trailers save fuel and money. Then maybe we have something to talk about.”


Dry van trailers are at the top of the list in terms of aerodynamic improvements because there are more of them than any other type of trailer model on the road — and their boxy shape is the pure antithesis of “aerodynamic” right from the get-go.

“The basic shape of a trailer is ideal for hauling freight but terrible for cutting through air; they really ought to be shaped like submarines,” says Hyundai's Stuart. “The problem is a submarine's shape would lose a vast amount of cube if it had to haul palletized cargo. My personal belief is that cargo capacity is the controlling factor here; pity the first fleet owner to buy a 53-ft. trailer with the carrying capacity of, say, a 45-ft. trailer due to its aerodynamic shape, and it might be even worse than that.”

It is Stuart's belief that fleets will always keep in mind the basic reason to buy a trailer: it hauls freight. “Whatever else happens to that trailer is secondary,” he explains.

“Cube is what it is all about today,” adds Craig Bennett, senior vp-sales and marketing for Utility Trailer Manufacturing, City of Industry, CA. “You have to get it in to haul it. If fleets can't get the freight into the trailer, they don't like that.”

Mark Roush, director of engineering for Vanguard National Trailer Corp., Monon, IN, believes the key will be designing and building aerodynamic dry van trailers on the production line for an economic cost, adding no more than $1,500 to the cost of the trailer as a whole.

“We need to be concerned with weight too, as the variety of add-on aerodynamic devices for trailers out there — from side fairings to ‘boat tails’ — can add anywhere from 300 to 1,000 lbs. to them,” he explains. “That's why many of them, going forward, will be made of composites to decrease weight and add flexibility while making them easier to repair and replace.”


That's exactly the track Seattle-based Freightwing, an aftermarket manufacturer of trailer aerodynamic devices, is following. For example, while Freightwing's current line of trailer belly fairings — devices shown to improve fuel economy by 4% in SAE J1321 tests — are made from aluminum (adding 150 lbs. to the trailer), it is now testing fairings made from plastic composites to reduce weight while boosting fuel efficiency further.

“The Aeroflex, our new skirt product, recently demonstrated a 7% fuel savings with it at the Energotest 2008 J1321 testing project,” says Sean Graham, Freightwing's president. “It is constructed of plastic panels that are very durable and can flex to absorb ground and side impacts. This flexibility also allows us to maximize aerodynamic performance, which is further enhanced by an angled mounting configuration. The angled mount also helps to avoid side impacts altogether and allows intermodal use. We started fleet trials of this product this year and have already sold over 1,000 units to fleets that were impressed with demo units.”

Graham notes that the fuel crisis last year boosted sales of his company's belly fairings to 2,000 units, which he calls “the best proof we have that trailer aerodynamics work and are gaining industry acceptance.”

Andrew Smith, CEO of San Francisco-based Advanced Transit Dynamics (ATDynamics), added that his company's Trailer Tail device for covering the cargo doors also gained a lot of traction in the market due to the surge in fuel prices in 2008, and he expects sales to remain strong despite the recent falloff in oil prices.

“Oil prices fluctuate wildly; that's one guarantee you have about them,” he says. “So the question isn't whether fuel costs $5/gal. or $1/gal., it's a question of how many miles your trailer logs in a year and whether, based on fuel prices, you see a return on your investment [in aerodynamic devices] of four months or four years.”

Smith noted that third-party SAE J1321 testing conducted by Robert Transportation at Energotest 2007 in Montreal showed the Trailer Tail boosted fuel efficiency by 5.1% at 62 mph, while at 68 mph potential efficiency gains surpassed 6%.

“The least aerodynamic way to carry goods down the highway is in a large rectangular box,” explains Smith. “That's why forward-thinking fleet operators are now serious about improving the aerodynamics of their fleets, especially when it comes to trailers.”

Aerodynamic improvements aren't reserved for dry van trailers alone either. Freightwing is currently conducting belly fairing tests on flatbed and tanker trailers, reports Graham, though he stresses the fuel efficiency gains may not be as large as those for dry van products.

“The benefit for both flatbeds and tankers is in the airflow through the undercarriage,” he says. “And there are definitely ones serving in high-mileage capacities where fairings could offer a rapid return on investment.”

“You can definitely make aerodynamic improvements to flatbed and [intermodal] container chassis; I've seen skirt designs for them,” says Charlie Fetz, vp-research and development for Great Dane Trailers, Savannah, GA. “I see no reason why aerodynamic devices can't be added to gain air flow efficiencies underneath flatbeds and the same goes for the rounded underside of tankers. It just requires more complex research and wind-tunnel testing.”

“The key is managing the airflow underneath the trailers, whatever the design, to direct it away from the suspension and axle components,” adds Vanguard's Roush, noting that his company is testing new “underside” trailer skirts around the landing gear and rear axles to help improve the fuel economy profile of its 53-ft. dry van trailers.

“We think these types of under-side trailer skirts could potentially improve tractor-trailer fuel economy by 7% or more,” he says.

The tricky part with any aerodynamic improvement to trailers — dry van, flatbed, tanker, etc. — is controlling the cost component for fleets, and not just in terms of the purchase price.

“There is still not yet enough real data to show what the damage incidence on aerodynamic treatments will be or what it will cost to fix them,” says Hyundai's James. “Within months of installing aero treatments, the major fleets will develop cost-per-mile data for repair costs to those elements. If they find that repair costs exceed fuel consumption gains, then they will remove them.”

Wabash's Hancock believes there's a clear hierarchy among aerodynamic devices, ranked in terms of their fuel savings against the cost to purchase and maintain them: underside fairings (1); boat tails (2); nose cones (3); and reducing the tractor and trailer gap (4). Yet it doesn't necessarily mean any one device is better than the other either, stresses Hyundai's James, proved by the fact that the most gains are achieved when they are all on one trailer, working together.

“The manufacturers of each component naturally assert that they are ‘tops,’ but there is not yet sufficient real-live data generated in service rather than in lab [i.e., wind tunnel] conditions to be sure,” he notes.

“What we can say is that when used in combination, the sum of the whole exceeds the sum of the individual elements alone. If I were forced to guess, I would say that gap-closers and belly-mounted fairings are likely to come out on top — but don't forget things like low rolling resistance tires when it comes to fuel savings for trailers. Some of the data I have seen on them is impressive.”

Until the economy rebounds and until freight starts to flow in profitable amounts again, fleets are going to closely monitor the cost-versus-savings calculations when it comes to trailer aerodynamics — and jump in only when the numbers work in their favor.

“These are challenging times in this industry. I spend most of my time on airplanes, trying to find people willing to buy equipment,” says Utility's Bennett. “There's a lot of hesitation in the dry freight sector — and uncertainty freezes buying. That's why trailers must be more economical than ever.”

Dynamic benefits

So what are the potential fuel economy gains from trailer aerodynamic improvements? Depending on how many miles a fleet covers per year at highway speeds, the savings can vary. Here's a quick thumbnail breakdown on what's available.

  • Side or belly fairings: Mounted on the side of the trailer, between the landing gear and suspension, they offer potential fuel economy savings of 4% to 7%, depending on design and fleet operation.

  • Boat tails: Affixed to the rear of the trailer, covering the cargo doors when in use, they offer potential fuel economy savings of 5% to over 6%, depending on vehicle speed and type of operation.

  • Nose cones: Typically mounted to the upper portion of the front of the trailer above the cab of the tractor, they offer a potential fuel economy savings of 2% to 4%, depending on fleet operation.

  • Tractor/trailer gap fairing: Retractable “wings” that cover the open space between the tractor and trailer, they offer a potential fuel economy savings of 2% to 4%, depending on fleet operation.

  • Underside fairings: Mounted under the trailer, covering the landing gear and suspension, they offer a potential fuel savings of up to 7% at highway speeds.

Note: Generally, for every 2% reduction in vehicle drag at highway speed, there's a 1% gain in vehicle fuel efficiency.

The vocational view

At first glance, the rough-and-tumble world of dump and refuse trailers may not seem amenable to aerodynamic improvements — but you'd be wrong.

Randolph, OH-based East Manufacturing found that out after rolling out a new “flat-sided” dump and refuse trailer design called Genesis in 2002. Dave Tate, the company's president, says the driving reasons behind the new design were image, durability and strength — but discovered along the way some extra “gravy” in terms of fuel savings.

“Dump and refuse models in particular used to have the side posts exposed on the trailer sides, forming ‘pockets’ that captured air and created drag,” he explains. “Having that smooth side vastly reduced drag, thus improving overall tractor-trailer fuel economy.”

Though East hasn't been able to conduct wind tunnel tests to date to quantify those fuel savings (“That's really expensive,” Tate says), research conducted by vocational fleets so far indicates such smooth sided trailer designs can improve fuel economy as much as 3/10th to 5/10th of a mile per gallon.

Tate stresses, however, that those kinds of gains are not possible for every vocational fleet. “If they are driving long haul on the highway — 100 mi. or more — than they'll see those kinds [of gains],” he says. “But if they are running primarily 30 to 40 mi. a day at low speed, they won't see them.”

Still, that hasn't stopped East from pursuing even more aerodynamic improvements — again, with the main reason relating to looks and trailer strength, with fuel savings as a happy by-product. The company's Genesis II product, for example, incorporates the crossmember supports into the subfloor of the trailer itself, leading to a smooth shape underneath the trailer that helps push airflow off to the side of the vehicle to cut down on drag.

Tate also points out that the trucking market is responding to these improvements. “Since 2002, about 80% of the dump trailers we sell are smooth sided, with easily over 50% of total dump body trailer sales these days smooth-sided units,” he says. “So we're going to keep looking for more aerodynamic improvements, for dump and refuse models as well as for flatbeds, too, to help our customers maximize the value they can get from their trailers.”

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