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Aerodynamic advantages for trucking fleets

The impact of aerodynamics on fuel economy and emissions is becoming increasingly important. The difference between perception and reality can be a wide chasm, however, according to experts in the aerodynamics industry.

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Doug Kaufman has been with Babcox Media since 1987 serving in a variety of editorial and publishing roles and titles. He is currently publisher of Engine Builder. He also has been editorial liaison between Babcox and the National Association for Stock Car Auto Racing (NASCAR) for the past 12 years. Doug has a Bachelor of Science in Journalism from Bowling Green State University and remains a committed MAC enthusiast.

Though many things have changed in this industry over the past century-plus, certain things haven’t. Trucking fleets still try to deliver goods and products as quickly and economically as possible—and the air does its best to disrupt the success of that journey.

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Scientific studies have shown that a truck and trailer combination moves tremendous amounts of air—at 55 MPH, trucks displace as much as 18 tons of air for every mile traveled. To get to that point, half its engine horsepower and half of its fuel are required just to overcome aerodynamic drag.

The impact of aerodynamics on fuel economy and emissions is becoming increasingly important, a fact not lost on Californians. The California Air Resources Board (CARB) approved the Tractor-Trailer Greenhouse Gas regulation that requires the use of EPA SmartWay verified aerodynamic techniques and low rolling resistance tires on all affected vehicles operating on California highways, regardless of where they’re registered.

“For 53-ft. box trailers, aero devices must cut fuel consumption by 5% or more and 53-ft. refrigerated vans must have aero devices that cut fuel consumption by 4% or more,” explains Andy Acott from Laydon Composites. “The rule went into effect Jan. 1, 2010, and covers all trailers designated as 2011 model year or later.”

Small and large fleets have slightly different compliance schedules, but by 2020, every truck and tractor operating in California must comply with regulations. And as we’ve seen in the past, California’s reach can be mighty, so fleets across the country are already addressing aerodynamic issues.

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The difference between perception and reality can be a wide chasm, however, according to experts in the aerodynamics industry.

According to Jim Reiman of Aerofficient, it’s important to continue to educate fleets and independent drivers about the advantages of fairings.

“We speak to as many operators as possible at shows and in private meetings. We explain the physics, the aerodynamic processes and forces involved, why fairings work and why some work better than others. We run fuel economy tests for customers and potential customers, demonstrating and calculating real life road usage savings using our customers’ own equipment,” Reiman explains.

“In addition, our employees are active in industry trade associations and work to create industry standards. Active committee work and involvement includes work with the TMC, SAE, ATA and OTA (Ontario Trucking Association) and other groups,” says Reiman.

“The technology is a lot more widely accepted than it was just a year or two ago,” says Sean Graham of Freight Wing. “We’ve seen a tremendous increase in interest and acceptance of the technology in the industry. As fleet managers become more familiar with the products and see them out on the road, it’s really knocking down a lot of perceived barriers.”

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Graham concedes that overcoming misconceptions has been a laborious process. “When we started introducing fairings to the market, the primary objection we got from fleet managers was ‘Do they really save fuel?’ There have been so many false claims made by people in the past that no one really believes anything until people see if it works for them. Some of the best advice we got at the beginning was from fleet managers who told us ‘No one is going to believe you unless you employ testing by a respected third party using an industry standard test procedure.’ That’s been very important,” Graham says
Andrew Smith of ATDynamics explains how some of this third party testing has been used, particularly with his company’s rear trailer fairing.

“ATDynamics helps fleets track fuel savings in three ways: 1) We’ve been providing detailed third party studies following specific SAE Type II J1321 protocol and wind tunnel drag reduction studies; 2) Assisting fleets in conducting their own on-road modified SAE Type II tests with their own tractor-trailers and auxiliary fuel tanks; and 3) Providing reference phone calls with other customers who have seen statistically significant fuel saving impact as the result of full fleet retrofits,” Smith says.

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Acott from Laydon says ongoing testing is important, as well. “Laydon regularly conducts aerodynamic drag reduction tests at either the Goodyear proving grounds, ARC wind tunnel or our own CFD in-house. We take these results to the end users for presentations and offer free samples for fleet trials.”

Areo Mechanics
Taming the wind is impossible, experts concede, but understanding it is important.

Experts say turbulence of air swirling under the trailer, or getting caught in the gap between the tractor and trailer or trailers, as well as friction of air clinging to the side of the trailer, can impact your fleet’s efficiency. When it interacts with the rotating tires and the suspension assembly, airflow underneath the trailer can cause significant turbulent flow patterns. Additionally, the air coming off the rear of the trailer can create a low-pressure vortex that can actually increase drag and reduce efficiency further. And the gap between the tractor and trailer should be addressed, although new tractors are more and more aerodynamic than ever.

No matter how much emphasis you put on driver training or effort you put into cost-effective efficiency measures, there is one element of the trucking business you will never be able to control. And it’s an invisible opponent.

Call the wind Mariah or any other name—whether it’s a squamish, a barat or a chinook, it’s out there. A Brubu, a zephyr or a sirocco has no mercy. You can’t beat any of them—you can just hope to manage the wind. Fortunately, today’s aerodynamic technology can help you have the upper hand.

According to Jack Latimer of AirTabs, there are two types of airflow that occur on all vehicles: “attached flow” and “separated flow.”

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Aerodynamic designs are employed to make attached flow, which occurs when air flows smoothly over the surface contours of a moving body, the rule rather than the exception.

“However, if that attached flow encounters an excessively sharp corner, bend radius or blunt object in the body shape, it breaks free of the surface and becomes wildly chaotic and turbulent,” Latimer explains. “Once that happens, the airflow no longer follows the contours of the body shape. This chaotic, turbulent flow is called separated flow.”
aerodynamic devices are simple in principle, but can have subtle differences. durability and quick installation are important considerations.
Latimer explains that separated airflow is turbulent air, which increases drag. “When separated flow is created, it effectively expands the size of the hole the vehicle makes as it passes through the air by adding to the dimensions of the sides, the top and the undercarriage so that aerodynamically, it is larger than it physically is. The vehicle punches a larger hole through the air. This requires more energy and therefore more fuel to move it through the air than if the airflow was attached,” explains Latimer.

Separated flow can be caused by any number of vehicle design elements or components mounted on the exterior of tractor or trailer. But it can also be a natural occurrence, Latimer says.

“Separated flow is also caused by crosswinds. In no wind conditions, separated flow caused by the tractor usually reattaches to the sides of the trailer about 1/3 of the way back. With a strong crosswind, the flow on the ‘downwind’ side of the trailer may never reattach. In addition, real life crosswinds come in gusts and this variation in wind forces caused by the gusts facilitate the formation of separated flow.”

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Each company representative says test data have been able to show that aerodynamics really do work and save fuel. 

“We don’t have to fight a negative perception nearly as much,” Graham explains. “We’ve been at it for a long time now. The products have evolved considerably and we’ve learned a lot.”

Graham says convincing fleets that aero products worked was relatively easy compared to conquering the next barrier: Questions have changed from “Do they work?” to “Are they worth the investment?”

Reiman agrees that when purchasing a fairing system, total cost of ownership is more important than just the purchase price. “The total sum of money spent on a product during its entire intended operating life includes purchase price, installation cost, maintenance costs, repair costs, down-time for the trailer while the fairing is being repaired, and all other costs associated with owning and operating a fairing system,” he explains.

In particular, Reiman continues, fleets need to assess the durability of the product offerings and determine whether a fairing’s strength/durability characteristics match their uses and needs. “Factors that materially affect durability include the fairing materials’ ability to withstand temperature extremes of hot and cold without expanding/contracting excessively; to withstand road salts and not collect snow/ice; to withstand bumps/dings etc. from contact with yard and road hazards; to successfully negotiate drop down docks; to flex over (or push) snow/ice piles in tight yard maneuvers in winter; and to flex when ground contact occurs from pot-holes, railroad crossings or driver error,” he says.

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Fleets also need to know that size matters. “The bigger the fairing, the better the aerodynamic performance. There are three areas where size counts: distance from ground; length, and fairing area at the critical leading edge of the fairing (is the leading edge square and low to the ground, or angled upward, thus reducing fairing area?),” explains Reiman.

Lastly, shape matters. Some fairings are parallel to the side of the trailers. Others are straight, but installed at an angle. Still others are parallel, but the front section angles in. Fleets should discuss the thinking and science behind the design with company representatives to understand the test results each manufacturer presents.

Acott from Laydon suggests investigating the full range of aero devices for tractor/trailers to completely understand what’s correct for which application. “Products include truck mounted roof fairings and chassis fairings, trailer side skirts and gap reduction fairings. Our presentations include the different types of products on the market and how they compare not only aerodynamically, but how they stand up to everyday use and abuse. Since CARB has implemented a retrofit program for 53-ft. trailers operating in California, installation of side skirts has to be easy. The lowest amount of fasteners, quickest installation and most robust skirts will win the day.”

Smith from ATDynamics says the most critical factors a fleet should look for when selecting a rear-drag aerodynamics device for its trailers may be very specific to his product. “Length of device is critical—shorter tail devices may look like they would cost less initially, but installing a reduced length tail (as is still required in Canada until the government upgrades its regulations, which is expected this year) costs fleets thousands of dollars over the life of the trailer. The ideal TrailerTail length is 4+ ft. with incremental loss of efficiency with shorter tails.”

But he also explains recommendations can apply industry-wide.

“Look for proven on-road performance,” Smith says. “A buyer should be wary of any device without several million miles of proven performance in the field. Every rivet, hinge and panel needs to be field-tested. ATDynamics’ 2012 TrailerTail technology has now logged over 80 million highway miles on thousands of trailers in all temperature extremes.”

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Says Graham, “One of the tricky things about fairings is that, for the fuel saving performance, it’s really not rocket science. To make them save as much fuel as you can, you have to get them as close to the ground as you can. There’s a trade-off there—because they’ll get hit.”

Graham says his (and other suppliers’) mission is to “design a product that is made to get hit. That’s where it’s extremely important to look at the design and construction of the product, and the materials used. We’ve found that some materials are better than others for these ground-impact situations and for getting dragged over pavement,” he says.

“We and a number of other suppliers have made good progress in the past few years in developing the product with durability as a top criteria. Due to that, longevity isn’t an issue…we’ve achieved much more acceptance,” says Graham.

Jack Latimer says AirTabs—small, stick-on air deflectors (or vortex generators)—can help bridge the gap between tractor and trailer airflow. They can also help ease airflow around the rear of the trailer. Fuel savings are real, he says, but his customers regularly tell him about other benefits.

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“We advertise the product as more than a fuel saver,” he says. “It also reduces the amount of splash and spray coming off the back, permitting the driver to have better mirror visibility when driving in rain and snow. Drivers can see cars approaching better. Handling is also better, especially in cross winds. Ladies love them because they don’t have to fight the wheel as much.”

Latimer says because wind tunnel testing has its limitations, the proof is in the customer feedback. They came out of the aerospace industry, so it’s somewhat ironic that on-the-road testing has been so critical, he says. “Bean counters buy them for ROI—I try to sell them for safety.”

According to the experts we consulted, application is a key consideration to determining whether aerodynamics is a good fit for your operation. The performance of the product and its resulting return on investment will be directly proportional to the speed and distance you travel. A very wide range of potential ROI is to be expected; because some fleets have much better utilization of their trailers due to the type of operation. Basically, the further and faster you go, the better fit aerodynamics will be.

Other aerodynamic options include aerodynamic wheel covers, vented mud flaps and tarps for flat bed trailers. When combined with other efficiency measures, dramatic savings can be realized.

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“Investing in trailer aerodynamics, specifically tail and trailer skirt technology—which together deliver over 10% fuel efficiency at highway speed—is a no-brainer for any trucking fleet accruing over 25,000 miles per year on a trailer,” explains ATDynamics’ Smith. “Fleets that accrue over 40,000 miles per year are basically donating money to the oil industry. Fleets, such as reefer or dedicated high mileage operations with low trailer to truck ratios getting 80,000 up to 160,000 miles per year at highway speed on a trailer simply won’t be competitive in 2012 without full aerodynamic packages.”

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