Wind resistance is a total drag—literally. Wind resistance is one of the top forces working against the truck as it runs down the road. (The other factors being: grade resistance; tire rolling resistance; and engine accessory and/or drivetrain losses, according to Cummins MPG Guide: “Secrets of better fuel economy”.) Did you know that every 2% reduction in aerodynamic drag results in approximately 1% improvement in fuel economy? It’s no wonder that truck and trailer OEs, along with aftermarket suppliers, have unveiled the latest and greatest aerodynamic products to cut down on wind resistance, allowing the truck and trailer combination to carve a path toward fuel efficiency.
Tractor OE offerings
Freightliner Trucks
The Freightliner Cascadia Evolution standard features that improve airflow and aerodynamics include an air dam, bumper closure, hood-to-bumper fill, elliptical-shaped aerodynamic mirrors and an integrated antenna. Chassis side fairings and 20-in. side extenders also contribute to the truck’s efficiency.
“The Cascadia Evolution delivers up to an additional 7% improvement in fuel economy over an EPA 2010-compliant Cascadia equipped with a first-generation aerodynamic package, and up to a 5% improvement compared to a model year 2013 Cascadia equipped with the aerodynamic upgrades,” said Mary Aufdemberg, director of Product Marketing, Freightliner Trucks.
Kenworth Truck Co.
In 2014, Kenworth introduced the Kenworth T680 Advantage—Kenworth’s most fuel-efficient truck. The T680 Advantage features the latest PACCAR MX-13 engine, Eaton Fuller Advantage 10-speed automated transmission, fuel-economy drive axles (such as a 6×2 configuration) and special factory-installed aerodynamic package. Other fuel-efficient specs available for the T680 Advantage include the Kenworth Idle Management System, wide base tires, tire pressure monitoring system and Kenworth Driver Performance Assistant.
“The Kenworth T680 Advantage provides up to a 5% fuel efficiency gain compared to an equivalent 2013 Kenworth T680 with a PACCAR MX-13 engine and Eaton automated manual transmission,” said Kurt Swihart, Kenworth marketing director. “Customer acceptance of the T680 Advantage was high in 2014, and we expect excellent growth for the T680 Advantage this year.”
Navistar International Trucks
A new fuel efficiency package for the International ProStar—the International ProStar ES—made strides with enhancements in many tractor design areas, including bumper valance, chassis configuration, roof fairing surfaces and antenna locations that added up to several percentage points of aerodynamic improvement. According to Navistar, the ProStar ES will achieve up to an 11% improvement in fuel economy versus the 2010 ProStar/MaxxForce 13/10-speed manual baseline.
“At 55 MPH, aerodynamic drag accounts for about 50% of the fuel consumed so the benefit of aerodynamic drag improvements are significant at highway speeds and the aerodynamic benefits increase at higher speeds,” said Jodi Presswood, vice president and general manager, heavy truck product line, Navistar. “Since crosswinds are part of real world driving, it is important for aerodynamic development to include their effects.”
Mack Trucks Inc.
The Mack Pinnacle offers hood, tractor and sleeper designs that improves airflow, directing the wind up, over and around the vehicle. Standard features and available options include aero front bumpers and mirrors, full roof, side shield and chassis fairings. Additional features such as roof, side shield and chassis fairing extenders and ground effects packages are also available.
“Each component contributes to the overall effectiveness of the design. No single component can deliver all the fuel savings improvements alone, but there are specific features that can contribute to improved fuel efficiency,” said Phil Cary, Mack highway segment manager. “For instance, full roof fairings and side shields can deliver the largest improvement of up to 6% in fuel economy savings. Chassis fairings, as well as aero front bumpers and aero mirrors, can each deliver up to 1.5%.”
Peterbilt Motor Co.
Peterbilt’s Model 579 EPIQ package offers a complete aerodynamic configuration, including 18-in. sleeper side extenders with 8-in. rubber flares; full chassis fairings with rubber skirts from the quarter fender to the front of the tandem axle with rubber closeouts under the sides of the cab and sleeper; and roof fairings with an exclusive rear wall closeout. Aerodynamically-enhanced components include a three-piece aero-style bumper; multi-piece aero-style hood; painted outside sun visor and an aero-style aluminum battery box positioned on the passenger side, under the cab.
“The Model 579 EPIQ is the most aerodynamic truck in Peterbilt’s history,” said Robert Woodall, assistant general manager, sales and marketing, for Peterbilt Motors Co. “The Model 579 EPIQ features a number of aerodynamic closeouts and fairings to further improve fuel efficiency. In total, the Model 579 EPIQ improves fuel efficiency by up to 14% compared to previous models. Customer acceptance of the Model 579 EPIQ has been excellent.”
Volvo Trucks North America
All 2016 model year Volvo VN series trucks feature a more aerodynamic bumper that’s designed to direct air more efficiently around and under the truck. In addition, the VNL 630 and VNL 670 models now offer flared chassis fairings for smoother air flow around the rear tandem wheels with shorter wheelbases. The VNL 670 roof has also been modified to provide better airflow management with the adjustable trim tab. The 2016 VNL 670 will provide up to 3.5% fuel efficiency improvement when coupled with an aerodynamic trailer.
“The commercial truck industry has made significant strides in the development of more aerodynamic vehicles during the past 10 years. Because of these major improvements, future gains will be smaller and incremental,” explained Jason Spence, Volvo Trucks product marketing manager—long haul. “Where you might have seen aero-influenced fuel efficiency gains of 8 to 10% in the past, the improvements today are more in the range of 2 to 4% industry wide, year over year.”
Western Star Trucks
The all new Western Star 5700XE (XE standing for “extreme efficiency, according to the manufacturer) is the latest entry in the aero segment and it was specifically designed with bold edges and a unique look that sets it apart from other aerodynamic models. The chassis side fairings on the 5700XE feature optional rubber ground effects strips to help manage airflow under the truck. A new cab skirt was designed to work with the side fairings to block air from flowing under the cab. A new roof cap and 20-in. cab side extenders were developed to effectively move air around the typical box van trailer. Additionally, the exterior sun visor which, based on Western Star’s research, is an item many fleets wanted to keep both for looks and sun-shading effectiveness works with the ramp at the back edge of the hood to direct air over and around the top of the cab making the sun visor drag neutral.
“The aerodynamic performance of the 5700XE is roughly 12% better than that of the Western Star 4900SB model. It should be noted that the 5700XE meets the requirements to be placed in the highest EPA Greenhouse Gas category,” Guy Lemieux, marketing segment manager, Western Star.
Got you covered
Real Wheel Corp. offers its American-made Aero Covers, which provide lighter-weight, stainless steel wheel that will last the life of the truck and are available for both wide-base and dual wheels and for both tractor and trailer, according to the manufacturer. The Aero Covers Series includes: Aero Stainless; Aero Mirror Stainless; Aero Stainless Clear, which provides a viewing window for wheel inspections, eliminating the need to remove the cover; and Aero Plus Package, which combines Aero Wheel Covers, braided stainless steel air valve extensions and LED AirGuards.
“It is a well known fact that air turbulence slows the forward movement of large commercial vehicles, and greatly increases fuel consumption,” said Jan Polka, president of the Real Wheels Corp. “The newly designed Aero Series of engineered wheel covers from RWC greatly helps to streamline the rig, saving fuel while solving the challenges associated with vehicle inspections, maintenance and service.
“Test Data Shows 1 to 2% Fuel Savings with Aero Covers alone,” he continued. “In SAE type II J 1321 tests conducted by independent third parties, a standard tractor with four wheel covers was found to save approximately 1%. A tractor-trailer combination with eight wheel covers achieved a 2% increase in overall fuel savings. The Aero Plus package may yield 2.5 to 5% fuel savings through a combination of aerodynamics and proper tire inflation.”
Directing the flow
“Just as aerodynamics at the tail-end of the trailer is one of the most drag-intensive areas of the trailer, the rear of the tractor [the tractor tandem] and the rotating drive wheels create an enormous amount of drag,” according to Josh Butler, President, FlowBelow Aero Inc. “We’ve taken a different approach to reducing drag on the tractor by focusing on developing a complete system that controls the airflow around the tractor tandem.
The FlowBelow Tractor AeroKit consists of quick-release wheel covers and tandem fairings to provide smooth airflow across the entire truck. “As a complete system, the Tractor AeroKit provides over three times the fuel savings of wheel covers alone according to independent SAEJ1321 fuel economy testing,” Butler said.
An (aero) dynamic trailer market
“Fleets typically purchase tractors today that have an aero-package that interacts with the trailer’s front end construction and side skirts,” said Charles Fetz, P.E., vice president of design and development for Great Dane. “Larger fleets employ evaluation methods such as wind tunnel testing or CFD modeling to check the interaction between the actual tractor model and aero package with the trailer aero system to make this union optimally efficient. While this is economically feasible for the larger fleets, it’s typically not feasible for smaller operators.”
Great Dane offers a variety of SmartWay-verified drag-reducing components such as side skirts, undertrays and rear fairings, commonly referred to as “boat tails.” While some of these items can be factory installed on an assembly line, others are typically installed offline in Great Dane-owned or authorized service facilities. Yet, as with most components, the savings realized from these additions can vary from fleet to fleet. Fetz explains:
“Based on feedback we receive from our customers, real-world savings are often significantly less than advertised by third-party aerodynamic device suppliers due to the wide variation in conditions carriers face in actual operation, as compared to high speed test track results at constant speed,” he said. “That being said, the savings can still be substantial, especially for fleets that run long distances at highway speeds.”
Set for launch
Recently, Wabash National Corp. unveiled three new solutions designed to significantly improve trailer aerodynamics and fuel economy: the Ventix DRS (drag reduction system) utilizes a patent-pending segmented design to manage air flow across the entire length of the trailer and eliminate drag points; an aerodynamic tail device, named the AeroFin, manages airflow across the rear of the trailer to reduce aerodynamic drag; and the lightweight AeroSkirt CX, a trailer side skirt that provides up to 6% fuel economy improvement (SAE J1321-Type II Track Test) in a design that weighs nearly 30% less, according to the company.
“When used in combination with low rolling resistance tires, the Ventix DRS and AeroFin can improve fuel economy by more than 10%,” said Brian Bauman, vice president and general manager, Wabash Composites.
The utility of aerodynamics
Utility Trailer Mfg. Co. offers its Utility Side Skirt 120A-4, which is U.S. EPA SmartWay verified to achieve greater than 5% fuel savings and can be used in combination with low rolling resistance tires on Utility trailers to achieve California Air Resources Board (CARB) compliance for California operations. The USS-120A-4’s galvanized high tensile steel bracing system allows the side skirt to flex both inward and outward, which can be bent back to their original shape if damaged. The side skirt is also manufactured with a UV protected bi-directional Fiberglass Reinforced Plastic (FRP) construction. To further reduce impact damage the forward edge of the skirt is securely bolted with a “spring” attachment at the support leg assembly.
Reducing drag on the tail
With more than 35,000 installations in more than 500 fleets, TrailerTail by ATDynamics—recently acquired by Stemco LP—is leading the aerodynamic innovation charge when it comes to the back of the trailer.
TrailerTail technology reduces aerodynamic drag on a tractor-trailer by minimizing the low pressure vacuum that occurs at the rear of the trailer when moving at highway speed. TrailerTails also streamline turbulent airflow around and to the back of the trailer, explained Jeff Grossmann, vice president of engineering.
ATDynamics offers TrailerTail and side skirt products verified by EPA SmartWay as 5% or greater fuel saving technologies. Additionally, ATDynamics AeroTrailer packages (TrailerTail and EcoSkirt) deliver verified fuel savings of 9% or greater and are recognized in the SmartWay Elite category, EPA SmartWay’s new top-tier category reserved for maximum-efficiency combinations of aerodynamic devices. Fleets using TrailerTails typically see a 0.3 to 0.5 MPG improvement and fleets using AeroTrailer packages typically see a 0.6—1.0 MPG improvement, the company said.
“Fleets have already moved past the ‘rectangular box’ trailer mindset—they are adopting side skirts and boat tails at rapidly increasing rates to reduce underbody and rear drag,” said Grossmann. “While side skirt and boat tail adoption may be the primary focus over the next several years, we believe the EPA’s GHG Phase II program will also stimulate research and development to create the next wave of aerodynamic devices and improvements.”
Engineering aerodynamics
“It is important to have the tractor and trailer working together as a system,” said Thomas Gerst, product design engineer for Fleet Engineers, manufacturer of two models of aerodynamic side skirts called the Air Slipper and AeroSaver, in addition to AeroFlap aerodynamic mud flaps. “When you look at how aerodynamics are affecting the whole system, you are able to design solutions that offer the greatest savings.”
The Air Slipper is offered in two lengths designed for 48- and 53-ft. trailer applications. The AeroSaver is currently offered in a 53-ft. trailer application in either a white or grey color. AeroFlaps are available in lengths of 24, 27, 30 and 36 in. This spring, the AeroFlap will also be available for the wide base single tires. The AeroFlap pattern channels airflow into complementary directions reducing the drag on the vehicle, which helps to save fuel. The AeroSaver and the AirSlipper are designed to help stop the airflow from entering under the trailer and prevent drag. The AeroSaver and Air Slipper side skirts are able to realize savings by up to 7%; AeroFlap mud flaps offer savings of nearly 1%, according to Fleet Engineers.
Mind the gap
“The tractor trailer gap size is an important aspect of fuel economy in trucking operations and should be minimized as much as loads allow. If the gap between the trailing edges of the tractor fairing and the front of the trailer is greater than about 18 in. increased drag in this region begins to reduce fuel economy,” explained Jack Latimer, managing partner Airtab LLC. “For every additional 10 in. of gap size above about 30 in., aero drag will increase 2% and fuel economy will decrease by 1%. The operator can reduce this gap with side extenders and/or moving the fifth wheel forward. However, moving the fifth wheel forward can reduce maneuverability and can place more weight on the steering axle increasing steering gear and tire wear.”
Airtabs reduce drag by changing the dominant vehicle trailing edge turbulent flow mechanisms from large vertical eddies to a horizontal array of small vigorous solid body vortices. By altering the airflow in this manner, Airtabs artificially taper the trailer and make the airflow behave as if the trailer was slightly smaller than it actually is, said Latimer. Airtabs deliver fuel savings in the 2% to 5% range, according to test on a test track, in a wind tunnel and in over-the-road evaluations; 2% to 3% at the tractor/trailer gap and another 2% to 3% at the back of the trailer, he added.
Flaps in the wind
“Small aerodynamic products like Eco-flaps can add up to big benefits for fleets,” explained Barry Andersen, president of Andersen Flaps, manufacturer of Eco-flaps, mud flaps that feature molded, aerodynamic channels that reduce wind resistance and drag, moving air and water through the flap surface with minimal drag to improve fuel economy up to 3.5%.
Available in 24-, 27-, 30- and 36-in. lengths, Eco-flaps come in 24- and 18-in. widths, are available in standard black or white, and can be customized with logos and graphics. Yellow with “Caution Wide Turn” are available in 24- and 30-in. lengths.
