How To Cheat The Wind And Increase MPG
Truck aerodynamics or streamlining for the purpose of enhancing fuel economy has not received the critical attention that the other components and systems on the truck have received.
This lack of research is surprising in light of a statement made at last year's Maintenance Council meeting by Lawrence Livermore National Laboratory's FrankTokarz, Ph.D.
Dr. Tokarz said, "Aerodynamic drag has a higher potential leverage for reducing fuel consumption than any other technology improvement. If drag coefficient could be reduced by one-quarter, we could realize a ten- to fifteen-percent savings in fuel consumption."
Over the past decade the fuel efficiency of tractor/trailers, for example, has improved from an industry average of about 4.5 mpg to 6 mpg.
This has come about as a result of a number of efforts, such as the development of electronically controlled engines, training drivers to drive for fuel economy, more efficient transmissions, and improved aerodynamics. However, more can and should be done to improve heavy truck aerodynamics.
Since the mid-1980's, tractors/power units have received the lion's share of attention when it comes to aerodynamic redesign. Today's streamlined power units look like they've just emerged from aircraft wind tunnels, and they ease their way down the road and through the air.
Even square-nosed "large cars" will usually mount big deflectors on their roofs to smooth the flow of air over the van or reefer trailer behind.
The potential gains in fuel economy are not lost on the Department of Energy's (DOE) Office of Heavy Vehicle Technology (OHVT).
DOE says the projected increase in highway fuel consumption-- a figure expected to approach 12 BILLION gallons per day by 2020, in total, for all highway users - is mostly due to trucks.
DOE's objective is to reduce the fuel consumption and lower emissions of heavy trucks by reducing aerodynamic drag. To this end, the DOE has partnered with Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories, USC, Caltech and NASA on a project called Enabling Industry to Reduce Aerodynamic Drag of Class 8 Trucks.
The DOE's OHVT has another project underway with Georgia Tech Research Institute's (GTRI) using wind tunnel testing and pneumatic aerodynamic technology to obtain those elusive miles-per-gallon.
LLNL's Frank Tokarz, Ph.D., and Robert J. Englar, principal research engineer at GTRI's Aerospace,Transportation and Advanced Systems Laboratory, made presentations at The Maintenance Council's 2000 Annual Meeting, during a study group session titled Practical and Advanced Innovations in Trailer Aerodynamics.
Tokarz said that for a typical tractor-trailergoing 70 MPH, 65% of the total energy expenditureis in overcoming aerodynamic drag, and that an eight percent reduction in drag at 70 MPH would result in an equal reduction in fuel use.
Tokarz also reported that the addition of boat-tail plates to the back end of a trailer--although incompatible with today's loading docks--reduced aerodynamic drag (in wind tunnel testing on a simple model) by as much as 20%.
"The truck should have an integrated design optimized for minimum frontal and base drag, "Tokarz continued. "Some areas to look at include an optimum design for minimizing drag, design of base shapes, improved frontal shapes, designing an integrated vehicle, body shaping and/or development of active flow devices.
ONE SUGGESTED APPROACH
With the exception of the tractor/trailer interface (which accounts for approximately 20% of that type truck's overall vehicle drag), the same principles of aerodynamics more or less apply to the medium duty straight trucks (Class 6 and7)which are the standard vehicle type for the expediting industry. To our knowledge, no laboratory or wind tunnel testing has been applied specifically to the class 6-8 trucks with cargo box.
However, improving aerodynamics is a much bigger challenge when it comes to trailers or cargo boxes. It would appear that the greatest obstacle to aerodynamic efficiency is the vacuum left behind a trailer or cargo box due to the need for a flat rear surface that matches up with loading docks.
Attempts to reduce cargo box or trailer drag by "boattailing" the rear of the box have so far not been successful because they entail physical changes to the rear of the box, either by panels or inflatable shapes.
These are considered unwieldy by most (having to manipulate panels in cramped loading dock areas is probably impractical, and is another task that already heavily burdened drivers would have to perform); and there have been difficulties with the Department of Transportation regarding possible violations of Federal regulations on trailer or cargo box dimensions.
Reduction of underbody drag has been investigated but it would seem that while beneficial it has operational drawbacks such as buildup of road dirt and snow and ice and severely limited accessibility for maintenance of trailer underbody parts and various air and electrical lines.
In addition to reducing fuel consumption, improving aerodynamics will further reduce splash and spray and wind blast on adjacent vehicles. Reducing splash and spray will enable truckdrivers to see better using their mirrors, and reduce passenger car drivers' anxiety.
The concern over wind blast on adjacent vehicles may grow as passenger cars become lighter to enhance their fuel economy. While not necessarily a safety factor, it is a concern related to being a good highway neighbor.
GTRI's Englar said a possible method of reducing trailer drag, currently under evaluation, is pneumatic aerodynamics-- blowing compressed air over the surface of the trailer or cargo box. According to Englar, this method would create the same effect as streamlining on the sides of the trailer, and that such a system has been proven successful in improving lift on aircraft.
The compressed air could be obtained from the truck's exhaust stacks, turbocharger or braketank, and would run through lines to be blown out at the back. Blowing slots could be positioned on all sides of the trailer/box and/or the front/top of the trailer/box. In his conclusions, Englar said, "pneumatic aerodynamic concepts offer significant potential for applications to heavy vehicles."
Some potential benefits, according to Englar, include additional lift for rolling resistance reduction, or reduced lift for traction and braking, instantaneously switchable; partial slotblowing for roll control and lateral stability; one-side blowing for yaw control and directional stability; no moving parts, small component drag and a very short aft addition; splash, spray and turbulence reduction; and reduced hydroplaning.
A REAL WORLD TEST
In May 2000, a prototype open-cavity designed by Clarkson University engineering students was mounted to the back of a trailer owned by Potsdam, NY-based Lavalle Transportation. After traveling to Washington, California, Georgia and back, numbers suggest that the tractor-trailer saved about 0.5 MPG, according to assistant professor ofa eronautical engineering, Ken Visser.
"The vehicle attained an improvement in fuel efficiency of about ten percent, from 5.80 MPG to 6.38 MPG," Visser said. "The device reduces the wake's size and decreases drag-- in wind tunnel scale-model tests, it reduced drag by 10 percent."
The device attaches to the trailer's rear doors and is inset from the trailer's outside edges by about seven inches. It looks like a second set of doors when closed, but opens into a box shape that extends overall length by 33 inches when manually engaged by the driver. To access the trailerdoors, the driver unlocks and folds the panels flush against the doors, then opens the trailer doors with the device still in place.
The sides of the device are fiberglass panels,while the top and bottom are made of canvas.Students are hoping to equip one of Lavalle's trailers with a five-ft version of the device for the next test.
"The pressure drag from the rear of a cargo box provides a large percentage of the aerodynamic resistance," continues Professor Visser. "There are a number of issues that make streamlining the rear of the cargo box a challenge."
Clarkson students conducted research on the rear end of trailers in a senior integrated design course and an independent study course. Visser gave the students some requirements in advance; the device must be easy to operate, must noti nterfere with docks and loading/unloading, and must conform to trailer length limitations.
The students got their project underway by way of a grant from the National Collegiate Inventors and Innovators Alliance, a non-profit organization.
Visser says, "We're going into the wind tunnel with models in the near future and we have another open-cavity prototype headed out on the road very soon."
SCANIA'S FUTURISTIC APPROACH
Recently, Swedish truck builder Scania unveiled its concept truck for the 2010s. The aerodynamicshape of truck and trailer have been optimized to such an extent, the manufacturer reports, that the air drag coefficient has been reduced to passenger car levels.
A small bonnet is mounted ahead of the cab to significantly smooth the airflow around the front, and acts as a crumple zone in case of a frontal collision. Cab height is at the maximum allowed and leaves no gap between the cab and top of the bodywork, eliminating the need for an air deflector.
Aerodynamic sideskirts, which double as under-run protection for the safety of passenger vehicles, run the entire length of the vehicle.
Possibly most significant among the concept vehicle's design features are boat-tails on the truck and trailer. The bellows on the truck are designed to bridge the gap between truck and trailer, to reduce turbulence in that area.
The trailer boat-tails are flaps which pop out at highway speed, extend overall vehicle length slightly, and allow airflow to smoothly depart behind the vehicle. Scania says wind-tunnel tests indicate that the boat-tail on the trailer aloner educes air drag for the tractor-trailer combination by over 10%.
Back in 1966, Joe Fitzgerald was designing a reefer unit to be mounted in what is now the standard location for the refrigeration unit - at the front and top of the trailer. During testing of the unit and the pod he had designed to contain the equipment, Fitzgerald began receiving reports from drivers about increased fuel mileage and better trailer stability. He had unintentionally created the first Nose Cone.
The Nose Cone Air Deflector system is marketed by Fitzgerald Corporation of Buena Park, CA. Made of reinforced fiberglass, a Nose Cone typically costs $550 to $750, weighs no more than 50 pounds and installs in less than two hours, says company president Jim FitzGerald, son of the Nose Cone inventer. A trailer version usually pays for itself in less than a year, or about 50,000 miles of operation.
The Nose Cone is hung on the upper front of a trailer or cargo box. It will save 10% to 15% in fuel, or customers can get their money back, the company advertises on its Web site.
Tractor-mounted fairings save 3% to 7% in fuel, Nose Cone's Web site says. But a Nose Cone saves additional fuel and is especially effective on a straight truck.
The company states that their tests show that a straight truck with a Nose Cone will save just as much fuel at 30 mph as a tractor/trailer will at 55 mph.
The reason for that is that the frontal area is close to the same size, but without the weight of the big truck - aerodynamics are the key to these savings.
Sales and Marketing Manager Kathy Rose, a ten year company veteran tells us, "The road handling of the straight trucks is improved so much by using our product that when some of the companies who have used Nose Cones have, for some reason removed them, they tell me that their drivers have threatened to go on strike!"
"We have around 135 different models, so we have a nose cone that fits anything from a small utility trailer to big trucks, any size to fit any need."
Aeroserve Technology Ltd is an Ontario,Canada-based company that was formed in 1996 and the principals in the company all share an aeronautical background. The company produces "AirTabs" which are specially designed for trucks and are applied to two specific areas-- at the back of the tractor just ahead of the tractor-trailer gap, and at the back of the trailer/cargo box.
The company refers to AirTabs as "small, efficient streamliners that are the first practical solution for reducing drag at the back of large vehicles."
Air Tabs are similar to the small slat-like"vortex generators" on the upper surfaces of wings on jetliners. These cause air to swirl and leave the wing's surface with less friction and without forming a vacuum at the wing's trailing edge. This increases lift, boosts payload, reduces drag and saves fuel.
An Air Tab is about 5.5 inches long by 3 inches high and 1 inch deep. Molded in tough ABS plastic with an adhesive-backed undersurface that attaches to the vehicle's skin, it comes in a standard white finish, but custom colors can be molded in or it can be painted with standard auto paint.
The company says drivers are reporting improved handling of the trailer, a fuel savings of 4-6% annually, and an extension of steer tire life of25-40%. Aeroserve also says its AirTabs conform to width restrictions, reduce spray for vehicles traveling behind the tractor-trailer in wet driving conditions, and reduce dirt build-up on the rear of the trailer.
"The tabs reduce turbulence in the gap by keeping the air from going in. At the trailer's rear, thetabs create air swirls well behind the trailer,where it's no longer attached," says Mark Adler,vice president of sales and marketing for Aeroserve.
"Drivers can feel the difference," he says. "There is less sway and less pull. One guy in Australia stopped to get out to make sure he still had a full load aboard because it felt like the truck was lighter. And he was one of the skeptics."
Fuel savings - the main point of the devices -will be at least 4% if tabs are on tractor andtrailer. The 4% is guaranteed, but some operators have seen 10% fuel savings, adds Adler.
Ron Davidson is the VP of Operations for Aeroserve Technologies and he states, "Our test trucks have had the airtabs on for 3 1/2 years and we've noticed appreciably less wear on steer tires because of less sway and less wander. We've put our Air Tabs on the back of RV's, and the owners have discovered that it tends to stabilize the vehicles."
Davidson says that AirTabs are easily installed by the truck owner; in the case of an expediting straight truck, a first time installation wouldr equire 30 minutes or so using the template and instructions provided with the Air Tabs.
He says that the typical straight truck cargo box installation would require an estimated 75 Air Tabs located on the trailing edge of the box, for a cost of around $150.00 US.