Truck Topics
Go With The Flow - Truck Aerodynamics
The next time you find yourself admiring one of the "classic" trucks like the Peterbilt 379, Freightliner Classic XL and Kenworth W900L, it might be wise to also consider how much more the owner of that truck is paying in miles per gallon to sport that classic big truck look.
A fuel economy expert at Kenworth's research and development lab in Renton, Wash., says that the Kenworth T2000 is approximately 15 percent more fuel-efficient than the W900L. And, he says, if the driver has a heavy foot, this increases the percentage.
This can also be expressed in terms of horsepower. At 75 miles an hour there is a 56-hp advantage to driving an aerodynamic truck. This is true despite other variables like weather, age of truck, driving style. It can add up to a savings of 5 to 6 cents per mile.
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. Some experts conclude that aerodynamic drag has a higher potential leverage for reducing fuel consumption than any other technology improvement.
Engineers say that if drag coefficient could be reduced by one-quarter, a ten- to fifteen-percent savings in fuel consumption could be attained.
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. Todays 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 "classic" trucks will be fitted with big deflectors on their roofs to smooth the flow of air over the van or reefer trailer behind.
Government studies
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 USC, Caltech, NASA, Georgia Tech and other research entities to obtain those elusive miles-per-gallon.
The experts say that for a typical tractor-trailer going 70 mph, 65% of the total energy expenditure is in overcoming aerodynamic drag and that an eight percent reduction in drag at 70 mph would result in an equal reduction in fuel use.
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 straight trucks which have become the standard vehicle type for expedited trucking.
Many of the Class 6 and 7 straight trucks of the last decade of so have been in the forefront of streamlining with rounded corners and sloped noses. Add to that, the increased utilization of the streamlined high roof, condo-type sleepers that are found on many of expediter straight trucks today and the problem of cargo box frontal wind resistance has been, if not eliminated entirely, at least greatly reduced.
Solutions
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 "bobtailing" 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 truck and trailer underbody parts and various air and electrical lines.
Vortex generators
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."
An AirTab 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, the AirTab 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.
Expediter Leo Bricker says that he believes the AirTabs he has installed on his Kenworth W9 chassis'D straight truck have resulted in enhanced stability and reduced buffeting, especially when being passed by another vehicle.
Bricker says that improved rearward visibility in rain and snow is another plus.
"On a truck without AirTabs, all I can see behind me in the rain is a foggy spray. With the AirTabs, I have a clear field of vision back there. I've also noticed that they help to gauge where the rear corner of the box is - they give a reference point that's helpful in backing."
Bricker says that installation is very simple and requires no more than 45 minutes. A complete set for the cargo box comes with 80 Air Tabs and template and costs around $200.00.
Would he use them on his next truck? "Oh yeah," Bricker states, "I would definitely use them again."
Expediter John Skinner has AirTabs on his 2006 International 9200 straight truck and he says, "I wouldn't drive a truck without them!"
He credits the AirTabs for his truck's enhanced stability in crosswinds, "and I can see clearly in my mirrors through the rain at what's happening in the rear of the vehicle. The spray goes straight back, not out to the sides."
Skinner feels that the devices have also helped his mpg: "Previously, I would get 1000 miles on a 100 gallon fillup. The last two fillups I noticed 1100 miles to each fillup. I love the increase in fuel mileage & reduced stress on my engine, but would buy Airtabs for the handling and increased visibility alone."
Jack Latimer, Manager of AirTabs for the America's, says that his company has received positive reports from AirTab users who have utilized them on everything from automobiles to cargo vans, horse trailers, RV's and of course, tractor-trailers.
Touching on the issue of enhanced rearward visibility, Latimer says, "If the AirTabs enable a driver to make safer lane changes and prevent an accident, that's worth the price of the product right there!"
Air deflectors
Nose Cone
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 weighs no more than 50 pounds and installs in less than two hours, says company president Jim FitzGerald, son of the Nose Cone inventor.
"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."
Wingmaster
As the company web site tells it, the inspiration for the Wingmaster's "Turbowing" air deflector came from the world of motorsports. The inventors wondered at the time how such an effect could be made possible on line-hauling big-rig tractor-trailer trucks, which critically face air drag more seriously than any vehicle in the world
After two years of development, the Turbowing was ready for market and the company states that the Turbowing has worked so well for the big-rig truckers; it has enabled them to reduce fuel costs substantially.
Visit these company web sites for more information about their aerodynamic devices: