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Flying like the wind

Aerodynamics is probably the single biggest contributor to the current low truck fuel consumption compared to 20-odd years ago, according to Kevin Cooper, principal research officer, Aerodynamics Labo...


Aerodynamics is probably the single biggest contributor to the current low truck fuel consumption compared to 20-odd years ago, according to Kevin Cooper, principal research officer, Aerodynamics Laboratory, at the Ottawa National Research Council.

“Aerodynamics improved more than tires and motors. The market should be more willing to accept new technology than it was a few years ago,” he says, adding there is a current push to bring forward fuel saving technology that was developed 20 years ago, but that was not commercially viable then.

The NRC has been conducting development tests using 1:10-sale models in its model wind tunnel and full-scale trucks in its large wind tunnel.

Cooper, along with Jason Leuschen, NRC’s Montreal road facilities manager, recently released a paper detailing the second round of full-scale wind tunnel tests on Class-8 tractor-trailer combinations.

“The primary intent of the program is to effect a reduction in greenhouse-gas emissions by reducing the fuel consumption of trucks through aerodynamic drag reduction. Add-on aerodynamic components developed at the NRC several decades ago have become important contenders for drag reduction. This program has encouraged the commercialization of these technologies and this round of tests evaluated the first commercial products,” says Cooper.

Robert Transport has also been involved, offering up a Volvo VN 660 tractor for the testing. Claude Robert, president of Robert Transport, says this kind of testing and investment costs money, but that if you don’t do it, you won’t be in business.

“We are testing new trailers right now with single tires, side skirts. We already have some on the road and are going to put about 20 altogether and monitor them very closely. We already know that a lot of the things we’ve been doing for the last 10-15 years were very good. Now we are going to add a little more on to the skirts, do a little more fine-tuning at the back of the cab. In our company, we have lost, even though we’ve put in idling devices, and we’ve got speed limiters on all our trucks, on the average, on our fleet, mostly 0.6 miles a gallon over the last four years, or $4 million a year. And this has to do with the new engines, which are not performing as well as they were supposed to. Our average would have probably gone down to 5.7, 5.8 mpg if we had not put on these devices,” he says.

Involvement from fleets like Robert Transport has become more and more necessary to run aerodynamics and other road tests, says Cooper, who fears a reduction in government funding in the near future.

“We’ve had funding from Natural Resources Canada to do this work. And of course all those programs are now currently being reconsidered. The NRCan program has been cut back a lot. The big fleets really are the answer – that’s the approach we’re taking. Not that the owner-operators aren’t important, but the important thing is to have exposure and trial of this equipment, and to sort out any problems with it. Most things can be dealt with either by change of mindset or design modifications,” he adds.

(Speaking of mindset, Cooper notes that better aerodynamics in smaller vehicles like pickup trucks, which many truckers may own, can make a major contribution to fuel efficiency. “I would like to convince people with pickup trucks not to put the tailgate down or take them off because it wastes fuel,” he says.)

The NRC/NRCan program has advanced through three phases. The first phase utilized 1:10-scale model and full-scale development programs to reintroduce the concept of tractor/trailer gap closure, trailer skirts and trailer boat-tails. The second test program optimized the component designs. The third program tested commercial products of these and prototypes of other possible devices. The test program was run in March 2006 in the 9-meter wind tunnel of the NRC, located in Ottawa.

“The strength the wind tunnel has is to measure all the conditions that can occur on the road and there’s a technique that lets you calculate the average drag coefficient of the truck under the average winds that are occurring around North America. (i.e. if it ran all the way around North America for the year). The only way to test what’s really going on is to test several trucks over a long period of time, which for engineering road tests, is really expensive. There has never been a case in 38 years of wind tunnel tests on all vehicles where if the wind tunnel said it doesn’t work, it then worked. So it’s a really powerful tool because you can capture very small differences from an aerodynamic point of view,” says Cooper, who adds that operational road tests bring out the user-friendly issues, like is this device in the way in the yard, for example.

The study evaluated three primary devices, with the combination able to reduce fuel consumption by approximately 6,700 liters (1,800 US gal) annually, based on 130,000 km (81,000 miles) traveled per truck at a speed of 100 km/hr (62 mph). There were devices to reduce the tractor-trailer-gap drag, to reduce trailer underbody and bogey drag, and to reduce trailer base drag. The analysis considered a single tractor-trailer unit and a tractor with the average three trailers. The former case paid for the aerodynamic modifications in five months. The latter required a payback period of 14 months, since two of the trailers were at rest at any given time. In either case, the economics are promising, the study suggests.

In the past, notes Cooper, aerodynamic improvements to heavy trucks, especially the current cab-mounted aerodynamic packages, have provided large improvements in fuel consumption.

“Similar gains are also possible with the combinations of devices just mentioned. However, as is usually the case, one has to work somewhat harder to make these gains. In this case, three devices can be used alone or in combination. Two of these devices are trailer mounted, which impairs their economics, since there are about 3 trailers per tractor, on average, across North America. In spite of this, their relatively low installed cost and the rising cost of fuel make them economically viable. In any case, where fewer trailers are run per tractor, the economics are even better. The third approach, closing the tractor-trailer gap, uses hardware that can be either tractor or trailer mounted. It would seem beneficial to use-tractor-mounted equipment, but both types of hardware are becoming available,” he says.

But Cooper adds a word of caution:

“When you lower the drag of the truck, it can potentially go faster, but if that’s done, you throw away the fuel savings. It’s only when the drivers maintain the same speed with the drag reduction that you see the savings. It’s a lot easier to do these days with an electronic speed limiter,” he says.

“The main remaining issue is to spread the word, to convince the trucking industry to try these new components and to encourage the manufacture of the long cab extenders. It is likely that there will be teething problems in the operational and service aspects of these devices. However, these will be overcome by the large financial incentive that they offer. The trucking industry will improve its competitive position in a time of high fuel costs, the country will benefit from reduced fuel demand and the environment will be cleaner. How can we lose?” says Cooper.


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