Press

Aerodynamics beat rising fuel costs

And improve stability and visibility

Specialist fleet operator Displayco is a designer and manufacturer of display and advertising materials that handles its own distribution via a fleet of seven rigid pan techs, mainly on the Melbourne-Sydney and Sydney-Brisbane routes. Their first trials of Airtabs in 2000, showed a fuel consumption improvement of 2.7% and that "was enough for me to make the decision to fit-out our fleet then and there," said Denis Walker, Managing Director. "But to be honest now that we've used Airtabs for some years, the big improvement in stability at highway speeds, the better rearward visibility in the wet and the cleaner tail lifts would have been good enough reasons themselves to take on Airtabs."

Airtabs are small plastic or vinyl vortex generators that fit around the trailing edge of the typically square and flat back of a truck or tailer. The Airtab product assists with turbulence and drag by addressing basic aerodynamic theory.

Chris Binks (pictured above) was sceptical at first but kept an open mind.

Chris Binks drives for Ballarat Refrigerated Transport from Melbourne to North Queensland, and Melbourne to Brisbane fortnightly. His refrigerated B-Double has had Airtabs since 2000. Chris was due for replacement trailers in July 2004, so a trial proposal was formulated where Chris would run the new trailers for three months without Airtabs, and then with, recording fuel consumption thoroughly. The results showed a 2.4% decrease in fuel consumption. "I wasn't surprised at all," said Chris. "I was relieved to be back to running with Airtabs and immediately noticed the reduced effort in driving. The trailers weren't 'waddling', I wasn't fighting the effect especially in cross winds and I was spending far less time cleaning, particularly the B-trailer fridge motor in the gap."

Denis from Displayco also speaks from experience as it's not unusual for him to be behind the wheel on the Hume or Pacific Highways. "Cross winds in particular can really make driving our pans a tough task and reducing that turbulence at the rear makes the driving far more comfortable. I also like the way we can see clearly behind us in the wet instead of dealing with that swirling mass of grimy spray. I can't understand why anyone wouldn't fit Airtabs if they're doing highway work. I look at them now as safety devices that also pay back real money."

With fuel prices rocketing, it's apparent this is food for thought for all truck operators.

(Airtab - taken from the kenworthallrig website)

Vortex generators claim fuel savings Just when you thought all the practical aerodynamic tricks had been uncovered, here comes another one.

And the claim is substantial -- 4%-plus fuel savings, guaranteed, and a six-month payback. Better yet, it really seems to work.

Just hitting the market now, 'Airtab' are small, triangular pieces of ABS plastic about four inches long and three wide tapering to a point, with a sort-of hollowed-out, scoop-like middle. From Aeroserve Technologies of Nepean, Ont., they're obviously heavily 'engineered', and indeed they're specially designed for trucks.

They borrow from aviation technology (even the U.S. National Aeronautics and Space Administration, or NASA, says they work) to create a controlled swirl of air, or vortex, behind a van box or trailer or at the gap between tractor and trailer.

Arrayed in a continuous line up the sides and over the top of a van or a tractor, at the trailing edge, they address the problem of air that has to rush in to fill the vacuum left by the truck. The air has to make a sharp bend around the squared-off back of the vehicle, which creates turbulence and thus drag. 'Airtab' produce a vortex of air from each side that extends for several feet behind, thus bridging the tractor-to-trailer gap and/or controlling the way air flows into the vacuum at the back of the truck.

That gap is always a challenge, and Aeroserve says that if it's larger than about 18 inches, you'll have power-robbing turbulence. But if you move the fifth wheel forward, you may have too much weight on the steering axle with potential handling problems and tire wear. Most people compromise between fuel economy and handling, and many use cab-side extenders.

These little tabs are said to take that compromise away. An early user of Airtab® is Tilmech Mechanical Enterprises of Tilbury, Ont., a manufacturer with a small fleet of one International 9200 tractor and 10 48-foot van trailers hauling auto parts to Toronto. With meticulous fuel records kept over several years, and a standard run, they represent a good test bed.

Tilmech's Ken Atkinson confirms the 4% fuel-savings figure, saying "There's probably a chance to go further depending on the aerodynamics of the tractor and trailer unit." That 4% saving represents $1000 a year in fuel and tire costs, he says. Among the benefits, according to driver reports, is reduced splash and spray and better visibility to the rear.

Tilmech (Tilbury Mechanical Enterprises) has proven that use of Airtab® vortex generators can save money for long-haul highway fleets. Today, the company is saving more than $1,000 per year per vehicle in fuel and tire costs through the use of this newly introduced device.

Aerodynamic drag has long been a target for fuel economy on trucks. Streamlined cabs and fairings have made improvements, but there is still the problem of the large flat area at the back of the vehicle and, for tractor trailer units, the gap between the tractor and trailer.

The large area at the back of the vehicle is an area where the air has to rush in, creating a lot of drag and turbulence. The gap between the tractor and the trailer can also create drag when air swirls into this space.The drag from both areas takes engine power to overcome, and therefore fuel.

Tilmech, located in Southern Ontario has a niche market in the automobile sector. All of it's driving is done on the 401, between Toronto and Tilbury. It has a small fleet and nearly identical load patterns.

Chuck Atkinson, the co-owner of Tilmech and Manager of Tilmech’s Transportation Division, says of fuel economy- "It's one of the things I watch out for, as it can make a big difference to the bottom line. We've been keeping accurate fuel figures for over 9 years. Since we have a consistent load, very flat roads, and normally light traffic, we were able to look at a lot of variables over the years. We measured fuel consumption carefully, and only changed one variable at a time. Our drivers have been very conscious of saving fuel, and have fully co-operated with us in keeping driving patterns the same. "

"For example, initially we tried different governed speeds, and determined that for our combinations, that 95 km per hour was the optimum, and have set all our tractors for that speed." "Naturally, we've got streamlined cabs and have paid attention to aerodynamics."

"We've also tried moving the trailers closer to the tractors to reduce the gap between the two. Truck and trailer manufacturers both said the closer together, the better. So we looked at different distances and found that we could get an improvement in fuel economy running with a separation of 22 inches."

"This caused a big change in the weight distribution on the axles. The front axle was now running at the maximum limit of 12,000 lbs and the drivers found this to be more difficult to control steering. We also went through steering tires very quickly (60,000 miles per set). We backed off the 5th wheel to a point where we the fuel penalty and front axle wear were balanced."

"Then we heard about vortex generators which might help to bridge the gap between the tractor and the trailer and reduce aerodynamic drag. I’d seen some on trucks in the USA and wondered what they were and how they worked. We obtained some prototypes Airtabs™ from the Aeroserve Technologies in Ottawa, and experimented."

"By installing these devices at the back of the tractor, we found that we could now move the 5th wheel back even farther, and retain the fuel economy, but with significantly improved front axle tire wear. We were quite pleased with gaining on the tire savings without losing ground on the fuel economy."

"The aerodynamics people from Aeroserve worked with us, and listened to our comments about appearance, installation and so on, and provided us with some later prototypes, which is what you see in the photographs. They also suggested to us that there may be some fuel savings by placing Airtab® around the back of the trailer. This has shown an overall improvement in fuel economy of about 4% from pre-Airtabs™ ."

"We've been delighted with the overall results. We not only see improvements in our fuel economy from before, but we're also getting more miles from the tires on the front axle. Our drivers have reported that they have better visibility to the back in wet weather. It seems these devices also affect the spray patterns, but we have no way to measure that effect. We also have seen some limited reduction in dirt on the back of the trailer. The devices were easy to install and need no maintenance."

Airtab® come from the aviation industry and are shaped to produce a controlled swirl of air. The ones on trial are designed, shaped and sized for the normal airspeeds that trucks would see, and for the aerodynamics of trucks. The swirl of air made by the device influences the air for some distance above and a long distance downstream.

For the gap between the tractor and the trailer, the effect is to ensure that air is controlled to swirl past the gap and not tumble into the gap from the side or top, creating turbulence and drag. At the back of the trailer, the controlled swirl guides the air into a smooth flow from the side and top. Not only does this prevent the air from tumbling, but it also tricks the air into the thinking the trailer has a more streamlined back end than actually exists.

Aeroserve Technologies was delighted. A company spokesman said "We know that these devices work and that facts prove it. The US National Aeronautics and Space Adminstration (NASA) has carried out extensive wind tunnel tests on these devices for a variety of applications and concluded that they are very effective.

Test track results from the UK by an independent body support our claims. Most over-the-road ‘tests’ have so many variables (loads, drivers, traffic, weather and so on) that without changing anything on the truck it is normal to see variations of 10% in fuel economy between runs. Our 6-8% savings show up in the long term or very closely monitored tests. Tilmech has a well developed fuel monitoring program, and an interest in saving money. We’re pleased to have such accurate results from a company with years of careful research into fuel savings."

Airtab® complement most existing air management kits on trucks involved in significant amounts of highway driving. They are unique in solving the drag at the back of the vehicle. Projected paybacks for a typical long-distance carrier would be in the order of 6-8 months.