Sexy skirt

by Harry Rudolfs

BOUCHERVILLE, Que. – In the last couple of years we’ve all noticed those skirted, tarted-up trailers rolling across the 401 from Quebec, but the latest bunch of 100 that the Robert Group just bought from Manac look even foxier.

This most recent incarnation of aero-fashion wears a mid-length belly skirt, hiked up and angled towards the fifth wheel, flashing a little bit of galvanized steel undercarriage. The skirt is a Freight Wing design: the top two-thirds made of softened aluminum, while the composite rubber hem (similar to mudflaps) glides four inches above the ground. Aluminum struts attached to the frame hold the entire assembly in place.

Robert has tried out other aerodynamic models in the last few years – an earlier generation wore a Laydon Composite skirt with cutouts around the wheel wells. This design stops in front of the tandem axles, leaving the Michelin X-Ones (XDAs and XTE super-singles) accessible for service. To lessen the gap between trailer and tractor, the kingpin has been set back 42 inches (instead of the standard 36).

I’ve never met Claude Robert in person, but I have a feeling he’s a huge fan of technology. Look at the features on this trailer: galvanized steel frame with rear fold-out steps, automatic tire inflation and greasing, anti-rollover and ABS package, pneumatically released bogie sliders, on-board Air Weigh scale, and Hendrickson SureLok struts to keep the trailer at dock level during loading. There’s even a nifty spotlight that lights up the undercarriage so you can check the disc brakes while you’re doing the pre-trip.

“This is the third generation of aero trailer,” Claude Robert tells me on the phone from his office in Boucherville, Que. “We’ve done all kinds of testing on different skirtings and each one has its pluses and minuses. Our engineers are working on a design for the end of the year which will be even more different.”

Although there are no published test results on this particular aero-configuration, Robert estimates that the aerodynamic and weight-saving features on this trailer will result in 5-7% fuel savings.

“With a good driver, it can easily be in the double digits. Right now we have trucks getting 8.5 and 9 mpg and others getting 6. But I’m still of the opinion that the best driver can compete with any of the fuel-saving devices, and the worst driver will only make those devices worse,” he says.

Clearly, aerodynamics does play a big part in fuel economy. In Canada we’re fortunate to have the National Research Council, an oasis of first-rate, practical scientific research labs operating across Canada. Its Ottawa campus has 10 wind tunnels, along with another full-size wind tunnel on a rotating platform near the International Airport.

They’ve tested everything from NASCAR racers to Olympic athletes. The day I called they were examining mailboxes. It was the NRC who dispelled the myth of the “open tailgate” on a pickup truck (it only helps your fuel economy if the box is over eight feet).

“There’s really nothing new in truck aerodynamics,” says Jason Leuschen, facilities manager for the NRC’s aerodynamics laboratory. “A lot of that research was done in the ’70s.”

Leuschen thinks that fleet managers understand the importance of drag-reducing technologies. But he also knows there are practical considerations.

“Fleet owners don’t dispute the fact that they would save fuel, but they also have other operational concerns. If they equip a trailer with 400 lbs of aero, they’re afraid that some of the drivers will damage the stuff and others will actively try to destroy it.”

The last round of NRC testing in 2006 yielded some interesting results, with Robert supplying the tractor. “I needed a truck and they had shown a lot of interest,” says Leuschen.

The session focused on aerodynamic hardware kits and components, most of which is currently available on the market, including skirts, caps, filler panels and boattail assemblies.

Vortex generators were proved to be “voodoo science.”

These are aluminum angle strips that are fastened to the rear of the roof and sides of the trailer. They’re being sold as energy-saving devices, while the opposite is true. The vortex generators Leuschen tested actually increased drag.

“Think of drag as a parachute, sucking you backwards,” says Leuschen. Bug deflectors and side-view mirrors were found to be large areas of drag, while surprisingly, Volvo’s deer bumper actually increased the aerodynamic properties.

The area right behind the trailer supplies one of the most active areas of untreated wind currents. Boattail kits scored highly in these experiments, especially Transtex Composites’ folding rear door trailer deflector and Aeovolutions’ inflatable rear door fairing, which channeled the splipstream into a narrow air-corridor significantly reducing drag.

“The boattail is the winner,” says Leuschen. “Ideally it should taper to a pinpoint behind the trailer, but you can still gain a lot.”

According to the research published by the NRC in 2006, Full-scale wind tunnel tests of production and prototype, second-generation aerodynamic drag-reducing devices for tractor trailers, a combination of a front end gap-reducing component, side skirts and some kind of boattail fixture will save 6,667 litres per year when operating at 100 km/h over 130,000 km. At $0.79 per litre that’s a savings of $5,283 yearly. The cost of installing the devices is around US$2,200, so that would mean the hardware could be paid for in five months.

Leuschen thinks it may also be time to look at replacing side-view mirrors with cameras. After all, Robert claims his side-view cameras help him see better at night and in the fog.

“Mirrors have been singled out because they are a large source of drag that are dictated by current safety regulations,” Leuschen writes. “It would be possible to eliminate mirror drag if regulations were changed to allow modern video cameras to replace mirrors as the means to providing rearward vision.”

In the meantime, Robert’s engineers are continuing to come up with new ideas. The president, himself, admits that R&D is expensive, and that the payback on some technology may not happen right away.

“Fuel economy is the key to survival in this business,” Robert says. “We don’t want to increase length or width. We just want to be able to take advantage of those devices that are available. The government should be trying to help us out instead of imposing restrictions, like penalizing us for using single tires.”

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