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  • Feature: Cutting Down Turbulence

Feature: Cutting Down Turbulence

Smoothing Out Pickups and SUVs for Big Payoffs

Dan Carney
Jan 7, 2005
Photographers: The Manufacturer
The phrase "truck aerodynamics" might seem like an oxymoron, especially when considering a truck's traditional brick-like shape. However, because the design baseline is so bad, there's plenty of room for improvement. Helping blocky utility vehicles slide through the air more easily is an area of significant effort by manufacturers. Heavy-duty highway tractors embraced aerodynamics some years ago; as conservatively styled as the tractors may be, their owners are more motivated by the opportunity to save fuel costs than anything else.

But pickup-truck and SUV buyers don't typically stay financially afloat based on the fuel economy of their vehicles, so these buyers may be a tougher audience for streamlined designs. Witness Ford's more muscular-looking 2004 F-150.
"You hit on the thing that makes our life tough in the Jeep and truck division," says Rick Aneiros, vice president of Jeep and truck design at the Chrysler Group. "Our customers are traditional and have a clear idea of what a Jeep or truck looks like."
Photo 2/4   |   63 0407 Turbulence02 Z
Designers can trick the eye and cheat the wind, making customers happy on the highway and at the gas pump. The Dodge Durango recently traded some of its macho design for a pointy-nosed look that carries a larger grille ahead of a sloping hood. That's the obvious part. Less obvious is the four-inch air dam at the bottom of the front bumper that keeps air from getting under the truck, where it swirls around the running gear and creates drag.
"That's a common trick, one we all do," explains Bill Pien, supervisor of vehicle aerodynamics, Ford Motor Company. "We spent a lot of time developing a spoiler for the front bumper of the new Explorer to help us increase the fuel economy."
Part of the reason trucks are getting more slippery is that manufacturers are gaining a firmer grasp of aerodynamic fundamentals. "There was some question years ago whether this was some kind of astrological science," chuckles Aneiros. Today, companies understand the sources of drag and can attack them using computer modeling and wind-tunnel testing, once the domain of race cars.

For example, the big mirrors that show cars lurking in blind spots are terrible sources of drag and wind noise. Big mirrors can add three to five percent to a truck's drag, but little mirrors don't work as well. The solution is careful attention to detail that can minimize the turbulence from big mirrors.
"For the current F-150's mirrors, we did computer-aided engineering and wind-tunnel work," says Pien. "The mirror must be functional, so you design around that criterion. Doing flow visualization in the wind tunnel cuts down on unwanted turbulence around the mirror."
Photo 3/4   |   63 0407 Turbulence04 Z
"The A-pillar can be very turbulent depending on its shape," says Aneiros. "We work with the offset of the glass, the shape of the A-pillar, and the relationship of base of the pillar to the mirror. It's one of the toughest areas to get right on a vehicle."
Sweating other small, but unnoticed details can also reap benefits. "We pay attention to the front bumper, how deep the wheel offsets are, and the size of body gaps," Pien says. "Smoothing the flow of air underneath the truck also helps, but plastic shields are expensive and tough to employ on trucks."
"We've tried that on several occasions," Pien adds. "But under the strain of vehicle testing, frame twist broke the shields." Also, the fuel-economy improvement was minor, so the company chose not to use them. Instead, designers ask the engineers to keep the drivetrain and suspension as high and close to the body as possible.

Runningboards help control turbulence under the truck, so manufacturers are happy to install them on as many vehicles as possible. "The runningboard is like a channel that controls the airflow," Pien explains. "We have them available on all of the SUVs, because they're usually helpful."
Photo 4/4   |   ford F 150 Pickup front
Future technology could include a grille that opens and closes slats according to the truck's cooling needs to minimize drag. "The problem is that owners could easily unplug the wire, leaving the slats open all the time, and the EPA won't accept easily defeated tweaks," says Pien.
Subtle adjustments to the shape of body parts has an important impact. Consider the rear edge of the hood. "The air has to be directed over the windshield wipers and stay close to the windshield. We designed a curved rear edge to the hood to get that air over the wipers," says Aneiros. "That makes a positive aerodynamic contribution."
Where will truck styling go from here? "I think we're going to see more aggressive action on aerodynamics in the future," Pien predicts. "Everybody's trucks are getting bigger, and to maintain the same energy consumption, you've got to reduce drag. In the future, we'd like to see a more streamlined vehicle."
Does that mean pickups and SUVs will follow the direction of pointy-noised tractor-trailers? "Could be," says Pien, "but I think macho is still going to be important."

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