14 JULY/AUGUST _ 201 POPULARMECHANICS.COM
slipping through the air with min-
imum drama. And this can lead to
some novel solutions.
Consider the grille of the electric
Jaguar I-Pace. Why does an electric
car have a grille, an artifact of the
internal-combustion engine? Stand-
ing next to a red I-Pace in the parking
lot of Jaguar Land Rover’s new North
American headquarters in Mahwah,
New Jersey, I ask. “We’re still build-
ing our brand,” says Wayne Burgess,
production studio director at Jaguar
Land Rover. “All the other models
have a grille, so we didn’t want to
abandon that with the I-Pace. But
we made it functional even though
there’s no radiator behind it.” He’s
referring to how the lower half of the
grille feeds air to heat exchangers for
the battery’s cooling system, and the
top half opens to the hood, creating
a path for air to accelerate over the
windshield and roof, down over the
rear window to the upright tail. “You
want to keep the air attached to the
car, and then suddenly detach it, to
will be skewed.
I always thought that wind tun-
nels blew smoke over cars so ever yone
could see how the air behaved. It
turns out no one really does that.
The process is messy, so it’s mainly
a stunt for photos or visitors. Natu-
rally, I want to see it. Tortosa points
a wand over the top of the over-
grown toy truck and smoke glides
smoothly across, tracing the shape of
the hood and roof before going cha-
otic over the bed and tailgate. She
moves the wand under the truck andlence. It’s an empirical
demonstration of why
manufacturers use
front air dams and
even height-adjust-
able suspension to
minimize air going
under the truck. You
want as much air as
possible going over theminimize turbulence,” he says. “That’s why, in the plan
view, looking down, the sides of the car are lat, but in
proile you see curves at the tops of the fenders.” It makes
sense. When it’s moving, this shape is eicient and dis-
tinct, a shark in moving through water. But Burgess does
seem a little bit wistful when he compares the I-Pace’s lat
lanks to the Jaguar F-Type’s curvaceous fenders. “The
F-Type has that beautiful Coke-bottle shape,” he says.
“But it creates turbulence. The air gets detached.” You
can’t have sexy lared fenders and low drag.AERO R&D
A few weeks later, I’m at GM’s Technical
Center in Warren, Michigan, standingand spins the rolling road
beneath a 40-percent-scale
Chevy Silverado. These
treadmill systems are
standard now in wind tun-
nels because, in the real
world, your car moves, but
the road and air don’t. The
wind tunnel must reverse both
parameters or else the resultsA TEACHABLE MOMENT
LE MANS, 1999:
Cresting a hill + low
downforce = light.
Somehow, no one was
hurt.GM also uses supercomputers to
run elaborate luid-dynamics
simulations, but the wind tunnel
produces quicker results. It’s in
use 24 hours a day, seven days
a week.