Popular Mechanics - USA (2018-07 & 2018-08)

@PopularMechanics JULY/AUGUST _ 201 15

AERODYNAMICS FACTOID NO. 1

The shape known in physics as

the Sears–Haack body produces

the lowest drag per volume

at supersonic speed. An

example: the double-

ended toothpick.

LIFT

The tendency

for air trapped beneath

the car to lift it of

the ground.

AE

RO-

VOCABUL

AR

Y

smooth parts up top instead of the
lumpy underbody.
GM also uses supercomputers to
run elaborate luid-dynamics sim-
ulations, the results of which guide
engineers toward problem areas. “It
showed a circulation bubble on the
quarter-panel of the Volt,” Tortosa
says. “We couldn’t see that in the
tunnel.” But a wind tunnel is still
essential. “Once I build a computer
model, if we change something, it
takes a day to run the new calcula-
tions,” says Ken Karbon, global head
of simulation for aerodynamics.
“Whereas, how many diferent iter-
ations could you test in the tunnel?”
He directs the question to Tortosa.
“Thirty,” she says. “We could try 30
diferent things in a day.” It’s a lot of
work that results in small but vital mar-
gins. “We can afect aero maybe 10 percent
one way or the other—if the coeicient of
drag is .30, maybe we can get it down to
.27,” Karbon says. “And that might repre-
sent three-tenths of a mile per gallon in
fuel economy, depending on the vehicle.”
We go next door to the center’s origi-
nal wind tunnel, which is unfathomably
huge. The fan looks like a propeller from
the Queen Mary, itted with six beautiful
laminated spruce blades—wood
is better than even carbon
fiber, because if a piece
of car lies of and dam-
ages a blade, technicians
can easily repair it. The
space is shaped roughly
like an oval track, so the
air circulates through the test
section with the vehicle and
back to the fan, requiring
less power. You could host
Wimbledon inside the cham-
ber behind the fan. Seeing
this stadium-size facil-
ity in person makes it
obvious why not every-
one has one. This is
an expensive tool, a
fantastic and com-
plicated machine, so
much so that no two
tunnels produce the same
results. “The three U.S. com-
panies all have wind tunnels, and we
all test each other’s cars,” says Tortosa. “We
share the results, because each wind tun-

cleanliness of its shape. “Well, there’s a lot

going on under the car that you can’t see,”

Wagener says. “But also, there’s active aero.

There is a big wing back there, but you don’t

see it when it’s parked.”

Active aero satisies both aerodynam-

icists and designers because it’s efective

and mostly invisible. Lamborghini’s ALA

(Aerodinamica Lamborghini Attiva)

system, as deployed on the Huracán Per-

formante, doesn’t look like much more

than a wing on the rear deck. But that

wing is hollow, with airlow through each

of its stanchions controlled by an electric

motor—and there’s a similar system in

the front spoiler to balance front–rear lift.

On a straightaway, the motors can chan-

nel air under the wing for low drag. Close

the air intakes and the wing makes high

downforce, for extra grip in corners. And

the car can vary the system from side to

side for “aero vectoring,” which gives even

more control when steering into a corner.

Now, I’ve driven the Huracán’s predecessor,

the Gallardo, at 200 mph on a supersonic

nel is diferent. So we like to know what our

truck got in Ford’s tunnel, and vice versa.”

This professional aero courtesy does not

extend to foreign companies.

TECHNOLOGY,

NOT COMPROMISE

Aerodynamic principles are fixed, non-

negotiable. So how will GM, Jaguar,

Cadillac, and every other manufac-

turer continue to make cars

more eicient while avoid-

ing homogeneity? How

do we get performance

cars that have a high

top speed (low drag)

and high downforce

(better handling)? One

answer kept coming up:

active aero, cars that

don’t just passively

travel through the

air, but manipulate it

to their beneit. This is

how you resolve the com-

promises in performance

and styling. You build

a Transformer. Mer-

cedes-AMG’s upcoming

1,000-hp supercar, the

Project One, is a case in

point. Before New Jer-

sey and Michigan, I’m at the

Miami International Boat Show

with Gorden Wagener, chief design oi-

cer for Mercedes. Looking at a full-size clay

model of the Project One, I remark on the

The Porsche 911

Turbo S can extend its

chin spoiler for less drag.

So can... the 2019 Ram

1500, which lowers its

front spoiler 2.5 inches

at highway speeds.

The AMG GT R uses

shutters controlled by an

electric motor to either

enhance cooling or lower

drag, depending on the

situation. So does... the

2019 Volkswagen Jetta.

The Ferrari 488 GTB

uses vortex generators

on the underbody to

increase downforce. Just

like... the Honda Civic

Type R, which uses the

top of its hatch to direct

air over the rear wing.

DIFFUSER

A difuser slows

down air as it passes

behind the vehicle,

creating a low-pressure

area under the car.

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DOWNFORCE

The opposite of

lift. Using wings or the

shape of the car itself to

push the car down and

increase the normal force

at the tires’ contact

patch.