Usually, aerodynamic shapes are rounded forms that slip through the
air. But the wind tunnel is proving that counterintuitive, edgy
automotive shapes such as the Ford Flex or Toyota FT-HS can reduce the
drag coefficient and save fuel or battery power.
Toyota’s FT-HS concept hybrid sports car has angles, edges and bulges that smooth the flow of air past the car.
Wayne Koester was pleasantly surprised. Koester, who was a Ford
aerodynamicist at the time, had been assigned to turn the popular boxy
Fairlane design study that was introduced at the 2005 Detroit Auto
Show, inspired by the woody station wagons of the 1940s, into the
production Flex crossover. But he had to produce a shape slippery
enough to provide acceptable fuel mileage, and he feared the boxy show
car would have to be radically revised. To his surprise, in hundreds of wind-tunnel tests the original edges
produced less drag than curved ones. In the bumper, headlights and
hood, in fact, aerodynamics were improved by carefully designed edges. Usually, aerodynamic shapes are rounded forms that slip through the
air. But the wind tunnel is proving that counterintuitive, edgy shapes
can reduce the drag coefficient and save fuel or battery power.
Ford Flex’s boxy shape doesn’t look like it should be aerodynamic in
the least. But to the surprise of its aerodynamicist, it is.
view of the FT-HS: “Aerocorners” will be a feature throughout Toyota’s
future designs. One discovery: The rear design of a car is key. It
smoothes airflow off the back and reduces drag.
design differences between a prototype and the production version of
the Chevrolet Volt have to do with aerodynamics, including the way the
back deck has been designed to cleanly release air.
Many people associate aerodynamics with getting rid of edges and
corners. But redoubled efforts to reduce drag have led engineers and
designers to some surprising shapes. The discoveries offer both
practical and aesthetic implications.
“Round is not always aero,” said J C. Mays, group vice president for
design and chief creative officer of Ford. Some cars, including
Porsches, have famously proved more aerodynamic when turned tail-first
in the wind tunnel.
Koester’s box turned out to be a success. His team at Ford found
that the box cut 0.02 off the Flex’s coefficient of drag, beating the
competitors and providing a respectable 24 mile-a-gallon highway rating.
The future of Toyota
Toyota has begun using the term aerocorner for angular but aero
shapes. The aerocorners include edges and bulges on the front of
Toyota’s small city car, the iQ, its FT-HS concept and the next
generation Prius hybrid. The idea, said Kevin Hunter, president of
Toyota’s Calty Design Research studio in Newport Beach, Calif., is to
smooth the flow of air down the sides of the car. The aerocorner pushes
airflow out to reduce turbulence around the front-wheel housing, he
The aerocorner is one of several aero elements Toyota has listed as
keynotes of all future design strategy, as decreed by Toyota’s design
chief, Wahei Hirai.
The other elements include forward-projecting front bumpers that
send air around the car rather than under it, avoiding the drag of the
messy underbody, still the aerodynamically crudest place on a car.
Covering the underbody completely would be expensive and impractical,
but some cars, including the Nissan GT-R and Ferrari California, cover
parts of the underbody.
The difference between the concept version of the Chevrolet Volt,
the plug-in hybrid that General Motors first showed in 2007, and the
production version shown in September, had to do with aerodynamics,
said chief designer Bob Boniface.
“Aero is more about the rear of the car than the front,” said
Freeman Thomas, director of strategic design at Ford, as he walked
through displays at the recent Los Angeles Auto Show. Problem-causing
drag behind the car stems not so much from frontal resistance as from
swirling eddies of turbulent air at the rear. Designers now speak of
managing airflow and having the air cleanly released at the back.
Efficiency is the key driver in aerodynamic design. “Remember, at
highway speed about 60 percent of energy is used overcoming air
resistance,” Hunter said. But aerodynamicists also have to worry about
interior noise, stability and potentially dangerous lift at higher
The new shapes of aero can take small forms: a tiny tablike shape
sits in front of the rear wheel of the Chevrolet Traverse crossover,
and its roof rack has been lowered flush with the roof. The Chevrolet
Volt lacks the wheel covers of earlier electrics and hybrids. “The
wheels fill the wheel wells and we don’t need those,” Boniface said.
The Volt also offers a surprisingly sharp upright edge on its rear
flanks, which makes for more controlled detachment of airflow from the
side of the vehicle. A small, almost invisible edge on the bulging
taillights of the new Mazda 3 is there to help snap the airflow neatly
off the back of the car.
Slits, not grilles
The new aero is visible in lower, wider grilles on many models. “We
are trying to redefine the grille,” said Hunter of Toyota’s future
designs. “It will be minimized quite a bit and given a different
proportion. It is possible to have a thinner slit versus a big opening.”
Lower grilles take advantage of higher air pressure close to the
ground. There is new emphasis across the auto industry on reducing
cooling drag, from air pulled into the engine and radiator, Hunter said.
Some grilles are larger for aesthetic reasons rather than functional
ones. “The grille is about symbolism,” Thomas said. Some small air
slits are disguised as larger “mouths,” with closed-off portions.
Reduced drag does not necessarily mean increased beauty, however.
The tall, humpbacked silhouette of the Prius is not exactly elegant,
but Hirai, the Toyota design chief, has said that it will continue in
the next-generation car. The grilles of the Ford Fiesta and Ford Ka are
larger at the bottom for better airflow.
Most cars have two-part grilles. The top area of the grille has been
the symbolic mouth — lower vents were visually disguised or
de-emphasized. Now there is a change, according to Hunter. “There is a
shift to emphasis on the lower grille,” he said.
“As designers, we are using that as an aesthetic advantage that we
can leverage into other models,” Hunter said. “It is also a positive
symbolic advantage for us, since fashion is still very important. It
gives a good blend of fashion and function.”
Aero: the early years
The idealized low-drag shape, the earliest aerodynamics researchers
decided, was the teardrop form: a rounded front and a long tapering
tail, like a drop of water falling from a faucet. But by the 1930s,
after research by Dr. Wunibald Kamm in Germany, it was widely
understood that slicing off the back of the vehicle produced an
aerodynamic result that was nearly as satisfactory and eminently more
practical. (Experimental designs like the Oldsmobile Aerotech of 1987
demonstrated the aerodynamic long tail.)
When aerodynamics became a concern, with the arrival of cars like
the Chrysler Airflow and Lincoln Zephyr in the 1930s, some designers
feared it would make all cars look alike. Harley Earl, the design chief
of GM at the time, said he thought 1940s streamlining was producing an
inverted-bathtub look, as seen in the Chrysler Thunderbolt concept car
or in postwar Hudsons.
But discoveries about the science of aero and new ideas about its
art created fresh shapes. Earl developed big fenders and the tail fin
to defeat the bathtub. In the 1990s, ovals were decorated with large
traditional grilles and aerodynamically harmless creases.
Still, the wind tunnel continues to bring new discoveries. “Aero,”
said Michael Simcoe, a veteran exterior designer at GM, “remains a