Pointing a wand to the hood, senior project engineer John Bednarchik performs a smoke test to demonstrate wind flow over the body of a 2013 Chevy Malibu, a car for which GM set high goals for reducing aerodynamic drag.
When he heard GM's aim to achieve 0.29 as the Malibu's drag coefficient, Bednarchik recalled thinking, "Well, this is going to be challenging." After all, the model that it was replacing had a drag coefficient of 0.35. To put that in context, the Toyota Prius hybrid (which spent more time in aero testing than any other Toyota model) has a drag coefficient of 0.25, while a 2012 Ford Ranger truck rates at 0.40. (A lower the drag coefficient reflects less resistance, which means less power is needed to move the object.)
(Related Photos: "Cars That Fired Our Love-Hate Relationship With Fuel")
Just a few years ago, Bednarchik said, aerodynamicists believed the shape of a sedan "would really have to change to reach 0.29. You can't go to a designer and say, 'Here's an aero book, design a car.'"
But he said the experts have learned how to improve aerodynamics by refining the vehicle shape and adding elements like underbody panels or active grille shutters that are programmed to close partially or fully based on variables like engine load and vehicle speed. The idea is to reduce air flow under the hood and through the engine compartment, allowing full airflow only when engine cooling or air-conditioning systems demand it.
From 3 to 11 percent of fuel energy is lost to aerodynamic drag, a waste that engineers are working to curb in the aero lab. They position the wheels of a car or clay model carefully on adjustable pads that rest atop risers. Beneath the floor, weigh beams, motors, controls, electromagnets, and levers work together like a supersized, complex version of a doctor's office scale. As wind blows through the tunnel and around the vehicle, the car's weight shifts on the balance, allowing the researchers to measure yaw, pitch and roll, downforce, and lift.
The aerodynamics engineers know they are an integral part of the drive to boost fuel economy. "It's made me feel a lot more important," Bednarchik said. Through his work on the Malibu, the most efficient version of which is rated at 29 miles per gallon, he added, "Personally I saved tons of money and tons of gas."
In total, U.S. regulators have estimated that the new efficiency standards would add $2,000 to the average cost of a new car in 2025, to be more than outweighed by fuel savings of $5,200 to $6,600 over the vehicle's lifetime.