Aero extension cuts drag in half

Huntington Beach, CA--Indy cars might be lapping the Brickyard a tick faster this year due to an unlikely source--their mirrors. Required equipment on many classes of race cars, including the open-wheel Indy Racing League and CART Championship Cars, exterior mirrors have received little to no aerodynamic optimization, says the inventor of a new drag-reducing design. By borrowing an idea originally developed to streamline the aft end of long-haul trucks and combining it with some wind tunnel work, Jim Wade has produced a shape which is said to cut wind resistance by 55% compared to standard race-car mirrors.

"I talked to race car people about the mirrors they use now," says Wade, a wind-tunnel model designer for Lockheed Martin in Sunnyvale, California, "and it seems they just bolt on what is out there." After testing several popular mirror designs in the wind tunnel, he concluded that many of the shapes were simply formed to look sleek and weren't actually efficient. "Some of the mirrors were so blunt that you got flow separation long before the {trailing edge}."

Wade's first step in developing an improved design was to optimize the general shape of the mirror body. This alone resulted in a 25% drag reduction. For the final 30% drag decrease, he then applied an aerodynamic technique described by engineers at Continuum Dynamics (Princeton, NJ) for use with semi tractor trailers.

Continuum Dynamics' idea involves the addition of an extension to the blunt aft end of a desired aerodynamic object. The extension is slightly smaller in diameter than the main body of the object, so that if you ran your hand from front to rear you'd feel a "step" down where the extension begins. Unlike a typical aerodynamic trailing end--which might taper off to a point--the extension ends abruptly after a short distance.

A NASA document explains how the tail extension could potentially reduce drag up to 10% on an already clean long-haul truck: "Drag reduction is achieved by causing the air flowing over the trailer's top and sides to turn inward as the air separates at the trailer's back. The plates cause the air to behave as if there was a tapered fairing, or 'boat-tail', on the back of the trailer."

Gaining inspiration from Continuum Dynamics' work, Wade thought to apply the aero-extension idea to a project of more manageable size for his small company, JLM Consulting (Sunnyvale, CA), and the aerodynamic mirror was born. Today he holds worldwide license to use Continuum Dynamics' concept on vehicle mirrors.

To find the optimum aero-extension shape, Wade built a one-component strain gauge balance and then wind tunnel tested more than a dozen combinations of mirror-body and extension configurations. "There is a definite relationship between the step down and the length of the extension," he says.

The final product is said to require 1.5 horsepower less to propel a pair of mirrors through the air at 200 mph than a typical Indy-car design, and almost 2.0 horsepower less at the 230-mph peak speeds seen at a super speedway like Indianapolis.

CIPA Mirrors (Eastpointe, MI) is manufacturing a new line of mirrors that leverage Wade's designs. Three models are offered in materials ranging from ABS to fiberglass to carbon fiber. But only the top-of-the-line Professional Formula Extreme (;$300/pair) will sport the unique aero extension.

"Right now, teams pay around $180 for a pair of mirrors," says Wade. "I think a horsepower-and-a-half at speed is worth the little extra."

Additional details...Contact Jim Wade, JLM Consulting, 1519 Kalmath Dr., Sunnyvale, CA 94087, (408) 756-1389,.

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Other Applications

- Trucks

- Any blunt-ended aerodynamic body