Slicker Than Skin

March 6, 2008
How much engineering can a company cram into a swimsuit? More than you might imagine.

Speedo of Australia’s LZR Racer full-body suit lets athletes swim faster than they can in bare skin, thanks to ultrasonically welded seams, pressure- reducing pads, and a fabric the firm says is slicker than human skin. The ultrasonic welds eliminate stitching, one source of drag. A silicon gripper at the ankle or knee (depending on style) ensures the suit doesn’t wrinkle or move. And a low-profile zipper, also bonded into the suit, is tucked inside to keep the surface smooth.

Speedo says independent testing shows the suit to be the world’s fastest. It has 10% less-passive drag than the Fastskin FSII launched in 2004 and 5% less than Fastskin FS-PRO launched last March.

To zero-in on a new fabric and design, Speedo tapped the expertise of NASA and several research institutes. Material samples go to NASA Langley for wind-tunnel testing to find their skin-friction coefficient.

Wind-tunnel testing has advantages over water tests. “For instance, although air has lower density and viscosity than water, it obeys the same physical laws of motion,” says NASA researcher Steve Wilkinson. “We used our two small low-speed tunnels to evaluate the surface-roughness effects of nearly 60 fabrics or patterns for the lowest drag,” he says.

Fabric testing presented challenges. “For example, we had to figure how to get the fabric on a test plate and prepare its edges so nothing would interfere with air flow over the fabric. We’ve done a good job with the help of Speedo coming up with a protocol that let us test the fabrics with ease and precision,” says Wilkinson. The skin-friction coefficient and plots then go to a CFD analyst to calibrate computer results.

Thirty pieces of material went into the older suits. In contrast, the LZR Racer is cut from just three with help of a 3D pattern to fit the shape of a swimmer. The company adds panels, actually sections of another material, to the suit to help compress the entire swimmer’s body into a more streamlined shape.

Speedo says part of the design work involved scanning the shapes of more than 400 swimmers and testing more than 100 different fabrics and suit designs. The CFD work pinpointed drag and highpressure areas on swimmers. This information guided placement of the hydroform compression pads.

Swimmers wore the suits in the water to verify performance predictions. “To test passive drag, a swimmer holds a handle while immersed in a controlled current while we measure tension on a tether line,” says Rick Sharp, exercise physiologist at Iowa State University, Ames. “In economy testing, the athletes swim their strokes at about five different speeds while breathing through a tube. From their expired air we measure oxygen uptake and efficiency. That gives an assessment of effort to maintain a speed.”

The result is an engineered swimsuit with a 3D anatomical shape and a corset-like grip to support and hold the swimmer. The support lets the swimmer maintain a best body position in the water for long periods without losing freedom or flexibility of movement. Tests show the suit design lets swimmers use oxygen more efficiently, letting them swim stronger for longer. “It makes it easier for them to swim faster,” says Sharp.

And despite what looks like a tight fit, the suit doesn’t restrict reach, rotation, freedom of movement, or ability to breathe. “When I hit the water, I feel like a rocket,” says Michael Phelps, holder of eight world records and a participant in the suit’s development. Phelps will wear the LZR Racer in the Summer Games later this year. But the suits will be available to all swimmers. In the U.S., three silhouettes of the LZR Racer for men and women will run between $290 and $550.

The CFD study conducted with Fluent software from Ansys Inc., Pittsburgh, shows streamlines that pinpoint turbulence and drag. High-pressure calculations from such studies guided the placement of the panels that further streamline swimmers.

Steve Wilkerson at NASA Langley tests swimsuit fabrics (blue material) in a wind tunnel for Speedo. Wilkerson runs air across the fabric at different speeds and angles to provide plots of drag and skin-friction coefficients needed to calibrate CFD studies.

The Australian Institute of Sport provided physical testing facilities. Tests indicate that swimmers wearing the suit improve starts, sprints, and turns by 4%.

The lighter colored panels on Speedo’s LZR Racer are said to reduce a swimmers skin vibration and muscle oscillations as part of its drag reduction. Speedo introduced the first nonwool swimsuit for athletes in 1920.

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