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NF 203
October 1993

NASA RIBLETS FOR STARS & STRIPES

America has won an Olympic medal and the America's Cup thanks to the same NASA technology that is saving commercial airlines hundreds of millions of dollars annually.

On February 4, 1987, skipper Dennis Connor and his ten-man crew guided the Stars and Stripes racing yacht past the finish line at Fremantle, Australia, to recapture sailing's most coveted prize, the America's Cup. Representing the San Diego Yacht Club, Connor and Stars and Stripes scored a 4-0 sweep in the best-of-seven finals over Australia's Kookaburra III.

Stars & Stripes
The hull's underside was coated with a "riblet" skin
that helped the craft slide through the sea more smoothly.
(photo credit: Sally Samins - PPL MEDIALINK)

A key piece of NASA technology assisted in the win. Stars and Stripes design coordinator John Marshall disclosed the boat's "secret weapon" as the hull's underside, coated with a "riblet" skin that helped the craft slide through the sea more smoothly.

The assist came from NASA Langley Research Center technology originally developed as a means of improving airplane fuel efficiency by reducing the drag caused by the friction of turbulent airflow over an airplane's skin. V-shaped and angled in the direction of the airflow, the grooves are no deeper than a scratch but have pronounced effect on air turbulence. This technology offers similar advantages for vessels moving through water.

The first riblets were machined on flat aluminum sheets and tested in a Langley wind tunnel. When engineers of the 3M Company, St. Paul, Minnesota, learned of the tests, they suggested molding the riblets into a lightweight plastic film with an adhesive backing. The film could be pressed into place on an airplane, eliminating the need for welding and allowing a relatively inexpensive retrofitting to existing airplanes. Langley accepted 3M's offer to produce riblet tapes for research and used them in 1986 tests on a Learjet. In flight tests, the film riblets demonstrated a drag reduction capability of about eight percent, similar to the results of wind tunnel tests using the metal sheets.

The technology also helps reduce hull friction for vessels moving through water, which increases speed. The Boeing Company, 3M and the Flight Research Institute of Seattle, Washington collaborated on the development of the first water tests of riblet film in 1984.

Among several boats fitted with riblet tapes was the U.S. rowing shell that competed in the 1984 Summer Olympics at Los Angeles in the Four-oar-with-coxswain category. The shell's crew won a silver medal, the first U.S. medal won in the event in many years.

More important than its contributions to racing is the technology's potential benefits to air transportation. Langley's long range goal of doubling riblets' drag reduction capability to 15-16 percent would translate into a five percent reduction in fuel costs, a savings in the hundreds of millions of dollars annually for U.S. commercial airlines. Riblets also could be used in oil, gas and water transmission lines, and on submarines and jet engine turbine blades.

NATURE'S VERSION OF A RIBLET

Early in the game of riblet research, Langley found confirmation of grooving's effectiveness in a clue from nature: it was learned that fast swimming sharks have riblet-like projections on their skins. Called dermal denticles, they are made of the same material as shark's teeth and typically have four or five grooves on what appears to the naked eye to be such a smooth surface.

One of the Congressionally mandated responsibilities of NASA is to promote economic and productivity benefits to the Nation by encouraging the transfer of aerospace-generated technology to the pubic domain.

NASA meets this objective through its Technology Utilization Program, that provides the link between the developers of aerospace technology and those either in the public or private sectors who might be able to productively employ the technology.

For more information, check out NASA Langley's Technology Commercialization Program Group (TCPO) Homepage.