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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.
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.
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