Tests using NASA's B-737 aircraft as a friction measuring device provide a better understanding of ground handling performance under adverse weather conditions.
The benefits to mankind from aerospace technology are becoming more and more commonplace thanks to scientists involved in the space program and private companies that transfer aeronautics and space technology into products and services for everyday living.
Accidents on slippery highways are down as much as 85 percent. Aircraft tire friction performance in wet conditions has been improved by 200 to 300 percent. Injuries caused by wet surfaces on swimming pool decks, playgrounds and work areas in refineries, factories and meat-packing facilities have also been reduced.
Lives have been saved in all of these hazardous locations thanks to NASA Langley Research Center's Safety Grooving research program, designed to reduce aircraft tire hydroplaning--considered the primary cause of uncontrolled skidding during wet weather conditions.
NASA researchers have proven that cutting thin grooves across concrete runways to create channels for excess water to drain reduces the risk of hydroplaning. As a result, hundreds of commercial airports around the world have been safety-grooved, and every state in the United States now has grooved some of its main highways. The Safety Grooving process has also been applied to interstate highway curves and overpasses; pedestrian walkways, ramps and steps; food processing plants and cattle holding pens.
The technology also has been shown to restore wet friction performance to worn or smooth pavement surfaces and to extend their service lifetime by five to 10 years, resulting in significant maintenance cost savings.
From January 1981 through January 1988, nearly 400 commercial airline traction-related accidents occurred. Aircraft ran off ends of runways or veered off shoulders. The resulting crew and passenger fatalities motivated intense research programs between government agencies and industry. "Our goal is to define runway surface maintenance requirements and minimum friction level limits in adverse conditions," said Tom Yager, senior engineer, Landing and Impact Dynamics Branch at NASA Langley.
In 1966, to determine if grooving highways would be
beneficial, a curved section of highway like this one in California
was selected for testing because of its high frequency of wet
pavement accidents. The two years of tests resulted in a 98 percent
reduction of accidents.
Right now, about 800 out of 1,500 United States commercial airport runways have been grooved. "With proper runway cross slope, some of these grooved runways provide dry friction levels in rain," said Yager. Grooved pavement provides escape routes for water compressed between tire tread and pavement, and consequently, enhances braking and cornering. "Last year the main runway at Langley Air Force Base in Hampton, Virginia, was transversely grooved. It has improved friction performance dramatically."
Grooving also applies to highways. The greatest use of highway grooving is found in California where wet pavement accident frequency has been reduced 98 percent on some highway sections. Maintenance costs were also reduced thanks to the grooving-grooved highways just last longer. The use of grinding to reduce highway pavement bumps has also been shown to provide better wet friction performance. At NASA Wallops Flight Facility on the Eastern Shore of Virginia, a special runway has been constructed with several different grooved and nongrooved pavement segments for evaluation by both aircraft, such as Langley's B737 aircraft, and a variety of cars and other ground friction measuring vehicles.
In the mid 1980s, tests were performed on 12 different concrete and asphalt runways, grooved and nongrooved, including dry, wet, and snow, slush and ice-covered surface conditions. Over 200 test runs were made with two transport aircraft, and over 1,100 runs were made with different ground test vehicles. Ground vehicle and B-737 aircraft friction tests were conducted on grooved and nongrooved surfaces under wet conditions. As expected, grooved runway surfaces have significantly greater friction properties than nongrooved surfaces, particularly at the higher speeds.
Research at NASA to tackle hydroplaning problems for aircraft and land vehicles began in the 1960s. The unique landing requirements of the Space Shuttle were also a basis for continued studies. Today the Shuttle Landing Facility runway at NASA Kennedy Space Center is equipped with safety grooving in the middle to optimize wet friction performance, and grinding in touchdown area to minimize tire-spin wear.
This technology was inducted into the U.S. Space Foundation's Technology Hall of Fame in 1990. Referred to in space circles as "The Academy Awards of Space Technology Spinoffs"- the Hall of Fame honors individuals and companies responsible for the practical application of aerospace research.
When aircraft tires or highway vehicle tires roll over watercovered or flooded pavements, water may penetrate between the tire and the pavement. This penetration results in the formation of water pressure which raises a portion of the tire off the pavement. This pressure increases as the speed of the vehicle increases, supporting more and more of the tire, until, at a critical speed termed the hydroplaning speed, the tire is supported only by the water and loses all contact with the pavement.
WHEN DOES HYDROPLANING OCCUR ON PAVEMENTS?
Research indicates that hydroplaning occurs when the paved surface is flooded or heavily puddled with water or slush. Most runways and roads are designed with a crown to drain water away readily. Crowned pavements can become flooded when very heavy rain falls or deep slush accumulates. In addition, excessively worn tires are more likely to skid.
WHAT ARE THE CONSEQUENCES OF TIRE HYDROPLANING?
Another important facet of the NASA Technology Utilization Program is its applications engineering projects, which involve the use of NASA expertise to redesign and re-engineer aerospace technology to solve the problems outlined by federal agencies or other public sector institutions.
A Technology Utilization applications engineering project is
considered successful when the technology developed under the
project is used or is manufactured for the market. Pavement
grooving is one of these successes.
For more information, check out NASA Langley'sTechnology Commercialization Program Office (TCPO) home page.