According to NASA, it was in 1973 that one of its employees became intrigued with how high speed tractor-trailer rigs created massive ‘suction’ as they drove-by slower moving vehicles. In 1975 a study showed that big-rig trucks moving at 55 miles per hour (the national speed limit at that time) displaced as much as 18 tons of air for every mile traveled. About half of the truck’s horsepower was needed just to overcome aerodynamic drag.
After leasing a cab-over tractor-trailer from a Southern California firm, Dryden (Edwards Air Force Base) researchers added sheet metal modifications that look very much like what you see on today’s big-rigs. They rounded the front corners and edges, and placed a smooth fairing on the cab’s roofs and sides extending back to the trailer. During the investigation of truck aerodynamics, the techniques honed in flight research proved highly applicable. By closing the gap between the cab and the trailer, for example, researchers discovered a significant reduction in aerodynamic drag, one resulting in 20% to 25% increase in fuel economy.
NASA estimates that its contribution to the ground vehicle industry has reduced fuel consumption by as much as 6-thousand-8-hundred gallons per year per vehicle!
Researchers also installed a boat tail structure on a passenger van. During the tests, the vehicle’s sides were fitted with tufts, or strings, that showed air flow. The investigators concluded that rounding the vertical corners front and rear reduced drag by 40%, with at a decrease in the vehicle’s internal volume by only 1.3%. Rounding both the vertical and horizontal corners cut drag by 54%, resulting in a 3% loss of internal volume. Adding a faired underbody helped reduce drag by about 15%.
In a kind-of control test, the passenger van was first covered with a sheet metal box with intentionally squared corners.
It was discovered that simply rounding the corners resulted in a huge reduction in aerodynamic drag.
One of the most effective, and simple, NASA discoveries is saving the trucking industry big money on fuel costs today; the ‘Airtab’.
Bare Metal: KC-135R GETS STRIPPED