The data gathered in the 747 studies complemented data from the previous (1973-74) joint NASA Flight Research Center and Federal Aviation Administration (FAA) Boeing 727 wake vortices study.
Six smoke generators were installed under the wings of the 747 to provide a visual image of the trailing vortices. The object of the experiments was to test different configurations and mechanical devices on the747 that could be used to break up or lessen the strength of the vortices. The results of the tests could lead to shorter spacing between landings and takeoffs, which, in turn, could alleviate air-traffic congestion. For approximately 30 flights the 747 was flown using various combinations of wing air spoilers in an attempt to reduce wake vortices. To evaluate the effectiveness of the different configurations, chase aircraft were flown into the vortex sheets to probe their strengths and patterns at different times. Two of the chase planes used were the Flight Research Center’s Cessna T-37 and the NASA Ames Research Center’s Learjet. These aircraft represented the types of smaller business jets and other small aircraft that might encounter large passenger aircraft on approach or landings around major airports or in flight.
Tests without the 747’s wing spoilers deployed produced violent "upset" problems for the T-37 aircraft at a distance of approximately 3 miles. From the magnitude of the problems found, distances of as much as ten miles might be required if spoilers were not used. With two spoilers on the outer wing panels, the T-37 could fly at a distance of three miles and not experience the "upset" problem. The wake vortex study continued even after the 747 was returned to its primary mission of carrying the Space Shuttle.
