During the 1970s, the focus at Dryden shifted from high-speed and high-altitude flight to incremental improvements in technology and aircraft efficiency. One manifestation of this trend occurred in the winglet flight research carried out on a KC-135 during 1979 and 1980. Richard Whitcomb at the Langley Research Center had originated the idea of adding small vertical fins to an aircraft's wing tips. His wind tunnel tests indicated that winglets produced a forward thrust, which reduced the strength of the vortices generated by an aircraft's wing tips and resulted in a reduction of drag and an increase in aircraft range. Whitcomb, who had previously developed the area rule concept and the supercritical wing, selected the best winglet shape for flight tests on a KC-135 tanker. When the tests were completed, the data showed that the winglets provided a 7 percent improvement in range over the standard KC-135. The obvious economic advantage at a time of high fuel costs caused winglets to be adopted on business jets, airliners, and heavy military transports.