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" On July 9 two specially instrumented C-17s took off from Edwards Air Force Base in California, heading to Hawaii. The pair of cargo airplanes carefully took their positions: one following the other just a few thousand feet behind, slightly off to the port side. The reason for the careful placement: The pair of C-17s was generating data for an experiment intended to figure out how to maximize the fuel savings that planes get by flying in formation. The wingtips of every plane generate swirling coils of air called vortices. If an airplane is positioned in the right spot, the updraft from the vortex will help keep the airplane aloft. &amp;quot;It&amp;#039;s like free lift,&amp;quot; says Donald Erbschloe, the chief scientist of the USAF Air Mobility Command (AMC). It&amp;#039;s called vortex surfing, and it&amp;#039;s the reason geese fly long distances in those V-shaped wedges. Erbschloe, who was on the trailing airplane during the test, says the trip to Hawaii reduced fuel by 6 percent. During the trip home on July 11, this formation flying saved 10 percent.  The key to airplane drafting is not to be as close as possible\u2014what Erbschloe calls &amp;quot;fingertip formations . . . white-knuckle, hard flying.&amp;quot; Instead, the trailing C-17 was spaced in sweet spots 2000 to 6000 feet behind the lead airplane, places where the vortices are fully formed and pushing air upward. (If a plane flies in a spot where the vortex is pushing down, it uses more fuel.) This updraft provides lift with no extra fuel. Compounded over many flights\u2014and Air Force Mobility Command averages more than 80,000 flights a year\u2014even single-digit percentages of fuel conservation would be counted in the millions of dollars. The researchers, part of a collaboration between Boeing, AMC, NASA, the Air Force Research Laboratory, and the Defense Advanced Research Projects Agency(DARPA), tweaked the C-17s&amp;#039; flight-control computer so the autopilot could maintain the correct distance and stay within the updraft part of the vortices. To do it, Erbschloe says, all they had to change was &amp;quot;a few dozen lines of code in the autopilot.&amp;quot; The trip back from Hawaii achieved better fuel savings because of changes to the software that enabled the airplane to use the rudder to keep its position, as opposed to using the airplane&amp;#039;s ailerons. The rudder can move an airplane in more subtle ways, keeping the wingtip exactly where the updraft is strongest and most beneficial. According to the data generated by this month&amp;#039;s flight and by earlier tests over Edwards, the ideal position for a drafting airplane is 3000 feet to the port side of the leading airplane. If there were a second drafting airplane, its ideal placement would be on the starboard side, about 6000 feet from the lead. This is pretty close to the tactical formations that large Air Force planes fly already, Erbschloe says, but this research will let the Air Force fine-tune the position of its planes to make sure they&amp;#039;re riding the updrafts, not the downdrafts. The tests are done, and the concept is validated. As always, the next step will take more money, and convincing AMC to fund an Advanced Technology Demonstrator to figure out the exact procedures and processes needed to introduce this fuel-saving concept to many airplanes in fleet. The two- to three-year project could begin as early as next year, Erbschloe says. "^^<http://www.w3.org/2001/XMLSchema#string>
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