Academy receives patent for wingtip design

  • Published
  • By Amber Baillie
  • Academy Spirit staff writer
U.S. AIR FORCE ACADEMY, Colo. --  A recently-approved patent submitted by an aeronautics professor here to reduce airplane drag may be the next cutting-edge concept implemented into aircraft design.

Almost two years ago, Thomas Yechout, a professor in the Academy's Aeronautics Department, designed a new type of wingtip device, for a wide range of aircraft models, combining a winglet, raked wingtip and blending called a "rakelet" to improve aircraft endurance, range and increase fuel savings. The patent was approved Feb. 26 and now Yechout hopes aircraft manufactures will carry out the idea.

"We're hoping Boeing and some of the other big, airplane manufactures will pick up on the idea of Rakelets because it will offer a potential percent and a half improvement in what we'd normally call optimized winglet designs, or optimized raked wingtip designs," Yechout said.

Yechout said the wingtip modification aims to reduce the strength of wingtip vortices, a mass of whirling air that trails off the wingtips of an airplane and steals energy.

"It takes a lot of energy to develop a vortex and it will always develop unless you try to curtail it," Yechout said. "The energy it takes to develop the vortex manifests itself in the form of drag. Strong vortices coming off the wingtip is a bad thing because it increases the drag on an airplane."

Yechout and Mario Avila Diaz, a 2011 graduate and Guatemalan exchange cadet, began research for the project in 2008, using a KC-135 model to test the concept. They developed an optimized rakelet configuration, optimizing the size, cant angle and toe-out angle of the winglet as well as the blending level between the winglet and raked wingtip.

"Through wind tunnel testing we conducted direct comparisons by testing a variety of configurations through different air speeds and angles of attack," Yechout said. "The number of different configurations we had to evaluate in order to hone in on the optimal configuration was the most challenging part. We probably spent about 120 hours of wind tunnel time developing this concept."

Yechout said the Air Mobility Command and Air Force Research Lab primarily funded the project to optimize a winglet for a KC-135 to lower fuel costs.

"We did that, but then took it to the next level and said, 'We'd also like to look at optimizing a raked wingtip and did that for them as part of the same grant,'" Yechout said.

Most winglets you see on aircraft have an abrupt transition with the boundary layer, the little region of air flow that is slowed down close to the surface, Yechout said.

"From an aero standpoint, that's not the smartest way to go," Yechout said. "That's the idea with blending, not to have abrupt changes in the boundary layer because it will spin off vortices."

Yechout said the idea of rakelets is applicable to a variety of aircraft looking for fuel savings.

"We'd love to see it picked up by the KC-135 tanker fleet," Yechout said. "The potential fuel savings fleet wide would be about $34 million per year."

Yechout said the research the Aero Department conducts is a unique opportunity for cadets.

"Most of the research we do here is at a graduate level so when they go off to grad school, they're ahead of the game as far as hands-on experience," Yechout said. "It also keeps our faculty engaged because its state- of- the- art research, so it keeps us sharp too."

The Academy is a very cost-effective place for the Air Force, the Defense Department and NASA to conduct research because it doesn't cost them as much as using another wind tunnel facility, Yechout said.

"The Academy has a track record of doing a good job for our research sponsors, is responsive as far as a timeframe and gets them an answer when they need it," Yechout said.