Thomas Yechout loves airplanes. He loves to design them, to talk about the way they work, to improve their design.
And that love of airplanes, combined with a passion for teaching, has led Yechout to his first patent — a new wingtip design that improves aircraft endurance and range while increasing fuel savings.
In fact, the aeronautics professor’s patent has the potential to save the Air Force about $34 million in fuel costs every year.
It started with a request. The Air Force’s Air Mobility command asked the Air Force Academy researchers to create an optimized winglet — a vertical wing at the wingtip — for a KC-135 tanker plane. So, Yechout and the cadets did just that.
“We came up with an optimized winglet configuration, with a potential enhanced range and endurance for the KC-135,” he said. “And then we went back to Air Mobility Command and asked if we could develop an optimized, raked wingtip, and we did that.”
A raked wingtip changes the sweep of the edge of the wing, reducing drag.
Both those projects led to another — a complete wingtip design change, combining a winglet, a raked wing tip and blending. For lack of a better name, Yechout calls it a rakelet.
The research-and-design process consumed about 18 months — and the patent took about two years, he said. Basically, the new design is more aerodynamic, using uplifted wingtips.
The design is a modification of winglets designed in the past 20 years. The winglet reduces the strength of the vortices — mini-tornadoes — that swirl around the tips of airplane wings.
“It takes a lot of energy to develop a vortex,” 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 drag.”
The vortices are created when low air pressure on the top of the wing combines with high pressure underneath. Air tends to migrate from areas of high pressure to areas of low pressure, and as it does, it creates a whirlwind, which in turn creates “induced drag” on the lift of the plane. Overcoming that drag forces planes to use more fuel to remain aloft.
In the past 10 years, Boeing used a modified raked wingtip design with an additional 20 percent sweep angle and reduced the length from the wing’s leading edge to its trailing edge, known in aeronautical circles as the chord.
“That approach reduces the strength of the wingtip vortex by reducing the chord and allow less air from the bottom to the top,” Yechout said. “But there’s no forward lift.”
Yechout’s design, a gradual curve upward of the airplane’s wings, allows for forward lift as well as reduced drag. Blending the wing upward, instead of at a sharp 90-degree angle, saves 1.5 percent in fuel costs, he said.
“That might not seem like much, but with today’s fuel prices, it’s actually a lot,” he said.
Yechout and a group of cadets used the Air Force Academy’s wind tunnel to test the optimized rakelet configuration — changing the size, angle of the wings and the winglet, and blending the 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 angle of attack,” he said. “The number of different configurations we had to evaluate in order to hone in on the optimal configuration was the most challenging part.”
Yechout says it took about 120 hours in the wind tunnel to develop the exact model that created the fuel savings.
Yechout is also waiting for his second patent on the process used to create the rakelet for the KC-135. The amount of blending and the slope of the rakelet will change with each aircraft, he said.
“The design is going to be different for every aircraft, in order to get maximum fuel savings,” Yechout said.
It makes the academy a cost-effective facility for the Air Force, NASA and the Department of Defense to conduct research, he says. Professors team with the cadets to produce transferrable technology to the rest of the government.
“The academy also has a very good track record of doing a good job for our research sponsors,” Yechout said.
“The cadets benefit because they’re doing graduate-level work as undergraduates. It puts them ahead of the game. It’s a win-win for everyone.”
Yechout, who also was on the design team for the AC-10 planes, is noticeably proud of the accomplishment. However, because he is an Air Force employee and used Air Force equipment to design and test the rakelet, he won’t receive any royalties from the patent.
“My name is on the patent,” he said. “But the Air Force gets the royalties. They own it.”
And while that might be a little disappointing, Yechout says he’s still excited about the possibilities.
“Not only can the Air Force use it to modify its planes, but they can sell it to Boeing and Lockheed Martin,” he said. “It has the potential to save a lot of money over time.”