We also made many discoveries along the way, one of which is a new aileron design and push rod control that has proved to be greater than the sum of its parts. Satisfying all of today’s Part 23 requirements ensured this would be the safest and strongest Cub ever produced. Along the way we encountered many hurdles, one of which is the strictest and most challenging iteration of Part 23 certification to date. Knowing modern materials and computer-aided engineering gave us a good shot at making these lofty goals a reality, we set off on what became a 6 year journey. The work is part of an Air Force Office of Scientific Research under the Young Investigator Program.We dreamed of a Cub that could reach farther, go faster and carry more than legacy technology would allow. The study, "Unsteady Flow Physics of Airfoil Dynamic Stall," was written by Rohit Gupta and Phillip Ansell. In other cases I may want to prevent the vortex from forming at all, and there are ways that I can use actuation to interact with the flow and prevent the vortex emergence and the dynamic stall process from happening," Ansell said. "I need to know when that vortex is going to form and get that increased lift and then have that somehow persist over the surface to give me a higher lift capability to, say, land on an aircraft carrier. One application might be to land an aircraft on a shorter airstrip. In understanding the physics of what's happening in the flow, Ansell said they can look at ways to interact with and control it in order to get desirable characteristics out on a larger scale and use it beneficially. For comparison, a 737 operates at up around 20 million. That's a part of the physics we're still trying to wrap our brains around."Īccording to Ansell, the goal is testing Reynolds numbers up to one million to learn at what point the large-scale vortex features begin behaving in the tiny multiple vortices. It's actually composed of little instantaneous small-scale vortices collectively acting together to behave like a larger scale. So this classical vortex isn't behaving like one giant structure. The vortex is peppered with smaller-scale features in the flow. In the vortex at higher speeds there are tiny flow structures instead. "We observed that the dynamic stall vortex structures that we see at low speeds, we don't see in the same way at high speeds. "We also used a high-speed laser and camera system to measure the flow velocity to get the entire map of measurements across the entire surface and how the flow evolves over time."Īnsell said one of the focal points of this study was understanding the turbulent fluctuation in the airflow, the frequency of that fluctuation, and the spatial scale and size of those fluctuations. From that we characterized some of the very fine details of the pressure oscillations that happen during this highly unsteady process," Ansell said. We measured the pressure with high-frequency transducers across the surface. "The motor is used in the wind tunnel testing to produce a very rapid pitch up motion of the airfoil. The airfoil shape was stretched wall-to-wall across the wind tunnel. One component of the study involved wind tunnel experiments using an airfoil, which is a cross-section of wing. At higher speeds the process becomes significantly disorganized and difficult to understand. In this study, he and his graduate student Rohit Gupta looked at higher speeds, still subsonic, but an order of magnitude higher than the speed of avian or insect flight. Reynolds numbers refer to the relationship between how fast the wing is going, the wing size, and the viscosity of airflow around it. After the dynamic stall vortex leaves the vicinity of the wing, there is a very sharp drop in lift as well as increases in drag and we're left with a very hard to control flow field," said Phillip Ansell, assistant professor in the Department of Aerospace Engineering in the College of Engineering at the U of I.Īnsell said the problem has been studied at low speeds, also known as low Reynolds numbers. We know that a large vortex forms at the leading edge of the wing and leads to very large increases in lift as well as increases in drag. "There are complex turbulence flow structures in play.
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