THE INVERTING AIRFOIL: An inverting airfoil can rotate its circular leading edge to pull in a fabric surface on one airfoil side while simultaneously paying out fabric to the other. With a pressurized interior and internal fabric supports maintaining the airfoil’s outer shape, inversion effectively flips the airfoil’s camber along its chord line. In turn, these airfoils can completely reverse their direction of lift without requiring mechanically complex or heavy control surfaces typical of most aircraft wings. Shown below are visualizations of inversion in two and three dimensions using a MATLAB plotter.

WIND TUNNEL TESTS: In the summer of 2021, I conducted 13 airfoil tests in the Swarthmore Wind Tunnel to determine an optimal inverting airfoil shape with a maximum lift coefficient for increased AWE generation output. NACA 4-digit airfoils showed most potential for conversion to inverting airfoils: they had generally convex shapes unlike most modern low-speed airfoils (making them feasible to inflate to), their upper and lower surfaces were defined as perpendicularly equidistant from the mean camber line (allowing a leading edge circle centered along the camber to be tangent to both surfaces), and most importantly, they were well studied for experimental validation of my own wind tunnel tests. Ultimately, a NACA 6412 airfoil with a leading edge circle centered 10% along the original mean camber proved most promising.

PRESENTATIONS & MEDIA: Aside from departmental and university-level speaking presentations, I have displayed this research with my advisor Professor E. Carr Everbach at a Sigma Xi poster presentation, the Tethered Aerosystems Working Group Summer 2021 Meeting, and soon with Jacob Sherman ’25 at the American Geophysical Union Fall 2022 Meeting. An article on inverting airfoils also appeared in the Swarthmore ITS Blog in April 2022. Note that the poster shown below has an outdated inner support design for inverting airfoils.

• Vandervelde, J., Sherman, J., Everbach, E. C., “Airborne Wind Energy Kites with Inverting Wings: Airfoil Optimization and Stability Testing,” American Geophysical Union Fall 2022 Meeting, December 12 – 16, 2022, Chicago, IL. Abstract accepted. (Virtual)
• Vandervelde, J., Everbach, E. C., “Inverting Airfoil Optimization for Airborne Wind Energy Kites,” Sigma Xi 2021 Poster Presentation, September 30 – October 1, 2021, Swarthmore College.
• Vandervelde, J. and Everbach, E. C., “Inverting Airfoils for Airborne Wind Energy Kite Design,” Tethered AeroSystems Working Group Summer 2021 Meeting, July 30, 2021. (Virtual)
• Tull, J. and Vandervelde, J., “Kites for Energy,” Swarthmore College ITS Blog, April 20, 2022, https://blogs.swarthmore.edu/its/2022/04/20/kites-for-energy/