A Low-Cost, Adaptable System for Lift and Drag Measurement in an Educational Wind Tunnel

Wind tunnel testing augments the undergraduate fluid dynamics curriculum by providing hands-on application of the course material, and a low-cost version of a force balance is desirable. To maximize the utility of wind tunnel-based lessons and laboratory demonstrations, there is also a need for a setup that is easily adaptable to different tests and loading applications. This paper provides such a force balance design, along with detailed evaluation and benchmarking to characterize the accuracy of the force balance. Our force balance uses readily available materials having a total cost under $125. Static load tests show that the force balance is accurate with a mean absolute percentage error of only 2.5%. We demonstrate the system's usefulness and adaptability with classic examples of measuring drag on a sphere and characterizing a NACA 0012 wing, as well as with measuring lift on a foldable wing. Finally, we pilot the force balance in an undergraduate mechanical engineering lab setting and find that students are able to explore the setup, understand the load cell functionality, and use the system to measure drag on a sphere. The force balance enables students to gain hands-on learning experience related to both fluid mechanics and statics, and our user study shows that the force balance is durable through classroom use. The low cost, robustness, and high adaptability of the system makes it suitable for incorporating in multiple labs or for allowing student project teams to utilize the system in their own experiments.