Tufts SEDS Rocketry Team

For the 2024-2025 year, I am serving as the Mechanical Engineering Lead for our competition rocket, HODGE. Extensive improvements over last year's rocket are being made, to improve our design quality and innovate new solutions to reaching our desired 10,000 ft apogee. Presented below are a few of the most involved projects I pursued in designing the most advanced rocket the club has seen thus far.

Having learned a lot about high-strength composites with CARM last year, the team is aiming to push the boundaries with our fin design. While we continue to use G10 fiberglass sheets to fabricate our fin cores, due to their stiffness and weight, we are reducing our fin thickness from 1/8” to 1/16”, lowering our vehicle’s weight and drag, therefore increasing its performance. To ensure that these changes are viable without risk of fin flutter, we are leaning heavier into our tip-to-tip layups and conducting testing and simulation to support our design decisions. 

In order to analyze fin flutter, a robust flutter velocity calculator was developed based on NACA Technical Paper 4197 and work by John Bennett, engineering professor emeritus at University of Colorado Boulder. Stock fiberglass datasheets were used to estimate thickness of fin core required to keep flutter velocity in safe margins. To account for added strength of tip-to-tip layups on shear modulus, instron tensile testing was conducted on dog bone samples of varying thickness and layup orientations. Using “Theory of Elasticity of an Anisotropic Body” by Lekhnitskii (1981), Young's modulus results were used to calculate a shear modulus for the reinforced material. These values were used to update the flutter velocity calculator and more accurate factors of safety were deduced. We determined that a 1/16” G10 fiberglass core with 4 layers of fiberglass cloth would best optimize performance while staying above a 1.5 safety factor. To analyze the flutter on the aft swappable fins, the flow velocity profile was analyzed in COMSOL and different fin materials were considered. Due to the lack of layup reinforcement, the risk of flutter was higher than anticipated in the aft fins despite the reduced velocity due to forward fin wake. Considering fin thickness, stiffness, and effect on apogee, ⅛” aluminum 2024-T3 sheets were decided to be used for the swappable fins.