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in golf balls. Of course, you might think to extend the shell well beyond the back of the pod to reduce separation, but other interdisciplinary constraints, such as weight and center-of-gravity, as well as manufacturing considerations, pushed us away from such a concept. After we reached a final design, we used a commercial computational fluid dynamics solver, STARCCM+, to get a more accurate evaluation of the aerodynamic drag.

THE SHELL MANUFACTURING AND STRUCTURAL DESIGN CHALLENGE Designing and building the aerodynamic shell posed many practical engineering challenges, and served as a good exercise in balancing mechanical performance, weight, manufacturability, production time, and costs — all key parameters similarly faced in the aerospace sector. As a result, this process applies a plethora of hands-on skill sets gained through the AeroAstro curriculum. For example, the structural design process and challenge faced for the shell was similar in many ways to that in aeronautical structures. The design configuration and materials selection was driven by key requirements in outer mold line geometry as previously defined in aerodynamic analyses, maximum aerodynamic loads, handling/transport loads, and weight budgets. Given their high mass-specific strengths and stiffness, carbon fiber reinforced plastics (CFRP) are increasingly being used in the aerospace industry (e.g., Boeing 787, Airbus A350) and were selected for our shell material to attain a lightweight, yet stiff shell structure. To predict the structural performance, micromechanical models were first used to determined carbon fiber/epoxy ply-level properties. Finite element analysis was performed and iterated to determine mechanical responses under maximum load case scenarios, such as ambient tube pressures, in the event of a qualifying atmospheric run at competition. Maximum deflections, stresses, and possible failure sites were calculated and compared with design allowables. Ultimately, a sandwich structure was chosen to increase the stiffness of the structure by placing high modulus carbon fiber reinforced plastic materials away from the neutral plane through the incorporation of a lightweight foam core. Areas that interfaced with fasteners and carried bolt-bearing loads were designed as monolithic laminates.

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AEROASTRO 2015-2016

MIT AeroAstro annual magazine 2015-2016Aeroastro 2015 16  

Annual magazine review of MIT Aeronautics and Astronautics Department research and educational initiatives.

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