The objective of this study was to develop a simulation method to analyze the body behavior and to clarify the most stable body position while freefalling during a skydive. Using the simulation method, we conducted an optimizing calculation to maximize an objective function with respect to the stability in the freefall. It was found that the most stable position became an arched one. In order to clarify the reason why the most stable position became arched, optimization with respect to a simple

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... shaped object consisting of 20 cylinders was conducted. Then the angle to maximize the restoring moment for each cylinder element was analytically calculated and compared with the optimized angle. From the results, we conclude that the most stable position becomes arched mainly since the restoring moment for each individual part is maximized at that angle. We also conclude that the magnitude of the arch in the most stable position is determined by the ratio of the normal and tangential drag coefficients.