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Journal of Guidance, Control, and Dynamics


A unique feature of airdrop systems is the inherent and large variability in flight dynamic characteristics. The same physical article dropped on two different occasions will exhibit significantly different dynamic response. The problem only becomes worse for different test articles. Control systems for autonomous airdrop systems explicitly or implicitly assume knowledge of the flight dynamic characteristics in some way, shape, or form. A question facing autonomous airdrop designers is whether to use precomputed dynamic characteristics inside the control law, or to compute the needed flight dynamic characteristics in-flight and subsequently employ them in the control law. This paper establishes conditions when in-flight identified characteristics, with a focus on the turn rate dynamics, should be used, and when it is better to use precomputed results. It is shown that with expected levels of system variability, sensor noise, and atmospheric wind, in-flight identification generally produces significantly more accurate dynamic behavior of the lateral dynamics than a precomputed model of the nominal system, even when the in-flight identification is performed with highly inaccurate sensor data. The only exception to this rule observed in this work is the situation where atmospheric winds are high and a direct heading measurement is not available. In this situation, a precomputed estimate of the time constant of the lateral dynamics is more accurate than an in-flight estimate. These conclusions are reached though a comprehensive simulation study using a validated airdrop flight dynamic model applied to both a small and large parafoil.





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Originally published in the Journal of Guidance, Control, and Dynamics, Vol 33, No 5, pp 1313-1326, 2010.