This article researches the improvement of dynamics stability of the ducted fan unmanned aerial vehicles by optimizing its mechanical–structure parameters. The instability phenomenon of ducted fan unmanned aerial vehicles takes place frequently due to the complicated airflow in near-earth space, which easily leads to the stability problems, such as out of control, shaking, and loss accuracy of command tracking. The dynamics equations mirror its dynamics characteristics, which are primarily influenced by the mechanical–structure parameters of the whole system. Based on this, the optimization of mechanical–structure parameters has a significant to improve the dynamics stability of the whole system. Therefore, this article uses the concept of Lyapunov exponents to build the quantification relationship between system’s mechanical–structure parameters and its motion stability to enhance its stability from viewpoint of mechanical–structural parameter design. The takeoff, landing, and hovering stage are respectively studied and the conclusions suggest that the optimization of mechanical–structure parameters can be used to promote dynamics stability.
This is a short summary of a paper which shows what a navigator can do to fix his position at sea using basic equipment (sextant, hand-held compass, almanac, four-figure mathematical tables) without the help of dead reckoning or the benefits of GMT.To proceed from an almost complete absence of spatial and temporal data the navigator has to observe the sextant altitudes The GMT having been found, the navigator can easily deduce his longitude. With care the results for both the latitude and longitude can be obtained to the nearest minute of arc. The penalty for the almost complete ignorance of one's position and time is a great deal of numerical work which may be too demanding for navigators with only an O-level in mathematics.The present method is different in principle from the now obsolete lunar distance method which requires the measurements of the altitude of the Moon and one star, and the angular distance between them.Readers who are interested in this subject are invited to write to the author, care of the RIN for details.available at https://www.cambridge.org/core/terms. https://doi
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