《[2016年必威体育精装版无人机技术]Lighter than Air Robots_Chapter 2 Modeling_fulltext》.pdf

Chapter 2 Modeling Abstract Nowadays, non rigid airships with a cigar shaped profile are the most common type. These airships do not have any rigid internal framework. The objec- tive of this chapter is to present kinematics and dynamics models of a lighter than air robot, taking into account wind effect. Newton-Euler and Hamilton-Lagrange ap- proaches are used for this discussion then the translational model is presented. Here, motion is referenced to a system of orthogonal body axes fixed in the airship, with the origin assumed to coincide with the bow. Finally, some aerology characteristics are briefly discussed. 2.1 Introduction The airship is essentially a low speed vehicle and is fundamentally a balloon with a means of propulsion but in order to produce an effective vehicle, the balloon element has to be considerably modified. The primary requirement of the envelope is that it should be of streamline form to reduce air resistance and improve controllability and that it should be able to sustain the additional loads imposed by aerodynamic forces and propulsive components. A representative mathematical model of a lighter than air vehicle differs from the usual aircraft model because the lighter than air vehicle displaces a very large volume and its virtual mass and inertia properties become significant and thus the aerodynamics and control characteristics are described quite differently. What makes a vehicle lighter than air is the fact that it uses a lifting gas (i.e. Helium as Hydrogen has been banned) in order to be lighter than the surrounding air. While Hydrogen gas is approximately 7 percent more buoyant, Helium has the advantage of being non-inflammable in addition to being fire retardant. The principle of Archimedes applies in the air as well as under water. The dif- ference between airships and balloons is that: balloons simply follow the direction of the winds. In contrast, airships are powered and have some means of con