![]() While flying out of control over a lake, the shadow of the airship revealed the cause of the controllability problem. By including the calculated derivatives in the linearised equation of motion system, it is possible to judge the stability and controllability of the investigated airship.Īs for most vehicles, the question of stability and controllability is also to be answered for airships, with the only exception that the answer is known in advance: airships do not fly stable! But is the magnitude of instability acceptable? Is the pilot still able to control the airship?Īt the beginning of the 20th century aeroelastic effects were observed for the Siemens–Schuckert airship (Haas and Dietzius, 1913). The change between the trimmed flight state and the disturbed one yields the respective aeroelastic derivatives. These constraint forces are then transferred into translational and rotational acceleration fields by performing an inertia relief analysis of the disturbed structural model. The application of small perturbations around a trimmed state produces reaction forces and moments. The equilibrium of the internal structural and the external aerodynamic forces leads to the structural response and a trimmed flight state for the specified flight conditions (e.g. VSAERO is based on the aerodynamic panel method using potential flow theory. On the structural side, the Finite-Element program package ABAQUS was extended with an interface to the aerodynamic solver VSAERO. ![]() As one possibility, the coupled aerodynamic and structural dynamic problem was handled using linked standard solvers. Due to these nonlinearities, the aeroelastic problem for airships can only be solved by an iterative procedure. The aerodynamic solution is also included in the nonlinear problem, because the deformed airship influences the surrounding flow. ![]() The main sources of nonlinearity are large deformations and the nonlinear material behaviour of membranes. In general, the structural model of an airship is physically as well as geometrically nonlinear. This scheme has to be extended for large airships, due to various nonlinearities in structural and aerodynamic behaviour. The aeroelastic derivatives for today's aircraft are calculated in the concept phase using a standard procedure. ![]()
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