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Figure 7.22 Limit-cycle condition for reduced-order aircraft model has been considered is the software rate limiter. Comparison of the predicted limit cycles with those obtained from time-domain simulation has shown that a simplification of the nonlinearities still produces a good estimate of the limit-cycle frequency and amplitude. Unfortunately, this procedure relies on the existence of reliable frequency-response data for all the linear elements of the system. In the case of the real...
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with an infinite number of harmonics. Neglecting these higher-order harmonics, the gain of the rate limiter can be expressed as for an input sinusoid of the form as shown in Figure 7.17. In order to derive the phase response of the rate limiter, consider the input output relationship of Figure 7.17 once again. From the figure, it can be seen that the phase lag between the two signals can be represented by the time delay, r. In order to obtain an expression for this time delay, it is necessary...
GFj
a position-control system in which the load exhibits a structural mode within the bandwidth of the closed-loop system. In this case, the characteristic equation for the system can be written as 1 Gn ja gt , E G, G2 ja gt Gr jto 0 7.1 The solution of the characteristic equation gives the limit-cycle condition, which can be predicted from a rearrangement of eqn 7.1 G, jco Gsijco GF j o 1 7.2 Provided that the describing function for the rate limiter can be derived, and that the linear components...
5312Safety
The AFCS design is greatly influenced by the results of the hazard assessment. This may recommend levels of redundancy and dissimilarity in either the system or sensor elements to eliminate common-mode failures. Additionally, the control laws may be segregated on an axis-by-axis basis across processor modules or flight control computer units necessitating mode logic and voting strategies to effect a change or a system reconfiguration. This has the physical restraintsp J logistics supports t...
53 System design considerations
Figure 5.4 illustrates the design considerations that flow from the overall consideration which is to achieve automatic flight control. The list of considerations may not be exhaustive and probably could be grouped or segregated under different headings. However, the reader can gain a basic understanding of how the considerations grow and become interdependent as the design is decomposed. The interdependency between levels is emphasised by the databus notation rather than connecting individual...