| Summary: | Several performance criteria methods for optimizing a prefilter model reference control system are reviewed, and the quadratic performance index is studied in detail. The prefilter model reference system consisted of a second-order model and a fourth-order follower. The form of this follower system was typical of that required for a VTOL aircraft in hover (e.g., the X-14B). For the VTOL problem, the quadratic performance index was found to be the most versatile and comprehensive criterion. A system designer can iterate weighting matrices for various system states until the desired system response is obtained; that is, if the response is too oscillatory, the elements of the weighting matrices can be changed to produce a less oscillatory response. A major advantage of the quadratic performance index is that it can be minimized through the use of readily available digital computer programs. The solution of these programs provides a set of optimal gains for a given system configuration and the chosen configuration. Constraints on the use of the quadratic performance index are that the index must be expressed in terms of states and the control vector, all stales must be observable, and only linear system formulations are acceptable
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