Eigenstructure assignment has enjoyed considerable success in applications where both the modal response and mode distribution are important. However, a significant constraint on eigenvector selection is defined by an allowable subspace, the range of which varies both with model parameters and desired eigenvalue. This paper presents a technique that explores this constraint, from which analysis and design methods result. A four-input, eighth-order helicopter model is presented. The application of the novel method reveals the achievable response rates in the helicopter states, and provides information on how parameter variations affect the system dynamics. A revised eigenstructure is developed, and the resulting closed-loop system is shown to comply with handling qualities specifications while reducing cross-coupling between modes.
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