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The task of designing a robust control system using structured H ∞ algorithm involves several issues: choosing the system topology, the controller structure and tuning parameters to achieve robust stability and performance. Its application can lead to a trial-and-error approach at some stage. In order to minimize that effort, a methodology is proposed. A step-by-step guide is provided and includes modelling an uncertain system and designing roll-off, notch and setpoint filters aided by singular value analysis. The step of choosing a suitable topology for the control system and the controller structure is accomplished by RGA matrix analysis. Using a mixed-sensitivity approach, the design of weighting functions to achieve desired frequency-based performance is carried out considering plant restrictions. Application of the structured H ∞ optimization algorithm is commented and results are validated by means of sensitivity function analysis and nonlinear simulation. A successful study case of control system for tight formation flight is presented which includes nonlinear disturbances, uncertainties, measurement noise, input saturation and restrictions due to RHP poles. Results are compared with those obtained with other robust control techniques. [ABSTRACT FROM AUTHOR]

This paper presents novel approach for utilizing deployable fin as a static control surface along with aircraft primary controls for flat-spin recovery. Comparative analysis of with and without deployment of the fin has been thoroughly examined. To demonstrate the present approach, a nonlinear constrained optimization technique based optimal fin deflection is determined, followed by aircraft response in a flat-oscillatory-stable-left-spin flight at optimal fin setting angle, which provides spin attribute compensation. Thereafter, sliding-mode based robust control is designed for commanded departure of the aircraft from flat-spin to steady-straight-level flight. It is shown that finite-time direct spin recovery is achieved without any timescales based separation in dynamics. The present work novelty lies in the proposed strategy of using deployable fin, wherein dynamics of the fin is modeled and incorporated in the standard equations of motion of aircraft, subsequently, robust control law is developed. It is found from closed-loop simulation results that the proposed controller not only reduces the number of turns about spin axis and altitude loss but also minimizes spin recovery time when the fin is deployed. Additionally, rudder control power requirement is reduced, and effectiveness of other aerodynamic control surfaces are regained earlier when the fin is used for spin recovery. The outcome of the present study promises its practical implementation since the proposed solution is simple and compatible to integrate with the existing aircraft. [ABSTRACT FROM AUTHOR]