EVALUATION OF DIGITAL FLIGHT CONTROL DESIGN FOR VTOL APPROACH AND LANDING.

Methods and results in the design and evaluation of a digital flight control system (DFCS) for a CH-47B helicopter are presented. The DFCS employs proportional-integral control logic to provide rapid, precise response to automatic or manual guidance commands while following conventional or spiral-descent approach paths. It contains attitude - and velocity - command modes, and it adapts to varying flight conditions through gain scheduling. Extensive use is made of linear systems analysis technques - the DFCS is designed using linear-optimal estimation and control theory, and the effects of gain scheduling are assessed by examination of closed-loop eigenvalues and time responses. The pre-flight-test evaluation described provides a direct comparison of alternate navigation, guidance, and control philosophies; confirms the practical merits of the DFCS design approach; and demonstrates techniques which will aid in the development of future guidance and control systems.