Determination of low-speed longitudinal manoeuvring criteria for transport aircraft with advanced flight control systems

Abstract

The application of Active Control Technology concepts and in particular the Relaxed Static Stability principle in certain categories of future transport aircraft will lead to the introduction of primary flight control systems incorporating full-time stability augmentation. For this category of transport aircraft adequate handling quality criteria applicable to system design as well as to airworthiness certification are required. In an attempt to establish a new insight in this matter, approach and landing flight simulation investigations have been performed at the NLR, using a moving-base flight simulator with simulated outside view. The conceptual aircraft simulated was a jet transport developed around the relaxed static stability concept and equipped with a primary flight control system of the rate command/ attitude-hold type for pitch and roll control.-Washed-out direct-lift control has been incorporated in a version of the conceptual aircraft with increased wing-loading. The short-term pitch attitude and flight path response dynamics were the characteristics varied in the experiment. Based on pilot/aircraft performance measures, pilot ratings and pilot commentary, boundaries for satisfactory handling qualities have been established for a number of handling quality criteria. Limits on rise time and .settling time combined with a limit on the product of stick force per g and pitch control sensitivity are considered useful as open-loop criteria. A criterion on closed-loop resonance and pilot compensation (Neal-Smith criterion), related to the pitch attitude control loop is identified in this program as the best format to be used as closed-loop criterion for the short period pitch dynamics. For those aircraft designs for which direct-lift control is required to obtain satisfactory handling qualities, an extension of the pilot-in-the-loop concept to the altitude control loop, based on a minimum bandwidth of this loop, is proposed by the authors.