Failures in advanced flight control systems of future transport aircraft

Report (1984)
Copyright: Campus only
Controllability Flight simulation Transfer functions Manual control Criteria Longitudinal control Pilot performance Aircraft control Ratings Control sticks System failures Fly-by-wire control
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Published Date

12-11-1984

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NLR-TR 84108 U

Abstract

Future transport aircraft will be different from to-day's in that they will be designed to be statically neutrally stable or even unstable to improve economics, while the stability will be provided by means of a fly-by-wire flight control system. Since this system will be flight critical it is necessary to develop a philosophy on the treatment of failures in these systems. If the probability of failure is higher than extremely remote, the effects of flight control system failures on the handling qualities must be assessed. As a contribution to the discussion, a simulator investigation has been carried out on the moving base flight simulator of NLR, using a medium-weight transport with reduced stability equipped with a side-stick controlled flyby-wire flight control system. A very simple electrical back-up system was used to reduce the pitch divergence when the primary flight control system failed. The results of the experiment indicate that a large variability in the pilot ratings can occur in this kind of investigation. However, careful analysis of the ratings and the associated commentary has provided a ranking of the configurations used from good to bad. These results are compared to the existing criteria for handling qualities. It is shown that these rankings correlate well with some criteria (closed-loop performance criterion, some Mil-F-8785 C criteria) , whereas other criteria are either not applicable (time history criteria), or inappropriate (static stability criterion, bandwidth criterion).