Aerodynamic model inversion for virtual sensing of longitudinal flight parameters

Introduction of Fly-By-Wire and increasing levels of automation improve the safety of civil aircraft significantly, and result in advanced capabilities for detecting, protecting and optimizing A/C guidance and control. However, this higher complexity requires the availability of some key flight parameters to be extended, to keep for a nominal behaviour of the flight control systems. Hence, the monitoring and the consolidation of those signals is a significant issue, usually achieved via many functionally redundant sensors to enlarge the way those parameters are measured. This solution penalizes the overall system performance in terms of weight, power consumption, space requirements, and extra maintenance needs. Other alternatives rely on signal processing or model-based techniques that make a global use of all or part of the sensor data available, supplemented by a model-based simulation of the flight mechanics (analytical redundancy). That processing achieves a real-time estimation of the critical parameters and yields dissimilar signals. Filtered and consolidated information are delivered in unfaulty conditions by estimating an extended state vector including wind components, and can replace failed signals in degraded conditions (virtual probes). Accordingly, this paper describes a new model-based approach allowing the longitudinal flight parameters of a civil A/C to be estimated on-line, through an Aerodynamic Model Inversion. To facilitate onboard implementation, the main aerodynamic coefficients are approximated by a set of surrogate models. Results are displayed to evaluate the performances of that approach in different flight conditions, including external disturbances and modeling errors. They correspond to different simulations and real flight tests.