Sensitivity Analysis of Model-based Synthetic Air Data Estimators

Abstract

The sensitivity of a synthetic air data system estimates of airspeed, angle of attack and sideslip angle to sensor output errors and aircraft model uncertainty is analyzed. The analysis shows that using low quality inertial sensors with large output errors requires a non-traditional, federated estimator architecture. With respect to model uncertainty, it is shown that a single linearized aircraft model can be used in lieu of a high-fidelity, non-linear model to provide reasonably accurate estimates of airspeed (less than 2 m/s error), angle of attack (less than 3 deg error), and sideslip angle (less than 5 deg error). This performance is shown to be relatively insensitive to off-trim attitudes but very sensitive to off-trim velocity. Methods for reducing the sensitivity to sensor error and model uncertainty are discussed. Flight test results are used to confirm the findings of the sensitivity analysis.