Validation of a nonlinear observer implementation for empennage loads estimation

Abstract

The monitoring of aircraft structural loads shows promising potential for improvement in terms of aircraft maintenance. Monitored loads can be used for component specific overload detection and for targeted inspections on ground. This results in a reduction of the necessary on-ground time after in-flight events and consequently in a reduction of maintenance costs. Focusing model-based approaches for loads monitoring, a nonlinear Luenberger observer is adapted for the flight test aircraft UW-9 Sprint. The implementation of the observer structure containing a state and a disturbance observer, as well as the determination of the included feedback gains is explained. Within this article, the Loads Observer method is validated against flight test data, exemplarily for empennage loads. For this purpose, the empennage of the test aircraft is equipped with strain gages. The test equipment and its calibration are described. Regarding the assessment of combined maneuver and gust loads, the flight test execution including the performance of maneuvers in gusty conditions is demonstrated. Finally, the component loads estimation is compared to the loads measurement.