Aeroelastic Response Estimation of a Slender Body with Time-Varying Mass Using a Kalman State Estimator Approach
| The structural modes of slender aircraft, such as space launchers or missiles, vary during flight as fuel consumption changes the mass of the body. The time-varying structural modes present a challenge to the flight control system, that typically relies on a rigid-body model whereas the measured response, commonly measured by an inertial measurement unit (IMU), includes both the rigid-body dynamics and the time-varying elastic response.
Conventional approaches estimate a-priori the time-varying elastic response and define digital filters that filter out the elastic frequencies of the measured signal. To accommodate the uncertainty of the variation of the elastic response, broad stop-band filters are used, often limiting control bandwidth and degrading performance. This study presents a novel methodology to estimate the in-flight dynamic aeroelastic response of a slender flexible structure with time-varying mass using a Kalman State Estimation (KSE) approach. The approach utilizes a stepwise approximate aeroelastic model combined with multi-sensor data to estimate modal deformations, rates, and accelerations. These estimated states enable reconstruction and subsequent removal of the IMU data elastic component, isolating the rigid-body response and thus circumventing the need to filter the data. A case study involving a slender missile subjected to gust load demonstrates the method. A simplified model is used to simulate the flight and generate IMU and other sensor data. The same model is used to create a series of aeroelastic state-space models corresponding to different flight stages and form a stepwise aeroelastic database for the KSE. Numerical results show that the proposed method accurately reconstructs the elastic response and effectively removes it from the IMU measurement, acting as an adaptive filter for the elastic response of the time-varying structure.
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