Frequency-Domain Approach to Calculating Dynamic Stability Coefficients from Forced Oscillation Tests

Dynamic wind tunnel tests have been used for decades to determine dynamic stability coefficients. Forced oscillation testing is one of the most common approaches and involves oscillating a rigidly mounted vehicle to extract these coefficients through data reduction techniques. Two widely used methods are the specific point and integration methods, both of which are prone to errors arising from the filtering process, the persistence of low-frequency noise, and discretization errors caused by sampling rate limitations. In this work, a frequency-domain approach to data reduction is derived, which utilizes the frequency spectrum of a force or moment time series to determine the dynamic stability coefficients. This method is demonstrated on an analytical test problem to be more robust against signal noise without requiring filtering and less sensitive to discretization errors. The method is further applied to a forced oscillation experimental data set obtained from NASA Langley’s 12-Foot Low-Speed Tunnel for two configurations of a [Formula: see text] nose cone entry capsule with different ellipsoidal backshells. The stability coefficients derived using the frequency-domain approach show good agreement with the traditional specific point and integration methods. A method to propagate measurement uncertainty through the frequency-domain approach is also derived and applied to the experimental data.