DETERMINATION OF STABILITY AND CONTROL DERIVATIVES FROM FLIGHT DATA—CASE STUDIES

intention of estimation of stability and control derivatives and performance charac­teristics. To the extent possible, the experiments were conducted very carefully, data were gathered with adequate sampling rates, and where necessary data compatibility analysis was carried out and the corrected data were used for parameter estimation. In a few cases, the data generated from the flight simulator have been used. For the sake of brevity Cramer-Rao uncertainty bounds are not given and the aerodynamic derivatives are based on only a few data sets, where the repeat runs are not available, due to cost and time constraints in conducting several flight tests. Despite this, the results are found to be reasonably good and are representative of the characteristics of the specified aircraft or vehicle. Since most of the data analyzed for these case studies are real flight data, it gives a good feel and experience of the application of flight data analysis procedures and parameter-estimation methods. Wherever applic­able the multiple maneuver analysis and model validation were carried out. Often the aerodynamic derivatives are obtained as a function of AOA or Mach number. The plots of these derivatives with respect to these independent parameters would be very useful. These plots would depict the trends, linear or nonlinear, and thus, reveal the specific characteristic variation of the derivatives. Also, it would be a good practice to plot these derivatives with respect to say AOA, such that any graphical difference in the variation or any discerning effects during comparison of the values with other derivatives show the correct correlations in the percentage differences and the graphical distances of these variations. For this purpose, the minimum and maximum values of all derivatives are determined and then the y-axis scale is chosen by multiplying these extreme values with the same factor, say 1.5. This factor remains the same for all the derivatives. With this method, any graphical difference (meas­ured in a distance unit) in any derivative will correspond to the same percentage difference in the numerical values.