Appendix B: Aircraft models for parameter estimation

One of the important aspects of flight-testing of any aircraft is the estimation of its stability and control derivatives. Parameter estimation is an important tool for flight test engineers and data analysts to determine the aerodynamic characteristics of new and untested aircraft. The flight-estimated derivatives are useful in updating the flight simulator model, improving the flight control laws and evaluating handling qualities. In addition, the flight determined derivatives help in validation of the predicted derivatives. These predicted derivatives are often based on one or more of the following: (i) wind tunnel; (ii) DATCOM (Data Compendium) methods; and (iii) some analytical methods. The aircraft dynamics are modelled by a set of differential equations (equations of motion already discussed). The external forces and moments acting on the aircraft are described in terms of aircraft stability and control derivatives. Using specifically designed control inputs, responses of the test aircraft and the mathematical model are obtained and compared. Appropriate parameter estimation algorithms are applied to minimise the response error by iteratively adjusting the model parameters. Thus, the key elements for aircraft parameter estimation are: manoeuvres, measurements, methods and models.