Determination of airplane longitudinal stability derivatives from transient responses

Abstract

This study was carried out in an effort to determine the longitudinal stability derivatives of a Ryan Navion airplane using dynamic flight testing methods. This was done by recording the transient response of the airplane to elevator forcing functions in the form of steps or pulses. Data reduction was carried out using the equations of motion method and the derivative method. Due to partial failure of the instrumentation the results from the equations of motion method were disappointing. More successful results were obtained using the derivative method in conjunction with the useful data acquired from the equation of motion method. Concurrent with this report an investigation was carried out to find the stability derivatives of the same airplane from both theoretical considerations and from steady state flight testing. This investigation is described in Reference 7. An effort has been made to correlate the flight test results obtained from the dynamic and steady state methods and predictions made from theory. This correlation appears in Appendix B.