Flight-Test Techniques for Quantifying Pitch Rate and Angle-of-Attack Rate Dependencies

Abstract

Three different types of maneuvers were designed to separately quantify pitch rate and angle of attack rate contributions to the nondimensional aerodynamic pitching moment coefficient. These maneuvers combined pilot inputs and automatic multisine excitations, and were demonstrated with the subscale T-2 and Bat-4 airplanes using the NASA AirSTAR flight test facility. Stability and control derivatives, in particular C m q and C m α , were accurately estimated from the flight test data. These maneuvers can be performed with many types of aircraft, and the results can be used to improve physical insight into the flight dynamics, facilitate more accurate comparisons with wind tunnel experiments or numerical investigations, and increase simulation prediction fidelity. I. IntroductionTHE pitch rate of an aircraft is a rate of change of the aircraft orientation with respect to an inertial frame, expressed in body axes. The angle of attack rate is a rate of change of the aircraft orientation with respect to the air-relative velocity. Arbitrary motion in flight can involve one, both, or neither of these rates. For relatively small perturbations, reduced frequencies, and Mach numbers, the effects of angular velocities on the aerodynamic forces and moments acting on the aircraft can be modeled using conventional stability derivatives, after Bryan. 1 The largest contributions from these rates are on the nondimensional pitching moment coefficient, and are represented by the parameters C m q and C m α . The former is usually attributed to the additional lift acting on the horizontal tail during rotation in pitch, whereas the latter is an approximation to unsteady aerodynamic phenomena. The following discussion applies to other similar pairs of parameters, such as C L q and C L α , but the associated results are not reported in this paper because the dependencies identified for these parameters were less important for the overall aircraft dynamic motion than the dependencies for the pitching moment.Model parameters C m q and C m α are not usually estimated separately and accurately from flight test data because conventional aircraft maneuvers performed for system identification

Bulletin of the Polish Academy of Sciences: Technical Sciences

“…The number of harmonics (which is a related feature when bandwidth is fixed), was shown in [16] for pilot modelling and path tracking. Manoeuvres with combined multisine and pilot inputs for aircraft system identification were used in [17]. Skipping selected harmonics of the multisine signals can be used to reduce nonlinear distortions.…”