Two complementary approaches to estimate downwash lag effects from flight data

Jategaonkar, R.V.; Gopalratnam, Girija

doi:10.2514/3.46060

Cited by 10 publications

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“…Solutions to this problem include combining dependencies to estimate a single lumped derivative, using other analyses to provide prior information on some of the parameters, and redesigning the maneuver so that the pitch rate and angle of attack rate are less correlated. 2,3 The approach taken for this paper was to redesign the maneuver.…”

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

Grauer

Morelli

Murri

2017

Journal of Aircraft

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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

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