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Stability derivative extraction from flight test data for a general aviation aircraft
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The Gulfstream Commander 700 (N700AE) aircraft owned by the Texas A&M Flight Mechanics Laboratory (FML) is currently being modeled on the Engineering Flight Simulator (EFS) for testing of an integrated cockpit system for general aviation (GA) aircraft. Due to a lack of technical information about the Commander's dynamics, the stability and control derivatives that govern its motion were estimated from flight test data. Two system identification techniques, the Modified Maximum Likelihood Estimator (MMLE) and the extended Kalman filter (EKF), were utilized to extract these parameters. Models of the takeoff, initial climb, cruise, and power approach configurations were obtained. Representative dynamic models were generated by both MMLE and the EKF for all of the above flight configurations. Cramer-Rao bounds for both the EKF and MMLE derivative estimates compared favorably with results obtained by other researchers. The modeled time history responses generated by the measured flight test inputs compared well with the flight test data. However, the modeled response to an aileron input did not emulate the aircraft response since the models produced adverse rather than proverse yaw. In general, the stability derivatives and flying qualities of each model responded to changes in flight condition as theoretically expected. Surprisingly though, the aircraft's directional stability decreased with decreasing airspeed. Test flights of both models on the EFS also indicated that both were representative of the Commander. Comparison of the performance of the MMLE and EKF algorithms indicated that, on average, MMLE predicted the stability derivatives with a slightly lower uncertainty than the EKF. MMLE was also less computationally expensive than the EKF and could provide rapid convergence to a fairly accurate model from poor starting conditions. During simulated flight tests, the pilot was unable to distinguish between the two models. Future efforts to improve the simulation should focus on obtaining accurate estimates of the drag polars, producing proverse yaw, and improving the thrust model. Flight testing is suggested as a possible means of extracting this information. Finally, development of an automated derivative extraction procedure is recommended for improving the accuracy and efficiency of the estimates with a reduced user workload.
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Includes bibliographical references: p. 97-100.
Issued also on microfiche from Lange Micrographics.
Randall, Brian Edward (1996). Stability derivative extraction from flight test data for a general aviation aircraft. Master's thesis, Texas A&M University. Available electronically from
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