Applications of state estimation in aircraft flight-data analysis (original) (raw)

Journal of Aircraft, 1985

Abstract

This paper traces the evolution of the use of state estimation in the analysis of aircraft flight data and discusses some recent applications associated with airline turbulence encounters and high angle-of-attack flight tests. A unifying mathematical framework for state estimation is reviewed, and several examples are shown that il- lustrate a general approach for estimating variables that are difficult to measure. The diversity of the applica- tions discussed and examples presented serve to demonstrate the potential advantages of using state estimation methods. curate determination of angle of attack, pitch angle, and vehi- cle velocity during dynamic maneuvers. These "states" were obtained by integrating functions of measurements from the pitch-rate gyro and normal and longitudinal accelerometers. Initial conditions and bias terms were determined from airspeed and altitude measurements at the steady-state end points of the maneuver. The resulting "smoothed" time- histories were then used as a basis for subsequent parameter identification studies. As Gerlach has pointed out, the technique of state estima- tion provides both a check on instrument accuracy and data consistency, and estimates of unmeasured or poorly measured variables. These items have been the primary objectives in most of the studies that followed Gerlach's original work. His students later improved and formalized the techniques that Gerlach had developed.3'4 In this country, early advocates of the use of state estimation for flight-path reconstruction were Wingrove5'6 at NASA, Eulrich and Weingarten7 at Cal- span, and Molusis8 at Sikorsky Aircraft. Over the past few years, the work in this field has been evolving toward the use of more complete kinematic models, the development of more sophisticated algorithms, and the treatment of more difficult applications. State estimation as a means of checking instrument ac- curacy and data consistency is now used by many flight-test groups.9"21 Once a consistent, smoothed set of time-histories is obtained from the data, other analyses, such as identification of stability and control derivatives, are readily performed. In fact, relatively simple routines may be used for identification tasks, allowing the analyst freedom to develop a proper aerodynamic model. Since the data-consistency application has been extensively treated in the literature, it will not be discussed further here. Instead, the paper will address some of the more recent applications of aircraft state estimation in ob- taining estimates of difficult-to- measure variables.

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