Simulated Flight Data Research Articles

Identification of Nonlinear Aircraft Spoiler Parameters

A modified stepwise regression procedure employing several selection criteria used in the identification of an aircraft model structure from flight test data is presented. The aircraft equations of motion are evaluated in general form, expressing the force and moment coefficients as polynomials in state and control variables. Nonlinear aerodynamic parameters are represented by spline functions in one or two variables. Results from the analysis of both simulated and real flight test data utilising the regression algorithm are discussed briefly. The accuracy of the algorithm is first assessed using simulated flight data, then a real flight test case is analysed with a focus on estimating the nonlinear spoiler contribution. The resultant simulated response is compared with both the flight data and the response obtained through a linear maximum likelihood procedure

Aileron and sideslip-induced unsteady aerodynamic modeling for lateral parameter estimation

Aileron inputs and sideslipping motion of an aircraft will give rise to a trailing vortex system that is a function of time. To account for such unsteady aerodynamic effects into the lateral equations of motion, a model is proposed based on a simple vortex system. The expressions for induced sidewash and downwash angles obtained for such vortex system are recast so that the resulting equations of motion can be used for parameter estimation. Maximum likelihood method in frequency domain is used to analyze simulated flight data of an example airplane to study the effects of inclusion and omission of unsteady aerodynamic modeling on estimated parameters. Sensitivity of the extracted parameters to different control input forms is shown to reduce with the inclusion of unsteady aerodynamics.

Postflight data-reduction techniques for hovered kinetic energy weapons

One of the major concerns in attitude control of kinetic-energy-weapon vehicles proposed for exoatmospheric engagements is that error sources such as vehicle center-of-gravity variations and thrust misalignments of divert thrusters may induce excessive parasitic torques on the vehicle. These torques may result in significant attitude perturbations that are undesirable for target tracking, especially when using strapdown seekers. In an effort to identify and characterize these error sources in a quantitative way, it has been proposed to explicitly estimate them by using the data obtained from kinetic-energy-weapon hovered interceptor test flights. An estimation procedure based on extended Kalman filtering is developed for the postflight data reduction that includes the estimation of the center-of-gravity location and thrust misalignments. Some modifications to the basic extended Kalman filter algorithm are made to reduce the sensitivity of the estimator to uncertainties in divert thrust timing. The proposed estimation scheme is then used to process simulated flight data and actual test data. The data-reduction results are provided in this paper.

Unsteady aerodynamic modelling for aircraft lateral parameter estimation

SummaryA mathematical model of unsteady aerodynamic effects for use in lateral aircraft dynamics has been proposed based on Weissinger’s arrangement of trailing vortex system. The suggested model is shown to be suitable for use in parameter extraction algorithm. Simulated flight data of an example airplane has been analysed through maximum likelihood parameter estimation algorithm in frequency-domain to show the effect of inclusion and omission of unsteady aerodynamics on estimated parameters.

Real-time comparison of X-29A flight data and simulation data

This paper presents a technique for comparing, in real time, the flight test time histories for X-29A aircraft with time histories computed from linearized mathematical models. Such a comparison allows the flight test personnel to verify that the aircraft is performing as predicted, to determine regions of nonlinear behavior, and to increase the rate of envelope expansion. The types of mathematical modeling and equipment required, the procedure used, and actual flight test results are discussed.

Frequency-domain application of Gauss-Newton method to extract aircraft longitudinal parameters

SummaryA simplified output error method based on the Gauss-Newton minimisation technique is formulated in the frequency-domain and its application demonstrated for extraction of aircraft longitudinal parameters from simulated flight data. A study is carried out to show the effects on the accuracy of estimated parameters due to use of different input forms to generate the flight data, using different initial values to start the algorithm, presence of measurment noise in the flight data and fixing some weak parameters at a priori values. It is shown that the use of Packing Theorem to increase the sparsely sampled frequency data does not lead to better accuracy by the proposed method, as has been reported for the maximum likelihood method in the literature. Finally, relative advantages of the frequency-domain approach as against the time-domain approach are pointed out by analysing the same flight data in these two domains. It is shown that frequency-domain approach is better equipped to analyse noisy-data and can yield better estimates at reduced computational time.

Frequency-domain application of an input-error method to estimate aircraft longitudinal parameters

An input-error method for estimating parameters of a single-input-multi-output linear time-invariant system is formulated in the frequency domain. The input-error method includes the Gauss-Newton minimization technique as a part of the estimation procedure. Two possible ways of defining the objective function are presented and the results obtained from these two approaches are compared. The method is applied to extract the longitudinal stability and control derivatives (parameters) of an aircraft from simulated flight data. Flight data for the short-period dynamics of the aircraft are analysed for different control input forms to identify the effect of the input forms on the accuracy of estimation. The effect of the variations in the intensity of noise present in the input and/or output data and the effect of the choice of initial values to start the identification process, on the accuracy of estimation, is also studied. The method is shown to be quite robust to estimate parameters from flight data having...

Aircraft parameter identification by the Gauss-Newton method in the frequency domain

Abstract A frequency-domain output-error method based on the Gauss-Newton minimization technique has been developed for the estimation of aircraft parameters from flight data. The method has been validated on simulated flight data. The effect of the intensity of measurement noise present in the flight data is studied and the method is shown to work satisfactorily even in the presence of high noise levels. Six different types of rudder and aileron control inputs have been used to generate the flight data; the analysis of such data is carried out to identify the suitable control input forms for the parameter estimation. Results are presented to show the effect of using the ‘packing theorem’ to increase the sparsely sampled frequency data; assigning a priori values to some of the weak parameters; and starting the iteration process with different initial values. Finally, a comparison of the method in the time domain and the frequency domain is presented to point out the relative merits of the latter approach.

Qualitative Differences Between Shuttle On-Orbit and Transition Control

Two separate reaction control system digital autopilots evolved from one original Space Shuttle orbital autopilot concept. A computer overload forced this evolution. Part of the overload problem was due to unique performance requirements imposed on the reaction control system during each of several different flight regimes. The two resultant reaction control system digital autopilots yield different effector responses because they rely on different sources of sensory input and they process data differently. This paper describes the evolution of the two and illustrates their behavioral differences. The transition autopilot, used in orbital insertion and deorbit, is sensitive to Orbiter flexure due to its feedthrough character. The on-orbit autopilot is sensitive to transient rate control degradation from large disturbances due to feed-forward rate estimation. Simulation results and flight data are used to illustrate performance differences between the two autopilots under various conditions. These include computer failures where electronic stringing and procedural reconfiguration differences affect autopilot behavior.

Airplane model structure determination from flight data

A procedure for airplane model structure determination from flight data based on modified stepwise regression (MSR), several decision criteria, and postulated aerodynamic model equations is presented. The MSR is constructed to force a linear model for the aerodynamic coefficient first, then to select significant nonlinear terms and reject nonsignificant terms from the model. In addition to the statistical criteria in the stepwise regression, the prediction sum of squares criterion and analysis of residuals are examined for the selection of an adequate model. The procedure is used in examples with simulated and real flight data. It is shown that the MSR performs better than the ordinary stepwise regression and that the technique can be also applied to the large amplitude maneuvers.

An improved prediction method for the noise generated in flight by circular jets

A semi-empirical model for predicting the noise generated by jets exhausting from circular nozzles is presented and compared with small-scale static and simulated-flight data. The present method is an updated version of that part of the original NASA Aircraft Noise Prediction Program (1974) relating to circular jet noise. The earlier method has been shown to agree reasonably well with experimental static and flight data for jet velocities up to ∼ 520 m/s. The poorer agreement at higher jet velocities appeared to be due primarily to the manner in which supersonic convection effects were formulated. The purely empirical supersonic convection formulation is replaced in the present method by one based on theoretical considerations. Other improvements of an empirical nature have been included based on model-jet/free-jet simulated-flight tests. The effects of nozzle size, jet velocity, jet temperature, and flight are included.

Empirical model for inverted-velocity-profile jet noise prediction

An empirical model for predicting the noise from inverted velocity-profile coaxial or coannular jets is presented and compared with small-scale static and simulated-flight data. The model considers the combined contributions of as many as four uncorrelated constituent sources: the premerged-jet/ambient mixing region, the merged-jet/ambient mixing region, outer-stream shock/turbulence interaction, and inner-stream shock/turbulence interaction. The model for both mixing regions is developed from the NASA interim prediction method for jet noise. The noise from the merged region occurs at relatively low frequency and is modeled as the contribution of a circular jet at merged conditions (between inner and outer streams) and total exhaust area, with the high frequencies attenuated (since the high-frequency region of this fictitious jet does not exist). The noise from the premerged region occurs at higher frequency and is modeled as the contribution of an equivalent plug nozzle at outer stream conditions, with the low frequencies attenuated (since the outer jet is broken up rapidly, before much low frequency is generated). The shock noise for each supersonic stream is calculated from a modification of the Harper-Bourne and Fisher (1973) model.

Study of the Human Pilot as a Servo-Element

SummaryA method for describing the action of a pilot in mathematical terms is presented. The method applies for tracking tasks and gives a pilot describing function which can be used in conventional servo-analysis. Flight simulator data obtained in this way for a wide variety of aircraft longitudinal response characteristics are presented and the effect of these characteristics on the pilot's action is discussed fully. In order to illustrate that work of this kind can lead to a quantitative understanding of pilot's “handling qualities” opinion, the recorded pilot opinions are “predicted” from a knowledge of three simple aircraft characteristics.