Browsing by Author "Carnduff, S. D."

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    Application of aerodynamic model structure determination to UAV data
    (Royal Aeronautical Society, 2011-12-31T00:00:00Z) Carnduff, S. D.; Cooke, Alastair K.
    This paper concerns aircraft system identification and, in particular, the process of aerodynamic model structure determination. Its application to experimental data from unmanned aerial vehicles (UAVs) is also described. The procedure can be particularly useful for determining an aerodynamic model for aircraft with unconventional airframe configurations, which some unmanned aircraft tend to have. Two model structure determination techniques are outlined. The first is the well-established stepwise regression method, while the second is an adaptation of an existing frequency response approach which instead utilises maximum likelihood estimation. Example applications of the methods are presented for two data sources. The first is a set of UAV flight test data and the second is data recorded from dynamic wind tunnel tests on a UAV configuration. For both examples, the model structures determined using stepwise regression and maximum likelihood analysis matched one another, suggesting that the maximum likelihood approach and the chosen thresholds for its statistical metrics were reliable for the data being analysed.
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    Formulation and System Identification of the Equations of Motion for a Dynamic Wind Tunnel Facility.
    (Cranfield University, 2008-03) Carnduff, S. D.; Cooke, A. K.
    This document describes the equations of motion of an aircraft model tested in Cranfield’s 4 degreeof- freedom (DoF) wind tunnel facility. In previous research, the equations have been derived assuming that the model’s centre of gravity (cg) is coincident with the gimbal mechanism about which the model rotates on the rig. However, in this report a general approach is taken with the cg assumed to be located away from the gimbal. The equations are developed from first principles and reduced to a linearised form where motion can be represented as small perturbations about trim. The equations are also decoupled into longitudinal and lateral/direction expressions and converted into state space form. It had been found in practice that models tested in the facility are very responsive in heave and can only be operated open-loop if movement is restricted to purely rotational motion. Therefore, the equations for this 3DoF case are also developed. Having obtained theoretical expressions, a series of wind tunnel tests were conducted on a 1/12 scale BAe Hawk model in order to establish if the theoretical relations were valid in practice. The particular technique used in testing the model was dynamic simulation and the analysis of the experimental data was performed using system identification. An established model structure determination procedure is used to determine which stability and control derivatives should be included in the equations of motion. Frequency domain, equation error parameter estimation is then employed to obtain numerical values for the stability and control derivatives. For both the longitudinal and lateral/directional examples described, the final model structure obtained from experiment matches that derived from theory. Derivatives values obtained from parameter estimation and empirical analysis are also in good agreement.
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    System identification of unmanned aerial vehicles
    (Cranfield University, 2008-08-14) Carnduff, S. D.; Cooke, Alastair K.
    The aim of this research is to examine aspects of system identification for unmanned aerial vehicles (UAVs). The process for aircraft in general can be broken down into a number of steps, including manoeuvre design, instrumentation requirements, parameter estimation, model structure determination and data compatibility analysis. Each of these steps is reviewed and potential issues that could be encountered when analysing UAV data are identified. Problems which may be of concern include lack of space within the airframe to mount sensors and a greater susceptibility to the effects of turbulence in comparison to manned aircraft. These issues are investigated using measurements from two experimental sources. Firstly, Cranfield University’s dynamic wind tunnel facility is utilised, in which scale models are flown in semi-free flight. The control surfaces are actuated so that inputs, similar to those used when flight testing full-sized aircraft, can be applied and the resultant response of the model is recorded. Measurements from a 1/12 scale model of the BAe Hawk and a 1/3 scale model of the FLAVIIR project demonstrator UAV are used. An added benefit of the facility to this work is that the wind tunnel models are comparable in size to the miniature class of UAVs. Therefore, practical issues, similar to those faced for these aircraft, are encountered with the wind tunnel experiments. The second source of experimental data is UAV flight test data supplied by BAE Systems.