Aircraft parameter identification using Matlab

System identification techniques are routinely used in experimental stability and control studies throughout the aerospace industry. Over the years, various researchers at the College of Aeronautics have contributed to this field; most recently some of the latest methods have been employed to estimate the stability and control derivatives of a variety of aircraft types. Although the more recent investigations provide a useful insight into the capabilities and characteristics of several up-to-date methods, they have not resulted in tools which may be used on a routine basis. Consequently, the purpose of this report is to describe a set of procedures which are straightforward to apply, and produce reasonable solutions to the type of linear parameter identification problems which are often found in aerospace work. Recordings of the short period and phugoid modes from Handley-Page Jetstream G-NFLC are used throughout as examples. Firstly, those characteristics of the aircraft’s instrumentation system which influence the quality of the signals - sample rate, antialiasing filters, time delays - are considered. This information is used in conjunction with standard signal processing techniques to ensure that the data is of sufficient quality to be used in the parameter estimation process. Next, a basic Fourier analysis and a least squares algorithm are employed to produce non- parametric and parametric models respectively. The results thus obtained are comparable to those generated using more sophisticated techniques. In conclusion, standard signal processing methods combined with relatively simple estimation theory offer an adequate solution to the linear parameter estimation problem.Cranfield Universit

Analysis of two-cell swept box with ribs parallel to the line of flight under loading by constant couples

The method of oblique co-ordinates is used to analyse the problem associated with the strength and deformation of a uniform, rectangular, two- cell swept box beam having ribs parallel to the line of flight. The case of loading by constant couples is considered, but no account of root effects is taken. Continues

Formulation and System Identification of the Equations of Motion for a Dynamic Wind Tunnel Facility.

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

Tests on the general instability of a stiffened metal cylinder under axial compression

A thin stiffened metal cylinder liable to General Instability was tested under axial compression and an investigation was made into possible methods of predicting the critical load from non-destructive tests. Particular attention was paid to the perturbation loading technique. The cylinder was finally tested to destruction and the actual failing load compaired with the values given by various theories and empirical relationships

Effects of nonlinear flight control system elements on aircraft

This report presents the experimental method and results from a series of desktop simulation tests designed to investigate manual control characteristics of young and relatively inexperienced civil pilots (24 years average age and 66 hours flight experience). Subjects were asked to perform tasks during which they had to establish longitudinal control through pitch attitude shown on a primary flight display. A linear aircraft model coupled with nonlinear flight control system was used to produce realistic vehicle dynamics. Increased encroachment into nonlinear command gearing was found to make aggressive subjects resort to high levels of crossover regression. The combined effects of rate-limiting and nonlinear command gearing was observed only for demanding tasks during which over-control was a typical feature. The classical precision and bimodal models were used for an in-depth study of pilot dynamics observed during compensatory tasks. Model parameters were found through the definition of a constrained nonlinear optimisation problem. A single feedforward equalisation element was used for tracking tasks. It was found that subjects developed similar low frequency feedforward equalisations, whilst large inter-subject variations exist for high frequency equalisations. The resulting models also provided some insight into the Neal-Smith and Bandwidth handling qualities criteria. Actuator rate-limiting could not be directly correlated to any of the pilot model parameters

A potential flow model for the flow about a nacelle with jet

The inviscid incompressible flow round a thin nacelle from which a jet is issuing is considered. It is shown that the inhomogeneous motion which may be represented by two semi-infinite distributions of vortices in the two-dimensional case and by a semi-infinite distribution of circular vortex rings in the axi= symmetric case. ..

An approximate solution to the swept wing root constraint problem

This report presents an approximate solution to the problem associated with the root constraint in a swept wing

The economics of aircraft production : a study of the control of overhead costs in aircraft manufacture

This paper represents an attempt to appraise the different factors which must be considered in applying modern methods of cost control to aircraft production, and to suggest those positive measures best calculated to effect such control. The emphasis throughout is on control of overhead costs as these are by far the largest element in the total cost make-up

An investigation of the flexure-torsion flutter characteristics of aerofoils in cascade.

Part 1 of this report describes the results obtained from a series of tests on the flexure-torsion flutter characteristics of cascades of similar aerofoils having symmetrical sections. Continues … Part 2 of this report is a review of the theoretical studies on oscillating aerofoils in cascade. Continues

Flight experiments on the boundary layer characteristics of a swept back wing

This work consideres the measurement in flight of the boundary layer characteristics of an untapered, untwisted, 40 degree swept back half wing of thin symmetrical section, mounted vertically on top of the fuselage of an Anson Mart I aircraft. ..