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A numerical design synthesis methodology for new generations of combat aircraft has been developed. It incorporates advanced technology in the form of design for low observables. Aircraft capable of being modelled with this methodology will have internal or external Weapons carriage, side mounted intakes, a straight-tapered trapezoidal wing, aft-mounted tail with the option of single or twin ns, and one or two engines with rectangular or axisymmetric nozzles. The design methodology incorporates sufficiently accurate and realistic algorithms for the calculation of the geometry and the estimation of the aerodynamic, mass and performance properties of the aircraft. The inherent flexibility of the design permits the examination of a wide range of configurations whilst maintaining the accuracy required to examine minor changes in the design requirements. A numerical optimization routine was linked to the synthesis, allowing the determination of optimum aircraft design variables for a given set of mission and performance requirements. Results were obtained showing the usefulness of this design tool for setting up parametric trend studies. The numerical accuracy, flexibility of configuration options and high level of advanced aircraft technology of this synthesis make a significant contribution to the continuing development of automated design tools.

This thesis investigates new convex optimisation techniques for motion and pose estimation. Numerous computer vision problems can be formulated as optimisation problems. These optimisation problems are generally solved via linear techniques using the singular value decomposition or iterative methods under an L2 norm minimisation. Linear techniques have the advantage of offering a closed-form solution that is simple to implement. The quantity being minimised is, however, not geometrically or statistically meaningful. Conversely, L2 algorithms rely on iterative estimation, where a cost function is minimised using algorithms such as Levenberg-Marquardt, Gauss-Newton, gradient descent or conjugate gradient. The cost functions involved are geometrically interpretable and can statistically be optimal under an assumption of Gaussian noise. However, in addition to their sensitivity to initial conditions, these algorithms are often slow and bear a high probability of getting trapped in a local minimum or producing infeasible solutions, even for small noise levels. In light of the above, in this thesis we focus on developing new techniques for finding solutions via a convex optimisation framework that are globally optimal. Presently convex optimisation techniques in motion estimation have revealed enormous advantages. Indeed, convex optimisation ensures getting a global minimum, and the cost function is geometrically meaningful. Moreover, robust optimisation is a recent approach for optimisation under uncertain data. In recent years the need to cope with uncertain data has become especially acute, particularly where real-world applications are concerned. In such circumstances, robust optimisation aims to recover an optimal solution whose feasibility must be guaranteed for any realisation of the uncertain data. Although many researchers avoid uncertainty due to the added complexity in constructing a robust optimisation model and to lack of knowledge as to the nature of these uncertainties, and especially their propagation, in this thesis robust convex optimisation, while estimating the uncertainties at every step is investigated for the motion estimation problem. First, a solution using convex optimisation coupled to the recursive least squares (RLS) algorithm and the robust H filter is developed for motion estimation. In another solution, uncertainties and their propagation are incorporated in a robust L convex optimisation framework for monocular visual motion estimation. In this solution, robust least squares is combined with a second order cone program (SOCP). A technique to improve the accuracy and the robustness of the fundamental matrix is also investigated in this thesis. This technique uses the covariance intersection approach to fuse feature location uncertainties, which leads to more consistent motion estimates. Loop-closure detection is crucial in improving the robustness of navigation algorithms. In practice, after long navigation in an unknown environment, detecting that a vehicle is in a location it has previously visited gives the opportunity to increase the accuracy and consistency of the estimate. In this context, we have developed an efficient appearance-based method for visual loop-closure detection based on the combination of a Gaussian mixture model with the KD-tree data structure. Deploying this technique for loop-closure detection, a robust L convex posegraph optimisation solution for unmanned aerial vehicle (UAVs) monocular motion estimation is introduced as well. In the literature, most proposed solutions formulate the pose-graph optimisation as a least-squares problem by minimising a cost function using iterative methods. In this work, robust convex optimisation under the L norm is adopted, which efficiently corrects the UAV’s pose after loop-closure detection. To round out the work in this thesis, a system for cooperative monocular visual motion estimation with multiple aerial vehicles is proposed. The cooperative motion estimation employs state-of-the-art approaches for optimisation, individual motion estimation and registration. Three-view geometry algorithms in a convex optimisation framework are deployed on board the monocular vision system for each vehicle. In addition, vehicle-to-vehicle relative pose estimation is performed with a novel robust registration solution in a global optimisation framework. In parallel, and as a complementary solution for the relative pose, a robust non-linear H solution is designed as well to fuse measurements from the UAVs’ on-board inertial sensors with the visual estimates. The suggested contributions have been exhaustively evaluated over a number of real-image data experiments in the laboratory using monocular vision systems and range imaging devices. In this thesis, we propose several solutions towards the goal of robust visual motion estimation using convex optimisation. We show that the convex optimisation framework may be extended to include uncertainty information, to achieve robust and optimal solutions. We observed that convex optimisation is a practical and very appealing alternative to linear techniques and iterative methods.

A technique for the identification of aircraft stability and control parameters from flight test recordings made in either calm or turbulent air is presented. The maximum likelihood output error method is used with a steady-state Kalman filter incorporated to account for atmospheric turbulence. A modified Newton-Raphson search technique, enhanced by a line search, is employed for parameter identification. Separate algorithms are developed for estimating the biases and noise levels in the observations. Some areas of practical problems in the application of such methods are stressed. A computer program for the identification of longitudinal stability derivatives is described and the aircraft instrumentation required is exemplified by that in Gnat XPSOS. The wind tunnel calibration of the flow-direction sensing nose probe assembly of Conrad yawmeters on this aircraft is detailed. The problems of handling the flight observations recorded are covered and some of the troubles experienced with the instruments are noted. The performance of the identification technique is investigated. The data required, the choices open to the analyst and the statistical information produced being highlighted. The identification of the process noise level, in this instance the turbulence intensity, is addressed and it is found that the value specified for this level can influence the other parameters. The longitudinal stability and control derivatives obtained for Gnat XPSOS are presented.

Generally speaking, difficulties encountered during the improvement of an Analytical Dynamic Model (ADM) using vibration test data come from both the Spatial Coordinate Incompatibility (SCI) and especially the Modal Coordinate Incompatibility (MCI) between the ADM and the test data. Efforts were therefore made in this project to cope with these two problems by extending some of the existing methods and also by developing new methods with consideration of their feasibility, efficiency and accuracy. A general description of this part of the project and the literature survey of this study area are presented in part 1 of the thesis. In part 2, in order to solve the SCI problem, a new extended Complete Modal Expansion (CME) and a Branch Modal Expansion (BME) method were proposed especially for the case when using a branch mode method to produce the ADM. Application of these two methods and the existing physical expansion method were demonstrated in a beam example in this part and were also used in some of the examples later in this project. In part 3, efforts were made to extend the existing Direct Matrix Updating (DMU) and the Direct Parameter Identification (DPI) methods for solving the MCI problem using a direct approach. Firstly a new Direct Modal Extension (DME) method was proposed and compared with the DMU method when they were used to improve a reduced-size ADM. Secondly, in order to overcome the main limitation of the existing DPI methods in their practical use, an extended Corrected Modal Constraint (CMC) method was proposed. In part 4, in order to achieve the feasibility and accuracy of ADM improvement, efforts were then made in the study of the indirect approach. Firstly a procedure using a new Orthogonality Sensitivity Method (OSM) working together with a model reduction method was proposed. Secondly, a new Energy Error Estimation (EEE) method was also presented. The original contribution of the EEE method is that the poorly modelled stiffness and mass elements of an ADM can be identified and corrected accurately and effectively. Applications of these new proposed methods were demonstrated by taking beam examples. Further application of the EEE method was examined in a full-scale aircraft tail plane example. A general discussion, conclusion and recommendation for further study of these methods are presented in the fmal part 5. Based on the study of this project, it is concluded that the feasibility and accuracy of the direct methods described in part 3 of this thesis are at a low level for practical use. Therefore, the main efforts and contributions in this project were made in the study of the indirect methods described in part 4 of this thesis. It is concluded that both of the new proposed OSM and EEE methods provide feasible tools for ADM improvement and possess a high level of accuracy.

The work presented in this thesis is motivated by a need for an advanced understanding of the governing mechanisms for vibrations in complex structures. In order to obtain a simplified description of the complex structure with the dominant information of the structure enhanced, one removes some unimportant structural information from the description by identifying secondary contributing substructures and couplings, then describing them using simplified models. It is found that the secondary substructures are those substructures being required for their vibrational transmission characteristics only, and the secondary couplings are the weak couplings in the structure. Moreover, it is demonstrated that the transmission characteristics can be sufficiently described by using only the direct wave and the fIrst reflection in the structure, and the secondary coupling can be simplified as an idealised coupling. The procedure for establishing such a simplifIed description for the complex structure is illustrated by a two-element built-up structure. Finally, the efficiency of using such a simplifIed description to analyse the complex structure is demonstrated for two mechanical artefacts, one being a laboratory structure consisting of a cylindrical shell attached to a plate via two beams, and the other a full-scale aircraft - Eurofighter 2000.

The purpose of the research investigation was to study the application of semi-active control technology to the design of a suspension system to be used in a landing gear of a high speed military aircraft. A semi-active system was used because it will allow a system to be driven from the hydraulic systems already existing in the aircraft without extensive modification. The research work involved establishing a theoretical mathematical model for the semi-active damping system. This model involved a large number of non-linear dynamic phenomena and elements including a two-stage gas spring, lever geometry, break out friction, square law damping and the switching function needed to achieve the semi-active control. Validation of the model was carried out by means of an extensive study of the dynamic responses obtained from digital simulation. An extended programme of laboratory experiments was also carried out to confirm the theoretical and simulated results, and to demonstrate the potential benefits in performance which can be achieved with those obtained from standard and optimized passive suspension system. The experimental rig involved a physical model which used hydraulic elements of a general industry standard, but not specially approved for aircraft use. The apparatus was arranged to permit a considerable degree of freedom for implementing the control laws which facilitated the assessment of different control schemes and allowed, at the same time, the ready simulation of various passive damping arrangements. An extensive series of trials was carried out on the final design and involved frequency response tests and subjecting the experimental suspension to inputs obtained from a simulated runway profile. The profile simulation was a discrete representation of a particular runway chosen for its roughness which was characteristic of runways from which high-speed military aircraft operate. From the research investigation and these trials it was established that semi-active control of the damping function is superior to standard techniques and achieves a substantial reduction in the energy transmitted to the airframe during ground manoeuvres.

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Designing successful commercial aircraft is a difficult business; the stakes are high and the risks numerous. Researchers in the past have developed methods that assist the designers in reducing these risks. In recent years such methods have benefited from improvements in computer technology. The work described in this thesis extends these methods to the design of commuter aircraft. These aircraft are more sensitive to operational requirements than other types due in part to their high zero-fuel mass ratio. It is essential that, for such aircraft, the best information possible is available to the designers. The identification of the optimum aircraft configuration and mission characteristics constitutes a vital part of this knowledge. A review of literature, involving both modem computer-based and traditional search methods, has shown continuing interest in aircraft project design methods from the earliest times to the latest conference. The work presented in this thesis is seen to compliment this interest in computer methods and to apply these techniques to the relatively neglected area of commuter aircraft design. A survey of commuter operation and aircraft types revealed the often conflicting requirements and regulations which govern the design process in this area. Detailed statistical analysis on a collection of commuter aircraft showed no consistent data patterns, but did indicate the bouyant state of the market. Earlier research work on the design of twin-engined turbo-prop aircraft had provided some experience in the design of short-haul aircraft. The new work improves these methods and applies them to larger and faster turbo-fan commuter aircraft. Since the turbo-prop work, the optimiser developed at RAE (Farnborough) has been rewritten to work more efficiently and allow larger problems to be tackled. This new optimiser s linked to a new synthesis routine which simulates turbo-fan aircraft design. The synthesis program was calibrated against industrial design calculations and shown to give acceptably accuracte predictions. The resulting design program is fully described and computer listings are presented. To illustrate the use of the optimisation methods in the devleopment of a new aircraft, a series of industrially related design studies is presented. These studies range from the selection of the initial baseline configuration, through various parameters sensitivity investigations, to the evaluation of aircraft and engine stretch options. To demonstrate more general types of design study, a series of optimisations in which the engine size is variable was conducted. This provides the designer with a knowledge of the absolute (optimum) design surface and allows him to judge the 'penalties' inherent in his chosen configuration.