Micro Air Vehicles are currently receiving growing interest because of their broad applications in many fields. However, in MA V flight tests, the onset of unwanted large-amplitude roll oscillations for various designs has been reported, which has eventually led to difficulties in flight control and such undesirable selfinduced roll oscillations were investigated in the current study. More specifically, a common low-aspect-ratio wing, an AR = 2 rectangular flat plate, was researched, with the aim being to attenuate the self-induced roll oscillation of low-aspect-ratio wings by applying various flow control techniques. These flow control techniques were applied using in three completely different approaches using three different flow control techniques, i) global active excitation, ii) local active excitation and iii) passive flow control. The global active excitation was achieved by using external acoustic forcing and it is found that the self-induced roll oscillations of AR = 2 flat plate wing can be completely suppressed as well as the onset of the roll oscillations delayed using this method. Similar results were also obtained for wings with airfoil profiles of NACA0012 and SD7003-085-88. In addition, the velocity measurements indicated that acoustic excitation could restore a symmetric vortex flow over the free-to-roll wings and thus eliminate the self-induced roll oscillations. Frequency spectral study revealed that acoustic excitation could energize the shear layer instabilities and result in reattachment or a smaller separated flow region over the suction surface of the wings, thereby, attenuating the roll oscillations.

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Stall flutter is a nonlinear aeroelastic phenomenon that can affect several types of aeroelastic systems such as helicopter rotor blades, wind turbine blades and highly flexible wings. While the related aerodynamic phenomenon of dynamic Stall has been the subject of many experimental studies, stall flutter itself has rarely been Investigated. This thesis presents a set of experiments conducted on a NACA 0012 airfoil undergoing stall flutter oscillations in a low speed wind tunnel.

Three related methodologies relating to the modelling and design of aero elastic aircraft structures are considered. In the first study, a procedure for devel9pirig efficient aeroelastic Nonlinear Reduced Order (NROM) Models for aerospace structures containing geometric nonlinearities is described. The structural modelling is based upon a combined modal/FE approach (CMFE) that describes the nonlinear stiffening effects from nonlinear static analyses for a range of prescribed inputs. The prescribed load cases and resultant displacements from the static nonlinear test cases are transformed into modal coordinates using the modal transformation of the underlying linear system. A regression analysis is then performed to curve-fit the sets of nonlinear stiffness force / displacement maps in order to find the unknown nonlinear modal stiffness coefficients. Once the structural NROM has been defined, it is coupled to the Rational Fraction Approximation of the doublet lattice aerodynamic model corresponding to the wing planform. The aeroelastic model can then be used to predict the dynamic aeroelastic behaviour of the defined structure. The methodology is demonstrated on an aeroelastic model of a flexible high aspect ratio wing with the static deflections, limit cycle oscillation (LCO) behaviour and gust response being predicted. To further understand the aeroelastic behaviour of high aspect ratio wings, and to validate the mathematical model, an experimental model is developed. Experimental modal testing was employed to analyze the dynamical behaviour of the structure and the Finite Element (FE) representation updated to bring the model close to the experimental counterpart. The wing was analyzed in both deformed and undeformed shapes. The static and dynamic response of the wing was demonstrated and a comparison made with the numerical model; a good agreement was achieved. In the second study, an Ant Colony Optimisation (ACO) approach is used to maximize the flutter-divergence speed of a simple rectangular composite wing through determination of the best combination of ply orientations. An improved aeroelastic tailoring implementation is proposed based upon a combination of rank based and min-max ant system algorithms, and compared with several different implementations. A statistical investigation is performed on the example aeroelastic tailoring problem in order to investigate the effectiveness and robustness of the approaches. Consideration is also made to the best weightings of the pheromone addition and evaporation parameters. In the third study, innovative metallic wing structural designs are introduced that can be used to influence the bending I torsion coupling behaviour of aircraft wings, leading to the possibility of metallic aeroelastic tailoring. It is intended that the aeroelastic behaviour, such as the flutter I divergence speed or gust loads response, can be influenced in a beneficial way without any increase in weight. Two different approaches are demonstrated: using ribs with varying orientations, and making use of crenellations in the wing skins. The concepts are demonstrated using two simple FE models: a rectangular wing box and a more realistic wing model. In both cases it is shown that bending-torsion coupling can be achieved in metallic structures using both approaches and that this has an encouraging influence on the wing aeroelastic behaviour.

The relaxed certification requirements associated with amateur construction - "homebuilt" - aircraft, particularly in the USA, has led to a renaissance in the light aircraft industry. Europa Aircraft Ltd has addressed the current demand for a privately owned aircraft by producing a two seat, low wing aircraft of composite construction (fig 1). The aircraft is supplied in kit form and features detachable main wings to allow ease of storage. Critical structural components, such as the main wings, wing spars, and fuselage are fabricated by independent suppliers and inspected prior to being supplied to the customer. Final assembly of the fuselage and wing structure is performed by the customer. The following thesis details two composite motor-glider wings whose structure was designed and engineered by the author to meet set airworthiness requirements. This was the first time a retro-fit glider wing had been designed for a light aircraft, and the first time the Advanced Composites Group (ACG) LTM 26 low-temperature curing pre-impregnated carbon laminate material system was combined with Airex R62.60 core material to form a reinforced sandwich skin material on a manned flight vehicle. This thesis was performed under scholarships from both Strathclyde University and Europa Aviation Ltd. Testing of the structure was partially funded by the Department of Trade and Industry (DTI) under a SMART program award.

The inclusion of static aeroelastic effects is essential to the accurate calculation of the aerodynamic properties of a wing, the resulting wing loads, and ultimately the mass of the wing. Within an industrial aircraft design cycle, the computational time required for structurally coupled nonlinear flow solvers is impractical for the many different solutions required, even with the current development in computing power. The process currently used by most civilian aircraft manufacturers therefore makes use of time efficient linear panel methods for calculating the aerodynamics and modal data for calculating structural movements.University of Bristol.

Classical criteria of aircraft design involve adding a multiplier to the structure's inertial load to cater for various flight circumstances. The value of this multiplier depends on the type of aircraft designed, for example a high value is used in acrobatic variants to cater for their high g manoeuvres, as compared to a lower value in light non-acrobatic versions.

The preliminary design of aerofoils for use in versatile air vehicles is considered, with a view to addressing the sensitivity of the boundary layer transition to surface imperfections arising through surface contamination and degradation. An efficient multi-objective optimisation framework has been developed, enabling optimal trade-offs between key flight conditions to be quantified which include the impact of surface contaminants on the evolution of the design space. The impact of surface contamination and degradation on the design of optimal profiles is assessed through the reduction in the critical amplification factor of boundary layer disturbances at the point of transition onset and the resulting Pareto front compared with comparative 'clean' surface cases. A meta-model assisted global search alleviates the expense of coupling the algorithms with expensive CFD solvers, with an adaptive Kriging -based strategy adopted. The surrogate is iteratively refined in promising regions of the design space according to a probablistic adaptive sampling algorithm. Optimal solutions identified using the global multi-objective search are further improved using a novel local search and reparameterisation scheme. Additional degrees of freedom are iteratively introduced into the parameterisation resulting in an increasingly flexible geometry description. The proposed framework is benchmarked against traditional approaches and found to be superior in both accuracy and efficiency. The requirement that take-off be insensitive to contamination effects proves to be a key consideration and the physical mechanisms by which this robustness in design is achieved are discussed.

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