In the present work, the authors examine two computational approaches that can be used to study flexible flapping systems. For illustration, a fully coupled interaction of a fluid system with a flapping profile performing harmonic flapping kinematics is studied. In one approach, the fluid model is based on the Navier-Stokes equations for viscous incompressible flow, where all spatio-temporal scales are directly resolved by means of Direct Numerical Simulations (DNS). In the other approach, the fluid model is an inviscid, potential flow model, based on the unsteady vortex lattice method (UVLM). In the UVLM model, the focus is on vortex structures and the fluid dynamics is treated as a vortex kinematics problem, whereas with the DNS model, one is able to form a more detailed picture of the flapping physics. The UVLM based approach, although coarse from a modeling standpoint, is computationally inexpensive compared to the DNS based approach. This comparative study is motivated by the hypothesis that flapping related phenomena are primarily determined by vortex interactions and viscous effects play a secondary role, which could mean that a UVLM based approach could be suitable for design purposes and/or used as a predictive tool. In most of the cases studied, the UVLM based approach produces a good approximation. Apart from aerodynamic load comparisons, features of the system dynamics generated by using the two computational approaches are also compared. The authors also discuss limitations of both approaches.

This paper describes a combined experimental and numerical study on damaged and undamaged space shuttle tile thermal protection system (TPS). The principal objective of the study is to determine its thermomechanical behaviour and assess the structural integrity of the TPS. The TPS tile specimens are subjected to a temperature profile corresponding to the thermal loads of the Access to Space reference vehicle. Experiments are conducted in a vacuum chamber that allows re-entry static pressure to be simulated. Temperatures on the top and bottom surfaces of the specimen, and the strains in the underlying structure are recorded. The experimental results are used to guide the development of a refined finite element model, which is subsequently used to simulate the interactions between the high speed external flow past the cavity that represents damage. Using this model, the relative effects of damage on the thermal protection capability and the induced thermal stresses are determined by comparing the response of the damaged configurations with the undamaged configuration. Damage increases the thermal loads and significantly reduces the radiation heat loss from the surface of the tile, resulting in elevated temperatures. Results indicate that damage can raise the maximum temperature in the tile to values that exceed its melting point.

With this survey paper, the author proposes a new ‘tao’ – a new way of understanding – of how pilots do what they do. Research into the control of purposeful action in the natural world suggests that very rapid, efficient and ‘instinctive’ techniques have evolved based on the time to close on a goal, or close a gap, τ(t), and its derivatives. Purposeful actions involve the closure of one or more physical gaps, each with its own time to close, varying with time. Maintaining a constant rate of change of τ(t) with time (< 1) during an approach will ensure a successful arresting when the gap is closed, but an animal’s strategy can be adapted to the circumstances to achieve either a hard stop (aggressive action with ṫ > 0·5), or a soft stop (gentle action with ṫ < 0·5). Synchronous coupling of two motions, x(t) and y(t), such that the times to close are coupled, τx = kτy, results in the motion gaps x(t) and y(t) being related through a power law, x = Cy1/k, and closing smoothly together; examples of such coupling in the form of pursuit tracking in the natural world abound. Research has also shown that gaps can be closed by following ‘intrinsic’ guides, or self-generated mental models of desired motion, that have particular forms; for example, constant deceleration or constant acceleration. The gathering evidence from research into animal behaviour in the natural-world forms a background for the exploration of flight control in the man-made world. The implications for control theory, flight control developments and flight handling qualities, are considered to be profound. τ-theory suggests that natural control has a particular non-linear, albeit very simple, time varying form and that pilots learn control strategy skills by developing mental models, or internalised schemata, in the form of what are described as ‘τ guides’. In this context the author presents his perspective on flight control, briefly reviewing τ-theory and providing examples from research conducted at The University of Liverpool during the period 1999-2011, including the work of several PhD students. Concepts for guidance algorithms suitable for augmented manual or autonomous control are discussed and the implications for handling qualities developments, particularly relating to flight in degraded visual conditions, are presented. Some outstanding questions pointing directions for future research are raised.

High fidelity modelling and simulation are prerequisites for ensuring confidence in decision making during aircraft design and development, including performance and handling qualities, control law developments, aircraft dynamic loads analysis, and the creation of a realistic simulation environment. The techniques of system identification provide a systematic framework for ‘enhancing’ a physics–based simulation model derived from first principles and aircraft design data. In this paper we adopt a frequency domain approach for model enhancement and fidelity improvement of a baseline FLIGHTLAB Bell 412 helicopter model developed at the University of Liverpool. Predictability tests are based on responses to multi–step control inputs. The techniques have been used to generate one, three, and six degree-of-freedom linear models, and their derivatives and predictability are compared to evaluate and augment the fidelity of the FLIGHTLAB model. The enhancement process thus involves augmenting the simulation model based on the identified parameters. The results are reported within the context of the rotorcraft simulation fidelity project, Lifting Standards, involving collaboration with the Flight Research Laboratory (NRC, Ottawa), supported with flight testing on the ASRA research helicopter.

Waverider serves as a good candidate for hypersonic vehicles. The typical waverider has sharp leading edge and no control face, which is inappropriate for practical use. This paper puts forward a method modifying the waverider, and the modification impact on the performance of waverider at hypersonic flow conditions is studied. The modification is based on blunted waverider, includes cutting the tip and introducing two control wings. The modification’s effect on aerodynamic performance is obtained and analysed through Computational Fluid Dynamics (CFD) techniques. When blunted with 2cm radius, the waverider retains its good aerodynamic performance and the heat flux at the stagnation point can be managed. Three factors of the introduced wing are argued, the fixed angle, aspect ratio and wing area. Results show that influence on the aerodynamic coefficient is slight and the vehicle retains its high lift-to-drag ratio. The main influences of the modification are the control ability and trim efficiency, which is the motivation of this work and can be adapted when designing a practical waverider.

The complex aerodynamics of rectangular underslung helicopter loads can lead to severe stability problems, but are difficult to represent in flight dynamics models. Current models for box aerodynamics are highly unsatisfactory, being entirely empirical and requiring large amounts of experimental data to generate. This paper presents a new modelling approach, which takes account of the bluff-body nature of the flow, where loads are dominated by normal pressure forces. Existing experimental data is recast in body-axes form, with α and β replaced by velocity components perpendicular and parallel to the box faces. Force and moment data for a wide range of boxes then collapse onto a set of simple generic characteristics, with features that can be related directly to the underlying flow physics. Modelling of container aerodynamics is greatly simplified, and allowance for effects of turbulence, Reynolds Number, wind tunnel interference and geometry modifications becomes possible.

The state of the art as practiced by a handful of aerofoil designers is discussed. The methods used, both theoretical and experimental, are described. Aerofoil/application design integration and expansion of the design envelope to lower and higher Reynolds numbers are illustrated by examples, including the slotted, natural-laminar-flow aerofoil.

Simple, approximate relations are developed that allow rapid, yet accurate, estimates of the principal mass characteristics of modern civil transport aircraft. The method is based upon an ‘aircraft mass hypothesis’ combined with data taken from Type Certificates and manufacturers’ information for 44 different Boeing and Airbus aircraft types and variants. This hypothesis links the masses of the various aircraft components, including the operational items, and the maximum payload mass to just two parameters; the passenger cabin floor area, as exemplified by the ‘design passenger number’ and the ratio of maximum zero fuel mass to maximum take-off mass, as exemplified by the non-dimensional ‘design range’. In this context, the ‘design range’ is defined as the maximum possible range when the aircraft is operating at its maximum zero fuel mass. This approach leads to the formulation of three basic ‘laws’ for aircraft mass. Special consideration is given to the identification and separation of those components that are fixed either by the design, or the certification process, and those that are free, within defined limits, to be chosen by the operator.

Structural dynamics is a key discipline in aircraft design and certification. The realm of structural dynamics includes problems in which structure flexibility is important, such as dynamic loads (landing, taxi, gust, turbulence...), but it also includes other areas like environmental vibration or impacts technology. This is closely related with its sister discipline Aeroelasticity.

Linearity has been the cornerstone assumption in aircraft design engineering solutions. In the past, linearity allowed to solve many structural dynamics problems that otherwise would have been unaffordable. Nowadays, the necessity of highly optimised structures, combined to an increase of computer power, has made this assumption to be reconsidered.

This paper presents a wide survey on non-linear topics in structural dynamics and the way they have been solved at EADS-CASA (Airbus military) in the past 25 years. Although the paper has been mainly focused on numerical simulation using the Finite Element Method technique, component tests and full aircraft tests are also presented.

Civil aviation has instilled new perceptions of a smaller world, creating new opportunities for trade, exchange of cultures and travelling for leisure. However, it also brought with it an unforeseen impact on the environment. Aviation currently contributes to about 3·5% of the global warming attributed from human activities. With the forecasted rate of growth, this is expected to rise to about 15% over the next 50 years. Although it is projected that the annual improvements in aircraft fuel efficiency are of the order of 1-2%, it is suggested that the current gas turbine design is fully exploited and further improvements are difficult to achieve. A new generation of aero engine core concepts that can operate at higher thermal efficiencies and lower emissions is required. One possibility of achieving higher core efficiencies is through the use of an inter-cooled (IC) core at high overall pressure ratios (OPR). The concept engine, expected to enter into service around 2020, will make use of a conventional heat exchanger (HEX) for the intercooler. This paper seeks to introduce a heat pipe heat exchanger (HPHEX) as an alternative design of the intercooler. The proposed HPHEX design takes advantage of the convenience of the geometry of miniature heat pipes to provide a reduction in pressure losses and weight when compared to conventional HEX. The HPHEX will be made of a number of stages, each stage being made of a large number of miniature heat pipes in radial configuration, that will extend from the inter-compressor duct to the bypass split, thus eliminating any ducting to and from the intercooler. This design offers up to 32% reduction in hot pressure losses, 34% reduction in cold pressure losses and over 41% reduction in weight.

A unique patented mechanism, termed ‘RotaFlap’, which can move its wings in a figure-eight shape kinematically similar to insects or hummingbirds, has been investigated through the design, construction, integration and testing of various prototypes. In this paper, the most recent prototype is presented whereby the RotaFlap kinematics is characterised to understand some of its most pertinent parameters. A host of variations have been identified and in this study a subset of these have been tested. A preliminary characterisation of the force production, especially the vertical lift coefficient, has been completed. It is concluded that this mechanism produces vertical lift coefficient values similar to insect and hummingbird flight for similar Reynolds numbers.

This paper presents a methodology that permits accounting for acoustic fatigue effects when sizing safe-life structural skin-stringer panels at the conceptual design stage of aircraft product development. The approach is based upon estimation of the maximum noise radiated from an entry-into-service year 2020 turbofan. Sonic fatigue endurance is assessed for different skin-stringer panels having different values of skin thickness, rib pitch and stringer pitch. Three different materials were considered in this study: aluminium 2024-T3 alloys (Al 2024-T3); carbon fibre-reinforced plastics (CFRP); and, glass reinforced fibre metal laminate (Hybrid Glare-3). The study resulted in CFRP having the most favourable sonic fatigue performance. In order to link economic considerations into technical decision making, the sonic endurance methods were coupled with an industry grade costing analysis tool (SEER-HTM) to examine the impact of safe-life design on the panel cost and weight. The presented methodology has been shown to be sufficiently generic in nature and robust. This will not only assist in identifying acoustic fatigue as a potential critical design scenario, but will also increase throughput during conceptual design sizing and optimisation.

In this paper, the results of computational studies on the unsteady flow features in three-dimensional empty cavities and cavities with a representative store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard Reynolds-averaged Navier-Stokes (RANS) model within the attached boundary layer and as a Large-Eddy Simulation LES sub-grid scale model in the rest of the flow (commonly known as Detached-Eddy Simulation (DES)) are used in this study. The time-mean flow study showed the presence of three-dimensional effects inside the cavities. The mean flowfield visualisation also clearly showed the presence of a pair of ‘tornado-like’ vortices in the upstream half of the cavity which merge to a single, large recirculation further downstream. Visualisation for the cavity-with-store case revealed that the mean flowfield was effectively divided into two halves with significant reduction of the spanwise flow across the cavity width. In the unsteady flow study, near-field acoustic spectra were computed for the empty cavity and cavity-with-store cases. Study of unsteady pressure spectra for the cavity-with-store case found the presence of many peaks and the corresponding mode frequencies were found to agree well with the Rossiter modes. The blockage effect of store and strut on the spanwise flow is thought to have reduced the interaction, and subsequent non-linear coupling, between the Rossiter modes. This may be the reason for the co-existence of multiple modes without the coupling among them.

Flow separation is a source of aerodynamic inefficiency, by using vortex generators flow separation can be controlled. This is of particular benefit to flows around bodies which are susceptible to separated flows, such as bodies in ground effect. Previous studies on the ability of dimples to produce vortices for flow mixing concerned heat transfer applications. Experimental measurements using Laser Doppler Anemometry (LDA) were taken in the wake of the Tyrrell026 aerofoil (Rec = 0·5 × 105) with a dimple array machined in the surface. Results for a dimple array of three rows placed forward of x/c = 0·23 with 1·5D dimple to dimple spacing, showed significant flow recovery in the wake. The velocity deficit of u/Uo,min = −0·1 recovered to u/Uo,min = 0·3 with the dimple array and the size of the wake reduced by 50%; at α = 10°, h/c = 0·313. The positive effect of the dimple array on the wing reduced as the wing was brought closer to the ground.

This work presents a computational framework for the optimisation of various aspects of rotor blades. The proposed method employs CFD combined with artificial neural networks, employed as metamodels, and optimisation methods based on genetic algorithms. To demonstrate this approach, two examples have been used, one is the optimal selection of 4- and 5-digit NACA aerofoils for rotor sections and the other is the optimisation of linear blade twist for rotors in hover. For each case, an objective function was created and the meta-model was subsequently used to evaluate this objective function during the optimisation process. The obtained results agree with real world design examples and theoretical predictions. For the selected cases, the artificial neural network was found to perform adequately though the results required a substantial amount of data for training. The genetic algorithm was found to be very effective in identifying a set of near-optimal parameters. The main CPU cost was associated with the population of the database necessary for the meta-models and this task required CFD computations based on the Reynolds-averaged Navier-Stokes equations. The framework is general enough to allow for several design or optimisation tasks to be carried out and it is based on open-source code made available by the authors.

Fuel outgassing (oxygen evolution) within aircraft fuel tanks presents a serious flammability hazard. Time constants representing oxygen transfer rate, from the fuel into a tank’s ullage, are used to model the effect of outgassing on tank flammability. These time constants are specific to a single aircraft type and flight envelope and may not accurately represent fuel outgassing behaviour for other aircraft types with differing fuel tank configurations and flight envelopes. To improve current modelling practice for more accurate flammability analysis dimensional modelling has been used to determine the rate of oxygen evolution from Jet A-1 fuel in an aircraft fuel tank. Measurements of oxygen evolution rate, made on a dimensionally similar model, have been projected to an A320 aircraft. The evolution of oxygen from the fuel was found to increase monotonically with time. Fitting the test data with an inverse-exponential function enabled oxygen release rate and its associated time constant (τ) to be determined. Dimensional modelling of aviation fuel outgassing using model fuel tanks will enable oxygen evolution rate from aviation fuel to be determined for a wide range of aircraft fuel tank configurations and environments without the need for flight testing. In turn the accuracy of flammability assessment of aircraft fuel tanks will be improved and significant cost savings made.

A nonlinear aeroelastic model capable of assessing arbitrary morphing manoeuvres and calculating the associated morphing energy requirement is presented in this paper. The aeroelastic model consists of a close coupling between a corotational beam element, accounting for geometric nonlinearities, and a Weissinger method aerodynamic model, containing the Prandtl-Glauert correction for high-subsonic Mach numbers. The morphing deformations are discretised into three distinct morphing modes; fold morphing, twist morphing, and shear morphing, because of which virtually any morphed shape can be achieved, given a proper distribution of the three modes over the wing. The proposed aeroelastic morphing framework is used to design morphing winglets, and it has been shown that morphing winglets can improve the performance of fixed winglets significantly for regional airliners.

It is generally recognised that fuel can be saved on long haul routes if non-stop flights are broken down into a number of short stages. As fuel costs rise, these savings may eventually become economically attractive to airlines. ‘Staging’ may also play a role in the reduction of aviation’s impact upon climate change. To allow an accurate estimate of the potential benefits, an analytic model has been developed from first principles, with closure provided by data from existing aircraft. The analysis captures the relevant parameters and their influence is quantified. It has been found that significant savings are only available for distances greater than about 5,500km and a stop at the halfway point is either the best, or close to the best, strategy. For the longest routes, optimal staging with existing long range aircraft can give savings of up to 12%. However, if aircraft optimised for the stage lengths are used, this may be increased to up to 28% and, if the floor area per passenger is reduced to the short haul level, a limiting value of about 45% may be possible. The aircraft design passenger number and, provided it is constant, the load factor have little, or no, effect upon the percentage savings. Maximum use of staging on all current routes longer than 5,500km could reduce the total fuel consumed by between 3% and 20%, with a consequent reduction in global fleet annual fuel burn of between 1% and 6%. However, the savings for a given route are reduced as aircraft become more efficient.