Two numerical methods are presented for the computation of steady and unsteady Euler flows. These are applied to steady and unsteady flows about the NACA 0012 aerofoil, using structured grids generated by the transfinite interpolation technique. An explicit central-difference scheme is produced based on the cell-vertex method of Ni modified by Hall. The method is second-order accurate in time and space, and with flow quantities stored at boundaries the boundary conditions are simple to apply. This is a definite advantage over the cell-centred approach of Jameson, where extrapolation of the flow quantities is required at the boundaries, making unsteady boundary conditions difficult to apply. An explicit upwind-biased scheme is also produced, based on the flux-vector splitting of van Leer. The method adopts a three stage Runge-Kutta time-stepping scheme and a high-order spatial discretisation which is formally third-order accurate for one-dimensional calculations. The upwind scheme is shown to be slightly more accurate than the central-difference scheme for steady aerofoil flows, but it is not clear which is the more accurate for unsteady aerofoil flows. However, the central-difference scheme requires less than half the CPU time of the upwind-difference scheme, and hence is attractive, especially when considering three-dimensional flows. The transfinite interpolation technique is ideal for generating moving structured grids due to its simplicity, and grid speeds are available algebraically by the same interpolation as grid points. The method is also ideal for use in a multi-block approach.

A method has been given by Klitchieff for analysis of grillages of intersecting beams under lateral loading. Klitchieff's solution was in the form of infinite Fourier series and the expressions for bending moments converged approximately as Σ n–2, making numerical computation difficult. This paper shows that, for grillages in which one set of beams are evenly spaced, Klitchieff’s solution can be adapted to give finite series for deflections arid bending moments at the intersections of the beams. The number of terms in the series is not greater than the number of beams in the equally spaced set (referred to in this paper as set “ A ”). A numerical example is given and an accurate solution is obtained with appreciably less computation than other known methods would entail.

The natural frequencies and mode shapes of vibration of cantilever aerofoil cross-section blades of pre-twist angle in the range 0 to 90 degrees are obtained. The beams are 152·4 mm long and the width / thickness ratio is such that they may be regarded as slender. Theoretical frequency ratios and mode shapes of vibration, neglecting shear and rotary inertia effects, are obtained for two sets of beams, one with clockwise pre-twist relative to the root cross-section and the other with anti-clockwise pre-twist. The effect of variation in the value of the centre-of-flexure coordinates upon the natural frequency ratios and mode shapes of vibration is investigated. The theoretical results are compared to corresponding experimental results.

Experiments were carried out on jets issuing from circular nozzles with grooved exits and the results compared with those of the plain nozzle. The plain nozzle had an exit diameter of 10mm. Because of the introduction of semi-circular grooves at the exit, the effective or equivalent diameter of the grooved nozzles was 10·44mm. The groove lengths were varied as 3, 5 and 8mm. The nozzles were operated at fully expanded sonic and underexpanded exit conditions. The corresponding fully expanded Mach numbers were 1·0 and 1·41. The shock cell structure of the underexpanded jets from grooved nozzles appeared to be weaker than that of the plain nozzle, as indicated by lesser amplitudes of the cyclic variation of the Pitot pressure. The iso-Mach contours indicate that the jet spread along the grooved plane is significantly higher than that along the ungrooved plane. Off-centre peaks were observed in the mean pressure profile of underexpanded jets from grooved nozzles. They were probably due to the streamwise vortices shed from the grooves.

This paper presents infra-red signature data for a small-scale, low pressure ratio turbojet engine typical of that used in unmanned air vehicle applications. The aim of the study was to test a number of different convergent nozzle designs concentrating on those with trailing edge modifications. The engine used in the tests has a single stage centrifugal compressor and radial inflow turbine and is designed to produce approximately 150N of thrust at 103,500rpm using liquid propane fuel. The test rig consisted of a calibrated thrust stand whilst the engine was controlled through an electronic engine control unit and laptop PC. The jet plume was visualised using an infra-red spectroradiometer which yielded qualitative data across the infra-red spectrum. Simultaneous measurements were also made of the engine thrust. A Pitot probe was used to take pressure readings across different sections of the exhaust flow. Analysis of the infrared signature of the engine exhaust plume and any thrust penalty yielded a performance comparison for each of the nozzles tested. Correlation of engine thrust with engine rpm showed that, within the accuracy of the measurements, there was no significant thrust penalty associated with the notched nozzles. Infra-red imagery of the plain and 60° notched nozzles indicated that the latter reduced the length of the hottest part of the exhaust plume by approximately 33%. The spectroradiometer data shows a significant reduction in spectral radiance for the CO2 wavelength of approximately 4·3µm when the notched nozzles are used. The 60° notched nozzle appeared to perform best in reducing the spectral radiance at this wavelength. Centreline total pressure measurements in the exhaust plume correlated well with the infra-red imagery in that a potential core length reduction of up to 30% could be achieved using the 60° notched nozzle. Total pressure contours recorded 20mm (0·43D) downstream of the nozzle exit plane suggest that the notched nozzles are promoting increased mixing through radial spreading of the jet possibly associated with increased streamwise vorticity (although the latter could not be confirmed). There were also signs that the jet plumes being investigated were swirling.

The development of a parametric-based indirect aircraft structural usage monitoring system using artificial neural networks is described. Flight parametric data, captured during Operational Loads Measurement have been used to predict strains or stresses at key structural locations for several military aircraft types, using mapping relationships determined by artificial neural networks. A framework for the development of a neural network-based structural usage monitor is discussed and the basic architecture of the multilayer perceptron artificial neural network is described. Additionally, results from case studies are presented. It is concluded that this technology could provide the basis for accurate, cost-effective structural usage monitoring systems across the range of military aircraft types and roles.

The theory of modal control is concerned with the design of control loops for systems with governing equations which can be adequately approximated by linear vector-matrix equations of the form

where x is the system state vector, y is the control vector, A is the matrix of the uncontrolled system, and B is the control matrix.

To improve the crashworthiness of civil aircraft, the design concept of energy absorption structure for civil aircraft is investigated. Two typical different design principles could be identified. The first category includes Helicopter and Light fixed-wing Aircraft (HLA), and Transport, Mid-size and Commuter type Aircraft (TMCA) are classified into the second group. Frame, strut and bottom structure are the three kinds of energy absorption structure for TMCA. The strut layout of conventional civil aircraft is studied and some energy absorption devices are adopted. High efficiency energy absorption structures such as the foam and sine-wave beam are employed as the bottom structure for both of HLA and LMCA. The finite element method is used to analyse and design energy absorption structure in aircraft crashworthiness problem. Results show that the crashworthiness of civil aircraft could be largely improved by using proper strut layout and excellent energy absorption device. The stiffness combination of frame and strut should be considered to get better global aircraft deformation. Supporting platform and failure model are the two core problems of bottom energy absorption structure design. Foam and sine-wave beam under the lifted frame could improve the crashworthiness of civil aircraft.

The current understanding of the aerodynamics of birds in formation flights is mostly based on field observations. The interpretation of these observations is usually made using simplified aerodynamic models. Here, we investigate the aerodynamic aspects of formation flights. We use a potential flow solver based on the unsteady vortex lattice method (UVLM) to simulate the flow over flapping wings flying in grouping arrangements and in proximity of each other. UVLM has the capability to capture unsteady effects associated with the wake. We demonstrate the importance of properly capturing these effects to assess aerodynamic performance of flapping wings in formation flight. Simulations show that flying in line formation at adequate spacing enables significant increase in the lift and thrust and reduces power consumption. This is mainly due to the interaction between the trailing birds and the previously-shed wake vorticity from the leading bird. Moreover, enlarging the group of birds flying in formation further improves the aerodynamic performance for each bird in the flock. Therefore, birds get significant benefit of such organised patterns to minimise power consumption while traveling over long distances without stop and feeding. This justifies formation flight as being beneficial for bird evolution without regard to potential social benefits, such as, visual and communication factors for group protection and predator evasion.

The number of unmanned aerial vehicles (UAVs, also known as drones) has increased dramatically in the airspace worldwide for tasks such as surveillance, reconnaissance, shipping and delivery. However, a small number of them, acting maliciously, can raise many security risks. Recent Artificial Intelligence (AI) capabilities for object detection can be very useful for the identification and classification of drones flying in the airspace and, in particular, are a good solution against malicious drones. A number of counter-drone solutions are being developed, but the cost of drone detection ground systems can also be very high, depending on the number of sensors deployed and powerful fusion algorithms. We propose a low-cost counter-drone solution composed uniquely by a guard-drone that should be able to detect, locate and eliminate any malicious drone. In this paper, a state-of-the-art object detection algorithm is used to train the system to detect drones. Three existing object detection models are improved by transfer learning and tested for real-time drone detection. Training is done with a new dataset of drone images, constructed automatically from a very realistic flight simulator. While flying, the guard-drone captures random images of the area, while at the same time, a malicious drone is flying too. The drone images are auto-labelled using the location and attitude information available in the simulator for both drones. The world coordinates for the malicious drone position must then be projected into image pixel coordinates. The training and test results show a minimum accuracy improvement of 22% with respect to state-of-the-art object detection models, representing promising results that enable a step towards the construction of a fully autonomous counter-drone system.

Current state-of-the-art trajectory prediction tools typically model aircraft as three-dimensional point-masses, and make a number of simplifying assumptions about the actual and anticipated dynamics states of the aircraft. They are typically based on predefined settings obtained from existing databases such as Eurocontrol’s Bada rather than real-time information, including on the environment, available onboard the aircraft. This significantly limits trajectory prediction performance. This paper proposes a high-accuracy four-dimensional trajectory prediction model for use onboard civil aircraft, as well as by ground-based systems, which addresses these limitations. It is designed for strategic traffic capacity optimisation and conflict-detection and resolution over time-horizons covering the entire duration of a flight. The model incorporates a number of features including a novel flight-control-system and an enhanced flight-script that incorporates new taxonomy and content thereby enabling better definition of aircraft intent. The accuracy of the model is characterised using operational data acquired during a real flight trial. Results show that the performance of the proposed model is significantly better than the current models. Its accuracy is better than the required navigation performance for departure, en route and Non-Precision-Approach phases of flight.

This is a discussion of the various types of flow which may occur on thin swept wings when the air stream is not attached to the wing surface everywhere. In particular, the behaviour of vortex sheets which arise from such mixed flows is examined.

The aerodynamics of insect-like flapping are dominated by the production of a large, stable, and lift-enhancing leading-edge vortex (LEV) above the wing. In this paper the phenomenology behind the LEV is explored, the reasons for its stability are investigated, and the effects on the LEV of changing Reynolds number or angle-of-attack are studied. A predominantly-computational method has been used, validated against both existing and new experimental data. It is concluded that the LEV is stable over the entire range of Reynolds numbers investigated here and that changes in angle-of-attack do not affect the LEV’s stability. The primary motivation of the current work is to ascertain whether insect-like flapping can be successfully ‘scaled up’ to produce a flapping-wing micro air vehicle (FMAV) and the results presented here suggest that this should be the case.

This paper describes the development of a simple theory of the longitudinal static stability of the hang-glider. The classical theory, as developed for the conventional aeroplane, is modified to accommodate the particular features of the hang-glider. When the appropriate assumptions are made, the theory provides simple insight into the controls fixed and controls free stability and control characteristics of the hang-glider. The validity of the theoretical models is successfully demonstrated by application to a typical fifth generation hang-glider wing for which good quality aerodynamic data were available.

The interesting article by Archer, Sapuppo and Betteridge leads to the problem of determining the optimum lift distribution along the wing during flapping motion. Adopting the assumptions made in Ref. 1, the problem may be reduced to one of minimising the induced drag for a specified, periodically varying, bending moment at the wing root. The wing-root bending moment should be of primary importance to a bird or, for that matter, to a mechanical flapping-machine, since it is at this point that most of the flapping energy is introduced.

During the past two decades, with the advancement of avionics, control systems, design, product methods, and communication systems, UAVs have gained more interest from both civil and military customers. Hence, more researchers have dedicated their time to developing new applications for drones and improving their performance. In this study, a literature review on drone applications is conducted. It is explained that they can be more effective and beneficial when merged with preexisting systems, and thus making a system of systems. Further, we have classified UAV applications more comprehensively. This classification can be very useful for providing insights when designing new UAVs. Finally, previous works are discussed thoroughly and diagrams are developed to show the research focus in this field. These statistical diagrams can also be used as a gap analysis tool.

The work described here concentrates on under-expanded, axisym-metric turbulent jets issuing into quiescent conditions. Under-expanded turbulent jets are applicable to most aircraft propulsion applications that use convergent nozzles. Experimental studies used laser doppler velocimetry (LDV) and pitot probe measurements along the jet centreline. These measurements were made for two nozzle pressure ratios (2·5 and 4·0) and at various streamwise positions up to 10 nozzle diameters downstream of the nozzle exit plane. A computational fluid dynamics (CFD) model was developed using the Fluent code and utilised the RNG K-ε two-equation turbulence model. A mesh resolution of approximately one hundredth of nozzle exit diameter was found to be sufficient to establish a mesh independent solution.

Comparison of the jet centreline axial velocity (LDV data) and pressure ratio (pitot probe data) showed good agreement with the CFD model. The correct number of shock cells had been predicted and the shock strength agreed well between the experiments and numerical model. The CFD model was, however, found to over-predict the shock cell length resulting in a longer supersonic core. There was some evidence, based on analysis of the LDV measurements that indicates the presence of swirl and jet unsteadiness, which could contribute to a shortening of the shock cell length. These effects were not modelled in the CFD. Correlation between the LDV and pitot probe measurements was generally good, however, there was some evidence that probe interference may have caused the premature decay of the jet. Overall, this work has indicated the good agreement between a CFD simulation using the RNG k-ε turbulence model and experimental data when applied to the prediction of the flowfield generated by under-expanded turbulent jets. The suitability of the LDV technique to jet flows with velocities up to 500ms-1 has also been demonstrated.

The aircraft industry, as a whole, is striving to limit its impact on the environment. Improved engine design and operation may offer a reduction in emissions of a few percent. More efficient air traffic control (ATC) may offer a limited reduction in overall fuel burn. Improvements in aerodynamic design and materials available (e.g. on A350XWB, B787) might achieve a few percent increases in efficiencies. The use of alternative fuels is some way off. The ACARE objectives present a stiff challenge.

Our recent studies have shown that air-to-air-refuelling (AAR), well established in military circles, introduced to civil aircraft operations would provide fuel savings of the order of 30% – 40%. AAR will allow smaller (3,000nm range), more efficient (greener) aircraft, operating from shorter runways, to fulfil long-range route requirements. In addition, the ‘safety-net’ afforded by the availability of AAR will enable a host of hitherto borderline technologies to be accepted and utilised in future aircraft designs. Laminar flow will provide fuel savings and increased efficiency in its own right provided it is enabled within a civil AAR environment. Similarly, supersonic transport becomes an acceptable economic option.

Characteristic equations are derived for thin circular shells, based on various approximations to the linear elastic theory of small deformations. By representing the deformation in a Fourier series in the circumferential direction, the roots of these equations are computed for a range of the significant parameters and compared.

Jets issuing from rectangular slots cut in thin plates exhibit some unusual features, including unequal spreading rates in the spanwise and transverse directions, the appearance of velocity peaks near the “ends” of the jet and changing rates of centreline velocity decay in the downstream direction. This study examines the effects of aspect ratio on such flows. The flow field has been investigated using both total head tubes and hot wire anemometry. The results are presented in the form of three-dimensional plots of total pressure and contour maps of constant velocity, streamwise turbulence intensity and the Reynolds shear stresses. The decay of mean velocity and stream-wise turbulence intensity along the centreline are presented. The rates of spanwise spreading and the location of the velocity peaks at various downstream stations are discussed. If the aspect ratio is small enough, spanwise peaks in the mean velocity distribution are suppressed.