A new parameter estimation method based upon neural network is proposed. The method proposed here uses feed forward neural networks to establish a neural model that could be used to predict subsequent time histories given the suitable measured initial conditions. The proposed neural model would not represent a generic flight dynamic model. The neural model in this case develops point to point fitting of the input and the output data. Thus, it could at best be referred to as flight dynamic model in restricted sense. Gauss-Newton method is then used to obtain optimal values of the aerodynamic parameters by minimising a suitable defined error cost function. The method has been validated using longitudinal and lateral-directional flight data of various test aircraft. The results thus obtained were compared with those obtained through wind tunnel test, or those obtained using Maximum likelihood and/or Filter error methods. Unlike, most of the parameter estimation methods, the proposed method does not require a prior description of the model. It also bypasses the requirement of solving equations of motion. This feature of the proposed method may have special significance in handling flight data of an unstable aircraft.

Supersonic cavity flows driven by a thick shear layer at Mach 1·5 and 2·5 are studied by solving the two-dimensional unsteady compressible Navier-Stokes equations in terms of mass-averaged variables. The length to depth ratio of the rectangular cavity is three. The numerical scheme used is the finite-difference algorithm by Brailovskaya. A two-layer eddy-viscosity turbulence model is used. The results are compared with experimental data. The computations show the self-sustained oscillations at Mach 1·5 and 2·5. The continuous formation and downstream shedding of leading edge vortices is demonstrated. The oscillatory modes are correctly predicted. The first mode is attributed to a large unsteady trailing edge vortex moving in the transverse direction. Based on the analysis, it is considered that the oscillation in the length to depth ratio three cavity is a longitudinal one and is controlled by a fluid dynamic mechanism rather than a purely acoustic one.

Implicit large eddy simulations (ILES) of two different Royal Navy ships have been conducted as part of the UK Ship/Air Interface Frame-work project using a recently developed very high order accuracy numerical method. Time-accurate CFD data for fourteen flow angles was produced to incorporate into flight simulators for definition of safe helicopter operating limits (SHOLs). This paper discusses the flow phenomenology for the different wind directions and where possible reports on the validation of the ILES results for mean and fluctuating velocity components and spectra against experimental data.

2D numerical simulations of flows generated by a synthetic jet actuator with a circular orifice were conducted at two different diaphragm displacement settings, one representing a typical laminar case and the other a fully turbulent case. The flow in the cavity was included in the computation in order to provide more accurate predictions. A velocity boundary condition was applied at the neutral position of the diaphragm to account for its temporal deformation. Comparisons were made between the computational results and existing PIV and hot-wire data in terms of the time sequence of the velocity vector field, velocity variations in space and with time. It is found that computational results for the laminar case agree well with the experimental data. Four turbulent models were tested for the fully turbulent case. It was found that the predictions using the RNG κ-ε and Standard k-ε models were reasonably close to the experimental data. This initial study has produced some encouraging evidence for the capacity of FLUENT in simulating the key features of synthetic jets.

The present paper seeks to apply the ideas of discretisation to time dependent phenomena. As a suitable variational statement we may use Hamilton's principle. In practise this means that the time is discretised into a set of finite elements which are taken to be the same for all structural elements. A finite element in time consists simply of a fixed time interval. In our present discussion we detail in particular the case when at the beginning and end of the time interval the generalised displacements and velocities are given. For dynamic problems this is the minimum of information required, but the technique may easily be extended to account for additional “timewise degrees of freedoms”. Introducing an appropriate interpolation procedure we may obtain the displacement and velocity at any instant of time. It is then possible to carry out in the variational statement the time integration explicitly and to obtain hence a system of linear equations. The method is extremely simple, since the time interpolation of all structural freedoms of an element in space is the same. We also demonstrate that the general case of a multi-degree of freedoms system can be made to depend on the matrices which describe the unidimensional motion of a mass point.

It is shown that the rotational stiffness of a crossed flexure pivot varies considerably when subjected to an applied force. The type of variation can be radically changed simply by moving the point at which the strips cross. The relation between torque and rotation for a given applied force is not exactly linear and the extent of the non-linearity is determined by taking into account the small movements of the centre of rotation of the pivot. Finally, for design purposes, an analysis of the maximum stresses in the strips is given.

Crossed flexure pivots, of the type shown in Fig. 1, are extensively used in aeronautical research equipment to replace knife edges or ball bearings. Perhaps the most frequent use is for the fulcrum of the balance arm in a wind tunnel balance. Here, a null-point method of reading is almost invariably used, so that the prime considerations influencing the design of a flexure pivot for such a purpose are (a) that the applied loads should not cause instability of the pivot, and (b) that the rotational stiffness should be small enough to give adequate sensitivity.

Throughout the animal kingdom powered flight is a surprisingly common attribute and whenever it occurs both the sustenation and the propulsion are provided by the same structural and aerodynamic mechanism. There is, in fact, but a single aerodynamic reaction which is divided, for convenience, into thrust and lift. In earlier times this convention was presumably not recognised, for the ornithopter appears to have formed for some centuries the principal technical basis of man's aspiration to heavier-than-air flight. Of the exceptions, Leonardo da Vinci's helicopter is now, of course, an accepted vehicle, but this lecture is concerned mainly with fixed-wing aircraft for which it is significant that success came only with the aeroplane, or, as Lachmann has recently put it, with the powered glider.

The present experiment describes the behaviour of a turbulent boundary layer on a concave wall. At the onset of curvature there appears a fairly coherent wavelike transverse profile of mean velocity. This disturbance might be interpreted as a kind of large scale Taylor-Görtler type instability superimposed on a conventional turbulent boundary layer; further downstream the coherence degenerates as the turbulence level increases. Boundary-layer profile measurements were made at positions of maxima and minima of transverse profiles of (U-component) mean velocity. The boundary layer at the minima positions is found to be twice as thick as that at the maxima positions. Also, turbulent intensities inside the boundary layer are substantially increased as a result of the concave curvature of the surface.

The RemoveDEBRIS mission has been the first mission to successfully demonstrate, in-orbit, a series of technologies that can be used for the active removal of space debris. The mission started late in 2014 and was sponsored by a grant from the EC that saw a consortium led by the Surrey Space Centre to develop the mission, from concept to in-orbit demonstrations, that terminated in March 2019. Technologies for the capture of large space debris, like a net and a harpoon, have been successfully tested together with hardware and software to retrieve data on non-cooperative target debris kinematics from observations carried out with on board cameras. The final demonstration consisted of the deployment of a drag-sail to increase the drag of the satellite to accelerate its demise.

The imperfection sensitivity of cylindrical panels under compression loading is shown to be not only reduced but effectively eliminated using stiffness tailoring techniques. Shells are designed with variable angle-tow (VAT) laminae, giving their laminates variable-stiffness properties over the surface co-ordinates. By employing an asymptotic model of the non-linear shell behaviour and a genetic algorithm, the post-buckling stability was maximised with respect to the VAT design variables. Results for optimised straight-fibre and VAT shells are presented in comparison with quasi-isotropic designs. In the straight-fibre case, small improvements in the post-buckling stability are shown to be possible but at the expense of the buckling load. In the VAT case, on the other hand, considerable improvements in the post-buckling stability are obtained and drops in axial stiffness and load associated with buckling are reduced to negligible levels. The improvements are shown to be a result of a benign membrane stress distribution prior to buckling and a localisation of the buckling mode. The asymptotic results are compared with non-linear finite-element analyses and are found to be in good agreement. Potential future multi-objective optimisation studies are discussed.

A closed-form expression is derived which gives an approximate solution to the lift generated on a two-dimensional thin aerofoil in incompressible flow with a normal velocity component of the form exp [i (ωt–xx+yy)]. The inaccuracy of the solution when compared with other published work is compensated by the simplicity of the final expression, particularly if the result is required for the calculation of the sound power radiated by an aerofoil in a turbulent flow.

The paper deals with the free transverse vibration and stability analysis of circular cylindrical composite panels. The panels are assumed to be composed of an arbitrary sequence of 0° and 90° layers. The non-dimensional vibration and buckling parameters are computed for simply-supported panels consisting of antisymmetric crossply graphite-epoxy laminates. The influence of the coupling between bending and extension, shear deformation, the panel curvature, and the aspect ratio are then discussed.

Some new solutions for steady incompressible laminar boundary layer flow, obtained by Gortler, have been used to test the accuracy of two methods which are commonly used to predict separation. A modification of Stratford's criterion for separation is given in this paper and is probably the most accurate and the simplest of all methods at present in use. Modified numerical functions are also given for Thwaites's method of predicting the main characteristics of the boundary layer over the whole surface, which improve the accuracy of the method.

The post-buckling behaviour of flat square plates loaded along two opposite straight edges is analysed using the von Kármán equations, trigonometric series and Galerkin’s method. The unloaded edges are considered to be either free to distort in the plane of the plate or maintained straight but allowed to move bodily; all edges are simply-supported in the out-of-plane direction. The non-linear algebraic equations are solved approximately using a McLaurin’s series expansion technique which facilitates the development of explicit expressions for ultimate load, end shortening and stiffness. The effects of initial geometric imperfections are also studied and it is shown that the results for ultimate load prediction and end shortening are in good agreement with test results.

This paper explains how flight simulation has made a major contribution to flight safety over the last thirty years to become critical to the operation of civil airlines and military organisations. It not only provides effective training, but for many flight training organisations has reduced the cost of flight training significantly. The paper outlines the increasing role of flight simulation covering flight training and research and development of aircraft and systems. The contribution of the flight simulation industry to the UK economy, in terms of both employment and revenue, is highlighted.

The paper focuses on advances in the underpinning technologies of flight simulation, including mathematical modelling, real-time computation, motion actuation, visual image generation systems and projection systems.

The paper also summarises the broadening roles of flight simulation; from part-task trainers to zero flight-time training in civil aviation; in military aviation, extending to combat domes and mission rehearsal; in defence procurement, where synthetic environments are used widely in evaluation studies prior to major project commitments; in aircraft development, providing powerful design tools to enable system designers to evaluate prototype systems.

As a result of the acceptance of flight simulation in flight training, the use of simulators has been standardised throughout the world, with formal programmes of simulator qualification. These regulations, drawn up with the help of the RAeS Flight Simulation Group, ensure consistency for operators, regulators and manufacturers; the status of these regulations is outlined.

The paper concludes by reviewing the lessons learnt by the flight simulation industry over the last thirty years and summaries the potential areas of growth, which will lead to simulation becoming widespread throughout many industries, in addition to the aerospace industry.

The results of extensive measurements which are presented here show the presence of secondary flow in the laminar corner boundary layer which is opposite in rotation sense to that found in the turbulent corner flow. This secondary flow is associated with progressive changes of the form of the velocity profiles. These changes become marked prior to transition and may be linked with the transition process. The laminar corner flow separates readily under the influence of an adverse streamwise pressure gradient.

The elastic instability of a complete spherical shell under uniform external pressure is studied experimentally and theoretically. The premature snapping of a thin elastic shell, made of polyvinyl chloride, is seen to be classical in nature. The experimental maximum pressure and pre-snapping bending deformation are correlated with the theoretical behaviour of an initially imperfect shell. The large deflection behaviour of a perfect shell is assessed experimentally, and the stable post-buckling states are observed to be rotationally symmetric. A fairly precise theoretical analysis of these states is performed, the use of a high-speed digital computer allowing a considerable advance over previous treatments. The experimental and theoretical post-buckling curves are in good agreement, yielding the first detailed correlation of post-snapping equilibrium states in the field of shell instability.

Separated and vortical flows are dominant over various unmanned air vehicles (UAVs). In this article, issues and challenges of vortical flows for future UAVs are reviewed. These include shear layer instabilities, vortex breakdown and wing stall, vortex interactions, nonslender vortices, multiple vortices, and manoeuvring wing vortices. There are also issues relating to vortical flows in certain flow/structure interactions, as well as in aerodynamics/propulsion interactions. Separated and vortical flows are even more dominant at low Reynolds number flows. The main features of vortical flows, unsteady aerodynamics, and propulsion related vortical flow isssues relevant to mini- and micro air vehicles, are discussed.

Based on earlier theories of mechanical, electrical and magnetic relaxation phenomena, the paper discusses a simple mathematical model representing qualitatively the basic characteristics of “internal” damping in solid materials. The model is assessed with respect to variation with frequency of stiffness and loss factor at simple harmonic oscillations, and is applied to oscillatory systems with discrete parameters and to continua.

The problem considered is the buckling of a rectangular plate, tapered in thickness in a direction parallel to two sides, and uniformly compressed in that direction. Curves are presented showing the variation of buckling stress coefficient with the side ratio and the amount of taper, for each of two types of thickness variation, namely exponential and linear, and for each of two sets of boundary conditions, namely all edges simply-supported, and ends clamped and sides simply-supported. It is shown that, unlike the case of a uniform plate, there are no discontinuous changes of buckling mode.