A systematic discussion of partitioning as a tool for matrix inversion is presented, together with various methods and applications which have been of help in actual computations. New concepts are introduced, among them those of super-matrix and of square partitioning. The most usual type of partitioning, that into 2x2 sub-matrices, is discussed in detail, showing the orderly arrangement of the calculations in an auxiliary matrix. Further sections deal with matrices of the continuant type, and with special types of symmetry in the arrangement of the sub-matrices. The greatest advantage of the method of partitioning for the inversion of these types (as compared with the elimination method) lies in a considerable reduction in the number of arithmetical operations.

A standard flat facet approximation for finite element analysis of general thin shells has been sought after for many years, but fundamental difficulties hindered the development of a definitive solution. Recent advances in the finite element method, however, have provided more rational resolutions of some of these difficulties than the kind of artifices which were employed formerly. This paper completes the theory of a basic triangular flat shell element which incorporates modern developments and meets practical criteria of mathematical simplicity and general applicability. The flat facet shell element is also, potentially, an appropriate basis for constructing a better curved approximation to a shell surface in order to achieve improved accuracy. Numerical results are given for a variety of shell test problems to provide comparisons with accepted benchmark solutions and to assess the available accuracy relative to other finite element formulations.

Aerodynamics is the foundation on which we build aircraft, as did the Wright Brothers. In their day, it was something of a mystery. It has become a profession in itself—a Science and an Art.

Its parent science—the mechanics of fluids—is one of the most difficult branches of the general science of mechanics, which is itself possibly not one of the easier departments of science. The simplest of our flying machines is aerodynamically excessively complex. We have always been prepared to design and build aircraft to meet extraordinarily severe conditions. There is only one yardstick by which we can expect to be judged—results. We need all our skill—and skill is art, though not the whole of it.

Equations are derived which enable the stresses around a compactly reinforced hole in an infinite sheet to be computed. The only restrictions placed on the shape of the hole are that it has at least one axis of symmetry and that the region outside it can be conformally mapped on to the region outside the unit circle by a transformation function in the form of a polynomial of any order. This admits a very wide range of holes of practical importance, including circles, ellipses, and squares, triangles and rectangles with rounded corners. Two loading cases are treated; the first corresponds to uniform tensions at infinity in directions parallel and perpendicular to the axis of symmetry of the hole, and the second to uniform shear at infinity in these directions. Superposition of these basic loading cases enables the stresses to be determined for any uniform state of stress at infinity. The equations are in an ideal form for use with a digital computer.

The problem discussed is that of the elastic local instability of a uniformly compressed thin-walled strut composed of a number of flat component plates. The strut is essentially “ open ” in cross-sectional form, while reinforcing flanges are attached to the extreme edges. An overall stability equation, based on the small deflection theory of plate bending, is derived from the conditions which must hold at the common and extreme longitudinal edges of the strut.

It is shown that the critical compression stress induces a mode of buckling which involves a whole number of sinusoidal half-waves in the longitudinal direction. Furthermore, the number of half-waves is common to all component plates of the strut. The general’ stability equation—a zero determinant of high order—lends itself to expansion in terms of 4th order minors, which may again be expressed in terms of seven basic functions. A knowledge of these functions is sufficient for the solution of any problem, however complex, within the scope of the general analysis.

Application of the basic functions to the solution of three different problems yields results which indicate the need for considerable care in the design of thin-walled struts with reinforcing flanges. In struts of this type a longer wavelength of buckling is possible than is commonly associated with local instability problems.

Eigenstructure assignment has been widely used in the past for the synthesis of flight control systems in the time domain. The method, although offering a straightforward way of determining static compensators which satisfy the specifications in terms of desirable time response characteristics, lacks the property of guaranteeing stability margins like the linear quadratic regulator (LQR) methodology. The present paper analyses the performance-robustness properties of eigenstructure assignment against the standard LQR in order to define a loop transfer recovery procedure similar to that of the LQG/LTR. Two applications are described in which helicopter flight controllers are synthesised by eigenstructure assignment and possess robustness properties comparable to those of similar quadratic regulators and yet resulting in a simpler compensator structure. The applications are chosen to correspond to two flight conditions reflecting the aim of generality of the comparison.

Parts 1 to 5 of this paper (February, September and November 1947 issues of the JOURNAL) investigated the stresses and deformations of closed tubes in which the thicknesses were governed by the t s * and t * laws. In the present part, the analysis is extended to multi-cell tubes with openings, open tubes with or without St. Venant torsional stiffness, and to tubes formed by joining elements of different cross-sections. To illustrate the theory a numerical example of the stressing of a four-boom wing consisting of seven joined elements is fully worked out. Finally, an appendix gives practical methods of dealing with tubes which do not conform to the t s * and t * laws, and of finding approximate solutions for four-boom tubes with direct stress carrying covers.

The Short brothers were pioneers in the true sense of the word. They were inspired by the vision of flight and had the driving force while still in their early twenties to build and fly their own balloons (Refs. 1, 2). Through their practical skill and thoroughness they were soon making balloons for other enthusiasts, including the Hon. C. S. Rolls, a co-founder of my Company. Horace Short, the Hon. C. S. Rolls and Griffith Brewer are seen with the Wright brothers in the Rolls-Royce Silver Ghost in 1908 (Fig. 1).

For centuries man had dreamed of flying. Kites, gliders, balloons and ornithopters were built but none achieved sustained controlled flight until the brilliant practical experimental work of the Wright brothers brought success in 1903. Some gloomy predictions of eminent academics were thus confounded.

The linear buckling of circular cylindrical shells is considered with particular attention to the cantilever shell subjected to either a pure bending moment (M) or transverse load (P)—see Fig. 1. It is believed that the conclusions reached have wider application to more general loading cases.

A unified account is presented of the various inviscid models used to represent three-dimensional vortex flows in aerodynamics; essentially those relying on vortex sheets and linevortices. Recent developments in extending the scope, accuracy, and stability of these models are described. An evaluation of their relative strengths and weaknesses suggests that the different models all have continuing roles to play. It is claimed that vortex modelling has come of age, in the sense that we can now learn about the real world from the behaviour of models, after decades of trying to make the models conform with reality.

Aviation brings great commercial and social benefits and, as the global economy develops, the demand for air transport is expected to grow. However, aviation also contributes to climate change and there is increasing international pressure to limit mean global temperature rise. Therefore, the future success of aviation is likely to depend upon the industry's ability to hold its environmental impact within politically acceptable limits. This paper describes aviation's interaction with climate and sets out, in broad terms, the challenge facing the industry. The prospects for mitigating the adverse effects by advanced technology working through aircraft design and manufacture are assessed and some potential restrictions imposed by airport infrastructure are identified. Some consideration is also given to the practicalities imposed by airline economics and the likely impact of the recent ICAO regulations, plus the proposed global-based market measures scheme for aviation carbon offset. It is argued that the environmental problem is not just about carbon dioxide emissions and that aircraft technology improvement alone is unlikely to provide a complete solution. The observation that, in current operations, the total fuel used is almost twice the minimum required suggests a need to recognise a broader ownership of the problem and broader responsibility for the solution. However, improvements in the overall system efficiency will probably need to be driven by additional regulation and the imposition of other financial measures.

The overall conclusion is that the actions currently being taken and currently being proposed are probably not sufficient in themselves to meet the challenge of climate change. However, it appears that there is more that can be done and, provided that action is taken soon, there are some grounds for optimism that aviation will still be able to meet the needs of society in the 21st century.

This paper evaluates six supersonic business jet (SSBJ) concepts in a multidisciplinary design analysis optimisation (MDAO) environment in terms of their aerodynamics and sonic boom intensities. The aerodynamic analysis and sonic boom prediction are investigated by a number of conceptual-level numerical approaches. The panel method PANAIR is integrated to perform automated aerodynamic analysis. The drag coefficient is corrected by the Harris wave drag formula and form factor method. For sonic boom prediction, the near-field pressure is predicted through the Whitham F-function method. The F-function is decomposed to the F-function due to volume and the F-function due to lift to investigate the separate effect on sonic boom. The propagation method for the near-field signature in a stratified windy atmosphere is the waveform parameter method. In this research, using the methods described and publically available data on the concepts, the supersonic drag elements and sonic boom signature due to volume distribution and lift distribution are analysed. Based on the analysis, low-boom and low-drag design principles are identified.

In demand of simpler and alternative ground flutter test, a new technique that emulates flutter on the ground has recently emerged. In this paper, an improvement of the test technique is made and verified through the experimental work. The technique utilizes general ground vibration test (GVT) devices. The key idea is to emulate the distributed unsteady aerodynamic force by using a few concentrated actuator forces; referred to as emulated flutter test (EFT) technique. The EFT module contains two main logics; namely, real-time aerodynamic equivalent force calculator and multi-input-multi-output (MIMO) force controller. The module is developed to emulate the subsonic, linear flutter on a specified target structure, which is a thin aluminum clamped-plate with aspect ratio (AR) of 2.25. In this study, doublet hybrid method (DHM) was applied to model the subsonic aerodynamic force, which restricts the application to a 2-dimensional structure. Given that, correlation of several experimental works, such as wind-tunnel flutter test, EFT using laser displacement sensor (LDS), and EFT using accelerometer, on the target structure are investigated to verify the technique. In addition to the flutter boundary, flutter mode shape and trend of aerodynamic damping effect are also presented in this work. Together with these various kinds of test results, application of more compact actuator and an accelerometer as a sensor, makes the current technique the most advanced ground flutter emulation test method.

The hovering performance and the lifting capability of tiltrotor aircraft are strongly affected by the aerodynamic interaction between wing and rotors. The tiltwing concept represents a promising technology to increase the hover performance by reducing the wing-rotor interference. The present work describes an experimental activity carried out on a ¼ scaled tiltwing aircraft half-model to achieve a detailed insight about the main issues characterising the aerodynamic interaction between wing and rotor in hover. The results of the experimental campaign, including both force measurements and Particle Image Velocimetry surveys, enabled to evaluate both the aircraft performance for different configurations of the tilting wing and to achieve a detailed insight about the flow physics of the rotor wake in the interaction with the wing. The test activity provided a comprehensive experimental database that was obtained over a not confidential aircraft configuration.

Product development, especially in aerospace, has become more and more interconnected with its operational environment. In a constant changing world, the operational environment will be subjected to changes during the life cycle of the product. The operational environment will be affected by not only technical and non-technical perturbations, but also economical, managerial and regulatory decisions, thus requiring a more global product development approach. One way to try tackling such complex and intertwined problem advocates studying the envisioned product or system in the context of system of systems (SoS) engineering. SoSs are all around us, probably in any field of engineering, ranging from integrated transport systems, public infrastructure systems to modern homes equipped with sensors and smart appliances; from cities filling with autonomous vehicle to defence systems.

Since also aerospace systems are certainly affected, this work will present a holistic approach to aerospace product development that tries spanning from needs to technology assessment. The proposed approach will be presented and analysed and key enablers and future research directions will be highlighted from an interdisciplinary point of view. Consideration of the surrounding world will require to look beyond classical engineering disciplines.

An investigation of the flow around an obstacle positioned within the wake of a rotor is described. A flow visualisation survey was performed using a smoke wand and particle image velocimetry, and surface pressure measurements on the obstacle were taken. The flow patterns were strongly dependent upon the rotor height above the ground and obstacle, and the relative position of the obstacle and rotor axis. High positive and suction pressures were measured on the obstacle surfaces, and these were unsteady in response to the passage of the vortex driven rotor wake over the surfaces. Integrated surface forces are of the order of the rotor thrust, and unsteady pressure information shows local unsteady loading of the same order as the mean loading. Rotor blade-tip vortex trajectories are responsible for the generation of these forces.

Rocket motor nozzle flow geometry is considered through its influence on the thrust vector control (TVC) performances. Extensive research is conducted using theoretical and software simulations and compared with experimental results. Cold and hot flow test equipments are used. The main objective of the research is to establish the methodology of flow geometry optimisation on the TVC hardware system. Several geometry parameters are examined in detail and their effects on the system performances are presented. The discovered effects are used as guidelines in the TVC system design process. A numerical method is presented for the determination of dynamic response time upper limit for the TVC system based on the gas flow dynamics performances.

Exergy efficiency can be used as an objective function in order to improve systems efficiency. Thus, the most efficient regions for the operation parameters can be searched easily. Exergy efficiency data of a turboprop engine’s components that have been calculated using basic engine parameters in the previous studies are modeled using cubic spline curve fitting methodology. Spline curves are on the two dimensional plane, where x axis is the input parameter and y axis is the exergy efficiency of the component. A spline curve is defined by the points subject to arbitrary selection of number and position. Initially positions of the points are located with two different methods and then in order to obtain better accuracy point positions are improved by ‘Ant colony’ and ‘Goldsection’ optimisation methods. Sum of Squares of the errors between the fitted value and data value was used as the fitness function. Least square error of 5 × 10−9 is assumed as acceptable accuracy which yields to a minimum R = 0.9998 linear correlation coefficient. In the optimisation step, independent engine variable versus calculated engine performance parameters were checked against spline fitted values. Improvement of the fitness function is observed as the number of fitting points is increased. Ant colony optimisation in engine exergy efficiency parametric modeling is a new approach in authors’ point of view.

The prediction of the future is always a relatively uncertain process. The only certain fact is that the prediction is unlikely to be wholly accurate. Even the prediction of trends following examination of past performance will be uncertain regarding the future rate of advance and may be entirely upset by new discoveries and their application. This is as true for examining the future of airframe materials as it is for prediction of economic growth, which itself significantly affects the development of materials technology in the aircraft industry. However, 100 years of powered manned flight does give a solid database from which to begin. In that period airframes have moved from wood, wire and canvas, through to riveted and stressed skin metal structures to adhesively bonded polymer composites. In each case the use of new materials is associated with a change in fabrication methods and it may be confidently anticipated that this will remain true in the future. This fact accounts for a justified conservatism in embracing new materials, not simply because of the need to develop experience and confidence in them, but also because of the costs associated with new constructional methods entailed in their application. It also, in part, accounts for the generally slower pace of application of new materials relative to what is initially predicted: the other powerful brake being the state of the economy and the market for new aircraft at any particular time. The early prediction of the demise of aluminium and its replacement by polymer composites made in the 1980s being a case in point, while the failure of alloys containing lithium to replace conventional aluminium alloys had more to do with cost and decreasing fuel prices than any alloy development problems. It can, however, be expected that, as in the twentieth century, military aircraft will exploit larger mass fractions of advanced materials and at earlier dates than civil transport aircraft, given their very different operational requirements and much shorter design lives. The likely advent of unmanned combat aircraft may well accentuate this difference.

A review is given of some recent research, mainly at low speeds, into the development of dynamic lift. Sudden movement of aerodynamic surfaces can generate dynamic lift due to the transient development of separated flow. These dynamic effects are large and well established for aerofoils. They are considered likely to be small for highly swept wings and negligible for slender wings, but there is little experimental evidence to support this inference. The dynamic lift might be increased if conventional sinusoidal motions can be replaced by appropriate periodic saw-tooth motions.

The control of large-scale flow separations by rapid movements of aerodynamic surfaces requires further investigation to resolve some of the controversial issues raised in the review.