bluuebunny/crossref_metadata_2025 huggingface dataset:
Transition and separation control in the leading edge region
Authors: Wong P. W. C. , Maina M. , Cobbin A. M.
Published: July 2016

This paper describes an investigation of methods of controlling transition and separation in the leading edge region of military aircraft wings. For wings with the high leading edge sweep relevant to some military aircraft, if attachment line contamination can be prevented then transition is predominantly caused by crossflow instability close to the leading edge. The use of surface suction or cooling for suppressing these instabilities in order to delay transition, has been investigated in a parametric study. The placing of a short suction panel close to the leading edge has been found to be an effective means of controlling instability. Conversely, the level of cooling required to suppress crossflow instability may be too high for practical aircraft applications. The use of suction for preventing laminar separation for pressure distributions with a leading edge suction peak has also been included in the parametric study. The suction quantity required is strongly dependent on the peak height. The suction quantity that can be achieved in practice will limit the maximum peak height that can be attained without laminar separation. An investigation of leading edge stall and control has also been carried out. The analysis suggests that it is important to be able to identify whether the stall is due to laminar bubble bursting or turbulent re-separation, since different methods of controlling the stall may be required.
Non-inertial multiblock Navier-Stokes calculation for hovering rotor flowfields using relative velocity approach
Authors: Zhong B. , Qin N.
Published: July 2016

A three dimensional Navier-Stokes solver is presented for calculating the hovering rotor flowfield using Osher's approximate Riemann solver. The Navier-Stokes equations are recast in the attached blade relative system using relative flow velocities as variables. Multiblock techniques are used to obtain a structured grid around the blade. A modified MUSCL scheme is proposed to alleviate the inaccuracy in the discretisation of the relative variable formulation. The calculations are performed for a two-bladed model rotor on C-H, O-O and C-H cylindrical grid topologies respectively. Computational solutions show reasonably good agreement with the experimental data for different lifting cases. The difficulty and suitability of different grid topologies for capturing the tip vortex is illustrated. The differences between Euler and Navier-Stokes solutions and between wake modelling and wake capturing approaches are also revealed. The results indicate that the relative velocity approach can give reasonable results for hovering rotor flowfields if due care is taken in minimising possible numerical errors.
The accuracy of internal wind tunnel balances for wind tunnel force measurements, the problem of definition and verification
Authors: Ewald B.
Published: July 2016

For the definition of the acccuracy of an internal strain gauge balance no general agreement exists. So it is difficult or even impossible, to compare balances from different manufacturers or balances used at different places.

Since most wind tunnel tests at least in the aeronautical field are done on a reference basis i.e. the results are compared with earlier results achieved with a more or less different configuration, repeatability is at least as important as absolute accuracy or even more important. So also repeatability, which in a physical sense is quite different from accuracy, must be defined and proven for each balance.

With the examples of several balances manufactured for the DNW (Deutsch-Niederländischer Windkanal) and ETW (European transonic tunnel) accuracy and repeatability definitions are discussed.

A proposal for a generally binding definition of accuracy and repeatability is given.
Visualisation of flow separation with shear-sensitive liquid crystals
Authors: O’Brien S. , Zhong S.
Published: July 2016

Coatings of chiral-nematic liquid crystals are known to change colour under different levels of surface shear stress. In this study, the liquid crystal coating was used to provide information about flow separation and reattachment on a backward facing step and a delta wing respectively. The tests were carried out at a free-stream velocity of 25ms-1. The Reynolds number based on the step height of the backward facing step is 16,000 and based on the chord length of the delta wing is 270,000. The study revealed that the locations of boundary-layer separation and reattachment can be identified from spatial variations in the surface colour. Agreement was obtained between the results acquired from liquid crystal and surface oil flow technique. The variation in hue was used to improve the determination on the location of flow characteristics. This study showed that the liquid crystal coating is an effective method for the qualitative study of separated flow characteristics.
An all weather millimetre wave imaging radar for UAVs
Authors: Britton A. , Joynson D.
Published: July 2016

In this paper we describe a new 35GHz air-borne radar developed jointly by DERA and Alenia Marconi Systems. This radar is a functional prototype of a more highly configured imaging radar which is designed to meet the needs for all-weather imaging both for future unmanned air vehicles (UAV) and for seekers in the next generation of surface attack weapons.

The radar achieves high range resolution through a combination of pseudo-random phase coding and frequency agility. This is then augmented by synthetic aperture techniques to allow forward looking high resolution 2D imagery to be obtained. The radar has been installed on a fixed wing aircraft and has been used to gather fixed and relocatable target signature data under tactically representative conditions.

The paper begins with a discussion of the requirements for such a radar and then a review of its design and performance is presented. This is followed by examples of target signatures gathered during the initial system flights and a discussion on their exploitation for surveillance, target acquisition and tracking.
Active control of fan noise from high-bypass ratio aeroengines: a numerical study
Authors: Traub P. , Kennepohl F. , Heinig K.
Published: July 2016

Under the national research project, dubbed Turbotech II, in which MTU Aero Engines, DLR Institute of Propulsion Technology and EADS Corporate Research Centre participate, active noise control (ANC) has been tested with a scale model fan of one metre diameter for a high bypass ratio aeroengine. MTU’s task in this project was to develop a computer code to predict the sound field in the intake duct of the fan-rig by the use of active control. The primary objective of the numerical study was to specify numbers of actuators (loudspeakers) and error sensors (microphones) and their positioning to control the harmonic sound power, radiated upstream to the duct intake. The computer model is based on the geometry of an annular or circular duct of rigid walls and infinite length, containing a subsonic axial uniform flow. The modal amplitudes of the primary sound field are input data. The actuators are modelled by acoustic monopoles. Two control algorithms have been used for achieving the control objective. The first consists simply in the reduction of the in-duct mean squared pressures. The second, so called modal control, is designed to cancel dominant modes selectively. Numerical results are presented using a typical configuration of wall mounted actuators and error sensors in the form of a number of rings uniformly distributed along the length of the intake duct. Guidelines have also been derived to design a favourable configuration of actuators and sensors. The findings of the numerical study are compared with the results of the ANC tests.
Wing aerodynamics and the science of compromise
Authors: Jupp J.
Published: July 2016

From Lanchester to the A380; from the era of the great pioneers to the integrated engineering teams and sophisticated analyses required to develop todays airliner. The ‘art’ of Aerodynamics has progressed a long, long way in the intervening century, but even with todays computational power it is still relevant to understand the basics and the early theories as developed by Lanchester and his contemporaries. In this lecture, the relevance of some of that early work and the compromises that must be made in optimising a modern wing design will be presented. These will include optimisation of spanwise loading, including trimming effects and winglets, and high and low speed aerodynamic and structural interactions, with examples drawn from the author's career in helping to develop the wings for the HS146 (now the RJX) and the Airbus family.

With the exponentially increasing computer power available over the last 30 years, the ‘art of compromise’ has progressively become the ‘science of optimisation’ and the lecture closes with a brief reference to techniques used to optimise current wing designs for the Airbus family.
An assessment of the 2D vortex method in aircraft wake simulation
Authors: Graham W. R.
Published: July 2016

Recent interest in aircraft vortex wakes has highlighted the need to identify appropriate algorithms for their simulation. The problem is not well-suited to grid-based techniques, due to the large domain and the need to avoid introducing artificial viscosity. A promising alternative is offered by Lagrangian formulations. This work aims to assess the usefulness of one such approach - the 2D vortex method -via comparison with experimental results. One in-house and two external (from DLR and ONERA) data sets are used. The results show generally good agreement in vortex locations and size, with the calculation performing best when initialised downstream of the strongly-three-dimensional trailing edge region. The neglect of viscosity can lead to some asymmetry in the vortex cores, but, even here, excellent agreement can be obtained when the field is integrated to give circulation (as a function of radius). The 2D vortex method is thus an accurate and efficient tool for wake vortex prediction.
Trimmed deep stall on the F-16 Fighting Falcon
Authors: Evangelou L. D. , Self A. W. , Allen J. E. , Lo S.
Published: July 2016

High performance fighter aircraft have problems with handling qualities, at high angles of incidence. Pilots are limiting combat effectiveness by cautiously avoiding hazardous regions of the flight envelope. This paper presents and extends existing work on the F-16 aircraft's handling characteristics during the deep stall condition. Inflight experience shows that there are two types of control problems when flying at high angles-of-attack, the ‘pitch departures’ and the ‘deep stall trim’. This paper investigates the critical deep stall condition, assesses the effectiveness of the proposed method of recovery and suggests an augmented and reliable method of returning to normal flight.
Impacts of aero-engine deteriorations on military aircraft mission's effectiveness
Authors: Naeem M. , Singh R. , Probert D.
Published: July 2016

International political and socio-economic developments have led the armed forces of many countries to become more aware of how their increasingly-stringent financial budgets are spent. One major expenditure for military authorities is upon aero-engines, because in-service deterioration in any mechanical device, such as an aircraft's gas-turbine engine, is inevitable. Each deterioration has an adverse effect on the performance and shortens the reliable operational life of the engine, thereby resulting in higher life-cycle costs. For a military aircraft's mission-profiles, the consequences of an aero-engine's deterioration upon the aircraft's operational-effectiveness as well as its fuel consumption and life have been predicted in this project using validated computer-simulations. These help in making wiser management-decisions, so leading to the achievement of improved engine utilisation, lower overall life-cycle costs and optimal mission effectiveness for squadrons of aircraft.
Multigrid upwind Euler/Navier-Stokes computation on adaptive unstructured meshes
Authors: Zheng Y. , He L.
Published: July 2016

An unstructured flow solver with adaptive mesh refinement and multigrid acceleration is developed to efficiently compute two-dimensional inviscid and viscous steady flows about complex configurations. High resolution is achieved by using the upwind scheme coupled with adaptive mesh refinement. An aspect-ratio adaptive multigrid method is developed and applied to effectively accelerate the solution convergence of the explicit time-marching in the near wall regions with high aspect mesh ratios. Numerical examples are presented for configurations and conditions ranging from transonic to low speed flows to demonstrate accuracy, speed, and robustness of the method.
Embedded direct numerical simulation for aeronautical CFD
Authors: Sandham N. D. , Alam M. , Morin S.
Published: July 2016

A method is proposed by which a direct numerical simulation of the compressible Navier-Stokes equations may be embedded within a more general aeronautical CFD code. The method may be applied to any code which solves the Euler equations or the Favre-averaged Navier-Stokes equations. A formal decomposition of the flowfield is used to derive modified equations for use with direct numerical simulation solvers. Some preliminary applications for model flows with transitional separation bubbles are given.
A data exchange method for fluid-structure interaction problems
Authors: Goura G. S. L. , Badcock K. J. , Woodgate M. A. , Richards B. E.
Published: July 2016

This paper presents and illustrates an interpolation method for the exchange of displacement data between fluid and structural meshes in a fluid-structure interaction simulation. The method is a local method where element volume conservation is central, and does not rely on information from the structural model. Results are evaluated for several two and three dimensional problems. Comparisons with the infinite plate spline method show that the new method gives a more realistic representation of the recovered surface than currently used methods.
A dual-time method for the solution of the
unsteady Euler equations
Authors: Gaitonde A. L.
Published: July 2016

A “dual-time” method for solving the three-dimensional Euler equations describing the compressible flow about wings undergoing arbitrary motions and deformations is presented. A finite-volume formulation is chosen where the volumes distort as the wing moves or deforms. Independent motion of the inner and outer boundaries of the grid is permitted with a sequence of grids generated using transfinite interpolation.

An implicit real-time discretisation is used, and the equations are integrated in a fictitious pseudo time. This approach allows the real-time step to be chosen on the basis of accuracy rather than stability. It also permits the acceleration techniques commonly used to speed up steady flow calculations to be used when marching in pseudo time, without compromising real-time accuracy. A two-dimensional version of the method has also been developed and results for both two and three-dimensional transonic flows are presented and compared with experimental data where available.
Phenomena observed during aerofoil ramp-down motions from the fully separated state
Authors: Green R. B. , Galbraith R. A. McD.
Published: July 2016

Unsteady pressure data from seven aerofoil models performing constant pitch rate “ramp-down” motions from the fully separated state to low incidence have been analysed. It is observed that the time delay between attachment at the leading edge and the occurrence of minimum normal force is, to a first order, independent of reduced pitch rate. As a result, at sufficiently high pitch rate, negative normal force may be generated at large positive incidence. In contrast to this, the re-establishmeht of attached flow to the upper surface is strongly dependent upon pitch rate. The paper also contains a description of smoke flow visualisation tests. These were at a much lower Reynolds number than the pressure data tests, and consequently are of qualitative interest. Results of flow visualisation show that during a ramp-down test the near wake is much larger than in the corresponding static case, and that attachment is significantly delayed.
Asymptotic analysis of the classical aircraft stability equations
Authors: Graham W. R.
Published: July 2016

A new approach to deriving analytical approximations for the free modes of motion of an aircraft is presented. Based on an asymptotic analysis, it eliminates the need for a priori assumptions regarding the characteristic motion of each mode, and is thus particularly suitable for an introductory exposition. In its basic form, it yields expressions for natural frequencies, damping factors and time constants which agree, to leading order, with well established results. At a more advanced level, it allows us to assess the validity of these results. In particular, we find that the two degree-of-freedom approximations to the short period oscillation and Dutch roll are asymptotically incorrect. This is unlikely to have a significant effect on the accuracy of the former, but is the reason for the poor damping predictions of the latter.
Optimisation of composite wind-tunnel wing models for frequency, flutter and divergence
Authors: Taylor J.M. , Butler R. , Harrison C.
Published: July 2016

A comparison has been made between the composite beam designs produced by minimum mass optimisation using two different sets of constraints. The first approach constrained the design to have a given separation between fundamental bending and fundamental torsional natural frequencies; the second constrained the design to have a given flutter and divergence speed. The beams are modelled as a series of elements, stepped in thickness at discrete nodes, with the Dynamic Stiffness Method being used for calculation of their natural frequencies. The aeroelastic constraints are obtained from the Fortran program CALFUN. The results show that for similar flutter and divergence speeds, the optima produced using aeroelastic constraints have a slightly lower mass (up to 4% lower) and a less ‘hard’ flutter onset. However, the time taken to produce these optima is significantly longer (in excess of 2 orders of magnitude). A preliminary study discusses the merits of a combined optimisation method where frequency constrained optimisation is used to provide a near-optimum starting point for flutter and divergence constrained optimisation. In addition, a wind-tunnel model of one of the optima has been manufactured and subject to both modal analysis and wind-tunnel tests to validate the flutter speed calculations. This shows that when using strip theory, CALFUN predicts a conservative value of flutter speed for this design. Further investigation has shown CALFUN's lifting surface theory to be more accurate for low aspect ratio models.
The near-field flow characteristics of some wall-mounted mixing tabs
Authors: Yu S. C. M. , Chua L. P. , Goh E. K.
Published: July 2016

It is well known that passive vortex generators can be very effective in controlling separation by ‘re-energising’ the low momentum fluids at the boundary layers. They have been used extensively in many practical aerodynamic applications; both in external and internal flows. Typical examples include aerofoil stall alleviation and engine face distortion control in the jet aircraft intake during high angles of incidence. The general flow feature behind a vortex generator is that a pair of contra-rotating streamwise vortices would be formed which will significantly strengthen the flow at the boundary layers. However, the rationale for successful vortex generator designs is often poorly understood. In many cases, vortex generator designs have even been shown to be arbitrary. Anderson et al and Reichert and Wendt used rectangular fin and tapered fin vortex generators respectively, to eliminate the internal flow separation of S-shaped intake ducts. Both geometries were found to be equally effective. Weng and Guo successfully applied aerofoil shape type of vortex generators to suppress the swirl on the engine face of an S-shaped intake duct at high angles of incidence.
Three-dimensional fibre optimisation with computer aided internal optimisation
Authors: Reuschel D. , Mattheck C.
Published: July 2016

Big efforts have been made to optimise the behaviour and the properties of fibre reinforced materials. The fibre-matrix bonding, the influence of the fibre-matrix content and many other relations of several systems have been intensively investigated. Nevertheless, the arrangement of the fibres within a structure was a neglected subject of research.

CAIO (computer aided internal optimisation) was developed to predict the optimal arrangement of fibres for given load and boundary conditions. The mechanism of the method has been adapted from biological structures. CAIO is based on the finite elements method (FEM). In a first step the force flow of a structure is calculated by using FEM. The CAIO routine changes orientation of orthotropic axes into the directions of force flow with respect to the FE-results. A following stress analysis leads to a reduced shear stress distribution. The optimum fibre arrangement is calculated by an automatically iterative process of alternating FE-run and CAIO calculation. The latest version of CAIO allows the calculation of the optimum fibre arrangement in three-dimensional shell structures as well as in three-dimensional volume structures.
The aerodynamic performance of paragliders
Authors: Babinsky H.
Published: July 2016

An analysis of paraglider performance has revealed that wing section drag is the most significant contribution to overall drag. Wind tunnel measurements performed on two-dimensional hollow models indicate that intake drag is less significant than previously thought. An experimental investigation into the characteristics of a ‘quasi ’ -two-dimensional flexible model consisting of solid ribs covered with a fabric skin was performed at realistic Reynolds numbers. The main cause of performance deterioration was found to be a significant reduction in section lift coefficient when compared to a similar solid wing section. This is believed to be mainly due to two factors: a large trailing edge separation and the deformation of the wing between ribs. The deformation was measured and it was shown that the deformed shape is less capable of generating high lift coefficients than the design section. It is thought that the extent of the trailing edge separation is increased due to the presence of streamwise grooves caused by the shape deformation of the wing. The shape of the separated region was found to be strongly three-dimensional with the separation point being about half a chord-length further upstream along the ribs. A small separation bubble was also observed immediately behind the lip of the intake, due to the fabric ‘flaring’ open. Based on the observations presented a number of suggestions for improved wings have been made.
Demonstration of cluster computing for three-dimensional CFD simulations
Authors: McMillan W. , Woodgate M. , Richards B. E. , Gribben B. J. , Badcock K. J. , Masson C. A. , Cantariti F.
Published: July 2016

Motivated by a lack of sufficient local and national computing facilities for computational fluid dynamics simulations, the Affordable Systems Computing Unit (ASCU) was established to investigate low cost alternatives. The options considered have all involved cluster computing, a term which refers to the grouping of a number of components into a managed system capable of running both serial and parallel applications. The present work aims to demonstrate the utility of commodity processors for dedicated batch processing. The performance of the cluster has proved to be extremely cost effective, enabling large three dimensional flow simulations on a computer costing less than £25k sterling at current market prices. The experience gained on this system in terms of single node performance, message passing and parallel performance will be discussed. In particular, comparisons with the performance of other systems will be made. Several medium-large scale CFD simulations performed using the new cluster will be presented to demonstrate the potential of commodity processor based parallel computers for aerodynamic simulation.
Numerical solution of Euler equations for
aerofoils in arbitrary unsteady
motion
Authors: Lin C. Q. , Pahlke K.
Published: July 2016

This paper is part of a DLR research programme to
develop a three-dimensional Euler code for the
calculation of unsteady flow fields around
helicopter rotors in forward flight. The present
research provides a code for the solution of Euler
equations around aerofoils in arbitrary unsteady
motion. The aerofoil is considered rigid in motion,
and an O-grid system fixed to the moving aerofoil is
generated once for all flow cases. Jameson's finite
volume method using Runge-Kutta time stepping
schemes to solve Euler equations for steady flow is
extended to unsteady flow. The essential steps of
this paper are the determination of inviscid
governing equations in integral form for the control
volume varying with time in general, and its
application to the case in which the control volume
is rigid with motion. The implementation of an
implicit residual averaging with variable
coefficients allows the CFL number to be increased
to about 60. The general description of the code,
which includes the discussions of grid system, grid
fineness, farfield distance, artificial dissipation,
and CFL number, is given. Code validation is
investigated by comparing results with those of
other numerical methods, as well as with
experimental results of an Onera two-bladed rotor in
non-lifting flight. Some numerical examples other
than periodic motion, such as angle-of-attack
variation, Mach number variation, and development of
pitching oscillation from steady state, are given in
this paper.
Aerodynamic characteristics of delta wing–body combinations at high angles of attack
Authors: Viswanath P. R. , Patil S. R.
Published: July 2016

An experimental study investigating the aerodynamic characteristics of generic delta wing-body combinations up to high angles of attack was carried out at a subsonic Mach number. Three delta wings having sharp leading edges and sweep angles of 50°, 60° and 70° were tested with two forebody configurations providing a variation of the nose fineness ratio. Measurements made included six-component forces and moments, limited static pressures on the wing lee-side and surface flow visualisation studies. The results showed symmetric flow features up to an incidence of about 25°, beyond which significant asymmetry was evident due to wing vortex breakdown, forebody vortex asymmetry or both. At higher incidence, varying degrees of forebody-wing vortex interaction effects were seen in the mean loads, which depended on the wing sweep and the nose fineness ratio. The vortex breakdown on these wings was found to be a gradual process, as implied by the wing pressures and the mean aerodynamic loads. Effects of forebody vortex asymmetry on the wing-body aerodynamics have also been assessed. Comparison of Datcom estimates with experimental data of longitudinal aerodynamic characteristics on all three wing-body combinations indicated good agreement in the symmetric flow regime.
Some observations on the dynamic response to wing motion of the vortex burst phenomenon
Authors: Greenwell D. I. , Wood N. J.
Published: July 2016

The “post-stall” manoeuvre capabilities of current and projected combat aircraft have prompted a resurgence of interest in the dynamic response to wing motion of the vortex burst at high angles of attack. A large number of experimental studies have been reported, but these have tended to be restricted to a limited range of motion profiles and a single specific wing configuration. Presumably due to the complexity of the phenomenon, no attempt appears to have been made to undertake a systematic study of the burst response for a range of wing planforms and motion profiles. Hence, a survey was made of the published data and a semi-empirical correlation derived using a system identification methodology. For preliminary performance studies, the dynamic response of the vortex burst is modelled adequately by a second order lag transfer function. The physical significance of this system model and the implications for the design of a systematic experimental study are discussed.
A new approach in the analysis of linear systems with periodic coefficients for applications in rotorcraft dynamics
Authors: Wu D.-H. , Sinha S.C.
Published: July 2016

A numerical technique for the stability analysis of linear mechanical dynamic systems with periodically varying parameters is proposed. The technique is based on representation of the solution vector in terms of Chebyshev polynomials defined over the principal period. Two formulations have been presented. The first formulation is suitable for systems described by state space equations, while the second can be applied directly to a set of second order equations with periodically varying mass, damping and stiffness matrices. As an illustrative example, the flap-lag stability of a multi-bladed rotor is examined. The numerical accuracy and efficiency of the proposed technique is compared with standard numerical codes based on Runge-Kutta, Adams-Moulton and Gear algorithms. The results indicate that the suggested approach is by far the most efficient one, particularly for systems with larger dimensions.
Three-dimensional vortex interactions with a stationary blade
Authors: Doolan C. J. , Coton F. N. , Galbraith R. A. McD.
Published: July 2016

Surface pressure measurements were obtained during a three-dimensional vortex interaction with a NACA 0015 aerofoil. The upper and lower surfaces of the blade experienced different aerodynamic loads which appear to be controlled by the impact of the vortex axial core flow on the blade surface. On the upper surface of the blade, where the vortex core flow was away from the aerofoil, the interaction was characterised by the generation of a suction peak. On the lower surface, where the axial component was towards the blade, a pressure pulse developed and seemed to be influenced by the vortex approach angle. These features resulted in rapid changes in normal force and quarter chord pitching moment during the interaction. This impulsive loading of the blade may provide some explanation for sound generation and control degradation problems associated with the tail rotor of helicopters.
Investigation of the certification and operational procedures for turboprop aircraft in icing
Authors: Simpson M. P. , Render P. M.
Published: July 2016

A study was conducted to identify possible improvements to the current certification and operational procedures for turboprop powered aircraft operating in icing conditions. Information was gathered through a series of interviews with airframe and engine manufacturers and also, operators and aircrews in Europe and Canada. The significant issues raised during the interviews are discussed, and a number of recommendations are made for future research and development activities in die area of aircraft icing. These recommendations identify the need for improved ice protection methods, enhanced thermodynamic models in ice prediction computer codes, and development of an ice prediction probe to warn aircrew that they will soon be entering icing conditions. Recommendations also include improvements to pilot training, and the need to make weather forecasts of icing more accurate and specific.
An analytical procedure for asymmetric store flutter
Authors: Liu J. K.
Published: July 2016

A simple but effective method is presented to analyse the effects of asymmetric external stores on flutter of an aircraft in this paper. The method is a kind of ‘direction derivative’ technique, and can be easily applied to predict whether the asymmetric external stores increase or decrease the flutter speed. By using the present technique the varying tendency of flutter speed can be determined preliminarily. This can be very useful and valuable to the designers at the beginning stage of flutter analysis. The effectiveness of the proposed method is proved analytically.
The compound helicopter — why have we not succeeded before?
Authors: Orchard M. N. , Newman S. J.
Published: July 2016

Compounding offers a way of advancing the performance of the standard helicopter significantly for a moderate increase in complexity through the addition of wings and/or auxiliary propulsion. The compound helicopter configuration has the potential advantages of increased speed, range, agility, productivity and reduced vibration levels over conventional helicopters. Despite several significant efforts, however, no compound helicopter has ever been put into production. This paper looks at three aircraft that came close to being accepted by operators and examines the reasons why they were not ultimately put into production. The cancellation of these projects appeared to be of a political nature rather than technical. Also addressed are the issues that still face prospective designers of compound helicopters and the lessons that can be extracted and applied to modern day efforts to build and sell an aircraft of this configuration.
Automated surface shape optimisation in the MDO project
Authors: Gould A. R. B.
Published: July 2016

Surface shape optimisation was one of several topics researched under the multi-disciplinary optimisation (MDO) project. Several project partners participated in this activity which set out to develop, validate and demonstrate a number of technical issues related to automated shape design. Each of the participants brought together in-house and/or commercial analysis tools, a variety of different modelling and optimisation techniques, and common database and model generation methods. The objectives of this work were to validate the methodologies established in the preliminary MDO project phase and to demonstrate the optimisation process when applied to a simplified civil aircraft wing design problem. Several issues were central to the investigation, including alternative means of parametric descriptions for the wing surface shape, alternative optimisation strategies for wing MDO, and the impact of different levels of physical and geometrical modelling on MDO performance and resulting product optima. The outcomes of this work demonstrate the need for advanced analysis tools to be incorporated into aerospace vehicle design problems at a relatively early stage and highlight the dangers of over-simplification of the vehicle model.
Multidisciplinary design optimisation (MDO) methods: their synergy with computer technology in the design process
Authors: Sobieszczanski-Sobieski Jaroslaw
Published: July 2016

The paper identifies speed, agility, human interface, generation of sensitivity information, task decomposition, and data transmission (including storage) as important attributes for a computer environment to have in order to support engineering design effectively. It is argued that when examined in terms of these attributes the presently available environment can be shown to be inadequate. A radical improvement is needed, and it may be achieved by combining new methods that have recently emerged from multidisciplinary design optimisation (MDO) with massively parallel processing computer technology. The caveat is that, for successful use of that technology in engineering computing, new paradigms for computing will have to be developed - specifically, innovative algorithms that are intrinsically parallel so that their performance scales up linearly with the number of processors. It may be speculated that the idea of simulating a complex behaviour by interaction of a large number of very simple models may be an inspiration for the above algorithms; the cellular automata are an example. Because of the long lead time needed to develop and mature new paradigms, development should begin now, even though the widespread availability of massively parallel processing is still a few years away.
Development and application of NASTRAN structural optimisation solution sequence within the BAe ECLIPSE system
Authors: Thompson D. , Haley C. , Ayres J. , Major M. , Golby D.
Published: July 2016

During the period 1970–1990 the Military Aircraft Division of British Aerospace based at Warton developed a structural sizing and optimisation system initially based on an “in-house” developed finite element analysis (FEA) system. This subsequently progressed to using NASTRAN, which was rapidly evolving to be the standard FEA system used within all divisions of British Aerospace (BAe).

The many problems associated with the development and application of this evolving system are described. These problems covered a wide range from software development, engineering application, resource management and hardware dependence.

One problems which has received a great deal of attention since 1990 is the incorporation of the panel buckling constraint particularly when applied to laminated structures. This paper describes an early attempt to incorporate this constraint followed by a brief description of the application and integration of a specialised Panel Buckling code.

The paper concludes by describing how BAe Military Aircraft Division is attempting to incorporate the buckling constraint using NASTRAN into a high performance computing (HPC) environment. In addition this development illustrates how many of the problems described earlier are being overcome by working in partnership with software vendors, hardware vendors and other business units within BAe.
Mutual interference between jets and intakes in STOVL aircraft
Authors: Saddington A. J. , Knowles K.
Published: July 2016

A series of experiments has been performed in an open-jet wind tunnel on a generic jet-lift STOVL aircraft in transition out of ground effect. In order to obtain information about the forces acting on the aircraft, static pressure measurements were made on the wing and intake lips. The model tested was equipped with a single vectored lift-jet and ‘powered’ intakes. Tests were conducted at a variety of nozzle pressure ratios and effective velocity ratios.

The experiments conclude that a mutual interference exists between the jet and intake flows which generates non-linearly-additive loads on the airframe. This questions the validity of testing jets and intakes separately on a STOVL aircraft of this type.
Aircraft flight control systems
Authors: McLean D.
Published: July 2016

This paper presents a short account of the flight control systems used in commercial transport, military combat and general aviation aircraft. The effects of aircraft safety, reliability and weather delays on satisfactory aircraft operations are shown to be significant reasons for the extensive use of flight control systems. The principles of flight control, the sensors and actuators required and the various modes which can be selected are treated, together with a short account of the primary flying controls and the use of manual reversion in emergency situations. The paper concludes with a consideration of the fly-by-wire (FBW) and fly-fby-light concepts, and covers relaxed static stability, carefree manoeuvring and the use of canards before discussing some FBW flight control systems which are used in passenger aircraft.
Unsteady aerodynamics: retrospect and prospect
Authors: Mabey D. G.
Published: July 2016

This paper reviews some current problems in unsteady aerodynamics and discusses some future challenges. The emphasis is on problems associated with separated flows, such as buffeting and limit cycle oscillations. Suggestions are made to indicate how experimental facilities (such as cryogenic windtunnels) and computational fluid dynamics might be exploited to address these questions.
Unsteady flow around helicopter rotor blade sections in forward flight
Authors: Shaw S. T. , Qin N.
Published: July 2016

The aerodynamic performance of aerofoils performing unsteady motions is important for the design of helicopter rotors. In this respect the study of aerofoils undergoing in-plane oscillations (translation along the horizontal axis) provides useful insight into the flow physics associated with the advancing blade in forward flight. In this paper a numerical method is developed in which the unsteady thin layer Navier-Stokes equations are solved for aerofoils performing rigid body motions. The method has been applied to the calculation of the flowfield around a NACA 0012 aerofoil performing in-plane motions representative of high-speed forward flight. Comparison of computed pressure data with experimental measurements is generally found to be good. The quantitative differences observed between computations and experiment are thought to have arisen mainly as a consequence of the low aspect ratio of the model rotor employed in the windtunnel tests.
Applications of multirate optical fibre code-division-multiplexing systems to high-speed data communications for air traffic control
Authors: Zhang J-G. , Sharma A. B.
Published: July 2016

Future air traffic control will be based on the distributed processing environment. This leads to the use of high-speed optical fibre networks and systems to connect many processors (for both general and specific purposes) and workstations in the air traffic control centres. To efficiently support such applications, communication systems should be capable of multirate operations. To achieve this aim, we propose an efficient optical fibre code-division multiplexing (OF-CDM) technique that can support multirate data communications without any increase of system complexity when compared with the equal-rate operation case. Unlike conventional optical orthogonal codes (OOCs), the use of our proposed unequal-length OOCs can eliminate any possible violation of the minimum cross-and auto-correlation constraint (i.e. ‘1’) in multirate OF-CDM systems. Thus, using unequal-length OOCs can achieve a better bandwidth efficiency and a lower bit error rate for multirate transmissions than employing conventional OOCs. Moreover, we present the design of cost-effective OF-CDM transmitters for multirate data transmissions. The proposed systems can be also employed to support future airborne real-time data distributions and computer interconnects.
An experimental and numerical study of synthetic jet flow
Authors: Mallinson S. G. , Reizes J. A. , Hong G.
Published: July 2016

The flow generated by a synthetic jet actuator with a circular orifice is investigated experimentally and computationally. The experimental data and computational predictions are in fair to good agreement with each other and with the theory for a steady turbulent jet. It is found, however, that the synthetic jet establishes itself much more rapidly than the steady jet, primarily because of turbulent dissipation. The oscillatory nature of synthetic jet flow also gives rise to a much greater entrainment of ambient fluid compared with the case of a steady jet. Finally, self-similarity seems to be established when the oscillations introduced by the actuator are reduced to negligible levels.
Extract from A Wrack Behind: Myself, when young
Authors: Norton Lord Kings
Published: July 2016

I was born on 6 June 1902, in Handsworth, a borough in Staffordshire, which in 1911 became part of Greater Birmingham. Handsworth, in those Edwardian days, could be described as a dormitory suburb of Birmingham. Its character is now vastly changed and today it houses large numbers of our immigrant population.

My father, William John Roxbee Cox, is described on his marriage certificate as a master jeweller and indeed was, at the time of his wedding, working with his father, Samuel James Cox, a reasonably prosperous manufacturing jeweller in Birmingham. Samuel had married an American lady, Emily Power Jones, who was, I believe, distantly related to him, and my father was their only child.

My mother was Amelia Stern, the third child of Henry Stern, a Pole who became a naturalised Englishman. My memory of him is vague but pleasant. I think he must have been a nice man. He was an engraver on glass. He died of pneumonia in 1904 at the age of 54. His brother Louis became a Church of England parson, but did not achieve major preferment.
Contributions of Harold Roxbee Cox (Lord Kings Norton) to specialist aspects of aeronautical technology
Authors: Pope Geoffrey
Published: July 2016

Prior to his departure from the Royal Aircraft Establishment in 1938, Roxbee Cox published an impressive range of specialist papers relevant to the design and analysis of airships and aircraft.

His earliest published paper (Refs are on p 227), on the external forces on an airship structure, was based on his work on the R101 at the Royal Airship Works, Cardington. This comprehensive monograph, which was awarded the R38 Memorial Prize by the Royal Aeronautical Society, addresses, in turn, the range of loading conditions that needs to be considered, safety factors to be used in design, calculation of individual load components, and estimation of stresses within the structure (this consisted of longitudinal and transverse members braced with wires).
The external forces on an airship structure with special reference to the requirements of rigid airship design
Authors: Cox Harold Roxbee
Published: July 2016

A system of external forces on the structure of a rigid airship can be analysed into two or more of the component systems due to

W. The Weights of the members of the structure and the weights of the masses carried by it;

L. The Lift and pressure of the gas;

A. The Aerodynamic forces consequent on the relative motion of the airship and the air;

T. The Thrusts of the airscrews;

R. The Reactions due to either the mooring arrangements, the hauling-in guys, the supports used in the shed, or handling on the ground.

As these component systems, though restricted by their interdependence, are individually variable, a very large number of complete systems is represented by the possible combinations and variations that can occur. It becomes necessary, therefore, for the purposes of design, to attempt to limit the number of combinations to be considered, and to restrict the variations of the components, but in such a way that the structure designed to carry the resulting systems with adequate factors of safety, shall be able to carry any other possible system with an appropriate factor of safety.
Problems involving the stiffness of aeroplane wings
Authors: Cox H. Roxbee
Published: July 2016

An aircraft may reasonably be said to be structurally safe if it is known that during the manoeuvres which it is likely to perform

(i) The stress in no part of the essential structure approaches the failing stress of the material,

(ii) It does not become unstable or uncontrollable on account of structural distortion.

I intend to discuss in this context the wing structure of the aeroplane.

For many years it was felt both in the design and airworthiness approval of the majority of aeroplane wing structures that the main responsibility for attempting to secure the former desideratum could rest upon the determination of the stresses induced in the wing structural material by load systems appropriate to a rigid aeroplane in certain conditions denned by specified combinations of flight attitude, acceleration, and factor of safety. These combinations — familiarly referred to as the C.P. forward, C.P. back, nose-diving and inverted flight cases—are designed to produce for a particular aeroplane a range of steady load systems which is more severe on the structure than the range of load systems corresponding to the manoeuvres contemplated for the aeroplane.