bluuebunny/crossref_metadata_2025 huggingface dataset:
Developments in RF simulator technology – approaching the affordable fidelity limit
Authors: Pywell M.
Published: February 2016

Technology developments in radar frequency simulators of the type used to verify the performance of complex electronic warfare systems are described. The successful verification of this performance prior to combat use is a necessary pre-requisite of military platform survivability and mission success. These simulators and associated modelling and analysis tools have enabled a major shift during the last 15 years from expensive and limited flight trials to repeatable laboratory and anechoic chamber tests, although they will never totally supplant those trials. Most limitations of the early days of many-channel simulators, 25 years ago, have been resolved or adequately and – as importantly – affordably mitigated, largely enabled by computing power increases. Limitations remain that will, within affordability constraints driven by Defence Ministries worldwide, prevent perfect simulation (‘emulation’) and the attendant, tantalising but utopian goal of laboratory and chamber test results that precisely match those from flight test and combat.
‘Greener’ civil aviation using air-to-air refuelling – relating aircraft design efficiency and tanker offload efficiency
Authors: Nangia R. K.
Published: February 2016

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.
Flight data reduction methodology for performance evaluation and comparison of model-following adaptive control laws
Authors: Perhinschi M. G. , Napolitano M. R.
Published: February 2016

Even small differences in atmospheric and/or flight conditions can potentially impact significantly the evaluation of the performance of the control laws and prevent a correct comparison, especially in the case of reduced size aircraft (autonomous or remotely piloted). Consistent deterministic control inputs can only be guaranteed through some form of computer-based on-board excitation system. In this paper, a methodology is proposed for flight data reduction with the purpose of accounting for non-homogeneous atmospheric conditions and inconsistent pilot inputs. The method is developed for the specific purpose of comparing model-following adaptive control laws. Performance evaluation parameters based on angular rate tracking errors are defined and used for the comparison. As a result of this approach, an additive correction is applied to the angular rate measurements to compensate for non-homogeneous turbulence effects. A multiplicative correction factor is applied to the angular rate tracking error to take into account non-identical pilot inputs. The procedure is validated with simulation and flight data obtained in the process of designing a set of fault tolerant control laws based on non-linear dynamic inversion with neural network augmentation for the reduced size WVU YF-22 aircraft model.
Dynamic inflow modelling for autorotating
rotors
Authors: Murakami Y. , Houston S.S.
Published: February 2016

The dynamic inflow model is a powerful tool for
predicting the induced velocity distribution over a
rotor disc. On account of its closed form and
simplicity, the model is especially practical for
studying flight mechanics or for designing control
systems for helicopters. Scant attention has,
however, been paid so far in utilising the dynamic
inflow model to analyse an autorotating rotor, which
is different from a powered rotor in the geometric
relation between the direction of the inflow and the
rotor disc. Autorotation is an abnormal condition
for helicopters, but for gyroplanes it is the normal
mode of operation. Therefore the theoretical
discussion on an autorotating rotor is of importance
not only to improve the understanding of present
gyroplanes, but also in the development of new
gyroplanes and to analyse the windmill-brake state
of helicopters. Dynamic inflow modelling is reviewed
from first principles, and this identifies a
modification to the mass flow parameter. A
qualitative assessment of this change indicates that
it is likely to have a negligible impact on the trim
state of rotorcraft in autorotation, but a
significant effect on the dynamic inflow modes in
certain flight conditions. This is confirmed by
numerical simulation, although considerable
differences only become apparent for steep descents
with low forward speed. It is concluded that while
modification of the mass flow parameter is perhaps
mathematically accurate, for practical purposes it
is required only in a limited area of the flight
envelope of autorotating rotorcraft.
Analysis of a reversible flight control system response to atmospheric turbulence
Authors: Raissi K. , Mani M. , Ghaffari H. , Nobari A.
Published: February 2016

A mathematical model was developed for the reversible longitudinal control system of a regional commuter aircraft using the available geometry, mass property and kinematics. The model was incorporated into a general multi-body dynamics code and validated using existing manufacturer’s data as well as recorded data from several flights. Analysis of the flight data revealed light atmosphere turbulence level. To investigate the effect of higher turbulence intensity on the reversible flight control system, a sever turbulence level was generated using Von Karman model for the same flight level and velocity. The result was used as a random input to the dynamic model for computation of the frequency response of control column. It was shown that turbulence could act as a random input through the hinge moment during the flight and introduced a new mode in the lower end of power spectral density curve. The energy induced by this low frequency input resulted in large displacement of control column in simulation which surpassed the existing limits. Therefore it should be taken into account when dealing with handling quality as well as autopilot design.
A low-Reynolds-number one-equation model of turbulence
Authors: Elkhoury M.
Published: February 2016

This work proposes an improved form of Menter’s single-equation eddy viscosity transport model. The new transport equation follows from the transformation of the k-ε closure that includes the Yap-correction term, which is known to improve the (k-ε) model’s prediction in adverse pressure gradient flows. The damping functions of the (low-Reynolds-number) LRN model are constructed using the ingenious approach of Baldwin and Barth. Hence, the model provides the correct wall-limiting behaviour of turbulence. Furthermore, the destruction term is modified to better account for non-equilibrium anisotropy effects. An assessment of the present proposed model against experiments, as well as Menter and Spalart-Allmaras (SA) turbulence models is provided via several boundary layer computations. Good agreement with experimental data is indicated, which merits the model to be considered for further refinement.
Some features of steady separated flow from low speed to hypersonic
Authors: Gai S. L.
Published: February 2016

Steady non-vortex shedding base flow behind a bluff body is considered. Such a flow is characterised by the flow separation at the trailing edge of the body with an emerging shear layer which reattaches on the axis with strong recompression and recirculating flow bounded by the base, the shear layer, and the axis.

Steady wake flows behind a bluff body at low speeds have been studied for more than a century (for example, Kirchhoff; Riabouchinsky). Recently, research on steady bluff body wake flow at low speeds has been reviewed and reinterpreted by Roshko. Roshko has also commented on some basic aspects of steady supersonic base flow following on from Chapman and Korst analyses.

In the present paper, we examine the steady base flow features both at low speeds and supersonic speeds in the light of Roshko’s model and expand on some further aspects of base flows at supersonic and hypersonic speeds, not covered by Roshko.
Converging towards synthetic environment interoperability
Authors: Lalonde B.
Published: February 2016

The evolution of simulators from proprietary hardware platforms to affordable commercial-off-the-shelf (COTS) platforms has gone on for the past 15 years and is now nearly complete. Nevertheless, past efforts to standardise simulator synthetic environments (SE) have only been partially successful and have engendered considerable aggravation for users in need of creating content that can be deployed to distributed full-mission simulators. This paper provides a detailed description of the SE generation pipeline and the reasoning that has modeled its evolution over the past few decades. The arrival of digital multi-spectral high-resolution satellite imagery and highly capable visual systems now requires orders of magnitude more storage and processing than equivalent databases just a few years ago. These factors are threatening the equilibrium of the SE pipeline and are becoming important elements affecting SE interoperability, portability and re-usability. Past design trade-offs and compromises, appropriate at the time, must now be re-examined along with all SE-related processes, starting from ingestion of raw source data right through to the processing by the simulator devices. Clearly, greater standardisation is needed within the simulation community and a comprehensive, open SE representation would palliate to the many challenges we now face. To this end, this paper provides a checklist of the characteristics for a future ‘ideal’ SE representation and evaluates four emerging synthetic environment initiatives against this extensive checklist.
Development of mechanical guidance actuators for a supersonic projectile
Authors: Massey K. C. , McMichael J. , Warnock T. , Hay F.
Published: February 2016

In this paper, the results of a series of experiments funded by DARPA to determine the feasibility of using small actuators to provide directional control for a supersonic projectile are presented. Controlling the flight of the projectile was accomplished by taking advantage of complex shock-boundary-layer interactions produced by mechanical devices. Experimental tests were conducted at GTRI to screen several control concepts and actuator locations. Further experiments were conducted on a scale projectile in a supersonic stream to investigate the rise time of the forces. Several different mechanical actuators were tested which served to provide guidance for future actuator designs. CFD results were also used to predict the results in flight as well as gain insights into the fluid mechanics involved. Flight tests of a Mach 4 round proved the viability of the guidance actuator.
Numerical simulation of rime ice accretions on an aerofoil using an Eulerian method
Authors: Cao Y. , Zhang Q. , Sheridan J.
Published: February 2016

Based on two-phase flow theory, an Eulerian method to simulate rime ice accretions on an aerofoil has been developed. The SIMPLE (semi-implicit method for pressure linked equations) algorithm on a collocated grid is employed to solve the governing equations for the airflow. In order to simulate droplets impinging on an aerofoil, a permeable wall is proposed to solve the governing equations for supercooled droplets. The collection efficiency and impingement limits are obtained from the droplets’ flowfield. The process of ice accretion is simulated using the assumption that ice accumulates layer-by-layer and the ice shape is predicted with the assumption that ice grows in the direction normal to the aerofoil surface. The rime ice accretions on a NACA0012 aerofoil at 0° and 4° angles-of-attack have been investigated and there is agreement between the simulated results and previously published experimental data. The change of the pressure coefficient along the iced aerofoil is also analysed.
Indirect aircraft structural monitoring using artificial neural networks
Authors: Reed S. C.
Published: February 2016

From necessity, military aircraft often operate in a highly fatigue damaging environment and history has shown in lost lives and aircraft the consequences of failure to appreciate fully the usage environment. The need for robust and cost effective structural usage monitoring of military aircraft to ensure operations are conducted within acceptable levels of risk is paramount. Furthermore, increased economic pressures require ever-inventive methods to be employed to maximise the lives of military fleets; structural usage monitoring will be a key asset in this drive. A highly cost effective indirect structural health and usage neural network (SHAUNN) monitoring system is proposed. A SHAUNN uses regression relationships determined by artificial neural networks to predict stresses, strains, loads, or fatigue damage from flight parameters. Within this paper the development of a SHAUNN monitoring system is described. Flight parametric data, captured during Operational Loads Measurement of the Royal Air Force Dominie TMk1 aircraft have been used to predict stresses at the key structural location in the wing, using mapping relationships determined by artificial neural networks. A framework for the development of the SHAUNN monitoring system is discussed and the basic architecture of the multilayer perceptron artificial neural network is described. It is concluded that this technology could provide the basis for an accurate, cost-effective structural usage monitoring system and further work to investigate the prediction of ground – based stresses in the wing is recommended.
Generic stability and control for aerospace flight vehicle conceptual design
Authors: Chudoba B. , Coleman G. , Smith H. , Cook M. V.
Published: February 2016

The recent period has been filled with exceptionally interesting developments and advances, resulting in high-performance conventional and non-conventional manned and unmanned aircraft. Although those vehicles seem to comply well with specific mission performance requirements, one is still confronted with an apparent weakness to reliably stabilise and control throughout the flight envelope. Since the provision of satisfactory stability and control characteristics invariably compromises flight performance, it becomes essential to identify and integrate performance-optimal stability and control design solutions early during the flight vehicle definition phase. In particular, the conceptual design of integrated control effectors for advanced aircraft is far from being trivial. Never before have we been presented with such tremendous wealth of specialised data and information suitable for detail design of controls. In contrast, never before has it been necessary to approach any one of the primary design disciplines still as entirely ad hoc and inconsistent as in the case of designing controls during the conceptual design phase. This need initiated the development of a configuration independent (generic) stability and control methodology capable of sizing primary control effectors of fixed wing subsonic to hypersonic designs of conventional and unconventional, symmetric and asymmetric configuration layouts. This paper summarises the methodology concept and demonstrates its versatility and validity by analyzing selected stability and control characteristics of the Northrop YB-49 flying wing.
The role of drag prediction in combat aircraft design and development
Authors: Newton J. B.
Published: February 2016

This paper gives an overview of combat aircraft drag prediction in the context of the overall design and development process.

Following a brief summary of the author’s experience in this field, the importance of drag prediction during initial configuration design is discussed, emphasising the need for the drag aerodynamicist to develop a good understanding of the other aerodynamic disciplines involved, as well as an appreciation of the of the total design process encompassing structural design, propulsion integration and systems installation.

A brief description is given of typical simplified prediction methods used in initial design, followed by an example of drag synthesis procedures based on wind-tunnel test and analysis, illustrating the need for good understanding of test techniques and the requirements of other aerodynamic disciplines.

Some future challenges are identified, requiring continual involvement in research and methods development programmes.
Aircraft gust load estimation due to atmospheric turbulence under different flight conditions
Authors: Abdulwahab E. N. , Hongquan C.
Published: February 2016

Based on power spectral technique and Lyapunov approach, methodology to determine the vertical gust load on aircraft encountering atmospheric turbulence under different flight conditions is presented in this paper. Modified longitudinal short period aircraft equations of motion to reflect gust inputs are solved. Family of five linear dynamics models of increasing gust excitation complexity are developed to describe the normal load factor throughout an aircraft due to vertical gust. These models (except Model 2) give a rapid estimation of normal load factor in case complete data are not readily available. Numerical model constructed for a Boeing 747 jet transport is solved to illustrate the results. These results show that Model 5 exhibits higher frequency contents when compared with other models under different flight conditions. The normal load factor of aircraft is estimated at different probabilities of not exceeding the corresponding load factor value based on statistical technique. The Models 1, 3, 4 and 5 predict the load factor with maximum 5% error when compared with Model 2 which considered all gust penetration effects. Finally, the results show a good agreement with the published work in load factor determination, at different probabilities of not exceeding this value when encountering a turbulent vertical gust.
One hundred years of aeronautics in East London
Authors: Ackroyd J. A. D. , Bernstein L. , Armstrong F. W.
Published: February 2016

This paper celebrates the centenary of Queen Mary College’s involvement in aeronautics, a celebration with a unique distinction since it was this College’s immediate forebear which was the first British higher education institution to begin teaching and research in this subject. Thus the emphasis is on the early years from 1907 until the 1950s, a period ripe for recording before it recedes beyond living memory, but also the period during which the degree course in aeronautical engineering became firmly established and its parent Department acquired its reputation for research. Section 2.0 gives a brief history of the College’s origins in the East London College. Subsequent sections deal with the foundation of the aeronautical laboratory there, from which the aeronautical department grew, and the activities of the two men who led these developments, A.P. Thurston and N.A.V. Tonnstein who changed his name to Piercy.
Balloons, airships and kites – lighter than air: past, present and future
Authors: Folkes J.
Published: February 2016

One hundred years on from the advent of aeronautics at Queen Mary, University of London, developments in lighter than air technology have progressed at a somewhat slower pace than the technology for heavier than air. Innovations afforded by the ‘discovery’ of helium, the development of the modern day hot air balloon and the application of new materials have all contributed to today’s technical innovations. A review is given of the past history of lighter than air, a note is made of the current state of the art and a brief overview of future applications is discussed. The author’s personal experience in long distance gas balloon flights is mentioned.
Technological aspects of gas turbine and fuel cell hybrid systems for aircraft: a review
Authors: Santin M. , Traverso A. , Massardo A.
Published: February 2016

The objective of this work is to make an overview of opportunities and issues related to the aeronautical application of solid oxide fuel cell hybrid systems. The great interest on fuel cells comes from their capacity of producing electric energy with high efficiency at low pollutant production. The application of these systems as full-time auxiliary power units is an interesting alternative in a future scenario, which is supposed to include a More Electric Aircraft and more restrictive environmental standards. A review of the technological aspects of this application is presented. The physical models found in literature were investigated and the results were compared and discussed.
System integration of high intensity energy subsystems – a thermal management challenge
Authors: Pratt D. M. , Moorhouse D.
Published: February 2016

Current and future Air Force weapons systems lack the necessary power and cooling capacity to provide full systems level capability as a result of energy and thermal management limitations. Cooling capacity of fuel is already fully utilised leaving little room for additional cooling needs. Additionally, increasing speed, power, and miniaturisation of future systems continue to stress any thermal management capability that we can now deliver. Thus, the focus of this paper is a conceptual assessment of the key energy and thermal management technologies to meet the future energy challenges. It presents an overview of the current state of the art and also possible future research.
Dimensionless analysis of the unstart boundary for 2D mixed hypersonic inlets
Authors: Chang J. , Yu D. , Bao W. , Qu L.
Published: February 2016

Inlet unstart boundary is one of the most important issues of the hypersonic inlet and is also the foundation of the protection control of a scramjet. To solve this problem, the 2D internal steady flow of a 2D mixed internal/external compression hypersonic inlet was numerically simulated at different freestream conditions and backpressures with a RANS (Reynolds-Averaged Navier-Stokes) solver using a RNG (Renormalisation Group) k-ε turbulence model, and two different inlet unstart phenomena were analysed. The dimensional analysis method was introduced to find the essence variables describing the inlet unstart boundary based on “numerical experimental” data in this paper. The dimensionless pressure ratios of the forebody and isolator were analysed respectively. The results show that the unstart boundary of the 2D mixed hypersonic inlet is determined by M0, α and Re0. Pressure ratio π increases with M0 increasing, and it increases firstly and decreases then with α increasing. Pressure ratio π increases with Re0 increasing. Re0 (Re0 < 2 × 107) has a major effect on π and Re0 (Re0 > 2×107) has little effect on π.
A timed method for the estimation of aeroplane take-off and landing distances
Authors: Gratton G. B.
Published: February 2016

This paper describes a method by which, without the use of external personnel or equipment, take-off and landing distances of an aeroplane may be estimated. An error analysis for the method, allowing determination of outcome accuracy, is also shown. The method is validated through use of flight test results from two certification programmes: one on a light aeroplane, and one on a microlight aeroplane.
Toward an intelligent, deterioration accommodating controller for aging turbofan engines
Authors: Turso J. A. , Litt J. S.
Published: February 2016

A method for accommodating engine deterioration via a scheduled linear parameter varying quadratic Lyapunov function (LPVQLF)-based controller is presented. The LPVQLF design methodology provides a means for developing unconditionally stable, robust control of linear parameter varying (LPV) systems. The controller is scheduled on the engine deterioration index, a function of estimated parameters that relate to engine health, and is computed using a multilayer feedforward neural network. Acceptable thrust response and tight control of exhaust gas temperature (EGT) is accomplished by adjusting the performance weighting on these parameters for different levels of engine degradation. Nonlinear simulations demonstrate that the controller achieves specified performance objectives while being robust to engine deterioration as well as engine-to-engine variations.
Helicopter load alleviation using active control
Authors: Voskuijl M. , Walker D. J. , Manimala B. J.
Published: February 2016

This paper discusses how structural load objectives can be included in a rotorcraft flight control system design in an efficient and straightforward way using multivariable control techniques. Several research studies have indicated that pitch link loads for various rotorcraft types can reach high or even unacceptable values, both in steady state and maneuvering flight. This is especially the case for high-speed aggressive maneouvers. Pitch link loads at high-speed flight are therefore taken as a case study. A novel longitudinal control system is presented, designed to reduce helicopter pitch-link loads during high-speed longitudinal manoeuvres whilst providing a pitch attitude command attitude hold response type. The design is based on a high-order model of a helicopter representative of the UH-60 Black Hawk. New metrics are presented for the analysis of structural loads that can be used in combination with ADS-33 handling qualities requirements.
Performance simulation of a high-bypass turbofan with a 2D representation of the intake and fan components
Authors: Mund F. C. , Pilidis P.
Published: February 2016

In conventional gas turbine performance simulation, engine components are represented by characteristics where the 3D properties of the flow fields are averaged providing key flow properties at the component interfaces. Even though a very efficient method, the simplification of 3D flows to an averaged value is not always desirable. In particular for high-bypass turbofan aero-engines, the fan generates significant pressure variations from hub to tip. These profiles are affected by the flow profile resulting from the intake where boundary layers introduce radial distortion patterns.

This study investigates a performance simulation method where the intake and fan component of a two-shaft high-bypass turbofan are represented in an axi-symmetric 2D fashion. The intake was modelled using a commercial computational fluid dynamics tool. The remaining engine components were modelled using an in-house conventional gas turbine simulation tool with a radial representation of the fan. The coordinated application of both tools required an iterative data exchange, which is described in detail.

The inclusion of the radial representation of fan and intake showed twice the effect on thrust per inlet loss at cruise conditions. It was therefore worth considering despite the significant numerical effort.
Dither-based compensating strategy for radome boresight error and gimbal friction
Authors: Lin Y.-C. , Lin C.-L. , Shi W.-C. , Huang S.-W.
Published: February 2016

This paper proposes an effective missile radome error compensator by incorporating a nondestructive dither on the missile guidance loop to improve tracking accuracy. The compensation strategy predicts the radome slope error by introducing the dithering techniques along with band-pass filtering mechanism. A new condition is derived to ensure the guidance and control system stability while there is in the presence of the compensation error. As an application, the design methodology is extended to deal with the gimbal friction compensation problem. Simulation study confirms efficacy of our proposed approach.
Solid propellants burning enhancement using foil embedding method
Authors: Darabkhanid H. G. , Mehdizadeh N. S.
Published: February 2016

The method of metal embedding is widely employed in solid propellant motors with end-burning configuration, thereby significantly improving the burning rate of the propellants. In this study, the cylindrical foil embedding method is applied to double-base solid propellant, as a new method, and the effects of the type and thickness of the foil on the burning surface, as well as the burning rate, are experimentally investigated. It is shown that by using the foil embedding method, the burning characteristics of solid propellants can be improved. Results have been compared to some available data. To the best of the author’s knowledge there are no published data available on this method.
Contrail avoidance in the aircraft design process
Authors: Noppel F. , Singh R.
Published: February 2016

As aviation is one of the fastest growing industrial sectors world wide, air-traffic emissions are projected to increase their stake in the contribution to global warming. According to studies, both carbon dioxide and contrails are the principal air-traffic pollutants, whereas the impact from contrails in terms of radiative forcing is possibly larger than that of all other air-traffic pollutants combined. New regulations with the objective of mitigating contrail occurrences might cause a change in the design requirements of aircraft. In light of this, a method considering contrail formation during the aircraft design process is presented in this paper. Aircraft performance and optimisation is carried out with NASA’s flight optimisation system. Combining historical meteorological data with air-traffic data enables an assessment regarding contrail formation. As an example, a particular aircraft type in terms of range, speed and payload is optimised for minimum block fuel consumption considering different altitudes. The change in contrail formation in terms of contrail-km formed is calculated. The results suggest that if aircraft of the considered class were designed for higher altitudes, contrail occurrences would diminish slightly at a non-negligible fuel burn penalty.
Trajectory optimisation of an aerobatic air race
Authors: Plas H. van der , Visser H. G.
Published: February 2016

This paper deals with the synthesis of optimal trajectories for aerobatic air races. A typical example of an air race event is the Red Bull Air Race World Series, where high-performance aerobatic aircraft fly a prescribed slalom course consisting of specially designed inflatable pylons, known as ‘air gates’, in the fastest possible time. The trajectory that we seek to optimise is based on such a course. The air race problem is formulated as a minimum-time optimal control problem and solved in open-loop form using a direct numerical multi-phase trajectory optimisation approach based on collocation and non-linear programming. The multiphase feature of the employed collocation algorithm is used to enable a Receding-Horizon optimisation approach, in which only a limited number of manoeuvres in sequence is considered. It is shown that the Receding-Horizon control approach provides a near-optimal solution at a significantly reduced computational cost relative to trajectory optimisation over the entire course. To avoid the path inclination singularity in the equations of motion based on Euler angles, a point-mass model formulation is used that is based on quaternions. Numerical results are presented for an Extra 300S, a purpose-designed aerobatic aircraft.
Air power and the future battlespace
Authors: Goulter C. J. M.
Published: February 2016

The aim of this paper is to consider the role of air power in the future, within the wider security environment and across the full spectrum of conflict. The key is to make some reasonable assumptions about the future strategic environment for the next ten to fifteen years, extrapolating from our experience since the end of the cold war and our existing knowledge of potential state threats and substate threats and challenges. One of our failings since the end of the cold war has been to focus on the operational level of war at the expense of thinking hard about national strategy. The formulation of national strategy is supposed to be directed by government, but if that government fails to provide strategic direction, as it has done over recent years, the result is short-termist perspectives, and a ‘hand to mouth’ approach to crisis management. This has been reinforced further by financial constraint and the electoral cycle. Ideally, a strategic perspective helps us not only to set our current age in a much wider context, thus preventing or making us less inclined to ‘knee-jerk’ reactions to single events, but it also assists in the making of correct judgements about the nature of a conflict or scenario, thus enabling us to apply the appropriate type of tool (air power or otherwise). History is littered with instances of the inappropriate use of military force, and air power is no exception, and we cannot afford nugatory manpower and material expenditure. The challenge is, therefore, enormous: to meet current commitments, while preparing for future possibilities.
VSTOL Aircraft market analysis
Authors: Howarth D. K.
Published: February 2016

This paper describes the market for air vehicles that offer Very Short Take Off and Landing (VSTOL) capabilities, also known as VSTOL aircraft. A commercial VSTOL aircraft will only succeed if it provides profits to both manufacturers and airlines. Being able to operate out of shorter fields offers airlines greater flexibility and therefore provides a benefit to the airline. However, adding VSTOL performance also adds cost. Successful VSTOL aircraft designs must balance the added cost against the additional benefits VSTOL performance will provide.

The first problem in any new VSTOL design is determining what field length provides the maximum benefit relative to cost. In order to be able to determine this one needs to know not only what it will cost to design and build the new aircraft, but its value to the airlines, as reflected by the demand for it and the price they are willing to pay. Only then is it possible to design the aeroplane the market wants at a sustainable price and in sufficient quantities to optimise the manufacturer’s return on investment.

This paper is a comprehensive parametric analysis of helicopters and aeroplanes that shows how much the market values short field performance by determining how much airline customers have been paying for it and how the market reacts to changes in its price. The analysis simultaneously considers over 230 currently produced models of fixed wing and rotary commercial aircraft, ranging in size from a Cessna 172 to an Airbus A380 and with balanced field lengths ranging from less than 150 to over 10,500ft.

The data show that a single, statistically significant demand curve exists for all of these vehicles, with prices that range across several orders of magnitude. This curve consists of several segments or sub-markets including those for regional and rotary wing aircraft. Both of those markets offer vehicles over a wide range of prices. The analysis shows that VSTOL price is a function of the balanced field length provided by the vehicles within these market segments. Comparing demand and sustained price against cost reveals particular field lengths for which it will be possible to make a profit building VSTOL aircraft.

Because the sustained price for a VSTOL aircraft is a function of its field length performance, and the quantity of a model sold is a function of its price, it follows that it is possible to predict the profit potential for a given VSTOL design in advance of its development. A thorough study of potential configurations therefore offers manufacturers the ability to design VSTOL aircraft that provide the maximum possible profit while fully satisfying the requirements of their airline customers.
Wind tunnel testing of powered lift, all-wing STOL model
Authors: Collins S. W. , Westra B. W. , Lin J. C. , Jones G. S. , Zeune C. H.
Published: February 2016

Short take-off and landing (STOL) systems can offer significant capabilities to warfighters and, for civil operators thriving on maximising efficiencies they can improve airspace use while containing noise within airport environments. In order to provide data for next generation systems, a wind tunnel test of an all-wing cruise efficient, short take-off and landing (CE STOL) configuration was conducted in the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) 14ft by 22ft Subsonic Wind Tunnel. The test’s purpose was to mature the aerodynamic aspects of an integrated powered lift system within an advanced mobility configuration capable of CE STOL. The full-span model made use of steady flap blowing and a lifting centerbody to achieve high lift coefficients. The test occurred during April through June of 2007 and included objectives for advancing the state-of-the-art of powered lift testing through gathering force and moment data, on-body pressure data, and off-body flow field measurements during automatically controlled blowing conditions. Data were obtained for variations in model configuration, angles of attack and sideslip, blowing coefficient, and height above ground. The database produced by this effort is being used to advance design techniques and computational tools for developing systems with integrated powered lift technologies.
Dependence of radiated sound frequency on vortex core dynamics in multiple vortex interactions
Authors: Zheng Z. C. , Li W.
Published: February 2016

With both theoretical analysis and measurement data, it has been identified previously that there exists a robust sound emission from a pair of counter-rotating aircraft wake vortices at the frequency of unsteady vortex core rotation. In a vortex system with multiple vortices, the sound emission frequency can be subjected to change because of interactions among the vortices. The behaviour of the influence, indicated by the ratio between the core size and the distance of the vortices and the underlining vortex core dynamic mechanisms, is investigated in this study. A vortex particle method is used to simulate the vortex core dynamics in two-dimensional, inviscid and incompressible flow. The flow field, in the form of vorticity, is employed as the source in the far-field acoustic calculation using a vortex sound formula. Cases of co-rotating vortices and a multiple-vortex system composed of two counter-rotating vortex pairs are studied for applications to aircraft wake vortex sound. The study shows, without vortex merging, individual frequencies can be clearly identified that are due each to core rotation (self induction) and co-rotating motion of a vortex centre around the other (mutual induction). The ratio of the core size and the distance between vortices does not seem to significantly influence the frequency of vortex core rotation. With vortex merging, a single frequency due to the merged vortex core is generated.
The leading-edge vortex and aerodynamics of insect-based flapping-wing micro air vehicles
Authors: Wilkins P. C. , Knowles K.
Published: February 2016

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.
Effect of aft wall slope on cavity pressure oscillations in supersonic flows
Authors: Vikramaditya N. S. , Kurian J.
Published: February 2016

An experimental study of supersonic flow over wall mounted cavities with different aft wall angles is carried out. Unsteady pressure measurements were made on the walls and floor of the cavity. Data analysis was performed on the experimental results using statistical methods. In the case of higher angled cavities, the presence of an upstream traveling acoustic wave could be confirmed. For lower angled cavities (60 degrees and less) where the acoustic wave could not be identified, the flow inside the cavity was more or less stable. Mode switching occurring in higher angled cavities was confirmed by spectrogram studies.
A new model for optimal TF/TA flight path design problem
Authors: Zardashti R. , Bagherian M.
Published: February 2016

This paper focuses on the three dimensional flight path planning for a UAV on a low altitude terrain following/terrain avoidance mission. Using an approximate grid-based discretisation scheme, we transform the continuous optimisation problem into a search problem over a finite network, and apply a variant of the shortest-path algorithm to this problem. In other words using the three dimensional terrain information, three dimensional flight path from a starting point to an end point, minimising a cost function and regarding the kinematics constraints of the UAV is calculated. A network flow model is constructed based on the digital terrain elevation data (DTED) and a layered network is obtained. The cost function for each arc is defined as the length of the arc, then a constrained shortest path algorithm which considers the kinematics and the altitude constraints of the UAV is used to obtain the best route. Moreover the important performance parameters of the UAV are discussed. Finally a new algorithm is proposed to smooth the path in order to reduce the workload of the autopilot and control system of the UAV. The numeric results are presented to verify the capability of the procedure to generate admissible route in minimum possible time in comparison to the previous procedures. So this algorithm is potentially suited for using in online systems.
Impact damage and repair of composite structures
Authors: Falzon B. G.
Published: February 2016

This paper gives an overview of the work carried out in a GARTEUR (Group for Aeronautical Research and Technology in Europe) program, under the chairmanship of the author, to develop and validate analytical and numerical methods to characterise real impact damage in composite structures, particularly those designed to sustain load in a postbuckled state, and to study the durability of bonded repairs. GARTEUR is an inter-governmental agreement between the seven European countries with the largest direct employment in the Aerospace industry, to mobilise scientific and technical knowledge between the member countries. A number of Action Groups have been launched, since GARTEUR’s inception in the early 1970s, to address specific technical issues of interest to the participating members. The research presented in this paper was performed under Action Group 28 with partners from ONERA, EADS-CCR (France), DLR, AIRBUS-Deutschland, EADS-M (Germany), CIRA (Italy), INTA (Spain), SICOMP, Saab, (Sweden), NLR (The Netherlands), QinetiQ, BAE Systems, Imperial College London and the University of Sheffield (United Kingdom). The Action Group tasks were divided into four Work Elements (WEs): WE1-Prediction and characterisation of impact damage, WE2-Postbuckling with delamination, WE3-Repair and WE4-Fatigue. This paper outlines the main developments and achievements within each Work Element.
A causal factors analysis of helicopter accidents in New Zealand 1996-2005 and the United Kingdom 1986-2005
Authors: Majumdar A. , Mak K. , Lettington C. , Nalder P.
Published: February 2016

Helicopter accidents cause many fatalities, and their avoidance is a major area of work for Civil Aviation safety authorities around the World. This paper uses helicopter accident data from the United Kingdom between 1986 and 2005 for 566 accidents and from New Zealand between 1996 and 2006 for 230 accidents to analyse helicopter accidents according to five categories of causes: airworthiness failure (engine); airworthiness failure (non-engine), operational failure, maintenance failure and mixed failure (i.e. operational and airworthiness combined). Factors associated with accidents, e.g. the engine types and weights of the helicopters involved; the nature of the operations and the phase of flight of the helicopter are also analysed. Operational failures were further analysed by Human Factors Analysis and Classification Scheme (HFACS) and airworthiness failures by a logical scheme of helicopter components. The results indicate that operational failures, especially due to unsafe acts, are the major cause of accidents in both countries followed by airworthiness causes. Light single piston helicopters are by far the major group associated with accidents in both countries, with few accidents for twin turbine helicopters. The majority of accidents were in non-public operations with few in public operations and in both countries, the cruise/flight/circuit phase has the largest number of accidents. Further analyses indicated statistically significant associations: type of helicopter and the cause of accidents; type of helicopter and the phase of flight; cause of accidents and nature of flights; cause of accidents and phase of flights; training flights and inadequate supervision; landing and procedural error and cruise and attention failure.
Improved models for runway debris lofting simulations
Authors: Nguyen S. N. , Greenhalgh E. S. , Iannucci L. , Olsson R. , Curtis P. T.
Published: February 2016

Numerical models used to simulate the lofting mechanisms of runway stones were developed to assess the threat to aircraft structures from runway debris impacts. An inflated aircraft tyre model, which was validated by comparison with experimental indentation tests, showed that over-rolling of stones under typical take-off conditions led to only modest vertical loft velocities of less than 5 m/s. Experiments using a drop weight impactor simulated a section of aircraft tyre descending upon stones. These tests demonstrated that lofting was achieved for impacts with low rubber thickness. However, for impacts with greater rubber thickness, lofting was suppressed. Using more realistic tyre geometries resulted in launches with backspin, but only horizontally along the ground in the direction of the tyre axis. The speed at which launches occurred was proportional to the rate of descent of the tyre section and would consequently determine the loft speeds due to potential asperity lofting.