bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady and unsteady pressure measurements on a swept-wing aircraft
Authors: Jansson N. , Stenfelt G.
Published: February 2016

Steady and unsteady pressure measurements are conducted for a tailless aircraft model. The main aim with the presented experimental work is to investigate the difficulties and possibilities involved in using an available pressure sensing system for accurate unsteady pressure measurement. The experimental procedure which is utilised for unsteady pressure measurements is described in detail. In particular, the importance of synchronised timing is recognised. For a harmonically varying pressure a small time delay in the measurement chain can result in a significant phase shift. Also, difficulties and uncertainties that are still present are pointed out. The results from these experiments are compared to numerical results based on unsteady potential flow theory. In general, the experimental and computational results show similar trends. Especially good agreement is found for the steady pressure measurements. For the unsteady pressure measurements a possible Reynolds number dependency is found for the considered test conditions.
Visual aspects of advanced sensors and helmet-mounted displays
Authors: Morgan-Warren P. J. , Woodcock M.
Published: February 2016

Visually coupled systems such as helmet mounted displays are designed to improve aircrew situational awareness by providing timely flight, targeting and other information overlaid on real or sensor-derived views of the external environment. Data can be presented in monocular, biocular or binocular fashion and are associated with visual conflicts and potential ophthalmic problems. Restricted sensor spectrum, limits of resolution, inherent system latency, the displaced visual input from remote sensors and restricted field of view may contribute to ophthalmic symptoms in aircrew. Disruption to binocularity and reliance on monocular cues for depth perception and hyperstereopsis from sensor-induced convergence disparity may cause distance estimation problems, whereas inappropriate accommodative stimuli and ocular dominance factors are common causes of eyestrain. Binocular rivalry from discordant imagery to each eye may compromise visual performance via several mechanisms. This article discusses the potential visual problems associated with visually coupled systems and the challenges of integrating complex systems with the aircrew interface.
Runway debris impact threat maps for transport aircraft
Authors: Nguyen S. N. , Greenhalgh E. S. , Graham J. M. R. , Francis A. , Olsson R.
Published: February 2016

Large transport aircraft are particularly susceptible to impact damage from runway debris thrown up by the landing gear. A methodology was developed to predict the trajectories of stones lofted by the nose wheel and subjected to aerodynamic forces due to the wake behind the nose landing gear and beneath the aircraft. In conjunction with finite element modelling of the stone/ground/tyre contact mechanics, an analytical model was used to perform a stochastic prediction of the trajectories of runway stones to generate impact threat maps which showed the relative likelihood of stones impinging upon various areas on the underside of a C-130 Hercules. The impact envelopes for the C-130 extended three to eighteen metres behind the nose wheel and two metres either side of the centre of the aircraft. The impact threat maps were especially sensitive to the values of the coefficients of lift and drag acting on the stone during its flight.
Modelling lay-up automation and production rate interaction on the cost of large stiffened panel components
Authors: Mullan M. , Murphy A. , Quinn D. , Price M. , Butterfield J. , Cowan S. , McElroy P. , Hawthorne P. , Robertson S.
Published: February 2016

This paper presents an integrated design and costing method for large stiffened panels for the purpose of investigating the influence and interaction of lay-up technology and production rate on manufacturing cost. A series of wing cover panels (≈586kg, 19·9m2) have been sized with realistic requirements considering manual and automated lay-up routes. The integrated method has enabled the quantification of component unit cost sensitivity to changes in annual production rate and employed equipment maximum deposition rate. Moreover the results demonstrate the interconnected relationship between lay-up process and panel design, and unit cost. The optimum unit cost solution when using automated lay-up is a combination of the minimum deposition rate and minimum number of lay-up machines to meet the required production rate. However, the location of the optimum unit cost, at the boundaries between the number of lay-up machines required, can make unit cost very sensitive to small changes in component design, production rate, and equipment maximum deposition rate.
A review of train aerodynamics Part 2 – Applications
Authors: Baker C. J.
Published: February 2016

This paper is the second part of a two-part paper that presents a wide-ranging review of train aerodynamics. Part 1 presented a detailed description of the flow field around the train and identified a number of flow regions. The effect of cross winds and flow confinement was also discussed. Based on this basic understanding, this paper then addresses a number of issues that are of concern in the design and operation of modern trains. These include aerodynamic resistance and energy consumption, aerodynamic loads on trackside structures, the safety of passengers and trackside workers in train slipstreams, the flight of ballast beneath trains, the overturning of trains in high winds and the issues associated with trains passing through tunnels. Brief conclusions are drawn regarding the need to establish a consistent risk based framework for aerodynamic effects.
Transonic aerofoils admitting anomalous behaviour of lift coefficient
Authors: Kuzmin A. , Ryabinin A.
Published: February 2016

Transonic flow past a Boeing 737 Outboard aerofoil and Whitcomb one with a defected aileron is studied. The flow simulation is based on the system of Reynolds-averaged Navier-Stokes equations. The numerical study demonstrates the existence of free-stream conditions in which small perturbations produce abrupt changes of the lift coefficient. Also the simulation reveals adverse conditions in which aileron deflections have no influence on the lift.
Evaluation of aero gas turbine preliminary weight estimation methods
Authors: Lolis P. , Giannakakis P. , Sethi V. , Jackson A. J. B. , Pilidis P.
Published: February 2016

The estimation of gas turbine engine weight during the preliminary or conceptual design phase is a key part of a Techno-economic Environmental Risk Analysis (TERA). Several methods that are available in the public domain are analysed and compared, in order to establish the physics driving them and their suitability for the weight estimation of modern gas turbine engines. Among the tested methods, only WATE managed to achieve acceptable accuracy for engine optimisation studies. This work demonstrates that the age and restrictions of existing ‘whole engine based’ methods, along with their dependency on old engine databases make them unsuitable for future and novel aero engines. A hybrid weight modelling approach is proposed as a solution permitting the creation of simple ‘whole engine based’ methods that do not depend on the availability of existing engine data, which are also subject to uncertainties and incoherencies.
Flow over a glider canopy
Authors: Jonker A. S. , Bosman J. J. , Mathews E. H. , Liebenberg L.
Published: February 2016

In order to minimise drag, the front part of most modern glider fuselages is shaped so that laminar flow is preserved to a position close to the wing-to-fuselage junction. Experimental investigations on a full-scale JS1 competition glider however revealed that the laminar boundary layer in fact trips to turbulent flow at the fuselage-to-canopy junction position, increasing drag. This is possibly due to ventilation air leaking from the cockpit to the fuselage surface through the canopy seal, or that the gap is merely too large and therefore trips the boundary layer to turbulent flow. The effect of air leaking from the fuselage-to-canopy gap as well as the size of the gap was thus investigated with the use of computational fluid dynamics. It was found that if air was leaking through this gap the boundary layer would be tripped from laminar to turbulent flow. It was also found that the width of the canopy-to-fuselage gap plays a significant role in the preservation of laminar flow. If the gap is less than 1mm wide, the attached boundary layer is able to negotiate the gap without being tripped to turbulent flow, while if the gap is 3mm and wider, it will be tripped from laminar to turbulent flow. The work shows that aerodynamic drag on a glider can be significantly minimised by completely sealing the fuselage-to-canopy gap and by ensuring a seal gap-width of less than 1mm.
Conflict detection and resolution algorithms for UAVs collision avoidance
Authors: Migliaccio G. , Mengali G. , Galatolo R.
Published: February 2016

Collision-avoidance is a safety-critical requirement to operate UAVs in non-segregated airspaces. In case of communication problems between a UAV and the corresponding pilot-in-command, a technology is required onboard the UAV to implement a capability to detect and avoid collision-hazards even autonomously. After an introduction to the problem of developing a so-called sense-and-avoid system and its avoid-function, this work presents a solution in terms of algorithms to implement the above capability. To detect and resolve potential mid-air conflicts, a geometric deterministic approach has been utilised: an intruder is modeled trough a moving-ellipsoid and a four-dimensional approach in the time-space domain provides the solution. The approach makes use of kinematics information to detect potential conflicts and to provide actions for conflict resolution, such as speed-changes in intensity and/or direction. The proposed solution also enables the UAV to meet the applicable vertical and horizontal minima of separation and to comply with real-time constraints.
Advanced open rotor noise prediction
Authors: Kingan M. J.
Published: February 2016

The purpose of this paper is to describe the current status of open rotor noise prediction methods and to highlight future challenges in this area. A number of analytic and numerical methods are described which can be used for predicting ‘isolated’ and ‘installed’ open rotor tonal noise. Broadband noise prediction methods are also described and it is noted that further development and validation of the current models is required. The paper concludes with a discussion of the analytical methods which are used to assess the acoustic data collected during the high-speed wind-tunnel testing of a model scale advanced open rotor rig.
Triangular tabs for supersonic jet mixing enhancement
Authors: P. Arun Kumar , Rathakrishnan E.
Published: February 2016

The mixing promoting capability of right-angled triangular tab with sharp and truncated vertex has been investigated by placing two identical tabs at the exit of a Mach 2 axi-symmetric nozzle. The mixing promoting efficiency of these tabs have been quantified in the presence of adverse and marginally favourable pressure gradients at the nozzle exit. It was found that, at all levels of expansion of the present study though the core length reduction caused by both the tabs are appreciable, but the mixing caused by the truncated tab is superior. The mixing promoting efficiency of the truncated tab is found to increase with increase of nozzle pressure ratio (that is, decrease of adverse pressure gradient). For all the nozzle pressure ratios of the present study, the core length reduction caused by the truncated vertex tab is more than that of sharp vertex tab. As high as 84% reduction in core length is achieved with truncated vertex right-angled triangular tabs at moderately overexpanded level, corresponding to expansion levelpe/pa= 0·90. The corresponding core length reduction for right-angled triangular tabs with sharp vertex and rectangular tabs are 65% and 31%, respectively. The present results clearly show that the mixing promoting capability of the triangular tab is best than that of rectangular tabs at identical blockage and flow conditions.
On the interaction of a racing car front wing and exposed wheel
Authors: Diasinos S. , Doig G. , Barber T. J.
Published: February 2016

A numerical investigation of generic open-wheel racing car wing and wheel geometry has been conducted, using original sub-scale experimental data for validation. It was determined that there are three main interactions that may occur, identifiable by the path that the main and secondary wing vortices take around the wheel. Interaction ‘A’ occurs when the main and secondary wing vortices both travel outboard of the wheel; interaction ‘B’ is obtained when only the main wing vortex passes inboard of the wheel; while interaction ‘C’ sees both wing vortices travel inboard of the wheel. The different interactions are achieved when geometric changes to the wing affect the pressure distribution about the endplate, either by altering the magnitude of suction generated by the wing or by changing the locations of peak suction and vortices relative to the wheel’s stagnation regions. As a result, the influence that the wing and wheel have on each other – in comparison to the same bodies in isolation – varies, resulting in significant consequences for downforce and drag.
Estimation of lateral-directional aerodynamic derivatives from flight data using conventional and neural based methods
Authors: Kumar R. , Ghosh A. K.
Published: February 2016

The paper presents the estimation of lateral-directional aerodynamic derivatives (parameters) using conventional and neural based methods from real flight data of Hansa-3 aircraft. The conventional methods such as least squares (LS) and maximum likelihood (ML) require an a priori postulation of mathematical model to estimate the parameters. Whereas the neural-based method such as Neural-Gauss-Newton (NGN) is an algorithm that utilises feed forward neural network and Gauss-Newton optimisation to estimate the parameters and does not require any a priori postulation of mathematical model or solution of equations of motion. In the paper, the LS, ML and NGN methods are applied to lateral-directional flight data in order to estimate parameters. The results obtained in terms of lateral-directional aerodynamic derivatives are reasonably accurate to establish LS, ML and NGN as parameter estimation methods along with NGN method having an additional advantage of non-requirement of a priori mathematical model. The paper also highlights the effect of different types of control inputs on parameter estimation. For this, three types of control inputs were used to generate real flight data. The ailerons and rudder were deflected in the first, the ailerons were deflected while keeping rudder at trim condition in the second and the rudder was deflected while keeping ailerons at trim condition in the third type of control input to generate the real flight data. The paper presents the effect of three different types of control inputs in terms of aerodynamic parameters estimated through conventional and neural based methods using flight data generated through these inputs.
Bayesian sensitivity analysis of flight parameters that affect main landing gear yield locations
Authors: Sartor P. , Worden K. , Schmidt R. K. , Bond D. A.
Published: February 2016

An aircraft and landing gear loads model was developed to assess the Margin of Safety (MS) in main landing gear components such as the main fitting, sliding tube and shock absorber upper diaphragm tube. Using a technique of Bayesian sensitivity analysis, a number of flight parameters were varied in the aircraft and landing gear loads model to gain an understanding of the sensitivity of the MS of the main landing gear components to the individual flight parameters in symmetric two-point landings. The significant flight parameters to the main fitting MS, sliding tube bending moment MS and shock absorber upper diaphragm tube MS include: longitudinal tyre-runway friction coefficient, aircraft vertical descent velocity, aircraft Euler pitch angle and aircraft mass. It was also shown that shock absorber servicing state and tyre pressure do not contribute significantly to the MS.
An unsteady numerical analysis of a generic non-axisymmetric turbine endwall in a 1½ stage turbine test rig
Authors: Dunn D. , von Backström T.W. , Snedden G.
Published: February 2016

As concern for the environment increases, so does the desire to reduce emissions and improve fuel efficiency. One avenue being investigated in the aerospace industry is the reduction in losses in a gas turbine engine through endwall contouring, which has shown some promise in improving efficiency. The current investigation was aimed at investigating the unsteady effects downstream of a rotor with a non-axisymmetric endwall contour originally designed for a cascade.

Previous investigations (numerical and experimental) have shown that the endwall contour improved the turbine efficiency by reducing the cross passage secondary flows. The contour however had a detrimental effect on the tip flow. The current investigation found that there were negligible unsteady differences between the annular and contoured rotor, with the average comparing well to the steady state results. It was also found that the effects at the tip were due to the experimental blades untwisting during operation.
Characterisation of a highly staggered spanwise cambered biplane
Authors: Traub L.W. , Waghela R. , Bordignon K.A.
Published: February 2016

An investigation is presented to elucidate the performance of a staggered, spanwise cambered biplane. The spanwise camber yielded wings forming a ‘∧’ or ‘∨’ when viewed streamwise. The configuration is examined in terms of its aerodynamic and stability characteristics. The feasibility of negating the requirement for a conventional empennage is explored. Geometric variation encompassed front and back wing anhedral/dihedral angles yielding 49 combinations. Evaluation of the geometry was accomplished using both wind tunnel testing and numerical simulation. The results indicated that front wing dihedral in conjunction with aft wing anhedral was most beneficial, such that the benefit of wake spacing was maximised. Aerodynamic benefit was indicated compared to a conventional empennage geometry. The greatest disparity in behaviour of the fore and aft wing anhedral/dihedral distribution was in the high lift regime, where the nature of the stall varied. Simulations to establish the viability of the geometry in terms of controllability were also conducted and indicated that the configuration is viable.
Flight in nature I: Take-off in animal flyers
Authors: Manzanera R.A. Jiménez , Smith H.
Published: February 2016

In this review paper, several take-off techniques of different species of animal flyers and gliders, both extinct and extant, are analysed. The methods they use vary according to animal group and size. Smaller animals, such as insects, rely on the use of transient aerodynamic techniques or the use of stored elastic energy. Medium-size flyers such as birds, bats, and other mammal gliders initiate flight by a jump which involves leg and wing movement coordination. The largest animals to fly, the extinct pterosaurs, are believed to have used a combination of aerodynamic and mechanic techniques in order to become airborne. The information presented here can be used as a resource for novel biomimetic unmanned aircraft design.
Compressibility effects for the AGARD-B model
Authors: Tuling S. , Vallabh B. , Morelli M.F.
Published: February 2016

A numerical study of the flow topologies over the 60° delta wing of the AGARD-B model at Mach 0·80 has revealed that vortex bursting occurs between 13°-15° angle-of-attack, while vortex separation occurs above 18°. These aerodynamic features have been identified as additional comparison criteria which need to be replicated for facilities using the model for calibration or inter-tunnel comparison purposes. The numerical simulations were performed using ANSYS Fluent V13, a structured mesh with near wall treatment and the Spalart-Allmaras and κ-ω SST turbulence models, and validated experimentally in a 5′ × 5′ transonic facility. Other aspects not previously identified or studied are firstly a recovery shock between the primary and secondary vortex that exists only when vortex bursting occurs, and secondly the lack of a shock between the wing and vortex when the flow topology corresponds to the centreline shock region as observed in other studies.
Numerical validation and back-pressure effect on internal compression flows of typical supersonic inlet
Authors: Ding F. , Shen C.-B. , Huang W. , Liu J.
Published: February 2016

A numerical study was conducted to analyse the performance of different turbulence models and different turbulence intensities and turbulence length scales specified for the boundary condition of the inflow to the internal compression flow field of a typical supersonic inlet. The effect of the back-pressure ratio on the properties of the flow field was also investigated. Computational results obtained by the commercial software FLUENT, which is used to solve the full two-dimensional Reynolds-averaged Navier-Stokes equations, were validated through both graphical and quantitative comparisons with previously published experimental data. The two-equation models that were considered in this study are the RNGk-ε, realisablek-ε, standardk-ε, and SSTk-ω turbulence models. The RNGk-ε model had the best performance among the four models and predicted good wall pressure distributions. The best agreement between the predicted results and experimental data was obtained when either the default values of the freestream turbulence intensity and length scale in the FLUENT solver were used, or the empirical formula was used to calculate the two parameters of the freestream turbulence properties. The shock wave pattern varied between the oblique mode and the fully developed normal mode with increasing back-pressure ratio, and the unstart phenomenon occurred when the back-pressure ratio was sufficiently high.
Downstream evolution of wingtip vortices produced from an inverted wing
Authors: Barber T. , Kurts P.
Published: February 2016

Counter-rotating vortices form from the opposite edges of lifting surfaces, and gradually move laterally and dissipate as they travel downstream (as seen in a wing-fixed reference frame). Under ground effect conditions, the vortex from a lifting wing – such as that used in an aircraft application – moves laterally outboard from the wingtip as it progresses downstream; for a downforce wing in ground effect – such as that used in an automotive application – the vortex moves laterally inboard. An interesting case is the situation where the inboard moving vortices become in close proximity to each other. The objective of the present study was to investigate counter-rotating vortices produced from a low aspect ratio downforce wing operating in ground effect. The pair of vortices move towards each other and mutually induce an upwards directed motion which in turn reduces the inboard movement driven by the ground effect. Experimental data gained from three-dimensional Laser Doppler Anemometry in a moving ground wind-tunnel was used to validate a Large Eddy Simulation computational result.
Maintenance test flying – an accident waiting to happen?
Authors: Poprawa S.
Published: February 2016

This paper focuses on maintenance test flying as pertaining to commercial jet aircraft. Aircraft maintenance manuals or regulatory prescriptions require aircraft to be test flown prior to being released to service, following specific maintenance, repair, overhaul or modification events. Further, such flights might be conducted to accept or return aircraft as demonstration of their serviceability. Similarly, test flights to verify aircraft performance are at times required.

Such maintenance test flights are mostly conducted by pilots rated to fly those aircraft primarily in commercial line operations, typically with no or little training on such specific maintenance or performance test flight procedures or techniques. The international regulatory environment remains in flux with discussion ongoing.

In conducting such flights a pilot is exposed to activities outside the normal aircraft standard operating procedures up to the edge of the operational flight envelope. Whilst not intentional, abnormal aircraft behaviour can nevertheless result in inadvertent flight outside the envelope with a consequential potential loss of control. History has shown that the predominant cause of fatal accidents during maintenance test flying result from complex loss of control scenarios not recovered or not recoverable. This raises the question of adequacy of pilot training.

Maintenance test flights are a necessary component for the industry to maintain its exceptional safety standards and minimising loss of life. But such flights in themselves remain demonstrably one or two orders of magnitude more risky than commercial flights.
Experimental and numerical study of the flight of geese
Authors: Dimitriadis G. , Gardiner J. D. , Tickle P. G. , Codd J. , Nudds R. L.
Published: February 2016

The flight of barnacle geese at airspeeds representing high-speed migrating flight is investigated using experiments and simulations. The experimental part of the work involved the filming of three barnacle geese (Branta Leucopsis) flying at different airspeeds in a wind tunnel. The video footage was analysed in order to extract the wing kinematics. Additional information, such as wing geometry and camber was obtained from a 3D scan of a dried wing. An unsteady vortex lattice method was used to simulate the aerodynamics of the measured flapping motion. The simulations were used in order to successfully reproduce the measured body motion and thus obtain estimates of the aerodynamic forces acting on the wings. It was found that the mean of the wing pitch angle variation with time has the most significant effect on lift while the difference in the durations of the upstroke and downstroke has the major effect on thrust. The power consumed by the aerodynamic forces was also estimated; it was found that increases in aerodynamic power correspond very closely to climbing motion and vice versa. Root-mean-square values of the power range from 100W to 240W. Finally, it was observed that tandem flying can be very expensive for the trailing bird.
Constrained multi-objective aerofoil design using a multi-level optimisation strategy
Authors: Cameron L. , Early J. , McRoberts R. , Price M.
Published: February 2016

A novel approach for the multi-objective design optimisation of aerofoil profiles is presented. The proposed method aims to exploit the relative strengths of global and local optimisation algorithms, whilst using surrogate models to limit the number of computationally expensive CFD simulations required. The local search stage utilises a re-parameterisation scheme that increases the flexibility of the geometry description by iteratively increasing the number of design variables, enabling superior designs to be generated with minimal user intervention. Capability of the algorithm is demonstrated via the conceptual design of aerofoil sections for use on a lightweight laminar flow business jet. The design case is formulated to account for take-off performance while reducing sensitivity to leading edge contamination. The algorithm successfully manipulates boundary layer transition location to provide a potential set of aerofoils that represent the trade-offs between drag at cruise and climb conditions in the presence of a challenging constraint set. Variations in the underlying flow physics between Pareto-optimal aerofoils are examined to aid understanding of the mechanisms that drive the trade-offs in objective functions.
Preliminary flight test correlations of the X-HALE aeroelastic experiment
Authors: Jones J. R. , Cesnik C. E. S.
Published: February 2016

An experimental, remotely-piloted aircraft has been designed and fabricated at University of Michigan that is aeroelastically representative of very flexible aircraft. Known as X-HALE, this Experimental High-Altitude Long-Endurance aircraft exhibits geometrically nonlinear behaviour and displays specific aeroelastic characteristics designed into the experiment. This paper presents the data from the initial flight tests of the lightly instrumented X-HALE Risk Reduction Vehicle that confirm the expected aeroelastic characteristics. This opens the way for future flight tests with a fully-instrumented platform which will provide data to support validation of coupled, nonlinear aeroelastic/flight dynamic codes.
Separation investigation of endo-atmospheric multi-stage space probe
Authors: Samani M. , Ghapanvary M. A.
Published: February 2016

This paper deals with selection and analysis of two-stage endo-atmospheric separation of supersonic parachute of a test projectile. Flight scenario reads that after the motor burns out, it is separated from the projectile, a few moments after which the parachute is ejected out of the payload and set in the open mode. It is important to study the modes of the stages involved and set a safe distance between them. As this process involves some random variables and needs more time, a shortcut statistical method has been employed in uncertainty variables functions to carry out the analysis. It is meant to take appropriate measures in order for the separation to be collision-free and safe. To do so, relative position of the two stages are modelled and simulated. A statistical method is employed to analyse the relative distance between the two stages in critical points. The results reflect that a safe distance is maintained in the stage of parachute deployment and after supersonic parachute is employed. In addition the said analysis is also carried out via Monte Carlo method. Comparison of the results of these two methods is indicative of a small error. The statistical method is validated and sufficient knowledge on relative attitudes of the stages is obtained.
Rotorcraft-pilot coupling analysis through state-space aerodynamic modelling
Authors: Serafini J. , Greco L. , Gennaretti M.
Published: February 2016

The terminology ‘rotorcraft-pilot coupling’ denotes phenomena arising from interaction between pilot and rotorcraft. Among these, the present work deals with ‘pilot-assisted oscillations’ that derive from unintentional pilot actions on controls due to seat vibrations, and are strictly related to rotor-aeroelasticity/airframe-structural-dynamics coupling, with involvement of blade control actuator dynamics. Focusing the attention on helicopters, a comprehensive rotorcraft model is developed and applied, with main rotor unsteady aerodynamics described in state-space form. This makes it particularly suited for stability and frequency-response analysis, as well as control applications. Numerical investigations address two critical rotorcraft-pilot coupling aeroelastic issues: stability of vertical bouncing and gust response in hovering. Results from main rotor unsteady aerodynamics modelling are compared with widely-used quasi-steady aerodynamics predictions. These suggest that, for accurate RPC/PAO phenomena predictions, mathematical modelling should include the three-dimensional, unsteady-flow effects, and that the pilot-in-the-loop passive behaviour produces a beneficial effect on the load factor generated by gust encountering.
Total pressure distortion levels at the aerodynamic interface plane of a military aircraft
Authors: Triantafyllou T. , Nikolaidis T. , Diakostefanis M. , Pilidis P.
Published: February 2016

Military aircrafts are often subjected to severe flight maneuvers with high Angles-of -Attack (AOA) and Angles of Sideslip (AOSS). These flight attitudes induce non-uniform in flow conditions to their gas turbine engines which may include distortion of inlet total pressure and total temperature at the Aerodynamic Interface Plane (AIP). Operation of the downstream compression system with distorted inflow typically results in reduced aerodynamic performance, reduced stall margin, and increased blade stress levels. In the present study the steady state total pressure distortion induced to the Aerodynamic Interface Plane due to the aircraft’s flight attitude have been estimated in terms of distortion descriptors. The distorted conditions at the interface between the intake and the engine have been predicted by using Computational Fluid Dynamics (CFD), where 33 different aircraft flight attitudes have been tested. Based on the obtained results the effect of Angle-of-Attack (AOA) and Angle of Side Slip (AOSS) on the distortion descriptors have been studied. The results showed that the distortion effect becomes more pronounced whenever this specific airframe configuration is exposed to incoming flow with an AOSS. Among the tested cases, the greatest total pressure defect at the AIP in terms of difference from the average value and of circumferential extent was calculated for the flight attitudes of 0·35M flight with 0° AOA and 8° AOSS and 0·35M fight with 16° AOA and 16° AOSS.
Estimating aerofoil lift from flow angle
Authors: Traub L. W.
Published: February 2016

Estimation of the lift of an aerofoil is one of the fundamental measurements of fluid mechanics. Lift is commonly measured using a load cell or a force balance. Non-intrusive methods to measure lift are usually pressure based. Aerofoils may be pressure tapped where small surface orifices are connected via tubing to a pressure measurement system, either a multi-tube manometre or an electronic system. Both measurement options add cost and complication, especially in an educational setting. Pressure tapping small aerofoils can also be difficult, especially if the models are rapid prototyped (RP). Low model surface resolution (from RP manufacture) and confined geometry complicate model assembly and finishing. Boundary-layer transition caused by poorly implemented tappings (too large a diametre or poorly aligned, i.e. straight aft) can also alter results. Wall pressure tappings may also be used and have the benefit of being non-intrusive. To implement, the test section roof and floor is tapped with a streamwise row of ports that facilitate measurement of the wall pressure signature. Integration of the pressure differential then relates to the lift produced. This measurement methodology still requires a multi-channel pressure acquisition system and modification of the wind tunnel. In Refs 4,5 methods are presented that facilitate calculation of the instantaneous forces acting on a body through flow field measurements determined using particle image velocimetry. However, the required flow field measurements encompass those surrounding the body, and are not a simple point measurement. In Ref. 6 a method is presented to estimate the lift of an aerofoil using two Pitot-static tubes that are used to measure the velocity above and below the aerofoil’s quarter chord. Wall corrections are required to yield an accurate lift estimate.
Predicting the certification basis for airliner air-to-air refuelling
Authors: Spencer R. J.
Published: February 2016

The premise is that in the future civil Air-to-Air Refuelling (AAR) will become an economic necessity if popular mass air travel is to continue. What is attempted is to provide a contemporary view of how such future operations could be safely undertaken. The intention is to predict the certification basis for demonstrating safe AAR operation of Cruiser-Feeder concepts. The necessary systems and aircraft functions are treated very much as they are today when civil certifying a large aeroplane type. The compliance demonstration required for environmental conditions, flight envelope, systems providing the necessary functionality, structural integrity, weight and balance are discussed.

Applicable existing civil certification requirements are identified and where necessary expanded in scope to accommodate AAR operation. Where contemporary material does not supply appropriate guidance then corresponding safety criteria are proposed to address the deficiency. Lessons learnt from military AAR include the drive for interoperability. This has resulted in extensive efforts to standardise equipment and systems, which are equally applicable to civil AAR. Extremely useful advisory material exists, ranging from flight testing techniques to related safety.

The importance of ensuring the consistency of failure condition categorisation at system and aircraft level is highlighted. The treatment of failures when two aircraft are in close proximity is something not considered by civil functional hazard analysis. The concept of AAR as an additional flight phase is introduced and affected system safety analyses identified. Examples of failure conditions that are not catastrophic at system level, but potentially could be at aircraft level during AAR are provided. Rendezvous scenarios are described to illustrate their influence on the certification basis. Combining such considerations with the factors that influence aircraft design leads to ramifications for handling qualities, performance and fuel system design. A viable and certifiable AAR configuration is consequently proposed. Consideration is given to treating operational certification in a progressive manner similar to existing LROPS (Long Range Operations).
3D UAV trajectory planning using evolutionary algorithms: A comparison study
Authors: Bagherian M. , Alos A.
Published: February 2016

This paper focuses on the three dimensional flight path planning for an unmanned aerial vehicle (UAV) on a low altitude terrain following\terrain avoidance mission. The UAV trajectory planning problem is to compute an optimal or near-optimal trajectory for a UAV to do its mission objectives in a surviving penetration through the hostile enemy environment, considering the shape of the earth and the kinematics constraints of the UAV. 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. The geographic information of the earth shape and enemy locations is generated using digital terrain model (DTM) and geographic information system (GIS), and is displayed in a 3D environment. Using 3D-maps containing the geographic data accompanied by DTM, and GIS, the problem is modelled by deriving the motion equations of the UAV. Two heuristic algorithms are proposed for this problem: genetic and particle swarm algorithms. Genetic and particle swarm algorithms are general purposes algorithms, because they can solve a wide range of problems, so they have to be adjusted to solve the trajectory planning problem. To test and compare the paths obtained from these algorithms, a software program is built using GIS tools and the programming languages C# and MATLAB.
An efficient method for predicting zero-lift or boundary-layer drag including aeroelastic effects for the design environment
Authors: Camberos J. A. , Kolonay R. M. , Eastep F. E. , Taylor R. F.
Published: February 2016

One of the aerospace design engineer’s goals aims to reduce drag for increased aircraft performance, in terms of range, endurance, or speed in the various flight regimes. To accomplish this, the designer must have rapid and accurate techniques for computing drag. At subsonic Mach numbers drag is primarily a sum of lift-induced drag and zero-lift drag. While lift-induced drag is easily and efficiently determined by a far field method, using the Trefftz plane analysis, the same cannot be said of zero-lift drag. Zero-lift drag (CD,0) usually requires consideration of the Navier-Stokes equations, the solution of which is as yet unknown except by using approximate numerical techniques with computational fluid dynamics (CFD). The approximate calculation of zero-lift drag from CFD is normally computed with so-called near-field techniques, which can be inaccurate and too time consuming for consideration in the design environment. This paper presents a technique to calculate zero-lift and boundary-layer drag in the subsonic regime that includes aeroelastic effects and is suitable for the design environment. The technique loosely couples a two-dimensional aerofoil boundary-layer model with a 3D aeroelastic solver to compute zero-lift drag. We show results for a rectangular wing (baseline), a swept wing, and a tapered wing. Then compare with a rectangular wing with variable thickness and camber, thinning out from the root to tip (spanwise direction), thus demonstrating the practicality of the technique and its utility for rapid conceptual design.
Night-time offshore helicopter operations: a survey of risk levels per phase of flight, flying recency requirement and visual approach technique
Authors: Nascimento F. A. C. , Majumdar A. , Ochieng W. Y. , Schuster W.
Published: February 2016

The analysis of risks per phases of flight is fundamental for safe helicopter operations, of which night-time offshore oil- and gas-related missions form an important part. The safe execution of such missions also depends on pilots’ recent flying practice and a stable visual approach segment prior to landing. However, the poor quality of the safety data currently available prevents accurate analysis of risk on a per-phase-of-flight basis, establishment of a meaningful flying recency requirement and identification of any preferable visual approach design. To redress these problems, this paper develops a bespoke taxonomy of phases of offshore helicopter flights and uses it as the basis for a questionnaire survey on the phase-specific risk levels experienced by pilots in the night-time, perceived optimal flying recency requirement and preferred visual approach design. With the responses obtained from pilots located in seven countries, extensive statistical hypothesis testing shows that the phases involving visual scan techniques at high speed regimes are problematic, especially the visual segment of instrument approaches. Moreover, the between-night-flights time gaps required for assured flying recency were found considerably shorter than currently standardised across the industry. Finally, no preferred visual approach technique was identified. A number of important implications have been highlighted and should form the basis for future safety interventions.
Serum concentrations of 25-hydroxyvitamin D and its association with bone mineral density and serum parathyroid hormone levels during winter in urban males from Guiyang, Southwest China
Authors: Zhang Qiao , Shi Lixin , Peng Nianchun , Xu Shujing , Zhang Miao , Zhang Song , Li Hong , Zhuang Huijun , Gong Mingxian , Wu Danrong , Wang Rui
Published: February 2016

Serum vitamin D (25-hydroxyvitamin D (25OHD)) may influence serum parathyroid hormone (PTH) levels and bone mineral density (BMD). In the present study, we assessed serum 25OHD concentration and its association with PTH and BMD in urban males from Guiyang (N26.57°), the capital city of Guizhou province, Southwest China. We recruited 634 males aged >20 years from the Guiyang Health Measures Survey, and stratified them into three groups according to age: young (20–39 years), middle aged (40–59 years) and older (60–79 years). We measured serum concentrations of 25OHD, PTH levels and BMD of the lumbar spine (L1–L4), femoral neck and total hip. In addition, we also explored the relationship between 25OHD and lifestyle, socio-economic characteristics and medical history by applying covariance analysis and locally weighted regression plots. The results showed that serum 25OHD was <50 nmol/l in 59·3 % of the subjects and >75 nmol/l in 12·6 % of the subjects. Higher level of serum PTH was detected in relation to lower concentrations of serum 25OHD up to 50 nmol/l. A negative correlation between serum 25OHD and PTH concentrations was observed (r −0·207, P=0·003). Mean concentration of serum PTH increased gradually and plateaued while concentrations of serum 25OHD decreased to 50 nmol/l. Gradual increase in serum PTH was observed as 25OHD concentration was <25 nmol/l (P=0·004). BMD values at all sites were greater in the higher serum 25OHD concentration group. This study shows that low concentrations of serum 25OHD were common in males, and bone health was likely to be improved when serum 25OHD values were between 30 and 50 nmol/l.
Assessment of nasal mucociliary activity in patients with Behçet's disease
Authors: Ozbay I , Kucur C , Temİzturk F , Ozkan Y , Kahraman C , Oghan F
Published: February 2016

Objective:

To investigate nasal mucociliary clearance in patients with Behçet's disease.

Methods:

Thirty patients with Behçet's disease, diagnosed on the basis of criteria defined by the International Study Group for Behçet's Disease, and 30 healthy individuals were recruited. In both groups, individuals with conditions that could affect nasal mucociliary clearance were excluded. Nasal mucociliary clearance time was evaluated using saccharin tests. The time between placement of a saccharin tablet and the tasting of the saccharin was measured and recorded as the saccharin clearance time.

Results:

The mean nasal mucociliary clearance time was significantly longer in the Behçet's disease patients than in the control subjects (p < 0.001). Furthermore, there was a positive correlation between Behçet's disease duration and nasal mucociliary clearance time (p < 0.001, r = 0.882).

Conclusion:

The results suggest that nasal mucociliary clearance time is longer in Behçet's disease patients than in control subjects, and is positively correlated with disease duration.
Stereoscopic imaging of dusty plasmas
Authors: Melzer André , Himpel Michael , Killer Carsten , Mulsow Matthias
Published: February 2016

The fundamentals of stereoscopy and their application to dusty plasmas are described. It is shown that stereoscopic methods allow us to measure the three-dimensional particle positions and trajectories with high spatial and temporal resolution. The underlying technical implications are presented and requirements and limitations are discussed. The stereoscopic method is demonstrated for dust particles in dust-density waves under microgravity conditions.
Widows, Family, Community, and the Formation of Anglo-Hindu Law in Eighteenth-Century India
Authors: NARAYAN ROCHISHA
Published: February 2016

Late eighteenth-century colonial agrarian and judicial reforms had a direct impact on women from elite and non-elite backgrounds. Informed by British liberal ideologies and upper-caste Brahmanical norms, colonial policies marginalized women's access to, and control over, resources in the emergent political economy. In this article, I reconstruct histories of the ways in which Anglo-Hindu law compromised women's status as heirs, businesswomen, and members of society who wielded social capital with other community groups. Focusing on widows in Banaras who commandeered their property disputes, I illustrate that pre-colonial precedents of case-resolution under the Banaras rulers, and practices of ‘forum shopping’ by disputants themselves, shaped the widows’ approach to the colonial courts. Colonial judicial plans being incommensurable to everyday life, the courts incorporated pre-colonial forms of dispute handling and maintained a flexible approach to the practice of colonial law under the supervision of an Indian magistrate for a period of time. These characteristics made the courts popular among local society in the Banaras region. However, British officials, insistent on applying abstract scriptural laws, aligned customary practice to the dictates of Anglo-Hindu law. This article shows that the narrow legal subject position available to widows under scriptural law reordered their relationships with family and community networks to their disadvantage.