bluuebunny/crossref_metadata_2025 huggingface dataset:
Extreme short take–off and landing regional jets – economic motivation and technological challenges
Authors: Gologan C. , Kelders C. , Kuhlmann A. , Seifert J.
Published: February 2016

A predominant problem in the US as well as in Europe is the imminent capacity shortage of major hub airports: Air traffic is assumed to increase significantly worldwide, while further runway extensions of airports are difficult because of residents’ resistance and limited land space availability. However, the increasing market size also provides a potential for new aircraft concepts. What type of aircraft will meet best the future market requirements is a question arising.

We show that currently discussed solutions to airport capacity problems are mostly not in line with market requirements and have therefore not the potential to alleviate the increasing capacity problems. We analyse to what extend an aeroplane with extreme short takeoff and landing (ESTOL) capability might be able to overcome these capacity problems and discuss resulting technical requirements. Subsequently we present some of the current technological challenges in this area of research and give an overview on ESTOL regional jet concepts that are currently investigated at Bauhaus Luftfahrt.
Systems and certification issues for civil transport aircraft flow control systems
Authors: Liddle S. C. , Jabbal M. , Crowther W. J.
Published: February 2016

The use of flow control (FC) technology on civil transport aircraft is seen as a potential means of providing a step change in aerodynamic performance in the 2020 time frame. There has been extensive research into the flow physics associated with FC. This paper focuses on developing an understanding of the costs and design drivers associated with the systems needed and certification. The research method adopted is based on three research strands:

1. Study of the historical development of other disruptive technologies for civil transport aircraft,

2. Analysis of the impact of legal and commercial requirements, and

3. Technological foresight based on technology trends for aircraft currently under development.

Fly by wire and composite materials are identified as two historical examples of successful implementation of disruptive new technology. Both took decades to develop, and were initially developed for military markets. The most widely studied technology similar to FC is identified as laminar flow control. Despite more than six decades of research and arguably successful operational demonstration in the 1990s this has not been successfully transitioned to commercial products. Significant future challenges are identified in cost effective provision of the additional systems required for environmental protection and in service monitoring of FC systems particularly where multiple distributed actuators are envisaged. FC generated noise is also seen as a significant challenge. Additional complexity introduced by FC systems must also be balanced by the commercial imperative of dispatch reliability, which may impose more stringent constraints than legal (certification) requirements. It is proposed that a key driver for future successful application of FC is the likely availability of significant electrical power generation on 787 aircraft forwards. This increases the competitiveness of electrically driven FC systems compared with those using engine bleed air. At the current rate of progress it is unlikely FC will make a contribution to the next generation of single-aisle aircraft due to enter service in 2015. In the longer term, there needs to be significant movement across a broad range of systems technologies before the aerodynamic benefits of FC can be exploited.
Control laws for a formation of autonomous flight vehicles
Authors: Chiaramonti M. , Mengali G.
Published: February 2016

This paper investigates the performance of a flight control system, based on nonlinear dynamics inversion theory, whose aim is to maintain a given geometry of a formation of unmanned aerial vehicles. A fundamental aspect is the complete three dimensionality of the formation geometry that provides a substantial improvement over existing two-dimensional control laws. The designed control system has been implemented in a Simulink® environment and its effectiveness has been tested with a campaign of numerical simulations.
Computational fluid dynamics application to aerospace science
Authors: Shang J. S.
Published: February 2016

A brief narration on significant accomplishments in computational fluid dynamics (CFD) for basic research and aerospace application is attempted to highlight the outstanding achievements by scientists and engineers of this discipline. To traverse such a vast domain, numerous and excellent contributions to CFD will be unintentionally overlooked by the author’s limited exposure. Nevertheless it is an ardent hope that the present abridged literature review will aid to reaffirm excellence in research and to identify knowledge shortfalls both in aerodynamics and its modeling and simulation capability. The future modeling and simulation technology needs, as well as potential and fertile research areas, are humbly put forth for consideration.
Optical space telescope structures: The state of the art and future directions
Authors: Santer M. J. , Seffen K. A.
Published: February 2016

Future space telescopes will be required to have significantly greater aperture and lower areal density than is currently achievable. Gossamer spacecraft structures have been proposed as a means of achieving this, but the technologies are far from mature. A state-of-the-art review is timely and necessary as new structural paradigms are being considered for the next generation of space telescopes. There is, however, a knowledge gap between the structural engineering community and the additional fields involved in the complete telescope system, leading to the proposal of structures which are unlikely to be launched. It is hoped that, by providing a resource by which structural engineers are made aware of the wider issues in telescope design, this review will serve to overcome this knowledge gap to facilitate productive collaboration.
A correction to sonic boom theory
Authors: Cain T.
Published: February 2016

Current sonic boom theory is based on linear midfield solutions coupled with acoustic propagation models. Approximate corrections are made within the theory to account for non-linearities, in particular for the coalescence of compression waves and the formation of weak shocks. A very large adjustment is made to account for the increasing acoustic impedance that the waves encounter as they propagate from the low density air at cruise altitude to the high density air at sea level. Typically this correction reduces the calculated over pressure levels by a factor of three. Here the method of characteristics (MOC) is used to prove that the density gradient within a hydrostatic atmosphere has no direct effect on the propagation or intensity of the wave. However gravity and ambient temperature both affect the wave propagation and the combined pressure level attenuation is not dissimilar to that previously attributed to acoustic impedance. Although the flawed acoustic theory has given reasonable predictions of measured sonic booms, the omission of gravity from the equation of motion and the inclusion of a false impedance modification, makes the model unreliable for prediction of future designs, particularly those focused on boom minimisation. As an aid to quiet supersonic aircraft design, Whitham’s theory is extended to include gravity and ambient temperature variation and shown to be in good agreement with a MOC solution for the real atmosphere.
Material state changes as a basis for prognosis in aeronautical structures
Authors: Reifsnider K. L. , Fazzino P. , Majumdar P. K. , Xing L.
Published: February 2016

The long-term performance of aeronautical structures is typically discussed in terms of concepts such as structural integrity, durability, damage tolerance, fracture toughness, etc. These familiar concepts are usually addressed by considering balance equations, crack growth relationships, and constitutive equations with constant material properties, and constant or cyclically applied load conditions. Loading histories are represented by changing stress (or strain) states, only. But for many situations, especially associated with high performance aircraft, the local state of the material may also change during service, so that the properties used in those equations are functions of time and history of applied conditions. For example, local values of stiffness, strength, and conductivity are altered by material degradation to create ‘property fields’ that replace the global constants, and introduce time and history into the governing equations. The present paper will examine a small set of such problems and offer a construct for using related solutions to estimate future performance based on history of use and current material state, a concept typically called prognosis.
Using deformation modes to identify cracks in turbine engine compressor disks
Authors: Brockman R. A. , John R. , Huelsman M. A.
Published: February 2016

Recent studies show that analytical predictions of crack growth in rotating components can be used in conjunction with displacement measurement techniques to identify critical levels of fatigue damage. However, investigations of this type traditionally have focused on the detection of damage at known flaw locations. This paper addresses the related problem of estimating damage associated with flaws at unknown locations, through the combined use of analytical models and measured vibration signatures. Because the measured data are insufficient to identify a unique solution for the location and severity of fatigue cracks, the function of the analytical model is to bound the extent of damage occurring at life-limiting locations. The prediction of remaining life based on estimates of worst-case fatigue damage and crack locations also is discussed.
Load transportation system based on autonomous small size helicopters
Authors: Bernard M. , Kondak K. , Hommel G.
Published: February 2016

This paper is devoted to modelling and control algorithms for a slung load transportation system composed of one or multiple helicopters, where the load is coupled by the means of flexible ropes (see Fig. 1). The coupled helicopter system overcomes the payload limitation of a single small size helicopter, while keeping most of its advantages: small costs of operation, low maintenance costs and increased safeness. Therefore, the system can be utilised whenever the use of full size helicopters is impossible, too expensive or prohibited by law. We focus on the deployment and repairing of distributed sensor networks, using a transportation system based on multiple small size helicopters. A possible real world application is the deployment of fire fighting equipment, where space limitation of the fire trucks prohibits the application of bigger UAVs and using full size helicopters is too dangerous. The problem of load transportation using one or two full size helicopters (twin lift helicopter system), connected to the load by means of flexible ropes, has been discussed in the aerospace research community at least since 1960. We have shown in our previous work that there is a fundamental difference in the mathematical description between small and full size helicopters. Therefore, also the control design for the case of small size helicopters needs to be different. To our knowledge, the control of a slung load transportation system composed of multiple small size helicopters has not been studied until now. In this paper, the complete mechanical setup of the slung load transportation system based on one or more small size helicopters is presented. This includes a short description of the used UAVs, the additionally required sensors, and how the load is mounted. A model of one/multiple helicopters transporting a load is introduced. This model is used in a simplified form for the controller design and in full form for simulation. The controller for one and two helicopters, which is based on a state feedback controller, as well as the controller for three and more helicopters, which is based on a non linear controller, are explained in detail. Both controllers utilise an underlying non-linear orientation controller. We propose a feedback loop, based on forces measured in the ropes, to compensate for the influence of the rope. The controllers were tested in simulation and in real flight experiments. The world wide first flight experiment with three coupled helicopters was successfully conducted at the end of 2007.
Estimates of the climate impact of future small-scale supersonic transport aircraft – results from the HISAC EU-project
Authors: Grewe V. , Plohr M. , Cerino G. , Muzio M. Di , Deremaux Y. , Galerneau M. , Martin P. de Saint , Chaika T. , Hasselrot A. , Tengzelius U. , Korovkin V. D.
Published: February 2016

The climate impacts of three fleets of supersonic small-scale transport aircraft (S4TA) are simulated. Based on characteristic aircraft parameters, which were developed within the EU-project HISAC, emissions along geographically representative trajectories are calculated and in addition the resulting changes in the atmospheric composition (carbon dioxide, ozone layer, water vapour) and climate (near surface global mean temperature) are deduced. We assume a fleet development with an entry in service in 2015, a full fleet in 2050. The results show a temperature increase of 0·08mK (0·07-0·10mK) with only small but statistically significant variations between the configurations, leading to a minimum climate impact for a weight optimised and hence lower flying aircraft. A climate impact ratio of 3·0 ± 0·4 between a S4TA and its subsonic counterpart is calculated, which is considerable less than for previous supersonic fleets because of a lower flight altitude, leading to smaller water vapour impacts.
Flight control using pin-protuberances for blunted cones
Authors: Samar R. , Zahir S. , Khan M. A.
Published: February 2016

This paper presents the concept of using cylindrical pins as short protuberances for trajectory control of a blunted cone in the supersonic and hypersonic regimes. Supersonic and hypersonic flow interactions for cylindrical protuberances, installed on a blunt cone are studied for their aerodynamic effects. The utility of these protuberances for aerodynamic control and trajectory shaping of a re-entry cone are explored. Static aerodynamic coefficients in the Mach range of 2–9·7 at various incidences are computed. The pressure distribution along the vehicle longitudinal axis in the presence of the pin-protuberance is studied using CFD analysis. With the altered pressure distribution, a net increase in the aerodynamic force is obtained which can be actively utilised for flight control and maneuvering of the vehicle during re-entry. After quantifying the aerodynamic effects of the protuberance, it is modelled and used as an effective actuation mechanism for flight feedback control. It is shown that this can work as an effective control device for Mach numbers less than five. An actuator design for insertion/retraction of the protuberance is presented and modelled, and a robust controller is synthesised which can in real time govern the position of the protuberance to control the flight attitude angle to achieve a desired trajectory. The controller takes in measurements of the vehicle’s pitch angle and actuates the pin height continuously to control the pitch angle to a desired value. The control performance is demonstrated on a high fidelity six degrees-of-freedom (6-DOF) nonlinear flight simulation.
Design and realisation of a two-seater aircraft powered by fuel cell electric propulsion
Authors: Romeo Giulio , Borello Fabio
Published: February 2016

The main objective of the project is to develop and validate the use of a fuel cell based power system for the propulsion of more/all electric aircraft. The Rapid 200-FC two-seater electric-motor-driven aeroplane which is powered by fuel cells is at present being completed and will be validated during a flight test in Autumn 2009. Several configurations have been evaluated in order to install the new energy and propulsion system on board while maintaining the centre of gravity within allowable limits. The fuel cell system and the electric motor are being integrated on board. The FC stack will be able to deliver a maximum continuous power of 20kW. A battery pack has to guarantee another 20kW of maximum continuous power for a limited time period (15 minutes), during take-off, climbing and, in the case of emergency, during landing.

The main goal of the project is to validate the overall high performance of an all electric aircraft system which is capable of remaining aloft for one hour. A parametric analysis has also been carried out to evaluate which key technologies influence the performance of future aircraft to the greatest extent.
Flutter control using resistively shunted piezoceramics
Authors: Kandagal S. B. , Venkatraman K.
Published: February 2016

This paper investigates the feasibility of flutter control using resistively shunted piezoceramics. 2D aerofoil model is elastically restrained in heave and pitch by a set of leaf springs modeled as Bernoulli-Euler beams. The piezoceramic transducers are bonded to the leaf springs. Unsteady aerodynamic theory is used to solve the flutter determinant incorporating the additive damping terms due to resistive shunting. Tuned dampers realised by resistive shunted piezoceramics in heave and pitch springs could enhance flutter speed in the range 25-50 % based on additive damping of 10 % achieved due to resistive shunting of piezoceramics in either pitch spring, heave spring or both.
Operation of small sensor payloads on tactical sized unmanned air vehicles
Authors: Patterson M. C. L. , Brescia A.
Published: February 2016

The miniaturisation of sensors has in recent years led to the ability to provide multiple sensor operations from a single Unmanned Aircraft System (UAS) platform. Multiple UAS platforms can be synchronised to link devices from separate UAS platforms thus proving a powerful capability for data collection, while opening up interesting opportunities in the way data is retrieved and used. A range of new sensors being investigated will be discussed with reference to selected case studies that have taken place. As we move into an increasingly growing, data rich environment, data management, quality and pedigree will become of increasing importance. Operations for both defence and non-defence applications will be discussed with reference to the present capability and what is required in future systems. This paper describes some of the sensors currently being evaluated. In the coming years it is expected that we will see a sharp increase in the use of small tactical sized autonomous vehicles in general and a large growth in the capability of the payloads being used.
An innovative evaluation platform for new aircraft concepts
Authors: Schmollgruber P. , Gobert J.-L. , Gall P.-E. , Goraj Z. , Jentink H. W. , Näs A. , Voit-Nitchmann R.
Published: February 2016

Within the European project NACRE (New Aircraft Concept REsearch), a team of research centres and universities focuses on the assessment of a test facility in the form of a flying platform. The goal of this Innovative Evaluation Platform (IEP) is to offer engineers a new tool to investigate areas of interest during the early design phases of advanced aeronautical systems.

After an initial phase during which the potential benefits of such a platform have been demonstrated, the go-ahead for the IEP design and manufacturing has been given. In this second phase, a lot of attention has been brought to the system specifications since the platform has to meet the requirements of both an aerial vehicle and a test facility. The subsequent design process followed a stringent course of actions to achieve the design of a competitive test facility. The consortium aims for a final integration and flight trials in fall 2009.
Aviation and climate change: confronting the challenge
Authors: Bows A.
Published: February 2016

Each year greenhouse gas emissions remain high the climate mitigation and adaptation challenges grow. The economic downturn was already in train in 2008, yet concentrations of CO2 increased unabated. Without concerted effort across all sectors there will be little chance of avoiding ‘dangerous climate change’ and the aviation sector has a clear role to play. Current and forthcoming technologies, operational practices and behavioural change offer widespread opportunities for other sectors to mitigate their CO2 emissions in absolute terms, but as they do so, aviation will become an increasingly important player. By comparing a range of global cross-sector emission scenarios with existing aviation projections, this paper illustrates the importance of understanding the future context with regard to other sectors when assessing the aviation industry’s potential impact. Given growth projections for aviation and the relatively slow pace of technological change, aviation’s proportion of 2050 global CO2 emissions is low only in those global cross-sector emission scenarios where there is a high probability of ‘dangerous climate change’. For a ‘reasonable’ (>50%) chance of avoiding ‘dangerous climate change’, the most technologically radical scenarios for aviation make up 15% of global CO2 in 2050 and conventional scenarios exceed the carbon budget entirely. Only by recognising that aviation’s currently projected emissions are incompatible with avoiding ‘dangerous climate change’ can the industry fully grasp the challenge of accelerating innovation and managing demand to deliver a more sustainable route to 2050 and beyond.
Exact strip analysis and optimum design of aerospace structures
Authors: Kennedy D. , Featherston C. A.
Published: February 2016

Minimisation of airframe mass reduces the costs of materials and manufacturing, as well as fuel consumption and atmospheric emissions. Fast, reliable analysis tools are required during preliminary design, when many alternative configurations and load cases are considered. The modelling and computational costs of finite element analysis are avoided by employing exact strip solutions of the governing differential equations, using the Wittrick-Williams algorithm to solve the resulting transcendental eigenproblems of buckling and vibration. This paper reviews recent enhancements to the exact strip method for analysis and optimum design of aerospace structures, using the specialist software VICONOPT. Lighter composite panels can be designed by obtaining reliable estimates of the reduced postbuckling stiffnesses when loaded in compression and shear. Further advances include discrete optimisation of layer thicknesses to allow for practical composite manufacturing constraints, vibration constraints, and a newly extended multi-level interface combining finite element analysis of a whole wing with exact strip postbuckling design of individual panels.
Application of a knowledge based design methodology to support fuselage panel design
Authors: van der Elst S. W. G. , Tooren M. J. L. van , Vermeulen B. , Emberey C. L. , Milton N. R.
Published: February 2016

Knowledge is a vital component of engineering design. Computer systems enriched with logic and engineering knowledge can support engineering design by automating repetitive and time-consuming processes. This automation is enabled using knowledge based engineering (KBE) techniques and can be obtained using dedicated KBE systems or augmented CAD systems, already pervasive throughout engineering industry. The development of these KBE applications is supported by a six-phase development process ranging from engineering process analysis to software development to business implementation. Distinctions and similarities exploiting alternative KBE platforms are addressed for each phase of the development process. An example KBE application is discussed, supporting the design of laminate aircraft fuselage panels. The implementation of the application is emphasised and five key-aspects required for a successful implementation are defined.
Maximum entropy approach to the identification of stochastic reduced-order models of nonlinear dynamical systems
Authors: Arnst M. , Ghanem R. , Masri S.
Published: February 2016

Data-driven methodologies based on the restoring force method have been developed over the past few decades for building predictive reduced-order models (ROMs) of nonlinear dynamical systems. These methodologies involve fitting a polynomial expansion of the restoring force in the dominant state variables to observed states of the system. ROMs obtained in this way are usually prone to errors and uncertainties due to the approximate nature of the polynomial expansion and experimental limitations. We develop in this article a stochastic methodology that endows these errors and uncertainties with a probabilistic structure in order to obtain a quantitative description of the proximity between the ROM and the system that it purports to represent. Specifically, we propose an entropy maximization procedure for constructing a multi-variate probability distribution for the coefficients of power-series expansions of restoring forces. An illustration in stochastic aeroelastic stability analysis is provided to demonstrate the proposed framework.
Numerical investigation of the role of hyper-mixers in supersonic mixing
Authors: Desikan S. L. N. , Kumaran K. , Babu V.
Published: February 2016

In this numerical study, the role of hyper-mixers on supersonic mixing is investigated for six different strut configurations. To this end, 3D, compressible, turbulent, non-reacting flow calculations with air as the secondary injectant have been carried out. A qualitative comparison of the predictions with experimental results is made through Schlieren and Mie scattering images. A quantitative evaluation of the predictions is made by comparison with experimentally measured exit stagnation pressure, wall static pressure and the degree of unmixedness. Based on these results, three strut configurations have been selected for carrying out simulations with hydrogen as the injectant. Results from the hydrogen simulations are compared with the predictions using air and also across the strut configurations. The results clearly demonstrate that castellated strut configurations are very effective in enhancing mixing in such high speed flows.
6U CubeSat design for Earth observation with 6▪5m GSD, five spectral bands and 14Mbps downlink
Authors: Tsitas S. R. , Kingston J.
Published: February 2016

The design of a 6U CubeSat including spacecraft systems and imaging payload is described for an Earth observation mission. From a Sun synchronous orbit at an altitude of 600km the design enables imaging with a 6.5m GSD, an optical MTF (on axis) of >59% at half Nyquist and >35% at Nyquist, a 26km swath, 12 bit digitisation and SNR of 120-200:one in five spectral bands; blue, green, red, red edge and near infrared. Data can be downlinked at the rate of 14 Mbps to a 3.7m S band ground station. This design allows an 8kg CubeSat to perform Earth observation missions equivalent to those of current 50-150kg microsatellites, with a corresponding reduction in cost.
Computer model for numerical simulation of emergency evacuation of transport aeroplanes
Authors: Hedo J. M. , Martínez-Val R.
Published: February 2016

The present paper describes a new, agent-based computer model that can simulate the evacuation of narrow body transport aeroplanes in the conditions prescribed by the airworthiness regulations for certification. The input data are extracted from a complete plan view of the cabin. The results include full egress details of all occupants, passengers and crew-members, and the most significant evacuation figures and diagrams. The model has been tuned and verified with real data of narrow body certification demonstrations. Numerical simulations of six narrow body aircraft, representative of current designs, show the capabilities of the model and provide relevant information on the relationship between cabin features and emergency evacuation results. Although the computer model has been developed for helping in the certification process it would be useful too in the design of new cabins.
The impact of flight simulation in aerospace
Authors: Allerton D. J.
Published: February 2016

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

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

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

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

The paper concludes by reviewing the lessons learnt by the flight simulation industry over the last thirty years and summaries the potential areas of growth, which will lead to simulation becoming widespread throughout many industries, in addition to the aerospace industry.
Numerical study of transonic cavity flows using large-eddy and detached-eddy simulation
Authors: Nayyar P. , Barakos G. N. , Badcock K. J.
Published: February 2016

Numerical analysis of the flow in weapon bays modelled as open rectangular cavities of length-to-depth (L/D) ratio of 5 and width-to-depth (W/D) ratio of 1 with doors-on and doors-off is presented. Flow conditions correspond to Mach and Reynolds numbers (based on cavity length) of 0·85 and 6·783m respectively. Results from unsteady Reynolds-averaged Navier-Stokes (URANS), large-eddy simulation (LES) and detached-eddy simulation (DES) are compared with the simulation methods demonstrating the best prediction of this complex flow. It was found that URANS was not able to predict the change of flow characteristics between the doors-on and doors-off configurations. In addition, the energy content of the cavity flow modes was much better resolved with DES and LES. Further, the DES was found to be quite capable for this problem giving accurate results (within 3dB of) experiments and appears to be a promising alternative to LES for modelling massively separated flows.
Parallel adjoint-based optimisation of a blended wing body aircraft with shock control bumps
Authors: Wong W. S. , Moigne A. Le , Qin N.
Published: February 2016

An Euler optimisation for a BWB configuration with winglets incorporating an array of three-dimensional shock control bumps is carried out by employing an efficient adjoint-based optimisation methodology. A high fidelity multi-block grid with over two million grid points is generated to resolve the shape of the 3D shock control bumps, the winglet as well as the overall BWB shape, which are parameterised by over 650 design variables. In order to perform such a large aerodynamic optimisation problem feasibly, the optimisation tools such as the flow solver and the adjoint solver have to be parallelised with a good parallel efficiency. This paper reports the parallel implementation efforts on the adjoint solver; especially on the calculation of the sensitivity derivatives, which has to be looped over the total number of design variables. Results from the optimisation of the wing master sections, winglet aerofoil sections and the three dimensional bumps indicate a significant improvement regarding the aerodynamic performance against the baseline geometry for the given planform layout of the aircraft.
Prediction of aerodynamic forces on a helicopter fuselage
Authors: Filippone A.
Published: February 2016

This paper presents a critical analysis of the aerodynamic loads created by the airframe of a conventional helicopter. The airframe is modelled and computed with an implicit, multi-block, multi-grid parallel Navier-Stokes solver. The flow solver has been optimised and run on up to 200 parallel processors. The cases reported include the effects of angle-of-attack (positive and negative), the effects of yaw (starboard and port) and side flow. Finally, the effects of the support strut in the wind tunnel experiments have been evaluated. Data are shown for the lift, drag and side force coefficients at flight Reynolds numbers (Re = 30m). A case of 30 degrees yaw at a flight Reynolds number is shown. We conclude that with the use of top-end computer resources it is possible to calculate the aerodynamic coefficients with a good degree of accuracy if the flow is mostly attached.
Analysis of composite plates with variable stiffness using Galerkin Method
Authors: Senocak E. , Tanriover H.
Published: February 2016

A solution methodology is developed to solve plane stress problem of composite plates with variable stiffness by using Galerkin technique and polynomials as trial functions. In the solution process, analytical computation has been done wherever it is possible, and analytical-numerical type approach has been made for all problems. The methodology is applied to two known case problems, composite plate with variable fibre content and laminated plate with spatially varying fibre orientations. The formulation of these problems results into coupled partial differential equations (with variable coefficients). The solutions of these equations are obtained using the polynomials as trial functions in the Galerkin method. The results are compared to that of Ritz and collocation technique published elsewhere. The method is found to determine closely both the displacements and the stresses with a few number of terms and in good agreement with other approximating methods. Computations on some examples show that, the method with the help of a symbolic math package is simple and efficient for solving these types of problems in engineering applications.
Modelling and vibration of a non-classical tilt-rotor wing system
Authors: Song O. , Kwon H. D. , Librescu L.
Published: February 2016

Problems related with the mathematical modelling and eigenvibration of a tiltrotor aircraft-wing system built up of anisotropic composite materials are investigated. The wing-mounted rotor that can tilt from the vertical position to a horizontal one is modelled and analysed from the vibrational point of view. In this sense, its behaviour is analysed as a function of the mass size, mass moment of inertia, tilt angle and spin speed of the spinning rotor and of its location along the wing span. While the rotor is considered to be rigid, the aircraft wing is modelled as a thin-walled beam that features a doubly-symmetric cross-section contour and incorporates the elastic coupling between flap-lag-transverse shear, on one hand, and between extension-twist, on the other hand. Numerical simulations are provided and pertinent conclusions are outlined.
A change in the calculated impact of supersonic aircraft NOx emissions on the atmosphere
Authors: Dessens O. , Rogers H. L. , Pyle J. A.
Published: February 2016

New model calculations suggest that the potential impact on the atmosphere of a future fleet of supersonic aircraft, for the year 2015, is highly dependent upon the amount of nitrogen oxides (NOx) emitted from the fleet. This result contrasts with the IPCC assessment which suggested that the impact of supersonic aircraft on the atmosphere was primarily through the role of water vapour emissions both on atmospheric ozone and climate change. These new findings are extremely important for atmospheric scientists, the aviation industry and policy makers, highlighting the importance of further development of low NOx combustors for supersonic aircraft, an aspect which has been largely ignored following the IPCC Special Report.
Investigation on the aerodynamic performance of an ejection seat
Authors: Chen D. H. , Wu W. H. , Wang J. J. , Huang Y.
Published: February 2016

A unique experimental method is used, in combination with numerical calculation and engineering estimation, to study the aerodynamic performance of an ejection seat at M = 0·60, 0·90 and 1·20, angles-of-attack α = 0°~360°, and sideslip angles (β = 0°~–90°. Several basic characteristics of the aerodynamic performance are explored. The normal force of the ejection seat varies in a sinusoidal way and the axial force in a cosinoidal way, with the angle-of-attack. The model is statically unstable longitudinally at most attitude angles and the longitudinal stability could be improved by a stabiliser. These characteristics result from a large low pressure area caused by the leeward separation and the windward high pressure area in the ejection seat flow field, at all α, due to the blunt configuration. A set of engineering calculation formulae is deduced, based on the aerodynamic characteristics of the ejection seat.
Use of Global Positioning System velocity outputs for determining airspeed measurement error
Authors: Gratton G. B.
Published: February 2016

Several methods have been derived since the advent of GPS (Global Positioning System) receivers in aircraft cockpits by which these receivers may be used to calibrate these aircraft’s other instrumentation; in particular the pitot-static system. This paper presents the four most suitable methods, two of which have been developed by the author. These methods are shown with a common symbology, and their strengths, weaknesses, analysis and operational use are compared.
Aircraft cost modelling using the genetic causal technique within a systems engineering approach
Authors: Curran R. , Castagne S. , Early J. , Price M. , Raghunathan S. , Butterfield J. , Gibson A.
Published: February 2016

The paper is primarily concerned with the modelling of aircraft manufacturing cost. The aim is to establish an integrated life cycle balanced design process through a systems engineering approach to interdisciplinary analysis and control. The cost modelling is achieved using the genetic causal approach that enforces product family categorisation and the subsequent generation of causal relationships between deterministic cost components and their design source. This utilises causal parametric cost drivers and the definition of the physical architecture from the Work Breakdown Structure (WBS) to identify product families. The paper presents applications to the overall aircraft design with a particular focus on the fuselage as a subsystem of the aircraft, including fuselage panels and localised detail, as well as engine nacelles. The higher level application to aircraft requirements and functional analysis is investigated and verified relative to life cycle design issues for the relationship between acquisition cost and Direct Operational Cost (DOC), for a range of both metal and composite subsystems. Maintenance is considered in some detail as an important contributor to DOC and life cycle cost. The lower level application to aircraft physical architecture is investigated and verified for the WBS of an engine nacelle, including a sequential build stage investigation of the materials, fabrication and assembly costs. The studies are then extended by investigating the acquisition cost of aircraft fuselages, including the recurring unit cost and the non-recurring design cost of the airframe sub-system. The systems costing methodology is facilitated by the genetic causal cost modeling technique as the latter is highly generic, interdisciplinary, flexible, multilevel and recursive in nature, and can be applied at the various analysis levels required of systems engineering. Therefore, the main contribution of paper is a methodology for applying systems engineering costing, supported by the genetic causal cost modeling approach, whether at a requirements, functional or physical level.
Application of synthetic jet actuators for the modification of the characteristics of separated shear layers on slender wings
Authors: Watson M. , Jaworski A. J. , Wood N. J.
Published: February 2016

This paper presents an experimental investigation related to controlling the unsteady characteristics of the separated shear layers occurring over highly swept wings, and in particular focuses on application of synthetic jet actuators for modification of unsteady dynamic loading on the wing surface due to the phenomenon referred to as vortex breakdown (vortex burst).

In the post burst flow region the surface pressure measurements reveal the presence of certain characteristic spectral peaks that are thought to represent the presence of a spiralling filament of vorticity inside the expanded vortex that is known to be present in the burst flow over swept wings.

This paper details an investigation into how the use of an array of 18 discrete synthetic jet actuators, distributed along the leading edge of a delta wing with a 60° sweep angle, can be used to alter the spectral content of this unsteadiness and reduce the level of unsteady pressure found in the post-burst region toward the wing trailing edge by up to 40%.

Measurements of the surface pressure spectral distributions over the wing are presented together with PIV measurements of the vortex cross-section, conducted in the successive planes parallel to the wing trailing edge. Additional surface flow visualisation indicates that the effect of the actuators on the leading edge boundary layer is to induce local separation delays close to each actuator orifice, which introduce ‘ripples’ into the shear layer as it separates. The results obtained are used to formulate an interpretative hypothesis attempting to explain the mechanisms responsible for modification of the spectral content and the level of excitation measured on the wing surface.
Modelling the interaction of helicopter main rotor and tail rotor wakes
Authors: Fletcher T. M. , Brown R. E.
Published: February 2016

The mutual interaction between the main rotor and tail rotor wakes is central to some of the most problematic dynamic phenomena experienced by helicopters. Yet achieving the ability to model the growth and propagation of helicopter rotor wakes with sufficient realism to capture the details of this interaction has been a significant challenge to rotorcraft aerodynamicists for many decades. A novel computational fluid dynamics code tailored specifically for rotorcraft applications, the vorticity transport model, has been used to simulate the interaction of the rotors of a helicopter with a single main rotor and tail rotor in both hover and low-speed quartering flight, and with the tail rotor rotating both top-forward and top-aft. The simulations indicate a significant level of unsteadiness in the performance of both main and tail rotors, especially in quartering flight, and a sensitivity to the direction of rotation of the tail rotor. Although the model thus captures behaviour that is similar to that observed in practice, the challenge still remains to integrate the information from high fidelity simulations such as these into routine calculations of the flight dynamics of helicopters.
Remarks on the nonlinear dynamics of a typical aerofoil section in dynamic stall
Authors: Galvanetto U. , Peirò J. , Chantharasenawong C.
Published: February 2016

We use standard tools of the theory of dynamical systems such as phase plots, bifurcation diagrams and basins of attraction to analyse and understand the dynamic behaviour of a typical aerofoil section under dynamic stall conditions. The structural model is linear and the aerodynamic loading is represented by the Leishman-Beddoes semi-empirical dynamic stall model. The loads given by this model are nonlinear and non-smooth, therefore we have integrated the equation of motion using a Runge-Kutta-Fehlberg (RKF45) algorithm equipped with event detection. We perform simulations of the motion for a range of Mach numbers and show that the model is very sensitive to small variations. This is evidenced by the presence in the bifurcation diagram of co-existing attractors or, in other words, by the existence of more than one steady-state motion for a given Mach number. The mechanisms for the appearance and disappearance of the co-existing attractors are elucidated by analysing the evolution of their basins of attraction as the Mach number changes.
Spacecraft control with constrained fast reorientation and accurate pointing
Authors: Mengali G. , Quarta A. A.
Published: February 2016

In this paper we study large angle rotational manoeuvres of spacecraft. The problem of attitude control is formulated and solved through potential functions, thus simplifying frequent reorientation manoeuvres. A combination of gas jet and FEEP thrusters is employed in order to obtain short settling times while meeting stringent pointing requirements. In this way, spacecraft reorientation is achieved in two integrated steps by means of a discrete/continuous control law. Autonomous avoidance of undesired space orientations is obtained and constraints due to the solar array pointing requirements are satisfied. A case study is discussed where the methodology is applied to a large space telescope.
Experimental investigation on wall pressure distribution in flaps’ separating regions
Authors: Zhang P. F. , Wang J. J. , Li Y. C.
Published: February 2016

The effects on the wall pressure of the plate caused by the introduction of a gap near the ground and the flaps were investigated experimentally. The mean pressure on the plate surface was found to decrease with the size changing of the gap near the ground when the gap size (g) is larger than the flap height (h), but the one in the recirculation region increase with the size of the gap when the gap size is about 0 ≤ g ≤ 2h. Three kinds of flow structure appear with increasing the gap sizes, and the transit point is at g/h = 0·2, 0·8 respectively. For the zigzag flap (d/h = 0·19, d is the height of the zigzag), the variation of wall pressure with g/h is similar to the flat flap in general. The zigzag affects the mean wall pressure in the region of 0 ≤ x/h ≤ 20 (the recirculation zone) and can decrease the fluctuating pressure in the region of x/h > 20 downstream.
A wind-tunnel based study of helicopter tail rotor blade vortex interaction
Authors: Coton F. N. , Galbraith R. A. McD. , Wang T. , Newman S. J.
Published: February 2016

The interaction of a helicopter tail rotor blade with the tip vortex system from the main rotor is a significant source of noise and, in some flight states, can produce marked reductions in control effectiveness. This paper describes a series of wind-tunnel tests to simulate tail rotor blade vortex interaction with a view to providing data for the development and validation of numerical simulations of the phenomenon. In the experiments, which were carried out in the Argyll wind-tunnel of Glasgow University, a single-bladed rotor located in the tunnel’s contraction was used to generate the tip vortex which travelled downstream into the working section where it interacted with a model tail rotor. The tail rotor was instrumented with miniature pressure transducers that measured the aerodynamic response during the interaction. The results suggest that the rotor blade vortex interaction is similar in form to that measured at much higher spatial resolution on a fixed, non-rotating blade. The combination of the two datasets, therefore, provides a valuable resource for the development and validation of predictive schemes.