bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flight simulator study on the influence of vortex curvature on wake encounter hazard using LES wind fields
Authors: Vechtel D. 
Published: February 2016

AbstractA flight simulator study has been carried out to evaluate the performance of modern flight control systems encountering curved wake vortices. During the decay process the shape of wake vortices alters significantly which has an influence on the encounter characteristics and thus on the encounter hazard. To analyse most realistic wake encounters, flow fields of matured vortices have been generated with large-eddy-simulations. These were used for the determination of induced force and moment histories during the encounter. The force and moment histories have been implemented into the equations of motions of a 6 DoF flight simulation. For the sake of comparison encounters have also been simulated with straight vortices as they were mostly used for many other investigations. The most important goal of the study was to analyse the difference between these ideally straight vortices and vortices with a more realistic shape regarding encounter acceptance. The simulator study was conducted in an A330 motion-based full-flight simulator with pilots-in-the-loop. The analysed scenario was a wake encounter during final approach. The encounter conditions corresponded to a heavy-behind-heavy situation for Instrument Flight Rules (IFR) operations. The aircraft was flown either manually (in normal law) or with autopilot engaged. Altogether 93 encounters have been simulated, 38 with straight and 55 encounters with curved vortices. For encounters under manual control the simulator study revealed a potential risk of pilot induced oscillations (PIO) during encounters with curved vortices. With autopilot engaged not even one encounter with curved vortices was classified to be unacceptable. Although significant aircraft response was experienced the autopilot never disengaged automatically in any encounter. Altogether about 12 percent of the encounters were not accepted by the pilots. This is indeed a significant number, especially as the analysed scenarios can be regarded to be realistic situations which can occur in reality even if the applicable separation distances are applied.
Factors affecting safety during night visual approach segments for offshore helicopters
Authors: Nascimento F. A. C. , Majumdar A. , Jarvis S. 
Published: February 2016

AbstractAccident rates for night sorties, by helicopters operating offshore, are estimated to be five times higher than for daytime. Recent attempts to redress this problem include new instrument descent procedures and changes to helideck lighting. However, there still remains a need for pilots to transition from automated flight to a manually flown night visual segment during the arrival, and three recent accidents have again highlighted the dangers of this phase. In order to explore what factors affect safety during night visual segments 33 semi-structured interviews were administered to pilots from a number of companies, and grounded theory was employed to analyse the narratives. From this, a template was developed representing pilots’ perceptions of factors affecting safety, and the relationships among factors were hypothetically mapped. Visual spatial disorientation figured as the main concern of participants, stemming from substandard pilot communication, loss of scanning skills during summer months, autopilot limitations, and the requirement to fly to too low meteorological minima. Concerted actions and further areas of research have been proposed to the different stakeholders involved in offshore nighttime operations, going beyond ongoing safety initiatives.
Factors affecting the apparent longitudinal stick-free static stability of a typical high-wing light aeroplane
Authors: Bromfield M. A. , Gratton G. B. 
Published: February 2016

AbstractFlying a light aeroplane involves a combination of pilot and aeroplane performing a set task, within a specific environment. The pilot is continuously sampling and selecting available sensory cues, interpreting those cues, making decisions and manipulating the primary controls (stick and rudder) to safely achieve flying objectives. The ‘feel’ of an aeroplane (a flying quality) is directly associated with the stick and rudder forces and how the aeroplane responds to control inputs. Classical theory has been applied to estimate the apparent (as felt by the pilot) longitudinal stick-free static stability (change of stick force with airspeed) of a typical, two-seat, high-wing light aeroplane. The theory has been extended to consider the effects of tail downwash and flap deflection. The results are compared with actual flight tests and show that the method may be used for the initial assessment of longitudinal stick-free static stability and more importantly, tendencies towards neutral or negative stability affecting flight safety.
Use of aerofoil section dynamic stall synthesis methods in rotor design
Authors: Chan W. , Perry J. 
Published: February 2016

AbstractThe introduction of the original time delay method of Beddoes, an engineering model for the unsteady response of an aerofoil section including dynamic stall, had a profound effect on the design and development of rotor systems in the UK. Over the years, the model expanded to include more and more features of the unsteady flow, with many contributors. It is now in use throughout the world as part of rotor analysis packages. Nevertheless, it retains its essential simplicity. Work to confirm the ability of the most recent version of the dynamic stall model from the University of Glasgow to replicate the complicated behaviour of an advanced rotor aerofoil section at full scale Reynolds and Mach numbers provides an opportunity to review the use of this new engineering model in the helicopter rotor design environment.This note discusses the application of dynamic stall synthesis methods to the problem of classifying and comparing aerofoil sections when designing rotors for the retreating blade stall condition that determines the rotor blade area requirement of the helicopter. The development of the dynamic stall models employed in UK rotor designs is reviewed in this paper and their use in the design process explained, with emphasis on the assumptions that overcome the limitations of the models and exploit their simplicity, enabling accurate and conservative rotor designs. The paper shows how the model may be used to structure the analysis of complex sets of dynamic aerofoil data. It illustrates how structured comparison between the model and the data yields a concise appreciation of the behaviour of the aerofoil and an understanding of the physical processes involved. Some previously unappreciated effects are identified and the model is used to transfer experience of the aerofoil section behaviour from the non-rotating wind-tunnel environment to that of the rotor. Finally, the application of the new engineering model developed at Glasgow University in the rotor design process is outlined. Some remarks on the use of engineering models in comparison with CFD models in the design context are included.
Advancement of aerofoil section dynamic stall synthesis methods for rotor design
Authors: Sheng W. , Chan W. , Galbraith R. 
Published: February 2016

AbstractDynamic stall is a complex process encountered by an aerofoil in the unsteady flow environment such as a helicopter rotor in forward flight as well as a fixed wing aircraft in manoeuvres and in other unsteady situations. The onset of dynamic stall effectively determines the flight envelope of the helicopter. Significant effort are being made to develop CFD to capture the dynamic stall behaviour, however traditional engineering models based on lifting line theory still offer fast turn-round and broad understanding required for the rotor design process. This paper describes a new engineering model for dynamic stall, developed originally for wind turbine application at a typical Mach number of 0·12. The new dynamic stall model, with a better definition of stall onset, is based on improvements made to Beddoes’ original trailing edge stall model. This paper will describe and demonstrate the improvements in identifying both the stall-onset and the pitching moment break at high pitch rates, when being applied to a generic rotor aerofoil RAE 9651 at M = 0·3. Further validation against oscillatory tests and other Mach numbers are still required. However the study has provided sufficient confidence for it to be employed in a rotor analysis code.
Aerodynamic shape optimisation, wind tunnel measurements and CFD analysis of a MAV wing
Authors: Nabawy M. R. A. , ElNomrossy M. M. , Abdelrahman M. M. , ElBayoumi G. M. 
Published: February 2016

AbstractThe aerodynamic shape optimisation of a micro air vehicle (MAV) wing is performed to obtain the basic wing geometrical characteristics which produce the maximum range and endurance requirements. Multhopp’s method based on Prandtl’s classical lifting line theory is used for the determination of the spanwise load distribution required during the optimisation process. The obtained lift and drag characteristics are used for the derivation of the range and endurance equations of an electrically driven micro air vehicle. The optimisation process is based on the modified feasible directions gradient based optimisation algorithm. Results are validated using wind tunnel measurements showing very good agreement. Results are also compared with solutions to the Navier-Stokes equations obtained with ANSYS-CFX finite elements using different turbulence models. These include the k-ε and the shear stress transport (SST) models as well as the Reynolds stress model.
A parametric associative modelling of aeronautical structural concepts under C0, C1 or C2 continuity constraints
Authors: Dattoma V. , De Giorgi M. , Giancane S. , Manco P. , Morabito A.E. 
Published: February 2016

AbstractIn this paper an associative-parametric approach is proposed in order to model the mesh of an aeronautical concept starting from a set of high-level structural primitives. This approach allows the designer to carry out the geometric modelling and the automatic mesh generation within one software environment in a fast and interactive way. The structural optimisation process is then simplified, with a relevant man-hours saving. A lower number of data transfers between different software is, moreover, involved with less problems related to the data corruption. To assure orders of continuity higher than C0 between adjacent instances, a suitable mathematical description of the structural primitives has been proposed. This description assures the maintenance of the required continuity constraints when the mesh is modified. Appropriate schemes of dependences are identified to guarantee the automatic propagation of the modifications complying with the continuity constraints.
Effects of targeting pod modification on F/A-18C Hornet weapons release
Authors: O’Brien C. W. , Snyder M. R. , Hallberg E. N. , Cenko A. 
Published: February 2016

AbstractThis paper describes a study that investigated the efficacy of modifications to the trailing end of the externally mounted advanced targeting forward looking infrared pod (ATFLIR) on the store separation characteristics of the F/A-18C aircraft. Prior work by Godiksen suggests that the trailing end of the geometrically similar targeting forward looking infrared pod (TFLIR) is the likely source of shock waves that can adversely impact the trajectory of a recently released store. In our study five different modifications to the aft end of the ATFLIR were analysed using computational fluid dynamics (CFD). The two most promising designs, an ogive shape such as that used in artillery shells and rockets, and a simpler extended but truncated cone shape were then further investigated. The moments that these trailing shapes produced on an adjacent released store were compared. CFD analysis revealed that the simpler cone shape resulted in weaker shocks from the aft end of the pod with a resultant smaller adverse moment on the store. While there is an extensive history of using CFD to predict store separation behavior, results from our study should be compared with wind tunnel data in order to validate the CFD simulations.
Shape optimisation in the design of thin-walled shells as components of aerospace structures
Authors: Suarez Espinoza P. A. , Bletzinger K-U. , Hörnlein H. R. E. M. , Daoud F. , Schuhmacher G. , Klug M. 
Published: February 2016

AbstractOne of the most resent efforts in aircraft design is the replacement of aluminium structures by carbon fibre reinforced polymer composites. Due to lower material and manufacturing costs, doubly curved shapes covering big areas are preferred over simpler surfaces which integrate stiffening profiles. In this context, CAD parameterisation of surfaces allows design solutions by means of classical shape optimisation. Related geometrical parameters are manipulated towards optimal design, generating innovative geometries and detailing.The presented structure is optimised by reducing the overall weight. The final optimum is guided using stability and strength restrictions in order to assure the safety of the component. Geometrical considerations are also included due to operational reasons. A hierarchical design procedure is developed which results in a work flow from preliminary ‘parameter-free’ form finding motivated by solving the minimal surface problem. The geometrical model for optimisation is recovered by generating B-Spline surface patches to preserve continuity requirements over large regions. The number of geometrical coefficients are defined by the accuracy in surface generation and the required freedom in surface control. The hierarchical approach reduces the possibilities of ending with an unsatisfactory optimum when several local minima characterise the non-linear problem, as it is usually the case in shape optimal design. A geometrical non-linear analysis is used to verify the performance of the optimum.
A framework for environmental risk management
Authors: Lloyd S. , Clifton A. , Lee J. , Elghali L. , France C. 
Published: February 2016

AbstractAero engine designs can have a life time of over 45 years, which is long enough for the understanding of environmental problems to change significantly. This places the aero engine designer in a position of uncertainty, as unforeseen environmental problems could affect the viability of a design. ‘Risk’ is used to describe future uncertainties that can lead to undesirable consequences. This paper presents a framework for environmental risk management that allows the designer to answer the question: what is the risk to a design from its environmental impacts over the life cycle? The framework provides a process for turning complex environmental business hazards into a form that can be used to develop mitigating actions within the design process. The paper demonstrates the framework through two examples and discusses findings, leading to conclusions on what is required to implement the framework into a business.
The benefits and limitations of ground-based upset-recovery training for general aviation pilots
Authors: Rogers R. O. , Boquet A. 
Published: February 2016

AbstractResearch by Rogers et al (2009) and Leland et al established that flight simulator training can improve a pilot’s ability to recover a general aviation aeroplane from an in-flight upset. To reach this conclusion, they administered simulator-based and classroom-based upset-recovery training to two groups of student pilots, then compared their performance in recovering an aerobatic Decathlon aeroplane from a series of four upsets with the performance of a third group of untrained control group pilots subjected to the same upsets. We extend this result by addressing the unanswered question of how much classroom-based training as opposed to simulator-based training contributes to improving a pilot’s upset-recovery manoeuvring skills. After receiving classroom-based upset-recovery training but no simulator training, our participants were subjected to the same series of four upsets in the same Decathlon aeroplane. We then compared the performance of the classroom-trained pilots with the performances of control group pilots and the two groups of simulator-trained pilots. Statistical analysis suggests that classroom-based instruction alone improves a pilot’s ability to recover an aeroplane from an upset. We summarise related research, describe the training experiment and the training program, analyse and interpret flight-test data, and explain what our research implies with respect to establishing career-long commercial pilot upset-recovery training requirements.
Performance and control optimisations using the adaptive torsion wing
Authors: Ajaj R. M. , Friswell M. I. , Dettmer W. G. , Allegri G. , Isikveren A. T. 
Published: February 2016

AbstractThis paper presents the Adaptive Torsion Wing (ATW) concept and performs two multidisciplinary design optimisation (MDO) studies by employing this novel concept across the wing of a representative UAV. The ATW concept varies the torsional stiffness of a two-spar wingbox by changing the enclosed area through the relative chordwise positions of the front and rear spar webs. The first study investigates the use of the ATW concept to improve the aerodynamic efficiency (lift-to-drag ratio) of the UAV. In contrast, the second study investigates the use of the concept to replace conventional ailerons and provide roll control. In both studies, the semi-span of the wing is split into five equal partitions and the concept is employed in each of them. The partitions are connected through thick ribs that allow the spar webs of each partition to translate independently of the webs of adjacent partitions and maintain a continuous load path across the wing span. An MDO suite consisting of a Genetic Algorithm (GA) optimiser coupled with a high-end low-fidelity aero-structural model was developed and employed in this paper.
Analytical Volterra-based models for nonlinear low order flight dynamics approximation systems
Authors: Omran A. , Newman B. 
Published: February 2016

AbstractAnalytical methodology is presented to conduct dynamical assembly of simple low order nonlinear responses for system synthesis and prediction using Volterra theory. The procedure is set forth generically and then applied to several atmospheric flight examples. A two-term truncated Volterra series, which is enough to capture the quadratic and bilinear nonlinearities, is developed for first and second order generalised nonlinear single degree of freedom systems. The resultant models are given in the form of first and second kernels. A parametric study of the influence of each linear and nonlinear term on kernel structures is investigated. A step input is then employed to quantify and qualify the nonlinear response characteristics. Uniaxial surge and pitch motions are presented as examples of the low order flight dynamic systems. These examples show the ability of the proposed analytical Volterra-based models to predict, understand, and analyse the nonlinear aircraft behaviour beyond that attainable by linear-based models. The proposed analytical Volterra-based model offers an efficient nonlinear preliminary design tool in qualifying the aircraft responses before computer simulation is available or invoked.
The perforation resistance of sandwich structures subjected to low velocity projectile impact loading
Authors: Zhou J. , Guan Z. W. , Cantwell W. J. 
Published: February 2016

AbstractThis article presents the findings of a study to investigate the impact perforation resistance of sandwich structures. The dynamic response of sandwich panels based on PVC foam cores has been evaluated by determining the energy to perforate the panels. The impact response of the sandwich structures was predicted using the finite element analysis package Abaqus/Explicit. The validated FE models were also used to investigate the effect of oblique loading and to study the impact response of sandwich panels subjected to a pressure differential equivalent to flying at an altitude of 10,000m.Low velocity impact testing has shown that the energy to perforate the sandwich panels is dependent on the properties of the core. It has been shown that increasing the density of the crosslinked PVC foams by a factor of two yielded a 600% increase in the perforation resistance of the sandwich structures. At higher densities, the crosslinked foam sandwich structures offered a superior perforation resistance to the linear PVC structures. The numerical analysis accurately predicted the perforation energies of the sandwich panels, as well as the prevailing failure mechanisms following impact. Finally, it has been shown that sandwich panels impacted at high altitude offer a similar perforation resistance to those tested at sea level.
Finite element modelling of sandwich panels with graded core under various boundary conditions
Authors: Kashtalyan M. , Woodward B. 
Published: February 2016

AbstractSandwich panels are widely used in the aerospace industry instead of solid plates due to their high flexural stiffness-to-weight and flexural strength-to-weight ratios. However due to the mismatch of properties between the face sheets and the core, stress concentrations can occur at the face sheet/core interfaces, often leading to delamination. One possible solution to this problem is the introduction of a graded core — a core in which the properties vary gradually from the face sheets to the core centre, eliminating any abrupt changes in properties. In this paper a 3D finite element method, fully validated through comparison with results from the literature and a 3D elasticity solution, is applied to modelling of sandwich panels with graded core. The approach makes use of graded elements to study the effect of varying the boundary conditions on the elastic deformation of the panel subject to uniformly distributed loading. Comparative analysis of stress and displacement fields in sandwich panels with homogeneous and graded cores is carried out under various combinations of simply supported, clamped and free edges.
Progressive failure analysis for the interaction of interlaminar and intralaminar failure modes in composite structures with an initial delamination
Authors: Ji W. , Waas A. M. 
Published: February 2016

AbstractThis paper is concerned with the development of a failure initiation and progressive failure analysis (PFA) method for advanced composite structures. The present PFA model is capable of predicting interactive out-of-plane and in-plane failure modes observed in fiber reinforced composite laminates including interlaminar behavior and matrix microdamage at the mesoscale. A probability analysis tool is coupled with the PFA to account for uncertainty in modelling parameters caused by material variability and manufacturing inconsistencies. The progressive damage response of a laminated composite panel with an initial delamination is studied and used to demonstrate the PFA modelling framework that is presented here.