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  Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 91 journals)
Acta Astronautica     Hybrid Journal   (Followers: 356)
Advances in Space Research     Full-text available via subscription   (Followers: 374)
Aeronautica     Open Access   (Followers: 5)
Aerospace     Open Access   (Followers: 6)
Aerospace and Electronic Systems, IEEE Transactions on     Hybrid Journal   (Followers: 59)
Aerospace Science and Technology     Hybrid Journal   (Followers: 362)
Affective Computing, IEEE Transactions on     Hybrid Journal   (Followers: 9)
AIAA Journal     Full-text available via subscription   (Followers: 587)
Air Force Magazine     Full-text available via subscription   (Followers: 3)
Air Medical Journal     Hybrid Journal   (Followers: 2)
Aircraft Engineering and Aerospace Technology     Hybrid Journal   (Followers: 172)
American Journal of Space Science     Open Access   (Followers: 37)
Annual of Navigation     Open Access   (Followers: 1)
Artificial Satellites     Open Access   (Followers: 15)
Aviation     Hybrid Journal   (Followers: 3)
Aviation in Focus - Journal of Aeronautical Sciences     Open Access   (Followers: 1)
Aviation Psychology and Applied Human Factors     Hybrid Journal   (Followers: 5)
Aviation Week     Full-text available via subscription   (Followers: 12)
Aviation, Space, and Environmental Medicine     Full-text available via subscription   (Followers: 5)
Canadian Aeronautics and Space Journal     Full-text available via subscription   (Followers: 15)
CEAS Aeronautical Journal     Hybrid Journal   (Followers: 24)
Chinese Journal of Aeronautics     Open Access   (Followers: 11)
Control Systems     Hybrid Journal   (Followers: 20)
Cosmic Research     Hybrid Journal   (Followers: 2)
COSPAR Colloquia Series     Full-text available via subscription   (Followers: 1)
Egyptian Journal of Remote Sensing and Space Science     Open Access   (Followers: 5)
Elsevier Astrodynamics Series     Full-text available via subscription   (Followers: 1)
Fatigue of Aircraft Structures     Open Access   (Followers: 5)
Frontiers in Aerospace Engineering     Open Access   (Followers: 5)
Frontiers in Astronomy and Space Sciences     Open Access  
Gyroscopy and Navigation     Hybrid Journal   (Followers: 32)
IEEE Aerospace and Electronic Systems Magazine     Full-text available via subscription   (Followers: 40)
IEEE Transactions on Circuits and Systems I: Regular Papers     Hybrid Journal   (Followers: 9)
International Journal of Aeroacoustics     Full-text available via subscription   (Followers: 6)
International Journal of Aerodynamics     Hybrid Journal   (Followers: 11)
International Journal of Aerospace Engineering     Open Access   (Followers: 43)
International Journal of Aerospace Innovations     Full-text available via subscription   (Followers: 11)
International Journal of Aerospace Sciences     Open Access   (Followers: 15)
International Journal of Applied Geospatial Research     Full-text available via subscription   (Followers: 4)
International Journal of Aviation Management     Hybrid Journal   (Followers: 1)
International Journal of Aviation Psychology     Hybrid Journal   (Followers: 4)
International Journal of Aviation Technology, Engineering and Management     Full-text available via subscription  
International Journal of Crashworthiness     Hybrid Journal   (Followers: 4)
International Journal of Flow Control     Full-text available via subscription   (Followers: 2)
International Journal of Hypersonics     Full-text available via subscription   (Followers: 3)
International Journal of Micro Air Vehicles     Full-text available via subscription   (Followers: 4)
International Journal of Satellite Communications Policy and Management     Hybrid Journal  
International Journal of Space Science and Engineering     Hybrid Journal   (Followers: 2)
International Journal of Space Structures     Full-text available via subscription   (Followers: 2)
International Journal of Space Technology Management and Innovation     Full-text available via subscription   (Followers: 2)
International Journal of Sustainable Aviation     Hybrid Journal  
International Journal of Turbo & Jet-Engines     Full-text available via subscription  
ISRN Astronomy and Astrophysics     Open Access   (Followers: 11)
Journal of Aerospace Computing, Information, and Communication     Full-text available via subscription   (Followers: 12)
Journal of Aerospace Engineering     Full-text available via subscription   (Followers: 167)
Journal of Aerospace Engineering & Technology     Full-text available via subscription  
Journal of Aerospace Operations     Hybrid Journal   (Followers: 3)
Journal of Aerospace Technology and Management     Open Access   (Followers: 1)
Journal of Aircraft     Full-text available via subscription   (Followers: 334)
Journal of Airline and Airport Management     Open Access   (Followers: 2)
Journal of Aviation Technology and Engineering     Open Access   (Followers: 6)
Journal of Guidance, Control, and Dynamics     Full-text available via subscription   (Followers: 60)
Journal of Konbin     Open Access  
Journal of Navigation     Hybrid Journal   (Followers: 37)
Journal of Propulsion and Power     Full-text available via subscription   (Followers: 269)
Journal of Space Weather and Space Climate     Open Access   (Followers: 4)
Journal of Spacecraft and Rockets     Full-text available via subscription   (Followers: 380)
Journal of Spatial Science     Hybrid Journal   (Followers: 1)
Journal of the American Helicopter Society     Full-text available via subscription   (Followers: 1)
Journal of the Astronautical Sciences     Hybrid Journal   (Followers: 2)
Microgravity Science and Technology     Hybrid Journal  
New Space     Hybrid Journal   (Followers: 2)
Nonlinear Dynamics     Hybrid Journal   (Followers: 5)
Population Space and Place     Hybrid Journal   (Followers: 2)
Proceedings of the Human Factors and Ergonomics Society Annual Meeting     Hybrid Journal   (Followers: 1)
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering     Hybrid Journal   (Followers: 24)
Progress in Aerospace Sciences     Full-text available via subscription   (Followers: 48)
Propulsion and Power Research     Open Access   (Followers: 2)
Recent Patents on Space Technology     Full-text available via subscription  
Research & Reviews : Journal of Space Science & Technology     Full-text available via subscription  
Russian Aeronautics (Iz VUZ)     Hybrid Journal   (Followers: 15)
Space and Polity     Hybrid Journal   (Followers: 2)
Space Communications     Hybrid Journal   (Followers: 2)
Space Policy     Hybrid Journal   (Followers: 16)
Space Research Today     Full-text available via subscription   (Followers: 26)
Space Safety Magazine     Free   (Followers: 4)
Space Science Reviews     Hybrid Journal   (Followers: 12)
SpaceNews     Free   (Followers: 247)
Transportmetrica A : Transport Science     Hybrid Journal   (Followers: 1)
Вісник Національного Авіаційного Університету     Open Access   (Followers: 2)
Вестник УГАТУ     Open Access  
Journal Cover CEAS Aeronautical Journal
   [26 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1869-5582
     Published by Springer-Verlag Homepage  [2210 journals]
  • Characteristics of PEMFC operation in ambient- and low-pressure
           environment considering the fuel cell humidification
    • Abstract: Abstract This paper summarizes experimental results of an air-fed polymer electrolyte membrane fuel cell system HyPM XR 12 (Hydrogenics Corp.) considering fuel cell temperature, stoichiometry, and load requirement variations at ambient and low-pressure operation. The experimental work realized at a low-pressure test facility designed and assembled by the German Aerospace Center, Institute of Engineering Thermodynamics is based on an experimental design. The experimental results confirm reduced fields of fuel cell operation as well as a decreased gross stack performance and efficiency at low operating pressures (950 mbar ≥ p ≥ 600 mbar) for the defined fuel cell temperature, stoichiometry, and load requirement. In addition, indexes of the operating parameters are introduced, characterizing the fuel cell operation with regard to the gross stack performance and efficiency at ambient and low-pressure levels. The discussion of the results considers analyses of fuel cell humidification.
      PubDate: 2014-12-05
  • Correction of aerodynamic influence matrices for transonic flow
    • Abstract: Abstract The authors present a novel correction approach for the doublet-lattice method in this paper. The doublet-lattice method is a standard tool for calculating unsteady aerodynamic loads in aeroelasticity. It solves the linear potential equations and is thus valid only at subsonic flow conditions. Hence, corrections have to be applied for transonic flow. The proposed correction method, CREAM (CorREction of Aerodynamic Matrices), uses surface pressure distributions obtained using computational fluid dynamics (CFD) simulations for the correction. It is based on a Taylor expansion of the aerodynamic influence coefficient matrix, where the Taylor coefficients are corrected successively. The approach can be applied to quasi-steady as well as to unsteady aerodynamic calculations. The method is demonstrated on the AGARD LANN wing at transonic attached flow conditions and compared to linearized unsteady CFD computations. Two different correction orders are examined: a “zeroth order correction” with a quasi-steady CFD sample as correction input and a “first order correction” with an additional unsteady CFD sample. It is shown that CREAM gives improved results for small reduced frequencies, where the first-order correction is always superior to the zeroth order correction.
      PubDate: 2014-12-01
  • Vortical flow prediction for the design of a wind tunnel experiment with a
           pitching lambda wing
    • Abstract: Abstract The IWEX wind tunnel model (Instationäres Wirbelexperiment, German for: Unsteady Vortex Experiment) was developed to study vortical flow at static and oscillating angles of attack. Numerical computations were performed beforehand to study important aerodynamic aspects. The focus of this paper is on those results that were affecting the design of the model. The experimental concept of a new test rig, wind tunnel walls and the new half wing model is briefly described. The lambda wing has a purely round leading edge with a constant nose radius to chord ratio of 0.5 %. The flow characteristics of the main vortex, generated at the nose of the main wing, and the smaller tip vortex are specified. The inboard motion of the main vortex with increasing angle of attack and the consequences for the load distribution are described. The free stream Mach number range of the test envelope is from 0.3 to 0.7. Therefore, transonic effects, especially shock–vortex interactions triggering vortex development, had to be analyzed for a safe design of the model. A peniche was designed to minimize the differences of the flow character compared to reference results of the model without wind tunnel walls. The effects of corner separation and displacement are specified at different stages of the iterative process. Finally, basic results for a pitching motion are discussed, based on global and distributed coefficients.
      PubDate: 2014-12-01
  • Model order reduction for steady aerodynamics of high-lift configurations
    • Abstract: Abstract In aerodynamic applications, many model reduction methods use proper orthogonal decomposition (POD). In this work, a POD-based method, called missing point estimation (MPE), is modified and applied to steady-state flows with variation of the angle of attack. The main idea of MPE is to select a subset of the computational grid points (control volumes) and to limit the governing equations to this subset. Subsequently, the limited equations are projected onto the POD subspace. This approach has the advantage that the nonlinear right-hand side of the governing equations has to be evaluated only for a small number of points (control volumes) in contrast to POD, for which the full right-hand side has to be evaluated. An error estimation for MPE in the continuous ODE setting is tackled. Numerical results are presented for the Navier–Stokes equations for two different industrially relevant, two-element high-lift airfoils, one which is normally adopted during landing and the other during take-off.
      PubDate: 2014-12-01
  • Semi-empirical modeling of fuselage–rotor interference for
           comprehensive codes: the fundamental model
    • Abstract: Abstract The flow field around the isolated HART II fuselage is computed by a computational fluid dynamics code. Velocities normal to the rotor rotational plane are extracted in a volume around the rotor as a data basis. A simple semi-empirical analytical formulation of the fuselage-induced velocities, based on parameter identification from computational fluid dynamics or measured data, is developed for use in comprehensive rotor codes. This model allows the computation of fuselage–rotor interferences on the rotor blade element level. It also allows the prediction of the rotor wake geometry deformation due to the presence of the fuselage in both prescribed wake and free-wake codes. Its impact on rotor thrust, power and trim is evaluated analytically using blade element momentum theory and by DLR’s comprehensive rotor code.
      PubDate: 2014-12-01
  • Investigation and analysis of deterioration in high pressure compressors
           due to operation
    • Abstract: Abstract Due to environmental and operational effects, the deterioration of all gas path-related jet engine components is a highly influencing parameter leading to an increase in exhaust gas temperature and specific fuel consumption over time. As a particularly strained engine module, the high-pressure compressor (HPC) is prone to a variety of abrasive and deforming effects that are responsible for a considerable part of overall engine performance losses. During HPC overhaul, new airfoils are typically mixed with reused parts whose refurbishment workscopes typically range from “passed inspection” up to “full leading and/or trailing edge restoration” as well as “tip weld repair”. Hence, a wide spread of airfoil geometries with a distinct statistical distribution can be found within an engine after operation. To allow a statistical analysis, a geometric survey on two full ex-service HPC blade sets and an assortment of equivalent new production parts was conducted. The blades were digitalized by a structured-light 3D scanner in conjunction with a photogrammetry system. Based on the measured three-dimensional data, a CAD model was generated for each blade. Afterwards, airfoil sections on different blade heights were analyzed to generate aerodynamic design parameters such as leading and trailing edge geometries (radius and thickness), their maximum profile thickness, their chord length and their stagger angle. By assessing the statistical results of both used and new parts, the effects of manufacture variations and in-service wear on HPC blade geometry can be compared in detail.
      PubDate: 2014-12-01
  • Development of a wind tunnel experiment for vortex dominated flow at a
           pitching Lambda wing
    • Abstract: Abstract A half wing model, a test rig and new wind tunnel walls were designed to study the vortex development at a lambda wing. The model has a sweep angle of 53° and a round leading edge. It is designed for pitching oscillations around a mean angle of attack of up to 20° up to a free stream Mach number of 0.7. Unsteady aerodynamic load data shall be delivered for aeroelastic simulations of Unmanned Combat Aerial Vehicles. Due to the highly nonlinear aerodynamic character, the design and sizing of the model had to take into account load cases with beginning and fully developed vortices. Furthermore, the different characters at subsonic and transonic speeds had to be included. Coupled simulations with a finite element model including the mounting and the connection to the actuation system were performed to assess the stability and the dynamic response of the model. Furthermore, the test concept and the process of the design of the model will be described.
      PubDate: 2014-12-01
  • SFB 880: aeroacoustic research for low noise take-off and landing
    • Abstract: Abstract This paper gives an overview about prediction capabilities and the development of noise reduction technologies appropriate to reduce high lift noise and propeller noise radiation for future low noise transport aircraft with short take-off and landing capabilities. The work is embedded in the collaborative research centre SFB 880 in Braunschweig, Germany. Results are presented from all the acoustics related projects of SFB 880 which cover the aeroacoustic simulation of the effect of flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new propeller arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of vibration excitation of aircraft structures, reduced by porous materials.
      PubDate: 2014-12-01
  • Comparison of real-time flight loads estimation methods
    • Abstract: Abstract Nowadays flight load exceedance monitoring is an important task to both: the aircraft manufacturer as well as the operator. The estimation of flight loads is required in several phases during development and operation of an aircraft. The requirements are usually different, for e.g. calculation of design loads for certification and operational loads monitoring of stress and fatigue. The ability to determine aircraft operational loads (more) precisely may reduce the time in maintenance. Being able to detect critical load exceedance events during flight or in a post-process is also an enabler for e.g. loads/fatigue monitoring at operator level. In this paper, a novel system identification method named local model networks is applied to the field of flight loads estimation and compared to approaches based on artificial neural networks as found in the literature. The presented approach tries to overcome some limitations with respect to model creation, robustness, inter- and extrapolation.
      PubDate: 2014-12-01
  • Revised approach procedures to support optimal descents into Malta
           International Airport
    • Abstract: Abstract This paper presents a proposal for new approach procedures for the most commonly used runways at Malta International Airport, runways 31 and 13, as a basis to facilitate the introduction of optimal descents in Maltese airspace. In addition, a standard arrival, one from the north from where the large majority of aircraft approach Malta, linking to runway 31 is proposed. The design, following ICAO recommendations, is described in detail. Current practice of aircraft inbound from the same entry point, observed using ADS-B recorded data, is also presented in a discussion leading to the identification of gains that could result from flying the proposed arrival and approach routes optimally.
      PubDate: 2014-12-01
  • Design and aeroelastic assessment of a forward-swept wing aircraft
    • Abstract: Abstract Aeroelastic effects strongly influence the design of an aircraft. To be able to assess those effects early on, reliable simulation models representing the global aeroelastic properties of a new design are required. At a conceptual or a pre-design stage, an intelligent parameterization concept allows for limited changes of the configuration while the simulation models are adapted accordingly. In the DLR project Integrated Green Aircraft, the goal was to investigate the impact of technologies for the reduction of fuel consumption on the aeroelastic properties of aircraft. One main aspect was the influence of laminar wing design on divergence, flutter and dynamic loads. As the reference aircraft in the project, the concept of a forward-swept wing aircraft with rear-mounted engines has been analysed. An aeroelastic model has been built up in the project. The model design procedure is based on the DLR in-house tool set MONA (ModGen/NASTRAN). Focus of this design process is the generation of a parameterized structural model, representing the global dynamic properties of the elastic aircraft, but as detailed as reasonable to capture relevant local effects and to result in a feasible structural design. In the article, the aircraft design is presented. The modelling and sizing process for the structure is described. Results of the loads analysis as well as of the aeroelastic stability analyses are discussed.
      PubDate: 2014-12-01
  • Assessment of leading-edge devices for stall delay on an airfoil with
           active circulation control
    • Abstract: Abstract The use of active, internally blown high-lift flaps causes the reduction of the stall angle of attack, because of the strong suction peak generated at the leading-edge. This problem is usually addressed by employing movable leading-edge devices, which improve the pressure distribution, increase the stall angle of attack, and also enhance the maximum lift coefficient. Classical leading-edge devices are the hinged droop nose or the more effective slat with a gap. The flow distortions generated by the gap become an important source of noise during approach and landing phases. Based on these considerations, the present work aims at evaluating the potentials of gap-less droop nose devices designed for improving the aerodynamics of airfoils with active high lift. Both conventional leading-edge flaps and flexible droop noses are investigated. Flexible droop nose configurations are obtained by smoothly morphing the baseline leading-edge shape. Increasing the stall angle of attack and reducing the power required by the active high-lift system are the main objectives. The sensitivities of the investigated geometries are described, as well as the physical phenomena that rule the aerodynamic performance. The most promising droop nose configurations are compared with a conventional slat device as well as with the clean leading-edge. The response of the different configurations to different blowing rates and angles of attack are compared and the stalling mechanisms are analyzed.
      PubDate: 2014-12-01
  • Hybrid structures in aero engines
    • Abstract: Abstract The continuous increase in already high specific performance of aero engines and growing optimization demands require further innovation in the fields of materials and design of structures to reach the primarily aerodynamic driven goals. In general, the improvement of materials on its own cannot guarantee success but rather the combination of different materials offers the potential for increased performance and additional functionality. For using different material properties, an adapted hybrid design is necessary. Within this design outstanding material characteristics should be addressed, whilst the lower performance properties must not be critical and provoke faults. By combining different materials within hybrid structures, the feasible increase in performance is accompanied with the challenges of handling a lot more parameters for optimization. Three examples are described in this paper, showing hybrid design approaches for aero engine structures. The design principles can be transferred to similar structures by using the shown basic mechanisms. The first example covers a hybrid ring structure used for simultaneous movement of stator vanes within an axial compressor. BLISK technology with high aerodynamic efficiency and low structural damping requires an accurate positioning of the stator vanes to avoid dynamic excitation in transient surroundings during a complete flight cycle. Additionally, the weight of the structure should be reduced compared to conventional in-service structures. A second example shows a hybrid fan blade. Here it is demonstrated how titanium can be combined with carbon fibre-reinforced plastics to create an airfoil. This concept can be implemented in generating stator vanes and rotor blades for aero engines. A special surface treatment leads to a non-aging jointbetween the two materials. The third example explains the basics for an alternative hybrid rotor design. Three titanium rotor segments are joined together by brazing under vacuum conditions. During the manufacturing process, the inner areas of the rotor are accessible which offers the opportunity to integrate cavities as well as fibre reinforcement.
      PubDate: 2014-11-28
  • Multidisciplinary pre-design of supersonic aircraft
    • Abstract: Abstract Forecasts predict a strong market for supersonic travel in the business sector. It is especially appealing for high-net-worth individuals because of both, the reduction of travel time and prestige. The ecological and economic challenges that are related to supersonic flight need adequate answers in terms of technology and tools to evaluate aircraft for the described task. This paper gives a short overview on research that has been conducted in the past, followed by the presentation of the work done by the authors. The integration of methods for the evaluation of supersonic business jets in the context of aircraft conceptual design is outlined. The determination of aerodynamic coefficients and loads is done by solving the inviscid Euler equations. Furthermore the propulsion module is extended and a mission analysis tool, which is used for fuel mass estimation is briefly explained. The methods for structural analysis are detailed. At the end the verification based on a reference configuration is described.
      PubDate: 2014-11-27
  • Simulation and validation of slat de-icing by an electromechanical system
    • Abstract: Abstract The Electro-Impulse De-Icing system is an alternative process of de-icing wing slat structures made of carbon fiber reinforced plastics or aluminum. It is especially qualified for no-bleed systems that are used in modern and future aircraft. Due to the time-dependent interactions between the induced magnetic field and the structural deformation it can be necessary to couple these physical fields in analyses. This paper presents a three-dimensional simulation as well as experiments of flat plates. The simulation is characterized by electrical and structural finite element calculations, which are two-way coupled in each time step. The current progress is based on real tests which are executed at a special test rig. A coil, which is connected to an impulse generator, is used to induce magnetic forces. Flat plates of aluminum or carbon fiber reinforced plastics (with an additional aluminum doubler) were tested at room temperature and deformation results were used to validate numerical simulations. Further research deals with the simulation of the de-icing process itself with a stress criterion for ice adhesion. Therefore, the test rig is mounted in a cooling chamber. The ice layer is produced by spraying cooled water through a nozzle with a droplet size of supercooled large droplets (SLD). The deformation progress with and without ice is analyzed at different impulse forces and ice thicknesses. The coupled finite element analysis gives the opportunity to simulate the process of de-icing in situ to the time-dependent loading of the plate by magnetic forces. Furthermore, the complex dynamic behavior of the structure can be simulated with excellent agreement to real tests.
      PubDate: 2014-11-25
  • Effect of an active high-lift system failure during landing approaches
    • Abstract: Abstract Simulation results of the longitudinal motion of a civil twin-engine aircraft with an active high-lift system are presented. The investigated system uses the lift-increasing effect of blowing over Coandă flaps along the wing. The core elements of the nonlinear model describing the dynamic behavior of an aircraft with this specific type of active high-lift system are explained. The main focus lies on the analysis of the aircraft’s reaction to an instant symmetric total failure of such a system. Initial investigations analyze the outcome of such failures, if throttle is set to maximum and elevator is controlled, without using stabilizer or flaps. Subsequently, an investigation has been performed estimating the effect of flap reconfigurations and stabilizer adjustments. The paper also considers a temporary failure of the system due to an engine failure combined with a too low power setting of the remaining engine which has to be increased first before the restart of the blowing system. The investigated situations vary from inconvenient to unrecoverable. Recommendations for backup systems and procedure changes are made to prevent such situations. A procedural approach is analyzed and respective simulations prove the efficiency of this solution.
      PubDate: 2014-11-19
  • Risks of linear design of joined wings: a non-linear dynamic perspective
           in the presence of follower forces
    • Abstract: Abstract Past work on Joined Wings pointed out the importance of including structural geometric non-linearities since the early stages of the design. However, the attention was mainly focused on conservative loading and several open questions needed an answer. In a effort to simulate aerodynamic-pressure-like loads, this research focuses on non-conservative follower forces. Several numerical evaluations demonstrate that follower loading exacerbates the risks of snap instability in Joined Wings. Snap type of instabilities introduce problems which do not pertain only to static responses. In fact, they are associated with the concept of bi-stable regions, with consequent risks of branch-jumping phenomena which are here shown to happen also for small vanishing perturbations and for load levels that are far from the limit one. The here studied phenomena suggest that the design process for Joined Wings has to be revisited and should focus, when stability is concerned, on the evaluation of the post-critical (if any) response: performing a non-linear analysis until the expected nominal limit load (set, for example, by the flight envelope) is reached is thus, a non-conservative approach and could lead to catastrophical consequences. Unfortunately, the above design directions may not be enough to guarantee a safe design: in this study, a case showing an isola-type of bifurcation is presented. Path-tracking techniques (i.e., arc-length family methods) could not detect such phenomena if not combined with ad hoc dynamic perturbation analyses. A further inherent property of the investigated cases is the sensitivity to parameters (e.g. the lower-to-upper-wing bending stiffness ratio): a small perturbation can produce a sudden appearance of a bi-stable region and isola type of bifurcation. This sensitiveness strongly interferes with the design process, being small deviation from the nominal properties (geometry, material, etc.) unavoidable at manufacturing level.
      PubDate: 2014-11-16
  • ALLFlight: blob-based approach to detect dangerous drift velocities during
           helicopter landing approaches
    • Abstract: Abstract The Institute of Flight Systems at the German Aerospace Center (DLR) site in Braunschweig is dedicating much effort to the goal of making helicopter flying safe. This paper concentrates on decreasing the danger of accidents caused by so-called “dynamic rollovers” which may result from undetected lateral velocities during the landing approach. Especially in degraded visual environment situations where pilots cannot visually evaluate the horizontal movement, accidents are likely to occur. While under normal circumstances the combination of INS and GPS is usually sufficient to detect critical lateral drift velocities, during the landing process, the INS drift may reach a dangerously high value quite soon after the GPS signal has been lost (for instance, in canyons, cities, or due to jamming). The vision algorithm that is proposed here uses a blob-based approach to solve this problem. Blobs are regions in an image that fit together bound by a specific criterion. In this paper, we will describe how an image is segmented, possible blobs are selected and characterized, how they are tracked, and how the velocity of the helicopter is calculated. Finally, the accuracy of this algorithm will be analyzed using data that have been recorded from flight tests conducted by the DLR’s flying helicopter simulator EC135 (ACT/FHS).
      PubDate: 2014-10-14
  • Joined-wing test bed UAV
    • Abstract: Abstract The future green aircraft will be required to meet demanding constraints, including weight reduction, high energy and aerodynamic efficiencies and high performance, to be compliant with pollutant emissions and noise generation regulations. The joined-wing concept is considered a trade-off variant for a green aircraft design with a lower cruise drag and lower structural weight. In addition, the requirements for low pollution and noise could be met using an all-electric aircraft. Hence, the aim of the present study is to design and produce a joined-wing unmanned aircraft test bed or flight laboratory. The basic design incorporates tip-joined front and rear wings with wing-tip vertical joints. The airframe is mainly composed of carbon and glass fibre composite materials. The power plant consists of an electric ducted fan, speed controller and Li-Po batteries. The aircraft integrates the Piccolo II Flight Management System, which offers a state-of-the-art navigation and flight data acquisition. Prior to production and flight testing of the prototype, aircraft aerodynamics and flight dynamics were analysed. Potential models with wind tunnel tests have been used to determine aircraft aerodynamics. One of the major problems found during simulation and flight experiments is the Dutch roll effect. This is thoroughly discussed in the paper. Some problems that concern autopilot tuning are also described.
      PubDate: 2014-10-07
  • POD approach for unsteady aerodynamic model updating
    • Abstract: Abstract A method for aerodynamic model updating is proposed in this paper. The approach is based upon a correction of the eigenvalues of the reduced-order unsteady aerodynamic matrix through an optimization with objective function defined through the difference in the generalized aerodynamic forces or on the aeroelastic poles. The high-fidelity model in reduced-order form is obtained by the proper orthogonal decomposition (POD) technique applied to the computational fluid dynamics Euler-based formulation. Many of the methods that have been developed in the past years for simpler aeroelastic models that use, for example, doublet-lattice method aerodynamics, can be adopted for this purpose as well. However, this model is not able to capture shocks and flow separation in transonic flow. The proposed approach performs the updating of the aerodynamic model by imposing the minimization of a global error between target aerodynamic performances, namely experimental performances, and an aerodynamic model in reduced-order form via POD approach. After a general presentation of the application of the POD method to the linearized Euler equations, the optimization strategy is presented. First, a simple test on a 2D wing section with theoretical biased data is performed, and then, the performances of different optimization strategies are tested on a 3D model updated by wind tunnel data.
      PubDate: 2014-09-23
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