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  Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 97 journals)
Acta Astronautica     Hybrid Journal   (Followers: 388)
Advances in Aerospace Engineering     Open Access  
Advances in Space Research     Full-text available via subscription   (Followers: 421)
Aeronautica     Open Access   (Followers: 6)
Aerospace     Open Access   (Followers: 7)
Aerospace and Electronic Systems, IEEE Transactions on     Hybrid Journal   (Followers: 71)
Aerospace Science and Technology     Hybrid Journal   (Followers: 408)
Affective Computing, IEEE Transactions on     Hybrid Journal   (Followers: 9)
AIAA Journal     Full-text available via subscription   (Followers: 640)
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: 197)
American Journal of Space Science     Open Access   (Followers: 40)
Annual of Navigation     Open Access   (Followers: 2)
Artificial Satellites     Open Access   (Followers: 15)
ASTRA Proceedings     Open Access  
Aviation     Hybrid Journal   (Followers: 5)
Aviation in Focus - Journal of Aeronautical Sciences     Open Access   (Followers: 2)
Aviation Psychology and Applied Human Factors     Hybrid Journal   (Followers: 8)
Aviation Week     Full-text available via subscription   (Followers: 19)
Aviation, Space, and Environmental Medicine     Full-text available via subscription   (Followers: 5)
Canadian Aeronautics and Space Journal     Full-text available via subscription   (Followers: 18)
CEAS Aeronautical Journal     Hybrid Journal   (Followers: 24)
Chinese Journal of Aeronautics     Open Access   (Followers: 11)
Control Systems     Hybrid Journal   (Followers: 24)
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: 2)
Fatigue of Aircraft Structures     Open Access   (Followers: 6)
Frontiers in Aerospace Engineering     Open Access   (Followers: 5)
Frontiers in Astronomy and Space Sciences     Open Access  
Gyroscopy and Navigation     Hybrid Journal   (Followers: 92)
IEEE Aerospace and Electronic Systems Magazine     Full-text available via subscription   (Followers: 43)
IEEE Transactions on Circuits and Systems I: Regular Papers     Hybrid Journal   (Followers: 11)
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: 44)
International Journal of Aerospace Innovations     Full-text available via subscription   (Followers: 11)
International Journal of Aerospace Sciences     Open Access   (Followers: 16)
International Journal of Applied Geospatial Research     Full-text available via subscription   (Followers: 4)
International Journal of Aviation Management     Hybrid Journal   (Followers: 2)
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: 3)
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  
Journal of Aeronautical Materials     Open Access  
Journal of Aeronautics & Aerospace Engineering     Open Access  
Journal of Aerospace Engineering     Full-text available via subscription   (Followers: 206)
Journal of Aerospace Engineering & Technology     Full-text available via subscription  
Journal of Aerospace Information Systems     Full-text available via subscription  
Journal of Aerospace Operations     Hybrid Journal   (Followers: 4)
Journal of Aerospace Technology and Management     Open Access   (Followers: 1)
Journal of Aircraft     Full-text available via subscription   (Followers: 373)
Journal of Airline and Airport Management     Open Access   (Followers: 3)
Journal of Astrobiology & Outreach     Open Access  
Journal of Aviation Technology and Engineering     Open Access   (Followers: 6)
Journal of Guidance, Control, and Dynamics     Full-text available via subscription   (Followers: 73)
Journal of Konbin     Open Access  
Journal of Navigation     Hybrid Journal   (Followers: 86)
Journal of Propulsion and Power     Full-text available via subscription   (Followers: 306)
Journal of Space Weather and Space Climate     Open Access   (Followers: 4)
Journal of Spacecraft and Rockets     Full-text available via subscription   (Followers: 432)
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: 4)
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering     Hybrid Journal   (Followers: 27)
Progress in Aerospace Sciences     Full-text available via subscription   (Followers: 50)
Propulsion and Power Research     Open Access   (Followers: 3)
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: 18)
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: 14)
SpaceNews     Free   (Followers: 270)
Transport and Aerospace Engineering     Full-text available via subscription  
Transportmetrica A : Transport Science     Hybrid Journal   (Followers: 1)
Unmanned Systems     Hybrid Journal  
Вісник Національного Авіаційного Університету     Open Access   (Followers: 2)
Вестник УГАТУ     Open Access  
Journal Cover   CEAS Aeronautical Journal
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1869-5582
   Published by Springer-Verlag Homepage  [2302 journals]
  • Reduced order modelling for static and dynamic aeroelastic predictions
           with multidisciplinary approach
    • Abstract: Abstract We implement reduced order modelling techniques for aeroelastic predictions of the HIRENASD and S4T wings in order to represent CFD based high-fidelity solutions efficiently. Model reduction techniques such as non-intrusive Polynomial Chaos Expansion and Proper Orthogonal Decomposition are applied to both static and dynamic aeroelastic cases. The high-fidelity solutions are obtained by fluid structure interaction analysis using a 3D Euler unsteady aerodynamic solver and structural modal solution from a finite element solver. The model order reduction strategy is based on a multidisciplinary approach since both structural and aerodynamic input parameters are employed. The model order reduction is performed not only to represent the high-fidelity computational analyses when small variations of input parameters are considered but also to characterize the flutter responses of the S4T wing in a broad range of input values over the entire flight regime for Mach numbers between 0.60 and 1.20. The efficient aeroelastic analyses performed using the developed reduced order models agreed well with the high-fidelity computational analyses.
      PubDate: 2015-04-14
       
  • Model validation and analysis using feedforward control flight test data
    • Abstract: Abstract The German Aerospace Center (DLR) operates the ACT/FHS research helicopter with a full model-based control system applicable from hover to 120 knots forward flight, including take-off and landing. The feedforward controller used in this system is based on linear model inversion of identified local models. Therefore, the overall performance of the feedforward controller is highly dependent on the accuracy of the used inverted models. While several approaches exist to analyze model accuracy in time and frequency domains, a validation method for inverse models is rarely considered in the literature. In this paper, a flight test campaign that has been conducted to analyze model validity of the feedforward controller is presented and evaluated. A new model validation method using the feedforward controller to follow a reference command is discussed. Measured deviations from the commanded references are evaluated in the time domain to highlight the model subsystems that are not precisely represented by the linear models. The obtained results are compared with a validation method from system identification. Model extensions are proposed to increase the model accuracy for feedforward controller usage.
      PubDate: 2015-03-16
       
  • Parametric design studies for propulsive fuselage aircraft concepts
    • Abstract: Abstract Breaking with the classical separation of airframe and power plant system, new synergy effects may be rooted in close design coupling and the approach of distributing the production of thrust along the main components of the airframe. Beside greater configurational flexibility, airframe structural relief, improved noise shielding, and, the potential for control power augmentation, distributed propulsion is particularly interesting due to the reduced propulsive power demands expected from the notion of aircraft wake filling. In previous work, the concept of a propulsor encircling the aft fuselage with intent to entrain the fuselage boundary layer was identified to be one of the most promising concepts for aircraft wake filling. In this paper, the analytical basis for the quantification of efficiency benefits connected to the propulsive fuselage concept is discussed. Appropriate control volume and consistent efficiency chain definitions are introduced. A simplified boundary layer model is derived from axisymmetric fuselage CFD simulation and used to determine the momentum deficit ingested by the fuselage propulsor. Based on a novel figure of merit for vehicular efficiency, the energy-specific air range, ESAR, the dependency of aircraft cruise efficiency on basic propulsion system and aircraft design changes is parametrically investigated. Specifically, the sensitivities of vehicular efficiency w.r.t. wing aspect ratio and flow transition characteristics, propulsor size, and aircraft design cruise Mach number are studied.
      PubDate: 2015-03-01
       
  • A predictive envelope protection system using linear, parameter-varying
           models
    • Abstract: Abstract A parameter-varying, model-predictive envelope protection system is developed simplifying the controller structures required to keep the aircraft within a safe angle-of-attack and normal load factor envelope. The idea of a quasi-steady flight condition is used to map the flight envelope limits onto the setpoint values of a single flight control law. Since no mode switching is required, the selected level of automation, i.e., autopilot and flight management functionalities, is independent from the proximity to any angle-of-attack and normal load factor limit. In contrast to previous approaches, the proposed algorithm makes use of a quasi-linear, parameter-varying control loop model to adapt to the true nonlinear aircraft behavior. A variance-based sensitivity analysis highlights the most significant scheduling variables within this control loop model and, therefore, indicates the option of model reduction and improvement in efficiency, respectively. The proposed envelope protection system is evaluated throughout virtual flight tests with the unmanned flight test platform ULTRA-Dimona showing promising overall performance also in the presence of wind and turbulence.
      PubDate: 2015-03-01
       
  • Analysis of trimmable conditions for a civil aircraft with active
           high-lift system
    • Abstract: Abstract This paper outlines recent flight dynamic analysis results of a civil aircraft with active high-lift system using blown Coandă flaps. The main focus lies in the trim analysis of the aircraft. Therefore, the basic structure and core elements of the nonlinear model, describing the dynamic behavior of an aircraft with this specific type of active high-lift system are presented. The center of gravity range allowing controllability and static stability of the aircraft is determined, and the resulting characteristics of the aerodynamic model and their impact on the trim results of the aircraft are analyzed. The results show specific flight dynamic difficulties related to the active high-lift system, namely in the flying characteristics necessary for safe take-off and approach procedures. The flight physics is explained and discussed. The necessity of the application of a wing leading edge device is outlined by preliminary studies and further remedial means are proposed.
      PubDate: 2015-03-01
       
  • 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: 2015-03-01
       
  • Influence of an imidazolium salt on the curing behaviour of an epoxy-based
           hot-melt prepreg system for non-structural aircraft applications
    • Abstract: Abstract This study investigates the influence of an imidazolium salt as initiator for the curing of an epoxy novolac-based hot-melt prepreg resin system for production of non-structural aircraft components. The salt decomposes at a specific temperature during curing, yielding an imidazole. This molecule initiates a fast anionic homopolymerization. The effect of the imidazolium salt on the curing kinetics is studied extensively by differential scanning calorimetry (DSC) as a function of its concentration. Onset and peak temperatures of the curing reactions are determined from dynamic DSC experiments at various heating rates. The curing behaviour at 140 °C is analysed in more detail by isothermal DSC measurements. Calculated isothermal conversion curves prove that the flame retarded epoxy novolac formulation can be cured within less than 60 min at this specific temperature by introducing six parts of the imidzolium salt per hundred parts of preformulated resin. At the same time glass transition temperatures above 130 °C evaluated by DSC or app. 155 °C determined by DMA can be reached.
      PubDate: 2015-03-01
       
  • 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: 2015-03-01
       
  • Numerical investigation of the influence of the camber distribution at the
           rotor tip on the efficiency at different tip clearances
    • Abstract: Abstract The present paper reports on numerical investigations into the relationship of compressor efficiency drop due to increased rotor tip clearance and the rotor tip camber distribution in a 1.5 stage low-speed axial flow compressor. Starting from a baseline compressor, six alternative designs were derived. In these redesigns the tip section camber line of the rotor was replaced by an analytically given camber distribution. These camber lines used for the redesigns ranged from extreme front load to extreme rear load. The new camber line styles were blended into the original blade over the upper 30 % of blade height. For each of these variations a design speed characteristic was calculated for five different rotor tip clearances. From these characteristics the compressor efficiency at the design flow rate was extracted. Based on these values an exchange rate could be calculated relating compressor overall efficiency to rotor tip clearance height. It turned out that the rotor tip camber line style does not have an impact on this exchange rate. It could be shown that rotor losses are only affected slightly by the rotor tip camber line style and that the pressure rise that the tip vortex experiences as it travels through the passage is generally unchanged from one tip camber line style to the other.
      PubDate: 2015-03-01
       
  • Speeding-up the computation of high-lift aerodynamics using a
           residual-based reduced-order model
    • Abstract: Abstract In this article, we propose a strategy for speeding-up the computation of the aerodynamics of industrial high-lift configurations using a residual-based reduced-order model (ROM). The ROM is based on the proper orthogonal decomposition (POD) of a set of solutions to the Navier–Stokes equations governing fluid flow at different parameter values, from which a set of orthogonal basis vectors is evaluated. By considering an initial set of few snapshots at different angles of attack, a ROM is constructed which is used to predict a solution at an angle of attack which is just outside the space spanned by the POD basis vectors. The ROM solution is subsequently used to initialize the flow solver for an accurate calculation of the aerodynamics at the same flow condition. This procedure is conducted repetitively for a series of angles of attack, whereby for each and every ROM prediction, the snapshots set is augmented with the latest CFD computed flow solution. Using this strategy, a considerable reduction in the total number of iterations to reach the converged steady-state solution is achieved when compared with conventional computational techniques used in industry for a series of computations such as drag polar computations. The methodology is applied and demonstrated on a two-element airfoil and a body-wing aircraft in high-lift configuration. Furthermore, an investigation is conducted on the behavior of the reduced-order modeling approach at angles of attack close to and within the static stall region, where aerodynamic hysteresis may occur and the aerodynamic coefficients are found to be multiple-valued functions of the angle of attack. It is revealed that by constructing the ROM from an appropriate set of basis vectors, it is also possible to model the resulting bifurcation.
      PubDate: 2015-03-01
       
  • Design considerations for the components of electrically powered active
           high-lift systems in civil aircraft
    • Abstract: Abstract To address the challenges of future air traffic, such as more accessible air travel with better public acceptance, this research work focuses on efficient active high-lift systems (AHLS). This system applies boundary layer suction combined with a controlled Coanda jet. Electrically powered compressors are located in the wings at each flap to supply the suction and blowing air mass flow rate to the AHLS, thus coupling the two in a useful way. This concept provides flexibility and controllability of lift generation and is consistent with the trend towards an “all-electric aircraft”. General models for assessment of such systems in preliminary aircraft design are not available yet as they require interdisciplinary expertise. This paper provides general design considerations for the components of this type of electrically powered AHLS, comprising compressors, motors, power electronics, system peripherals, and generators. The conceptual design for those components results in models for preliminary aircraft design which allows estimating power consumption, size and mass.
      PubDate: 2015-03-01
       
  • Alternative fuels in aviation
    • Abstract: Abstract During the last years, the aviation sector has been looking into alternatives to kerosene from crude oil, to combat climate change by reduction of greenhouse gas (GHG) emissions and to ensure security of supply at affordable prices. The efforts are also a reaction to commitments and policy packages. Currently, a wide range of possible fuel candidates and fuel blends are discussed in the triple feedstock, process, and product. Any (synthetic) aviation fuel must be certified; hence, a profound knowledge on its properties, in particular thermophysical and chemical, is inevitable. In the present paper, an overview is given on alternative jet fuels, looking into the short-term and long-term perspective. Examples focusing on experimental and modeling work of combustion properties of existing—coal to liquid, gas to liquid (GtL)—and possible alternative fuels—GtL + 20 % 1-hexanol, GtL + 50 % naphthenic cut—are presented. Ignition delay times and laminar flame speeds were measured for different alternative aviation fuels over a range of temperatures, pressures, and fuel–air ratios. The data are used for the validation of a detailed chemical reaction mechanism following the concept of a surrogate. Such validated reaction models able to describe and to predict reliably important combustion properties of jet fuels are needed to further promote the development of even more sophisticated jet engines and to optimize synthetic jet fuel mixtures in practical combustors.
      PubDate: 2015-03-01
       
  • 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: 2015-03-01
       
  • Flight control law design criteria for the transition phase for a tiltwing
           aircraft using multi-objective parameter synthesis
    • Abstract: Abstract Aircraft in tiltwing configuration combine the advantages of helicopters, such as hovering and vertical take-off and landing capabilities (VTOL), with the advantages of conventional fixed-wing aircraft, in particular long endurance and economic flight at higher velocities. During the transition phase between hovering and aerodynamic horizontal forward flight the aerodynamic forces and moments, the direct forces due to propulsion system and propulsion-induced aerodynamic forces and moments have to be properly balanced. Tilting the wing from vertical to horizontal position (and vice versa) poses a significant change in configuration. In combination with the given large velocity range this influences the control device efficiency significantly. At the same time, the tilting of the wing provides an additional control parameter. During flight control law design for an unmanned tiltwing aircraft with focus on the transition phase multi-objective parameter analysis and synthesis provides a powerful means to identify interdependencies and sensitivities. Key aspects of the longitudinal motion during the transition phase are investigated in this study using the multi-objective parameter synthesis tool MOPS, developed by the DLR Institute of System Dynamics and Control. Aim of this paper is to analyze quality criteria with respect to design and evaluation of control laws during transition phase. To achieve these parameters forward velocity and pitch attitude controller are optimized with respect to control and disturbance responses. At the same time the overall robustness against selected uncertain model parameters, such as actuator dynamics is considered explicitly. Different quality criteria characterizing these motions are developed and discussed in detail.
      PubDate: 2015-03-01
       
  • Multidisciplinary wing optimization of commercial aircraft with
           consideration of static aeroelasticity
    • Abstract: Abstract This article presents the development and application of a high-fidelity simulation process chain for commercial aircraft wing multidisciplinary optimization. Based upon a parametric CAD model the aerodynamic coefficients of the wing are determined through solving the Reynolds-averaged Navier–Stokes equations within a numerical flow simulation. Structural mass and elastic characteristics of the wing are determined from structural sizing of the wing box for essential load cases by usage of the finite element method. The interactions between the aerodynamic forces and the structural deformation of the elastic wing are taken into account in the process chain by fluid-structure coupling. To reduce the number of design variables, the design task is solved by a two-step approach. To design the inner wing, an optimization of the inner airfoil geometry and the wing twist with the lift-to-drag ratio as objective function has been conducted in the first step. Based on the inboard airfoil of this optimized inner wing, multidisciplinary optimizations of the wing planform have been performed in the second step. These optimizations include the wing twist and thickness distribution in span direction as design parameters but maintain airfoil shapes. A deterministic optimization method has been applied to locate the optimum within the design space. Range and efficiency, in terms of fuel consumption per range and payload, were used as objective functions in the wing planform multidisciplinary optimizations. Two approaches for the determination of the aerodynamic loads for the 2.5-g maneuver load case based on the aerodynamic loads under cruise flight conditions have been investigated. Both approaches have been integrated in the process chain for multidisciplinary wing optimization and have been used for the wing optimization of a long-range aircraft with backward swept wings. The results of the corresponding wing optimizations have been compared with each other.
      PubDate: 2015-02-27
       
  • Comparing different approaches for modeling the vertical motion of the
           EC 135
    • Abstract: Abstract Helicopters like the EC 135 with its bearingless main rotor design feature large equivalent hinge offsets of about 10 %, significantly higher than conventional rotor designs and leading to improved maneuverability and agility. For such a helicopter, the fuselage and rotor responses become fully coupled and the quasi-steady assumption using a 6-DoF rigid-body model state space description and approximating the neglected rotor degrees of freedom by equivalent time delays is not suitable. Depending on the intended use of the model, the accurate mathematical description of the vertical motion for these configurations requires an extended model structure that includes inflow and coning dynamics. The paper first presents different modeling approaches and their relationship. Next, identification results for the DLR EC 135 are presented for a model that only describes the vertical motion excluding coupling to the other axes. Here, the differences between the modeling approaches and the respective deficits are explained. Next, the modeling approach most widely used in the rotorcraft identification literature is extended to account for hinge offset. In addition, some model parameters are estimated instead of fixing them at their theoretical predictions which leads to a very good match with EC 135 flight test data. Results for a complete model of the EC 135 including flapping, coning/inflow, and regressive lead–lag are shown as a final result.
      PubDate: 2015-02-15
       
  • Simulation for temperature control of a military aircraft cockpit to avoid
           pilot’s thermal stress
    • Abstract: Abstract During flying, military pilots are normally subjected to a number of stresses like mild hypoxia, high accelerations, vibrations and thermal discomfort. Among all of these, thermal stress is the most predominant factor while operating in highly tropical regions. Despite the use of aircraft’s environmental control system, the temperature inside the cockpit may easily reach more than 10 °C above ambient temperature and sometimes it may even exceed 45 °C. When these extreme temperatures are coupled with high relative humidity, causes for the degradation of both mental and physical performance of the pilots are present. This situation becomes severe, especially during low altitude and high-speed operations due to aerodynamic heating of the external surfaces. Sometimes, at high altitude and low-speed operations, the cockpit temperature falls and cold stress can pose a serious problem on the health of pilots. It is necessary to protect the pilots from high thermal stress to keep them under safe thermoregulatory limits and also help them perform an intended mission. This paper develops and deploys a basic method that can be used at an early design stage of any military aircraft to analyse the environmental control system’s performance in avoiding pilot thermal stress. The method is also applicable to a design study for an enhanced environmental control system on an existing aircraft. Results present the effect of parameters including Mach number, altitude, ambient temperature, cockpit geometry, and solar radiation on cockpit thermal balance which have a direct impact on the thermal stress on pilots. A military aircraft with a cockpit volume of 1.5 m3 is considered for performing the thermal balance simulation studies. This paper also addresses the effects on engine bleed flow requirements, and corresponding air inlet temperatures to maintain the cockpit target wet bulb globe temperature of 28 °C as well as a pilot mean skin temperature target of 33 °C. These are some of the thermal stress indicators proposed by different aero-medical authorities. These requirements are to be maintained if the physiological stress and impairment of performance of the pilots are to be avoided while operating in hot and humid environments.
      PubDate: 2015-01-30
       
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    • PubDate: 2015-01-28
       
  • Synergies between suction and blowing for active high-lift flaps
    • Abstract: Abstract The present 2-D CFD study investigates aerodynamic means for improving the power efficiency of an active high-lift system for commercial aircraft. The high-lift configuration consists of a simple-hinged active Coanda flap, a suction slot, and a flexible droop nose device. The power required to implement circulation control is provided by electrically driven compact compressors positioned along the wing behind the wingbox. The compact compressors receive air from the suction slot, which also represents an opportunity to increase the aerodynamic performance of the airfoil. The present work investigates the aerodynamic sensitivities of shape and location of the suction slot in relation to the maximum lift performance of the airfoil. The main purpose of the study is the reduction of the compressor power required to achieve a target lift coefficient. The compressor power requirements can be reduced in two ways: obtaining a high total pressure at the end of the suction duct (compressor inlet) and reducing the momentum needed by the Coanda jet to avoid flow separation from the flap. These two objectives define the guideline of the suction slot design. As a result, a jet momentum reduction of 16 % was achieved for a target lift coefficient of 5 with respect to the same configuration without suction. Furthermore, the study yielded physical insight into the aerodynamic interaction between the two active flow control devices.
      PubDate: 2015-01-10
       
  • Influence of boundary layer transition on the flutter behavior of a
           supercritical airfoil
    • Abstract: Abstract This paper presents a flutter analysis for the supercritical CAST 10-2 airfoil in a flow with free boundary layer transition based on CFD computations with the \(\gamma \) - \(\hbox {Re}_{\theta }\) transition model. The results are compared to fully turbulent results obtained with the SST \(k\) - \(\omega \) turbulence model. Unsteady RANS computations at \(\hbox {Re}_{\rm{c}} = 2 \times 10^{6}\) are used to determine the aerodynamic derivatives. These derivatives are required to identify the flutter boundary for a 2 degree-of-freedom model by a k method. The transonic flutter boundary decreases for a flow with free boundary layer transition compared to a fully turbulent flow in the vicinity of the transonic dip. However, the flutter boundary at subsonic Mach numbers is raised for a transitional flow. In addition, the transitional frequency response is discussed: an aerodynamic resonance in connection with an instability of the transition region is observed and the possibility of a 1 degree-of-freedom flutter for transitional flows is shown.
      PubDate: 2015-01-07
       
 
 
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