Showing papers in "CEAS Aeronautical Journal in 2011"
TL;DR: A new data exchange file format called CPACS is introduced, which serves as central interface and common language between the disciplinary analysis tools and the integration framework, which allows the user to couple the single tools to multidisciplinary process chains for analysis and optimization tasks.
Abstract: In 2005, the German Aerospace Center (DLR) started an internal project, called TIVA, with the main goal to strengthen the multidisciplinary collaboration in the field of conceptual aircraft design. This approach was intended not only to couple disciplinary analysis tools from different institutes, but also to establish a process which keeps the disciplinary experts in the loop as well. Linking the tools and corresponding experts, this process should finally enable each discipline to study the consequences of their new concepts and technologies on overall aircraft level. One major component of this process is a new data exchange file format called CPACS, which serves as central interface and common language between the disciplinary analysis tools. The second key component is the integration framework, which allows the user to couple the single tools to multidisciplinary process chains for analysis and optimization tasks. Since the end of the TIVA project in 2009, the system is continuously being enhanced and extended in TIVA’s successor-project VAMP, as well as in several other research projects which are based on this technology. For the near future, it is further planned to open the system with its major components to external partners and to use it for common projects with Industry and Universities.
94 citations
TL;DR: This paper will focus on the prediction of aircraft structural strength using virtual testing analysis methods and the key challenges and enablers for future successful virtual testing demonstrations in an industrial context.
Abstract: This paper will focus on the prediction of aircraft structural strength using virtual testing analysis methods. Virtual testing is a concept with several attributes and is to be understood as the simulation of aircraft structure using advanced nonlinear finite element analysis. It will involve the combination of analysis software, methods, people skills and experience to predict the actual aircraft structural strength with a high level of confidence. This is achieved through the creation and execution of a detailed nonlinear finite element analysis model of an aircraft structure, which represents as accurately as possible the actual physical behaviour when subjected to a wide range of loading scenarios. Creating a virtual representation of an aircraft structure presents the analysts with several significant challenges, including the creation of the complex finite element model that accurately represents the global aircraft structure, and then adding the significant detail in terms of material and construction required to make accurate failure predictions with confidence. An overview will be provided of the general principles used in the process of virtual testing of both metallic and composite aircraft structures. The paper will focus on the key challenges and enablers for future successful virtual testing demonstrations in an industrial context.
77 citations
TL;DR: In this paper, the authors give a survey on active rotor control technologies for a long time and many different approaches have been investigated and most of them are not being followed any more.
Abstract: Modern helicopters still suffer from many problems that hinder a further increase in their efficiency, acceptance and hence their market share. The high level of vibrations and the noise generated by the rotor are the most important reasons for this. Vibrations are problematic not only for pilot and passenger comfort, but also give rise to an increase in maintenance effort. The high noise level limits the acceptance of helicopters in the public, e.g. landing of helicopters on or close to hospitals during Emergency Medical Services missions. High noise levels also lead to an early aural detection during military missions. Further drawbacks of helicopters are the high fuel consumption in high-speed forward flight and hence low range, limited speed of flight, etc. To overcome these drawbacks, active rotor control technologies have been investigated for a long time. Many different approaches have been investigated and most of them are not being followed any more. First investigations started with so-called Higher Harmonic Control (HHC) which has been replaced by Individual Blade Control (IBC). In a previous paper motivation on active rotor control technology was recapitulated as well as achievements on HHC. This paper continues that work and gives a survey on IBC concepts and achievements. An outlook on the idea of the swashplateless helicopter concludes the paper.
59 citations
TL;DR: The paper gives a survey of the typical problems and explains the vibration and noise issues of helicopters in more detail, and gives an outlook on the idea of the swashplateless helicopter.
Abstract: Since the early helicopter developments, these aircraft have made a tremendous progress in performance, handling qualities, comfort and efficiency. However, modern helicopters still suffer from many problems that hinder a further increase in their efficiency, acceptance and hence their market share. The high level of vibrations and the noise generated by the rotor are the most important reasons for this. While vibrations are a concern of pilot and passenger comfort, they also give rise to an increase in maintenance efforts and costs. The high noise level limits the acceptance of helicopters in the public, e.g. landing of helicopters on or close to hospitals during EMS missions. High noise levels also lead to an early aural detection during military missions. Further drawbacks of helicopters are the high fuel consumption in high speed forward flight due to the excessive power required, the limited speed of flight, the low range for the same reason, low lead-lag damping, etc. To alleviate these drawbacks of helicopters, active rotor control technologies have been investigated for a long time. Many different approaches have been investigated and most of them are not being followed any more. First investigations started with so-called Higher Harmonic Control (HHC) which has been replaced by Individual Blade Control (IBC). The paper gives a survey of the typical problems and explains the vibration and noise issues in more detail. Since active means have to compete with passive ones, such methods are also briefly addressed. Next, the paper gives a review on important HHC achievements. Due to space constraints, the paper mainly focuses on wind tunnel and flight test results. A second paper reviews IBC and gives an outlook on the idea of the swashplateless helicopter.
46 citations
TL;DR: In this article, the impact of the propeller induced slipstream on the aerodynamic coefficients and the stability analysis during transition phases between horizontal and vertical flight was considered. But the authors focused on the influence of the tiltwing configuration on aerodynamic coefficient.
Abstract: Within the EU and North Rhine-Westphalia funded research project AVIGLE, the Institute of Flight System Dynamics develops a multi functional flight platform in a tiltwing configuration. The different mission requirements as well as the specific requirements due to the tiltwing configuration influence the design process. Within each specification step, the impact on horizontal and vertical flight, including transition states in between has to be considered. Beside numerical flow analysis, extensive wind tunnel tests were conducted to confirm the calculated coefficients and derivatives and to gain data needed to build a six degrees of freedom simulation for development of controlling strategies in transition. Particular emphasis was put on the influence of the propeller induced slipstream on the aerodynamic coefficients and the stability analysis during transition phases between horizontal and vertical flight.
42 citations
TL;DR: In this article, a general outline is given of how vibration problems in landing gears can be treated by numerical analysis methods including a classification of typical problems, a short overview of classical papers, and explain typical approaches in addition, alternative approaches for stability analysis and for the detection of limit-cycle oscillations as well as state-of-the-art modelling approaches.
Abstract: Aircraft landing gears support the aircraft during ground operations, including take-off, landing impact, taxiing, gate handling and maintenance Mostly for reasons of minimum mass and ground clearance, landing gears are slender structures which exhibit a considerable dynamic response to ground load excitations As the landing gear is one of the few systems on the aircraft without redundancies, the knowledge of landing gear dynamics is crucial for aircraft design and aircraft safety Simulation of landing gear dynamics is a cornerstone of aircraft loads analysis, as well for vertical loads resulting from touch-down as for longitudinal and lateral loads resulting from braking, steering and towing Another important field of interest is landing gear vibrations like gear walk and shimmy Those phenomena can be brake induced or result from tire spin-up at touch-down or simply from a coupling of dynamics of the running tire and structural mechanics of the landing gear leg All those effects strongly depend on a number of parameters such as aircraft speed, landing gear vertical deflection, tire pressure and wear of the parts Many of those parameters can only be estimated and might change during the operation of the aircraft Numerical investigation is thus a challenging task Analysis methods exist both in the frequency domain and in the time domain As stability analysis is straight forward in frequency domain methods, this approach is still often used However, in many cases nonlinearities are dominant which lead to limit-cycle characteristics of the vibrations Here, multibody modelling or a mixture of multibody and finite element modelling including time domain simulation is used In the article, a general outline is given of how vibration problems in landing gears can be treated by numerical analysis methods The article will start with a classification of typical problems, give a short overview of classical papers, and explain typical approaches In addition, alternative approaches for stability analysis and for the detection of limit-cycle oscillations as well as state-of-the-art modelling approaches will be presented
35 citations
TL;DR: In this paper, the design and numerical investigation of constant blowing air jets as fluidic control devices for helicopter dynamic stall control is described, and three configurations using jets at 10% chord on the airfoil top were identified.
Abstract: The design and numerical investigation of constant blowing air jets as fluidic control devices for helicopter dynamic stall control is described. Prospective control devices were first investigated using 3D RANS computations to identify effective configurations and reject ineffective configurations. Following this, URANS investigations on the dynamically pitching OA209 airfoil verified that configurations had been selected which reduced the peaks in pitching moment and drag while preserving at least the mean lift and drag from the clean wing. Two configurations using jets at 10% chord on the airfoil top were identified, and one configuration using a tangential slot at 10% chord on the airfoil top, with each configuration evaluated for two jet total pressures. For the best configuration, a reduction in the pitching moment peak of 85% and in the drag peak of 78% were observed, together with a 42% reduction in the mean drag over the unsteady pitching cycle.
35 citations
TL;DR: The approach considered in this thesis is examined in the joint project called “Airspace Management 2020” (LRM2020) by DFS (Deutsche Flugsicherung GmbH) and DLR (Deutsches Zentrum für Luft- und Raumfahrt e.V).
Abstract: Balancing controller workload is part of the air traffic management (ATM). It is the current practice to organize airspace and balance its demand and capacity by partitioning airspace into sectors. This approach is naturally limited by the minimum size of sectors and the amount of possible controller coordination. The approach considered in this thesis is examined in the joint project called “Airspace Management 2020” (LRM2020) by DFS (Deutsche Flugsicherung GmbH) and DLR (Deutsches Zentrum fur Luft- und Raumfahrt e.V.). The aim is to provide a sectorless airspace. For this concept, the possibilities for the assignment of aircraft to air traffic controllers are examined. Different assignment strategies have been developed and selections of these are tested with various traffic scenarios on their capacitive properties.
24 citations
TL;DR: In this paper, a procedure based on numerical methods has been developed to predict the structural response of wedge-shaped folded cores under compressive and shear loading, and the results show a good agreement with the behaviour predicted by simulation.
Abstract: The problem of honeycomb sandwich structures with moisture ingression can be avoided by replacing the honeycombs through chevron-folded cores. The application to real aircraft components often requires wedge-shaped sandwich. With folded cores, this kind of geometric shape can be obtained only by special folding schemes which have a significant influence on the mechanical performance. A comprehensive experimental investigation of the relation between folding geometry and structural properties of wedge-shaped folded cores (WSFC) is very time consuming and expensive. Therefore, a procedure based on numerical methods has been developed to predict the structural response of this kind of cores under compressive and shear loading. The approach is based on a numerical tool that provides finite element models of arbitrary WSFC as well as the explicit finite element solver LS-DYNA for simulation. These tools were applied to investigate the influence of the inner core geometry and different materials on the mechanical properties of WSFC structures. To verify these results, a test programme was conducted. Test samples were manufactured using a newly developed folding process. Also special test devices to determine the compression and shear properties of the WSFC specimens were developed. The achieved test results show a good agreement with the behaviour predicted by simulation.
19 citations
TL;DR: S sizing methods for metallic and composite orthotropically stiffened fuselage structures have been reviewed and the derived rapid sizing method for postbuckling significantly reduces the computational time when compared to the computationalTime needed for a nonlinear finite element computation.
Abstract: The increasing use of composite materials in aircraft structures aims in reducing the structural weight significantly. In order to exploit the advantages of composite materials especially within a large-scale optimization calculation, a model for a computationally efficient structural analysis needs to be developed. In this regard, algorithms need to be developed to rapidly compute stress distribution and critical loads for both strength and stability of the composite aircraft fuselage. Therefore, sizing methods for metallic and composite orthotropically stiffened fuselage structures have been reviewed. For critical load computation, fibre fracture and inter-fibre fracture need to be taken into consideration with respect to strength. Regarding stability, the critical buckling loads of skins and stringers as well as the critical crippling load need to be taken into account. The buckling of stringers often occurs after the skin buckling load is exceeded. Hence, the postbuckling behaviour needs to be analyzed and load redistributions in the postbuckling range have to be taken into consideration. These load redistributions can generally be calculated numerically using either the finite element method or the finite strip method (Mocker and Reimerdes in Compos Struct 73:237–243, 2006) as well as analytically. In order to minimize the computational time, the postbuckling behaviour of the skins regarded as composite plates is computed analytically within this work by means of a computation of effective stiffnesses for global analysis and local failure load computation. Even though the postbuckling behaviour of metallic and composite plates has been widely studied in literature, only few work has been spent on the analytical or semi-analytical derivation of methods for the common load case of combined compression and shear loading. As the preliminary design of an aircraft fuselage requires a rapid and sufficiently accurate description of the postbuckling behaviour, the postbuckling behaviour of an orthotropic composite plate under combined compression and shear loading is analytically analyzed within the present work. The derived rapid sizing method for postbuckling significantly reduces the computational time when compared to the computational time needed for a nonlinear finite element computation. In this regard, it even allows for the consideration of postbuckling behaviour within a large-scale optimization computation of complete fuselage structures.
14 citations
TL;DR: In this article, an air-coupled ultrasonic scanning can detect the manufacturing flaws contact-freely as well as impact damages and thus enhances the inspection and damage tolerance capability of the sandwich structure.
Abstract: Despite its superior specific stiffness, the sandwich design is currently applied in commercial aviation mainly in secondary structures. A major reason for this is its low resistance to a concentrated out-of-plane load, such as impact loading by a foreign object. In this scenario, the resulting damage is also known as foreign object damage and may penetrate further into the sandwich core. An improvement of impact resistance shall be achieved to introduce sandwich into the primary structures. Within the German aeronautics research programme, a primary sandwich structure, i.e. the centre box for a next generation vertical tail plane, was developed. The geometrical characteristics of the sandwich shell of the box, which has a unique lens shaped or lenticular cross section, lead to a noticeable improvement of its impact resistance. The considered sandwich configuration consists of carbon-fibre reinforced plastic skins and a closed cell foam core in between, which allows manufacturing using liquid composite moulding, such as a vacuum assisted infusion process. Embedded core reinforcements and damage arresters, respectively, can be manufactured within the same process step. Furthermore, the developed novel air-coupled ultrasonic scanning can detect the manufacturing flaws contact-freely as well as impact damages and thus enhances the inspection and damage tolerance capability of the sandwich structure. For the proof of structural integrity, a cutout in the critical area of the sandwich panel was defined and modified, such that it has no significant eccentricity and fits into an available shear-compression test facility. Loads are increased stepwise to explore all structural responses including interactions. The results show excellent structural stability with respect to the damage tolerance, even after multiple impact loadings up to 50 J, which agree with previously conducted non-linear structural analysis. A cyclic loading scenario with 8,000 simulated flight cycles in the context of research induces no significant growth of the impact damages and no deteriorating of the structural behaviour, respectively. Finally, the sandwich panel was used to investigate expected thermo-mechanical loadings during the takeoff and landing phases of the reference aircraft.
TL;DR: In this article, the authors used a two-stage low speed research compressor with a shrouded stator row to investigate the interaction of non-axisymmetric endwall contouring at the stator hub with the leakage flow emanating from the shroud cavity.
Abstract: This numerical study uses a two-stage low speed research compressor with a shrouded stator row to investigate the interaction of non-axisymmetric endwall contouring at the stator hub with the leakage flow emanating from the shroud cavity. It can be shown that the contour is effective in reducing the hub corner stall caused by the separating endwall boundary layer. The leakage flow itself is not reduced. Subsequently, the height of the shroud seal fins is varied. A comparison of the results with and without non-axisymmetric endwalls shows that the effectiveness of the endwall contour in improving stator performance increases with the amount of leakage flow. Consequently, the sensitivity towards shroud leakage is decreased with contoured endwall. This leads to the conclusion that this design feature does not only serve to improve the flow quality in a given case, but also provides a means to the aerodynamic designer to introduce more robustness into the compressor.
TL;DR: In this paper, the authors present an index of airport capacity utilisation to assess the capacity reserve of an airport, which is designed to be applied on a global level and it is based on the concepts of the 5% peak hour and the average hour of an Airport which is deduced from so-called ranking curves.
Abstract: Current air traffic forecasts are mainly based on the hypothesis that airports have ample capacity to accommodate future growth, or, if this is not the case, that increasing airport capacity more than marginally is possible within an acceptable time frame. Improving airport capacity more than marginally usually means adding new runways; however, especially in highly developed countries, this may take many years to complete and for some airports, it is even an insurmountable task. This paper gives a brief overview over the historic development of global air traffic and compares it with the more recent developments at specific airports, which are important hubs in the global air traffic network. Thereafter, we develop an index of airport capacity utilisation to assess the capacity reserve of an airport. This index is designed to be applied on a global level and it is based on the concepts of the 5% peak hour and the average hour of an airport which is deduced from so-called “ranking curves”, i.e. operating hours of an airport are ranked according to their traffic volume in descending order. The more this curve is inclined, the greater is the capacity reserve of an airport. This procedure is carried out for around 2,500 airports worldwide on the basis of Official Airline Guide data. The number of flights of an airport serves as a measure for its importance in the global air traffic network. In connection with the airport capacity utilisation index, we are able to categorise airports with regard to the dimensions “level of importance for the global air traffic system” and “level of capacity reserve”, thereby, we are able to identify those airports that are critical for future growth of air traffic, i.e. those airports that serve a large share of the global flight volume and at the same time have only a small capacity reserve.
TL;DR: In this paper, a CFRP foam core sandwich structure with polymethacrylimide (PMI) foam core, named ROHACELL®RIST, is used as a primary structure in commercial aviation.
Abstract: The work presented in this article is directed towards the application of CFRP foam core sandwich structures as primary structures in commercial aviation. With closed cell rigid foams, it is possible to produce comparatively low priced high-integral sandwich components having a complex geometry in terms of a curved and a variable lateral cut. Sandwich structures are offering a good bending stiffness and strength to weight ratio. Thus, they are suited for using in structures which are at risk to fail by buckling (Herrmann et al. Sandwich structures 7: advancing with sandwich structures and materials, 2005). The investigations are focused on a CFRP sandwich structure with polymethacrylimide (PMI) foam core, named ROHACELL®RIST. Besides good structural stability at thermal conditions, the foam is characterized by a good strength and stiffness to weight ratio (Seibert, Reinforced Plast 50(1):44–48, 2006). Primary structures in aircraft applications are exposed to a superposition of in-service loads and environmental conditions. The typical working loads in combination with environmental conditions were investigated. The structure needs a sizing with respect to large temperature changes and influences of humidity. Thus, the time, temperature, and moisture dependency of the mechanical behavior were studied for the single components of the structure and for the composite itself. Therefore, Finite Element Models on macroscopic level were built with reference to the experiments. For each in-service case, the residual stresses arising during manufacturing have to be regarded and quantified (John et al. ECCM14, 2010). During manufacturing, the sandwich structure is cured at 180°C. Due to the different stiffnesses and coefficients of thermal expansion of the foam and the CFRP face sheets, residual stresses are induced by cooling down to service temperature. Among others, some tests were made at laterally closed CFRP sandwich structures with a storage time up to half a year at certain climate conditions. The aging process is not only controlled by external conditions, but also by a rearrangement of molecules, for example, the relaxation behavior of the PMI foam (Gutwinski et al. Verbundwerkstoffe. Wiley, Weinheim, 2009). Another question of the long-term behavior of the CFRP foam core sandwich structure is the characteristic of delamination of the face sheets from the inner core after an impact has occurred. To describe the crack growth behavior of the sandwich structure fracture mechanical principles can be used estimating the damage tolerance. Sandwich specimens with initial damage were loaded up to 3 million mechanical load cycles.
TL;DR: In this article, a software tool was developed to design aero-engine combustors on a preliminary level, where a small set of input parameters is required to design conventional as well as lean combustors.
Abstract: A software tool was developed to design aero-engine combustors on a preliminary level. Only a small set of input parameters is required to design conventional as well as lean combustors. During the design calculation the combustor contour, the geometry of the desired cooling concept and the air flow distribution within the combustor are optimized. Optimization targets are to minimize the cooling air consumption with respect to the material temperature limits and to reach homogeneous material temperatures as well as a stable combustion. In the case of a staged burner the burner air and fuel fractions are optimized regarding minimal NOx production (qualitative) for the design condition. Off-design calculations on the basis of designed combustors can be executed for engine conditions other than take-off to calculate the altered conditions within the combustor. This paper shows the design and off-design process of the combustor tool in detail. In a second part application examples are given. The presented results show the capabilities of the tool for the pre-design of lean combustors with respect to the trade-off between the reduction of NOx emissions and the reduction of the fuel consumption as well as the capabilities for identifying potential cooling issues.
TL;DR: The flexibility of a GLS offers the design and the execution of segmented steep precision approaches which are a compromise between the possible efficiency and the introduced operational limitations.
Abstract: As the international air traffic becomes more and more complex there is a growing demand for new operational procedures. Especially quiet and fuel efficient approaches are desired. As a Ground Based Augmentation System (GBAS) provides more flexibility than current precision landing systems, it is identified as a potential main technology for providing different approach procedures tailored for the demands at a special location. Especially steep precision approaches have a high potential for noise reduction as the aircraft stays at a higher altitude for a longer time. A GBAS uses GPS reference receivers to calculate corrections for the observed ranges of the satellite signals. Together with a VHF Data Broadcast that transmits the corrections as well as one or multiple desired approach paths the GBAS becomes a precision approach system (GLS). The possibility of broadcasting multiple approaches for a single runway end offers approaching aircraft to choose the most efficient and quiet approach that can be operationally achieved with the respective type of aircraft. As steep approaches with a single glide path angle introduce some operational limitations, the flexibility of a GLS offers the design and the execution of segmented steep precision approaches which are a compromise between the possible efficiency and the introduced operational limitations.
TL;DR: A simulator-based experiment was developed to provide the data for the later analyses and the identification of mathematical models suitable for that purpose and the very encouraging results obtained so far are detailed.
Abstract: Active side sticks offer the possibility to adjust the force-feel characteristics to account for various piloting tasks and flight conditions. This promises a decrease in pilot workload and an increase in handling qualities. However, the optimum force-feel characteristics are not well understood and modeled; therefore, their tuning still rely on experimental methods. Experimental pilot-in-the-loop methods are time-consuming, expensive and have to be repeated with every change in control law dynamics. If a purely mathematical method for force characteristics optimization could be developed based on a better understanding of the principles underlying good force-feel systems, then the optimization could be done more efficiently and offline. This paper presents our current developments and achievements towards this new understanding to assess if and how a purely mathematical method could be derived from selected experiments. Even if this final goal could not be derived yet, the paper presents the selected approach and the lessons learned so far. More precisely, a simulator-based experiment was developed to provide the data for the later analyses and the identification of mathematical models suitable for that purpose. For this experiment, a roll tracking task is considered whose evaluation is based on both a qualitative (Cooper–Harper rating) and a quantitative criterion. The very encouraging results obtained so far on this scenario are detailed.
TL;DR: In this article, parameter clustering methods are used to integrate all factors relevant for assessing aircraft's and procedures' impact on airport capacity, such that meaningful general results can be achieved limiting the effort required despite the big variety and individuality of airports worldwide.
Abstract: Due to the worldwide increasing air traffic demand being challenged by restricted airport capacities, the future aircraft designs and operational concepts need to be evaluated regarding their general impact on airport capacity already at the concept stage within the design process. Looking at different airport situations worldwide, however, reveals a high individuality and variety in airport infrastructure and air traffic structures suggesting that any kind of capacity assessment may only be valid for one specific airport and that the provision of general results requires careful consideration of all influencing factors. This paper’s objective is to initially introduce new applications of established methods in the fields of parameter clustering and scenario analysis, thus making them available to define operational cases for airport capacity impact assessments of new aircraft concepts. Clustering methods are used to integrate all factors relevant for assessing aircraft’s and procedures’ impact on airport capacity such that meaningful general results can be achieved limiting the effort required despite the big variety and individuality of airports worldwide. Scenario techniques are outlined that can complement the approach in order to additionally address uncertainties in the operational airport environment within the timeframe beyond the new aircraft concept’s potential entry into service. A proof of concept study is provided to show the general possibilities of application for the proposed approach.
TL;DR: It has been shown that the presented Eclipse technologies significantly advance the development of specialized as well as generic tools for supporting model-based systems design.
Abstract: The benefits of using Eclipse software technologies for developing tools for systems engineering are presented. Based on the challenge for designing the flap kinematics of a high lift system, a design process is presented and from that, requirements for tools as well as underlying software technologies are derived. Several Eclipse technologies are presented and it is demonstrated how they have been applied to implement a data exchange between the design tool CATIA and the simulation environment SimMechanics. It has been shown that the presented Eclipse technologies significantly advance the development of specialized as well as generic tools for supporting model-based systems design.
TL;DR: In this article, a flight test technique associated with boundary avoidance tracking was performed and the concept was investigated in detail Especially, the presumption was considered that this new technique can raise the pilot gains in a buildup fashion and can, therefore, be more effective than conventional techniques.
Abstract: Handling qualities research largely depends on the understanding of the pilot’s behaviour in the control loop Conventional pilot models are based on the idea that the pilot tries to achieve target conditions, eg a specific attitude In 2004, Gray introduced the so-called boundary avoidance tracking theory which considers the pilot as someone who tracks away from threatening conditions (boundaries) when they become dominant In the frame of a preliminary simulator study with five test subjects, the flight test technique which is associated with boundary avoidance tracking was performed and the concept was investigated in detail Especially, the presumption was considered that this new technique can raise the pilot gains in a buildup fashion and can, therefore, be more effective than conventional techniques Gray’s pilot inceptor workload criterion, a new pilot gain measure, was enhanced and used to explain these specific effects
TL;DR: The cooperative use of fast and real time simulation is reviewed and a five step cooperative strategy is suggested to allow for efficient scenario design that enables the validation expert to design scenarios with specific traffic situations using a fast time simulation tool.
Abstract: The DLR Institute of Flight Guidance is one of the leading establishments in the field of air traffic management research worldwide Research is conducted using different simulation models The fast time simulation tools (eg Simmod, AirTOp, etc) offer the possibility to examine various aspects of the air traffic in short evaluation cycles Especially long lasting, complex traffic flows can be well analysed with the help of these tools In contrast to the fast time simulation tools, the real time simulation facilities operated by the Institute allow the so-called human-in-the-loop research For instance, the Apron- and Tower Simulator (ATS) emulates the air traffic controller’s working environment at the airport Within this environment, the impact of new concepts on the controllers can be examined The influence of different traffic scenarios, additional assistant systems, work organization and the design of workplaces on controllers’ task- and workload can be researched in this way Inside the “Deutsches Zentrum fur Luft- und Raumfahrt” (DLR) project Remote Airport Traffic Control Center (RAiCe), an approach was developed to combine both types of the described simulation models Therefore, the fast time simulation was enhanced with elements representing typical tasks of a controller (eg separation keeping or radio communication) By this approach, it was possible to preselect appropriate traffic scenarios and to determine special traffic events At the ATS, air traffic controllers were confronted with the selected scenarios and events Based on their performance, conclusions concerning different remote tower operation concepts were made Within this paper, the cooperative use of fast and real time simulation is reviewed A five step cooperative strategy is suggested to allow for efficient scenario design that enables the validation expert to design scenarios with specific traffic situations using a fast time simulation tool Furthermore, harmonizing fast and real time simulation offers the possibility to use data of the fast time simulation as scenarios for real time simulations, and real time simulations can be used for the validation of fast time simulation models Data of the simulations within RAiCe are introduced The application of the cooperative use of fast and real time simulation for validation of future ATM concepts is indicated
Abstract: This paper reports on different parameters that influence the closed mould resin transfer moulding (CM-RTM) process for fiber-reinforced plastics. A sensitivity study of selective parameters is performed. This includes material parameters (i.e., viscosity, permeability), process parameters (i.e., temperature) and geometrical parameters (i.e., position of preform in the tool). Furthermore, fiber type and targeted fiber volume content are considered to validate the full range of fiber-reinforced plastics. As an example for the sensitivity study, the aeronautical carbon fabric G0926 and epoxy resin system RTM6 (both manufactured by Hexcel) are analyzed for targeted fiber volume contents in a range of ~60%. The infiltration of a rectangular panel was simulated with the flow simulation software RTM-Worx by Polyworx. It was found that the infiltration of a simple geometry can differ by app. Factor 3 in terms of duration, when only considering the tolerances of material and process parameters (“upper tolerance limit” vs. “lower tolerance limit” scenario). For different types of composite materials observed in this study, it can even go up to Factor 1,000. To achieve a reliable RTM process, these aspects—material types and range of tolerance—have to be considered.
TL;DR: In this paper, the effects of tip injection on the compressor performance were investigated in three different configurations at MTU Aero Engines and it was found that tip injection prevents the generation of stall cells almost completely.
Abstract: Within the European research project NEWAC (New Aero Engine Core Concepts), a multi-stage high-pressure compressor equipped with a tip injection system upstream of the first rotor was tested in three different configurations at MTU Aero Engines. One aim of the test campaign was to investigate the effects of tip injection on the compressor performance. This paper gives an overview of the influences of tip injection on the characteristics of the first three stages. Following an outline of the motivation for tip injection, it is assessed to what extent the surge behavior of the tested compressor is affected by tip injection. The assessment is made by evaluating the surge line extension due to tip injection. If the injection system is applied in an engine, re-matching of its turbo components will occur. Due to this fact, the focus is placed on evaluating the benefits afforded by the use of the injection system in an aircraft engine. The test results are integrated in an existing engine model for a next generation geared turbofan engine and off-design simulations are performed. In this way, changes in surge margin due to tip injection are evaluated. In addition to mere tip injection tests, measurement data of test cases is analyzed, in which mass flow recirculation was simulated. The evaluation of these tests is discussed analogously to the test cases of tip injection. It is found that tip injection prevents the generation of stall cells almost completely. The analyses also show that the stage matching of the multi-stage compressor is changed by tip injection at the front stage. According to the synthesis calculations carried out, recirculation increased the surge margin at part speed by up to about 35% relative to the reference compressor without tip injection.
TL;DR: In this paper, the integration analysis of novel trimmable horizontal stabilizer actuator (THSA) concepts with respect to the arrangement of load paths in the fuselage is presented.
Abstract: Commercial aircraft use a trimmable horizontal stabilizer to control the equilibrium of moments around the pitch axis independent of the elevator. The movement of the horizontal stabilizer is controlled by the trimmable horizontal stabilizer actuator (THSA). The limited testability of today’s systems is a huge disadvantage. To improve such systems, a variety of approaches are investigated, whose integration into the fuselage needs to be analysed. Considering the load transmission as well as their kinematics, this article deals with the integration analysis of novel THSA concepts with respect to the arrangement of load paths in the fuselage. Independent of the load path design (e.g. ball screw or hydraulic cylinder), THSA systems with two primary load paths are differentiated from those with one primary and one secondary load path. To evaluate innovative architectures, criteria are presented, which are the basis of multiobjective decision making. The procedure and the interpretation of results are shown in simplified examples of novel concepts.
TL;DR: Weinert et al. as mentioned in this paper proposed a three-dimensional view of the fatigue strength as a function of number of load cycles to failure and stress ratio R. This approach is more accurate compared to the traditional Goodman approach.
Abstract: The relation between fatigue strength and number of load cycles to failure is usually represented by Wohler curves. The four-parametric Weibull function shows a good relation between the static and dynamic strength in the low- and high-cycle fatigue range for a constant stress ratio R (minimum stress/maximum stress) (see Jarosch and Stepan in Fatigue properties and test procedures of glass reinforced plastic rotorblades. American Helicopter Society, 25th Annual National Forum, Paper No. 370, 1969; Och in Fatigue strength, AGARDograph No. 292, helicopter fatigue design guide, 1983; Bansemir and Emmerling in Fatigue substantiation and damage tolerance evaluation of fiber composite helicopter components, applied vehicle technology panel: applications of damage tolerance principles for improved airworthiness of rotorcraft, Corfu, Greece, 1999). However, in addition to the number of load cycles to the failure, fatigue strength also depends on the stress ratio R as well. In predicting the lifetime of a component, a more proper way for the presentation of fatigue life test data is the Goodman approach. This often used method affords the user to predict lifetime at any stress ratio, but does not represent the real material behaviour fully. The Goodman diagram does not take into account the combined effect of low-cycle fatigue and high-cycle fatigue. One better way to build an accurate relation between the fatigue strength, number of load cycles to failure and the stress ratio is to add the third dimension. The result is a three-dimensional view of the fatigue strength as a function of number of load cycles to failure and stress ratio R. Hence, the mathematical description of the fatigue strength as a kind of a surface function depending on the number of load cycles to the failure and the stress ratio is of high interest and indeed the focus of this study. The surface function represents the real material behaviour in low-cycle fatigue range as well as in high-cycle fatigue range more accurate compared to basic Goodman approach. For the determination of the Fatigue–Strength Surface, a so-called F–S Surface, test points with different stress ratios are necessary. The surface function can be adapted to the test points using a nonlinear regression analysis based on least square method. Therefore, it is advisable to use either the three-dimensional Weibull function or a surface function which consists of Tschebyscheff Polynomials. To enhance the regular two-dimensional Weibull function to a three-dimensional model, the four Weibull parameters are described as functions of the stress ratio. This method can be used to analyse the material behaviour based on the results of coupon or component tests. In case of coupon tests, this method is applied and validated as described in the paper. Furthermore, the use of material F–S Surface is compared with Goodman approach. For this purpose, mean surfaces of coupon test specimens with a survival probability of 50% are used. Especially in high-cycle fatigue range and for the stress ratios greater than zero, Goodman approach shows a slight deviation from the actual fatigue strength. In order to consider such effects, lifetime calculations are performed in Eurocopter Deutschland GmbH by using the reduced, so-called working S–N curves which are based on component test results. It has been found that the F–S Surface tends to describe the real fatigue strength in a more accurate way. This may lead to a longer lifetime of components and the possibility to extend the margins of components. This paper is developed from the Diploma thesis “Prediction of the dynamic strength behaviour of structural elements based on S–N–R surfaces created by nonlinear regression analysis of experimental data” (see Weinert in Prediction of the dynamic strength behaviour of structural elements based on S–N–R-surfaces created by nonlinear regression analysis of experimental data Technische Universitat Dresden 2011).
TL;DR: In this article, a new concept for autoclave process control is presented, which is currently developed in the DLR's (German Aerospace Centre) project OnQA (Online quality Assurance in Autoclave processing) in the new Centre for Lightweight-Production-Technology in Stade.
Abstract: A new concept for autoclave process control is being presented, which is currently developed in the DLR’s (German Aerospace Centre) project OnQA (Online quality Assurance in Autoclave processing) in the new Centre for Lightweight-Production-Technology in Stade The concept is based on sensors obtaining quality-relevant process parameters and a real time process simulation able to predict multiple scenarios of different control strategies The so called MASTERBOX is the centre piece of this new process control concept It serves as interface between the sensors including the data acquisition, the process simulation and the real autoclave and takes decisions for the process control based on sensor data, simulation results and databases This intelligent process control will be able to react to process and product deviations leading to an enormous reduction of scrap parts Also as the process is controlled directly in function of the product’s quality-development, the process time can be reduced dramatically Due to the fact that the quality-assurance is performed online during the process, the inline or offline part inspection could be reduced as well
TL;DR: In this article, a wind tunnel experiment for the validation of gust response computations has been performed, which consists of an active two-dimensional rigid front wing acting as a gust generator and forcing an elastic back-swept rear wing.
Abstract: A wind tunnel experiment for the validation of gust response computations has been performed. The model consists of an active two-dimensional rigid front wing acting as a gust generator and forcing an elastic back-swept rear wing. Results of numerical simulations with gust generation are presented. For the setup of the experiment, a simulation environment was established to identify the effect of different installation positions by parameter variation and to point out the efficiency of gust generation in the wind tunnel. The aerodynamic forces are computed by a subsonic Doublet-Lattice method (DLM) which provides considerable computational efficiency and flexibility of the numerical approach. DLM is used as a standard unsteady aerodynamic tool for gust problems and enables comparisons with CFD results. A large number of numerical results in frequency and time domain are used to obtain the forced motion of the elastic back-swept wing located downstream of the gust generator and to simulate the aerodynamic interaction in the wind tunnel. This enables a survey of gust loads on the back-swept wing in comparison to gust and turbulence loads calculated according to airworthiness standards. Furthermore, the numerical results are compared to the experimental results measured in the Transonic Wind tunnel Gottingen of the German-Dutch Wind Tunnels.
TL;DR: A unified description of flight phases and flight events was developed based on the CAST/ICAO Common Taxonomy Team (CICTT) Phase of Flight Definitions, allowing comparative analyses for simulations from different environments (e.g., FTS and RTS).
Abstract: The research activities of the DLR Institute of Flight Guidance include validation and verification of new systems and procedures, such as airport infrastructure, routes, or assistance systems for air traffic controllers and pilots. Research is supported by a number of different simulation environments. Real-time simulators (RTS) like the Apron and Tower Simulator or the Air Traffic Management and Operations Simulator, as well as several fast-time simulation (FTS) tools focus on different parts of air traffic and help to examine various aspects of the air traffic environment (e.g. controller view, pilot view, general traffic situation, etc.). The utilization of all simulation systems in the Institute of Flight Guidance is focused on scientific research, and thus significant effort is placed in the analysis of simulation results. To support this task, the Institute of Flight Guidance has implemented the software system Extensible Workflow Management for Simulations (EWMS) for simulation process and data management. EWMS supports most of the simulation environments used within the institute, and provides generic reporting algorithms independent of the simulation system used. As the different simulation environments use a wide range of output data types and formats, the simulated flight trajectories have to be converted into one common format for subsequent analysis using the generic algorithms built into EWMS. Therefore, a unified description of flight phases and flight events was developed based on the CAST/ICAO Common Taxonomy Team (CICTT) Phase of Flight Definitions (see Stepens and de Kock in Phase of flight definitions and usage notes, CAST/ICAO Common Taxonomy Team, Version 1.0.2, 2010) as well as flight event definitions from the EUROCONTROL CDM Implementation Manual (see Lagios in Airport CDM implementation manual, 2006), and taking into account the flight phase and event models of different simulation environments. A survey of the simulation environments used in the institute resulted in an initial set of flight phases that could be generated by the different simulators. These flight phases were mapped onto the CAST/ICAO definitions, and extensions were made where the CAST/ICAO model offered no corresponding flight phase. Conditions for each phase of flight (e.g., departure boarding, taxi to runway, initial climb, etc.) were documented. Similarly, conditions for the different flight events (e.g., estimated and actual landing time, estimated and actual in-block-time, etc.) and their relation to flight phase boundaries were defined and documented. The resulting unified flight phase and event model was validated through interviews with ATM and simulation experts, air traffic controllers, flight test engineers and pilots. Finally, the model was implemented within the EWMS parsers for the simulation-specific data files. To account for the different capabilities of different simulation environments, the model offers several levels of detail for the individual flight phases, e.g., where one environment may simply show an aircraft that has just taken off as “in flight”, another environment can provide more detailed information about initial climb, climb to cruise and en-route flight. The flight phase model accounts for the different levels of detail to enable meaningful comparisons between the different simulations. The generic flight phase and event model enables the implementation of simulation-independent algorithms for the institute’s heterogeneous ATM simulation environments, allowing comparative analyses for simulations from different environments (e.g., FTS and RTS). In turn, using the same well-validated algorithms for several environments significantly reduces the effort required for the analysis of individual simulation campaigns.
TL;DR: In this article, the authors present an approach for the systematic development of a nonlinear simulation model in MATLAB/Simulink for a high-agility model airplane, with a total of 16 different control inputs, together with the design of an appropriate rate command attitude hold (RCAH) controller.
Abstract: The simulation of the aircraft dynamics and behavior of the open loop as well as the closed loop system is a central part in the development of controllers for real flight tests. This paper presents an approach for the systematic development of a nonlinear simulation model in MATLAB/Simulink for a high-agility model airplane, with a total of 16 different control inputs, together with the design of an appropriate rate command attitude hold (RCAH) controller. The simulation model is capable to represent the behavior of the aircraft, including the dynamics of the motors, the actuators and the sensors, for the nominal case as well as in the case of severe structural damage and failures. The highly sophisticated model of the aircraft is used subsequently for the design of a controller. Dynamic inversion (DI) uses the knowledge of the nonlinear plant dynamics to transform the nonlinear dynamics into a chain of integrators, and after this transformation, a controller can be designed using methods from classical or robust control. A relative degree 1 (RD 1) rate command attitude hold controller, based on dynamic inversion, will be presented together with a semi-analytical approach to select and adjust the appropriate controller gains. The paper is completed by some simulation results encountering severe structural damage and failures. The derived controller can either serve as a stand-alone controller or as a baseline controller for more sophisticated control approaches.
TL;DR: The numerical evaluation and optimization of the feedback controller parameters of the model-based control implemented in the flying helicopter simulator is subject of this paper.
Abstract: The numerical evaluation and optimization of the feedback controller parameters of the model-based control implemented in the flying helicopter simulator is subject of this paper. The German Aerospace Center operates this helicopter as a flying testbed for numerous applications, e.g., pilot assistance and in-flight simulation. Initially, the elements of the model-based control are presented. A genetic algorithm and the Nelder–Mead simplex method used for optimization are described. Two simple objective functions to rate parameter sets in the time domain are presented, and a Simulink® model of the helicopter dynamics and the controller structure are used to find optimized sets. The first function, called “Delta Rating”, consists of a normalized integral of the absolute error between commanded and measured states. The second function incorporates the Delta Rating, but is enhanced by a penalty on overshoots. The controllers found are further evaluated using a frequency domain approach consisting of a weighted sum of the differences in amplitude and phase, also considering the coherence at the corresponding frequency. Apart from the Simulink® model, a ground-based simulator is used to evaluate the standard and the optimized controllers.