-> AERONAUTICS AND SPACE FLIGHT
(Total: 98 journals)
- Preparation and execution of the NICETRIP low- and high-speed wind tunnel
- Abstract: The present paper reports the preparation and execution of high- and low-speed wind tunnel tests of the tilt-rotor project NICETRIP. Within the NICETRIP project (Novel Innovative Competitive Effective Tilt Rotor Integrated Project), co-funded by the EU, wind tunnel tests were conducted for a heavily instrumented 1:5 scale model of a tilt-rotor aircraft (3.5 m wingspan, 1.48 m diameter rotors) based on the ERICA concept (Enhanced Rotorcraft Innovative Concept Achievement). The current paper provides an overview of the contributions of DLR to the low- and high-speed wind tunnel tests performed at DNW-LLF (German-Dutch Wind Tunnels Large Low-speed Facility) in 2013 and at ONERA-S1MA in 2014. It gives detailed information about the preparation activities, the model hardware and its control, the necessary adaptations for the model preparation at DLR, and results of the ground vibration tests. Additionally, the data acquisition and monitoring during the wind tunnel experiments, the trimming of the model in the wind tunnel and the conducted tests are described, including encountered problems and how they were solved. In the last section, some representative test results are shown.
- Possibilities and difficulties for rotorcraft using variable transmission
- Abstract: This publication shows advantages and possible applications for variable transmission drivetrains within rotorcraft. The power requirement of a generic helicopter with constant and variable rotor speed was calculated. Various drive train technologies that support a variable transmission were described. The prospects of this technology, its influence on the dynamic behaviour of a rotor and further areas that need to be investigated extensively are presented. This technology is applicable to some rotorcraft architecture. Requests from the rotorcraft industry underline the necessity for future rotorcraft using variable rotational speeds. However, the A160 or the EC145 and Mi-8 already show the potential of this technique. Reduction of required power of the rotor should be possible and also an extension of the flight envelope towards higher flight speeds, higher altitudes, better manoeuvrability, etc. By using a variable transmission gearbox, turbine and auxiliary units can still be driven at their design point, independent of the current rotor speed. Excessive loads may occur when discrete speed transmission are used. Frictional or fluid transmissions with continuous variable ratio may fail due to overheating. Other continuous concepts are favoured. The design of a variable speed rotor focuses specifically on its dynamic behaviours and on structural and geometrical optimisation to avoid operation at rotational speed resonance frequencies. Morphing structures may support this. Some rotorcraft architectures can benefit from a variable speed rotor technology. It probably will increase efficiency, decrease noise levels, fuel consumption and CO2 production, and the flight envelope may be extended.
- SPYDER: a software package for system diagnosis engineering
- Abstract: Modern aircraft systems comprise hardware and software with high complexity. In order to assure an operation at high availability and low maintenance cost, diagnosis functions become essential. These functions detect faults and failures, identify sources of faults and failures and assess the current state of health. A reduction in operating cost, better planning of maintenance actions, and new business cases for operator and equipment manufactures are gained as a result. A systematic approach for the design and test of diagnosis functions supported by an integrated model-based tool chain is introduced in this paper. That is the SPYDER concept, a Software Package for sYstem Diagnosis EngineeRing. Embedded into the general system development process, a stepwise design and test of diagnosis functions is performed. It focuses on failures and starts with failure–effect analysis, continues with sensor placement and proceeds further to configuration and testing. The method has been applied to multifunctional fuel cell systems that are used as illustrative examples.
- Validation of a nonlinear observer implementation for empennage loads
- Abstract: The monitoring of aircraft structural loads shows promising potential for improvement in terms of aircraft maintenance. Monitored loads can be used for component specific overload detection and for targeted inspections on ground. This results in a reduction of the necessary on-ground time after in-flight events and consequently in a reduction of maintenance costs. Focusing model-based approaches for loads monitoring, a nonlinear Luenberger observer is adapted for the flight test aircraft UW-9 Sprint. The implementation of the observer structure containing a state and a disturbance observer, as well as the determination of the included feedback gains is explained. Within this article, the Loads Observer method is validated against flight test data, exemplarily for empennage loads. For this purpose, the empennage of the test aircraft is equipped with strain gages. The test equipment and its calibration are described. Regarding the assessment of combined maneuver and gust loads, the flight test execution including the performance of maneuvers in gusty conditions is demonstrated. Finally, the component loads estimation is compared to the loads measurement.
- Economic optimization of cargo airships
- Abstract: Historical strengths and weaknesses of airships were investigated to determine a mission suited for airships. The transatlantic cargo mission was selected to take advantage of the high payload and endurance qualities of airships while minimizing the frequency of ground handling. An optimization was performed to minimize the cost per ton mile of the airship with maximum velocity as the variable. Other design parameters were held constant and based on historical airship studies. The cost per ton mile and von Karman efficiency were used to compare the optimized airship designs with other modes of cargo transportation. An airship with a volume of 200,000 m3, which was the volume of the Hindenburg, would achieve a cost per ton mile of $1.03. This value equates to about 85 % the cost of an airplane, and five times the cost of a truck. A graph of von Karman efficiency showed that the airships proposed by this study could occupy a niche market between airplanes and trucks in terms of both efficiency and velocity.
- Numerical assessment of the vibration control effects of porous liners on
an over-the-wing propeller configuration
- Abstract: An over-the-wing position of propellers comes with noise shielding and significantly reduced sound emission to the ground. A drawback of this configuration may be the additional impact due to the passing propeller blades on the airfoil’s surface inducing structure-borne sound in the wing. This structural sound propagates within the wing and the fuselage and can radiate further into the cabin as airborne sound. In order not to trade the advantage of reduced noise transmission to the ground with higher sound pressure levels within the cabin, a remedy is proposed, which consists in placing a poroelastic liner on the wing’s surface below the rotor where the blade tips move closely to the airfoil’s skin. In this work, a numerical approach to assess the effects of porous liners for an over-the-wing propeller configuration is presented. A simplified generic channelwing structure is exposed to pressure fluctuations on its surface which are caused by an over-the-wing propeller. Porous liners are applied to the wing’s surface where the blade tips pass in close proximity. Structural vibrations are determined using the finite element method in frequency domain. Surface data is obtained from CFD computations. The porous material is represented by Biot’s theory.
- Active flow control system integration into a CFRP flap
- Abstract: Investigations in the past show the considerable potential of active flow control (AFC) to enhance the aircraft aerodynamic performance. This publication describes the work carried out regarding the integration of an AFC system into a CFRP flap for Next Generation Aircraft considering operational aspects. Based on a two-stage fluidic AFC actuator, a system integration concept is developed. Robustness, simplicity and maintainability are the main drivers for the integration work. Using genetic and evolutionary multi-objective optimization the most promising flap concept regarding lightweight design and integration is developed at TU Dresden ILR. This concept is numerically sized and designed in detail. The concept feasibility is shown by a 2-m span full-scale demonstrator at Airbus Group Innovations. This demonstrator is successfully tested regarding system operational capability as well as for static and fatigue performance. To investigate the structural influence of AFC blowout slits within the upper flap surface, an extensive static and dynamic coupon test program is conducted at TU Dresden ILK and TU Braunschweig IFL. In parallel, analytic and numeric methods are used to verify stress concentration within the slotted area by TU Dresden ILR.
- Prediction and uncertainty propagation of correlated time-varying
quantities using surrogate models
- Abstract: The identification of correlated quantities is of particular interest in several fields of engineering and physics, for example in the development of reliable structural designs. When ‘time-varying’ quantities are analysed, pairs of correlated interesting quantities (IQs), e.g. bending moments, torques, etc., can be displayed by plotting them against each other, and the critical conditions determined by the extreme values of the envelope (convex hull). In this paper, a reduced order singular value-based modelling technique is developed that enables a fast computation of the correlated loads envelope for systems where the effect of variation of design parameters needs to be considered. The approach is extended to efficiently quantify the effects of uncertainty in the system parameters. The effectiveness of the method is demonstrated by consideration of the gust loads occurring from the aeroelastic numerical model of a civil jet airliner.
- Propagation of localized, unsteady heat loads in aircraft cabin air flows
- Abstract: We studied experimentally the propagation of heat, released from a local source, in aircraft cabin air flow using two different ventilation systems. Besides the state-of-the-art mixing ventilation system, a ceiling-based cabin displacement ventilation system was employed. As test environment we used the Do 728 test facility of the German Aerospace Center in Göttingen. To measure the response of the cabin temperatures to the released heat, we evaluated the cross-correlation function between the local temperatures and the normalized surface temperature of the heat source. The latter was heated periodically at three different nominal heating powers, ranging from 100 W through 400 W. By analyzing the data, we could observe the gradual change of the temperature from a passive to an active scalar. While the two ventilation systems reveal a similar behavior at the lower source powers, the distinguished air-guiding principles of the momentum-driven mixing ventilation and the buoyancy-driven ceiling-based cabin displacement ventilation imply different propagation paths at higher power settings of the heat source. For the first time, the spatial spreading of locally released heat in mixing ventilation and in ceiling-based displacement ventilation was determined in an aircraft cabin.
- Structural modeling and validation of an active twist model rotor blade
- Abstract: DLR has been researching on active twist rotor blade control for at least 15 years now. This research work included the design and manufacturing of model rotor blades within the blade skin integrated actuators. As a main subject, numerical benefit studies with respect to rotor noise, vibration, and performance were carried out with DLR’s rotor simulation code S4. Since this simulation code is based on a modal synthesis, it uses the natural blade frequencies and mode shapes to model the blade dynamics. Both, natural blade frequencies and mode shapes, are computed in advance employing a finite element beam model of the blade. Each beam element possesses certain structural properties that are derived from an ANSYS model for certain cross sections of the blade. Since model rotor blades are built for wind tunnel testing, they are highly instrumented with sensors and therefore vary in their structural properties along span. Modifications in the structural properties due to the instrumentation are not included in the ANSYS model. However, to account for these variations, two experimental methods have been developed. They allow the determination of the real values for the most important structural blade properties such that the structural blade model is improved. The paper describes the experimental methods, as well as the development of an advanced structural blade model for rotor simulation purposes. It shows a validation of the structural blade model based on the measured non-rotating and rotating frequencies.
- System analysis of aircraft with natural laminar flow and forward swept
- Abstract: The objective of this paper is an enhanced analysis and assessment of a short-to-medium range aircraft configuration with natural laminar flow (NLF) and forward swept wings (FSW) designed by DLR. It is intended to show how the proposed aircraft concept could contribute to a more economic and ecologic operation. By implementing a multidisciplinary simulation and assessment framework, the net-benefit on air transportation system level is evaluated from airline perspective under consideration of realistic airline network conditions. Therefore operational aspects (e.g. stage length) and environmental factors (e.g. insect contamination, cloud encounter) which affect the aircraft effectiveness are included into the assessment. Apart from modeling the technology intended effect of fuel saving on airline economics, the study also aims to determine unintentional repercussions (e.g. change in maintenance effort, emissions, noise) which arise due to the design and the operation of the FSW–NLF concept. The overall goal of the paper is to provide aircraft operators with a better understanding of the behavior of NLF aircraft under realistic operational boundary conditions as well as to demonstrate resulting trade-offs between economical and ecological effectiveness.
- Automated manufacturing of large, three-dimensional CFRP parts from dry
- Abstract: At present, the manufacturing of large parts from carbon fiber reinforced plastic in aerospace is mostly done by manual labor. One of the objectives of The Center of Lightweight Production Technology in Augsburg, Germany, is to transfer manual production methods into automated processes. This work addresses the process chain starting with dry textiles, via production integrated quality assurance, to a cured part. A gripper system is required to handle the pliable and delicate dry carbon fiber textiles in the preforming process. The project aims to develop such a system and establish an automated application. A final demonstration of the system’s capabilities allows evaluation of the current level of maturity and usability. Sensor technology is to be integrated into the production process for quality assurance purposes. The position and draping of cut-pieces are determined by laser light section technique and fiber angle measurement. This allows detection of process parameters and potential deviations in the production chain. Corrections can be applied early, which offers a clear advantage over the current inspection of the finished component. Yet another focus is the enhancement of the setup for resin infusion. The application of a pre-tailored VAP membrane using a mechanized lay-up system allows for fast, robust and repeatable vacuum bagging with a significant reduction of manual labor. The presentation will give insight to the development of the gripper system, quality assurance measures, and semi-automated vacuum bagging including their current level of maturity.
- On the history and prospects of three-dimensional human–computer
interfaces for the provision of air traffic control services
- Abstract: This paper is an essay on the history and prospects of three-dimensional (3D) human–computer interfaces for the provision of air traffic control services. Over the past 25 years, many empirical studies have addressed this topic. However, the results have been deemed incoherent and self-contradictory and no common conclusion has been reached. To escape from the deadlock of the experimental approach, this study takes a step back into the conceptual development of 3D interfaces, addressing the fundamental benefits and drawbacks of 3D rendering. Under this light, many results in the literature start to make sense and some conclusions can be drawn. Also, with an emphasis on the future of air traffic control, this research identifies a set of tasks wherein the intrinsic weaknesses of 3D rendering can be minimized and its advantages can be exploited. These are the ones that do not require accurate estimates of distances or angles. For future developments in the field of 3D interfaces for air traffic control operators, we suggest focusing on those tasks only.
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- DLR project Digital-X: towards virtual aircraft design and flight testing
based on high-fidelity methods
- Abstract: Numerical simulation is already an important
cornerstone for aircraft design, although the application of highly accurate methods is mainly limited to the design point. To meet future technical, economic and social challenges in aviation, it is essential to simulate a real aircraft at an early stage, including all multidisciplinary interactions covering the entire flight envelope, and to have the ability to provide data with guaranteed accuracy required for development and certification. However, despite the considerable progress made there are still significant obstacles to be overcome in the development of numerical methods, physical modeling, and the integration of different aircraft disciplines for multidisciplinary analysis and optimization of realistic aircraft configurations. At DLR, these challenges are being addressed in the framework of the multidisciplinary project Digital-X (4/2012–12/2015). This paper provides an overview of the project objectives and presents first results on enhanced disciplinary methods in aerodynamics and structural analysis, the development of efficient reduced order methods for load analysis, the development of a multidisciplinary optimization process based on a multi-level/variable-fidelity approach, as well as the development and application of multidisciplinary methods for the analysis of maneuver loads.
- Conceptual design studies of vertical takeoff and landing remotely piloted
aircraft systems for hybrid missions
- Abstract: Spurred by the rapid progress in sensor performance increase associated with contemporary miniaturization, many companies, organizations, and governments are interested in using new opportunities in civil remotely piloted aircraft system applications. Coupled with an enhancement in propulsion system performance as well as an optimized and well-matched aerodynamic design, flight envelope limits can be enlarged and new mission profiles arise. Due to these ambitions, resulting hybrid missions become more complex and individual with partially contradicting demands, such as vertical takeoff and landing capabilities, fast climb and cruise combined with a long-endurance loiter capability, and a hover capability up to altitudes of 5000 m. In order to fulfill the diverse mission requirements, several configuration concepts are investigated. The focus is laid on different propulsion system concepts where various technologies and energy storage types are considered, as well as their effects on the aerodynamic shape and the controllability of the configuration. The investigated concepts comprise tilt propeller, tilt ducted propeller, and tilt wing configurations with fixed and variable pitch propeller. Based on these studies, a feasible concept in the weight category of MTOW ≤150 kg was identified which accomplishes both the aerodynamic and performance demands and the controllability in all flight segments.
- Central Reference Aircraft data System (CeRAS) for research community
- Abstract: This paper gives an overview and presents the results of the project CeRAS, which stands for “Central Reference Aircraft data System”. CeRAS is intended to serve as an open platform hosting reference aircraft data and methods that can be used by a research community in aeronautic research projects. The technical topics of the addressed user group lie in the field of overall aircraft design as well as technology integration and evaluation on aircraft level. To enable the communication within the research community the CeRAS homepage has been created (http://ceras.ilr.rwth-aachen.de/) and filled with a first short-range reference aircraft dataset. The research community can contribute to and communicate via the CeRAS homepage that is intended to serve as living “open source” platform. The first reference aircraft is called CSR-01 and has been designed with the ILR aircraft design platform MICADO. The aircraft design characteristics are presented and discussed within this paper. Furthermore, common standards for monetary assessment methodologies are presented that have already been established and agreed within the CeRAS research community.
- A knowledge-based integrated aircraft conceptual design framework
- Abstract: The conceptual design is the early stage of aircraft design process where results are needed fast, both analytically and visually so that the design can be analyzed and eventually improved in the initial phases. Although there is no necessity for a CAD model from the very beginning of the design process, it can be an added advantage to have the model to get the impression and appearance. Furthermore, this means that a seamless transition into preliminary design is achieved since the CAD model can guardedly be made more detailed. For this purpose, knowledge-based aircraft conceptual design applications Tango (Matlab) and RAPID (CATIA) are being developed at Linköping University. Based on a parametric data definition in XML, this approach allows for a full 3D CAD integration. The one-database approach, also explored by many research organizations, enables the flexible and efficient integration of the different multidisciplinary processes during the whole conceptual design phase. This paper describes the knowledge-based design automated methodology of RAPID, data processing between RAPID and Tango and its application in the courses “Aircraft conceptual design” and “Aircraft project course” at Linköping University. A multifaceted user interface is developed to assist the whole design process.
- nxControl instead of pitch-and-power
- Abstract: A command
system for manual control of the longitudinal load factor in flight path direction of an aircraft is designed that completes existing flight control command systems (e.g. with sidesticks that command normal load factor). The system is called nxControl. It aims to assist pilots during manual flight by reducing the workload for monitoring flight parameters as well as for controlling thrust and airbrakes. Important for the nxControl concept is the direct flight mechanical relation between longitudinal load factor and changes of the total aircraft energy. This paper presents the system concept and a prototype realization. The nxControl system consists of the control law that combines the actuation commands for engines and airbrakes, a new input device for the longitudinal load factor command and augmented display elements informing pilots about aircraft energy states to assure situation awareness. In order to investigate the feasibility of the concept as well as to evaluate consequences on human performance, a flight simulator study with airline pilots was conducted.
The nxControl prototype was used by the pilots as expected. Changes in instrument scanning behaviour and thrust lever usage confirmed this. After just a short familiarization and practice, the pilots were able to perform standard flight tasks with nxControl without exceeding given tolerance limits. So, the results provide first evidence for the feasibility of the concept.
- About the interaction between composition and performance of alternative
- Abstract: Since the last decade, the aviation sector is looking for alternatives to kerosene derived from crude oil triggered also by commitments and policy packages, such as the ‘Flightpath 2050’ initiative and the comprehensive alternative fuels strategy, both released by the European Commission. An aircraft need with regard to a fuel is very strict, with severe constraints to ensure a safe and reliable operation for the whole flight envelope. When synthesizing a jet fuel from scratch, two important aspects need to be addressed: First, the safety aspect—the new fuel candidate must be certified, qualifying through several well-defined cost and time expensive tests, according to the approval protocol; secondly, the environmental aspect. Alternative aviation fuels alike Jet A-1 are composed of hydrocarbons; however, the amount and type of hydrocarbons (chemical family) differ considerably. The question is how the composition of the fuel will affect its suitability and performance: (i) thermo-physical and thermo-chemical properties of the new components to exclude any shortcomings with respect to performance and safety issues, and (ii) the new fuel combustion characteristics, i.e., ignition, flame speed, and emission pattern (pollutants), in particular. These issues are addressed in the present study. Thus, the road will be paved for developing a generalize science-based tool to investigate in an efficient way if a new fuel candidate may meet the fuel specifications.