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HOPLITE - A conceptual design environment for helicopters incorporating morphing rotor technology
No full textThe SABRE project has been initiated under the EU's Horizon 2020 programme for development of blade morphing technologies for helicopter rotors. The project targets reductions in fuel burn and NOx emissions of upto 5- 10% through the use of morphing rotor blades. A new design tool for rotorcraft, HOPLITE, is being developed to investigate the effects of rotor morphing on engine emissions and fuel burn. HOPLITE uses low-fidelity models for quick and reasonably accurate force and power calculations for major components of the vehicle. The main rotor is modelled using the Blade Element Method, and accounts for changes in blade shape due to rotor morphing and other geometrical modifications. Additionally, a robust fuselage parameterization method, and an equation based engine model have been incorporated in HOPLITE to include the impact of rotor morphing on the design of the helicopter as a whole. The main argument behind the development of HOPLITE is to combine various low-fidelity methods, such that quick design assessments can be performed for various purposes, and, simultaneously, have sufficient fidelity to capture changes in blade shape due to rotor morphing. Actuator disk models can perform a quick analysis, but are unable to match the required level of fidelity. In comparison, traditional CFD simulations or experimental campaigns will be cost and time intensive. Hence, there is a need for a new tool. Due to a multidisciplinary and modular approach used by HOPLITE, it can be used for a wide range of tasks, such as design space exploration and optimization. Furthermore, it can be used in conjuction with high fidelity methods. This paper describes the current work done towards the development of various modules of the tool, theoretical aspects of engine, fuselage and rotor modelling, and initial results obtained during development and testing of individual modules. Theoretical aspects of conceptual design capabilities of the tool have also been briefy described in this paper. Future work will involve development and integration of conceptual design functions in HOPLITE for conventional helicopters, and expansion of these algorithms to non-conventional rotorcraft designs
Flight testing and analysis of helicopter gas turbine engine performance - A multivariable approach
No full textHelicopter performance flight-testing is an expensive activity that requires efficient testing techniques and appropriate data analysis for good performance prediction. Regarding the flight testing techniques used to evaluate the available power of a Turboshaft engine, current methodologies involve a simplistic single-variable polynomials analysis of the flight test data. This simplistic approach often results in unrealistic predictions. This paper proposes a novel method for analyzing flight-test data of a helicopter gas turbine engine. The so-called 'Multivariable Polynomial Optimization under Constraints' (MPOC) method is proven capable of providing an improved estimation of the engine maximum available power. The MPOC method relies on maximization of a multivariable polynomial subjected to both equalities and inequalities constraints. The Karush-Khun-Tucker (KKT) optimization technique is used with the engine operating limitations serving as inequalities constraints. The proposed MPOC method is implemented to a set of flight-test data of a Rolls Royce/Allison MTU250-C20 gas turbine, installed on a MBB BO-105M helicopter. It is shown that the MPOC method can realistically predict the engine output power under a wider range of atmospheric conditions and that the standard deviation of the output power estimation error is reduced from 13hp in the single-variable method to only 4.3hp using the MPOC method (over 300% improvement)
Probabilistic approach and inertial tolerancing for H/C ramp-up in production
Get PDFThe functional Geometrical Tolerance Management is a top-down approach leading to systems specification at each level of the Aircraft assembly, and following the 3 main phases of the Helicopter lifecycle: Design phase, Development phase and Serial life. During Serial life, we shall provide optimized methods and tools matching with quality and production objectives (OTD, OQM, ramp-up) and viewing results format. Since the tolerances are represented by a network, we have defined a format for injecting the results at a given level as input data to the next level. Due to the nature and interconnections of this network, the volume of data to be processed can be significant. So we have implemented an appropriate numerical technique to deal with a continuous influx of measurement data. The objective is to purpose a comprehensible representation of the re-evaluated risks at each stage of the process, i.e.: Initial risks related to the current helicopter definition, Re-evaluated risks related to an aircraft serial number completed with each new measurement of characteristics for this aircraft, Re-evaluated risks related to the observed variability of the product / process at assembly level. Our new industrial model leads to change our approach from a curative model to another model applied to QN process with root cause identification and manufacturing process monitoring allowing deploying preventive and corrective action plan. Behind that our objective is to avoid recurring QN and to switch to a Risk management model by several lever deployments. When a functional geometrical target is too much tight, its cascade of tolerances is at the feasibility limit of production. In this case, Geometrical Tolerancing method loses its benefits. The aim of this paper focus on our process deployment based on the last A/C development in Airbus Heli-copters, presenting the first results, the advantages and drawback for Industrialization & serial phase based on the antitorque brackets integration. The antitorque bracket is the master element of the junction between Main Gear Box and fuselage. The antitorque bracket has tight tolerances due to the stress way and its functional geometrical tolerance cascade. Its manufacture is at the limit of production means. The production of antitorque bracket generates many QN. Each part is going to generate recurring cost and added time of production. To solve this problem, we have chosen to understand what phenomena are in cause and manage non-quality risk with the ap-plication of inertial Tolerancing approach. In function of the level of nonconformity calculated, an action plan is defined
Dynamic stall model optimization with CFD and assessment with comprehensive approach for improved blade design
Get PDFAn enhancement for comprehensive modelling of rotor in forward flight is proposed to enable inclusion of dynamic stall and study characteristic effects on rotor loads and performance in design phase. The characterization of dynamic stall behavior of the selected airfoil on the design is performed with validated CFD analyses. Parameter optimization is performed for the dynamic stall and unsteady aerodynamics model in CAMRAD II, comprehensive analysis tool, to attain maximum similarity with CFD based predictions. Optimized dynamic stall model is then utilized to study rotor loads at dynamic stall dominated flight condition. Using the improved analysis framework with optimized dynamic stall model, the effect of anhedral tip shape on blade loads and stall onset characteristics is studied. It is observed that, anhedral modification to a blade tip combined with dynamic stall phenomena, worsens rotor torsional loads. On the other hand, application of an up-wash twist at tip anhedral region, improves the degraded load characteristics. The aim of this study is practice estimation of dynamics stall characteristics of an airfoil of interest with CFD, optimize dynamic stall model in accordance and investigate effect on rotor loads in the presence of anhedral
Aerodynamic analysis of helicopter in interaction with wind turbine's wake
Get PDFOver the last 20 years wind energy has undergone a significant growth. The installation of new wind farms is increasing globally with an average rate (over the last five years) of 10 percent every year. Current commercial wind turbines (WTs) have diameters that range between 90 to 150 meters and their total height exceeds 200 meters. Manufacturer's ambition points towards even bigger turbines with rotor diameters that within the next decade will reach sizes of about 250m. The above development will consequently lead to larger areas occupied by future wind farms. On the other hand, helicopters often execute low altitude flights following trajectories that cross wind farm areas. Furthermore, helicopters are commonly used as transport mean for maintenance staff transportation missions to distant offshore wind farms (as for example in the North Sea where many wind farms have been deployed over the last years). It is therefore foreseen that in the coming years the possibility for a helicopter to fly in interaction with a wind turbine wake will increase. Lack of previous experience or evidence renders safety checks necessary. In this respect of particular significance is to know whether safe passage through or in strong interaction with the wake of an operating wind turbine is possible or in such occasion the turbine should be shutdown. In the present paper, the aerodynamic interaction of a helicopter main rotor with a wind turbine wake is analyzed on the basis of free wake vortex analysis. Helicopter forward flight crossings of wind turbine wakes are simulated using different wake flow models
Investigation on hovering rotors over inclined ground planes – a computational and experimental study
Get PDFThe influence of time-varying ground effect (e.g., induced by ship deck motion) or even of static, inclined ground planes (e.g., hillsides) on the flow field and on the rotor inflow in hover is not yet understood. Therefore, experiments and CFD simulations were performed to study the flow field below a two-bladed 0.8 m-diameter rotor in hover over a parallel and a 15 degree inclined ground plane at a height of one rotor radius above the ground plane pivot point. Particle image velocimetry measurements were used to measure the rotor wake, and CFD simulations were correlated to the experimental results. To investigate the flow field, instantaneous, phase-averaged, and time-averaged data were used. The flow field was found to be sensitive to the ground plane inclination angle. It was found that the inclined ground plane reduced the unsteadiness in the flow field. The phase-averaged experimental results were predicted well by the numerical simulation. The computations captured the flow phenomenology well, but underestimated the influence of the inclined ground plane on the rotor inflow
Low-order aeromechanics of tilt-rotor helicopters
Get PDFThe conversion corridor represents the safe region of flight for tilt-rotor aircraft during the transition between helicopter and aeroplane mode. A low-order rotary-wing model has been established and validated throughout the conversion corridor, showing good agreement with experimental data. Furthermore, the equations of motion for longitudinal flight have been derived and solved to determine the conversion corridor boundaries with the results correlating well with published data. The largest discrepancy was observed at the lower boundary which indicated a downwash model of the rotor wake over the wing was required. Additionally, from a trimmed flight perspective, it was found the tilt-rotor aircraft had transitioned from helicopter to aeroplane mode by the approximate shaft angle ? = 60
Design space analysis of an autonomous aerial crane VTOL concept with a detachable airship envelope
Get PDFThis paper will argue the concept of a logistics autonomous aerial crane type VTOL aircraft capable of being able to optionally attach an airship envelope so that it will contribute to the reduction of the total weight of the aircraft and requires less energy consumption for flight. In order to overcome the disadvantages or airships those are; first the difficulty of operation in gusty condition, and second its massive size of envelope when to rely fully the weight to be afloat solely by the floating gas, this concept is to attach a medium size flotation envelope to save the energy required for the craft to be airborne which will be only used when the weather is mild, and make the powertrain flyable either with or without the airship component. In order to pursuit the reality of this idea, this study will focus on three major issues: the design on the lifting and propulsion system, method to keep the shape of the envelope in health regardless of traveling in speed or under side winds while on ground, and discussion on the weather condition to become the boundary of the usability of the auxiliary airship
Investigation of a helicopter model rotor wake interacting with a cylindrical sling load
Get PDFAn experimental and numerical investigation on a four-blade isolated main rotor in hover condition has been carried out in order to investigate the effect of the rotor downwash on a tethered load. A sling load was located at different positions below the rotor disk in order to evaluate the mutual interference between the rotor wake and the immersed body. A radio controlled helicopter model, largely customized and modified for the scope of the experiment, was used as rotor rig. The sling load was reproduced by a low aspect ratio (l/d=2) cylinder being representative of typical loads as oil drums, water containers or engine canisters. Furthermore, the cylinder flow wake is a well known case largely investigated in literature and a good test case for computational fluid dynamics simulation. A six components balance measured the rotor loads calculating the figure of merit. The cylinder pressure distribution together with the flow field characteristics were also measured. Numerical simulation were carried out by using an unsteady, inviscid and incompressible free-wake vortex lattice boundary element methodology solver for multi-body configurations. The paper reports the main rotor wake characteristics up to 3 radii distance from the rotor plane with and without sling load. The effect of the downwash on the cylinder varying the distance and the changes induced by the presence of the cylinder are discussed
Automation of structural cross sectional rotor blade modelling for aeromechanical rotor blade optimization
No full textIt is often difficult to predict the behavior of helicopters, given their complex aeromechanical operating environments. Given these uncertainties, it is often the case that flight tests need to be conducted prior to a design being �frozen�. To improve the whole design and validation procedure, it is essential that the design freeze (and iterations within) occurs before the expensive and timeconsuming process of building and flying. However, in order to do so, the virtual modelling needs to be more accurate and thus with less uncertainty. The DLR project Victoria (Virtual Aircraft Technology Integration Plattform) with its work package �Virtual Helicopter� aims to lay the foundation for a next generation comprehensive rotor code to overcome these challenges. Improvement on structural modelling within this code has high potential enhancing the overall development process, regarding time and accuracy. The improvement of rotor blade design is often driven by aerodynamic shape optimization, which means changes in airfoil shapes and sizes as well as their distribution and alignment, to fit different demands. Such changes will always have a major influence on the structural properties, because the inner structure geometry depends on the outer shape. Thus to still maintain an accurate aeromechanical model for the rotor simulation in the optimization process structural properties have to be adjusted. The most common approach is to calculate cross section data for various cross sections over the rotor blade span and feed the information into a beam-based rotor blade model. This is typically done by using approximations and scaling laws e.g., or by reducing the geometry complexity e.g. A high fidelity structural FEM-model will provide higher quality structural data. In general such FEM models are complex and require significant time to setup and process, starting with generating the blades inner geometry with CAD software, then meshing and performing the actual FEM analysis. This is very time consuming and hardly feasibly for an optimization with multiple loops. This paper presents the development of a tool for the automation of this process. The inner geometry is generated in CATIA V. and can handle arbitrary cross section shapes (within reason). Additional parameters and boundary conditions are needed to obtain an inner geometry which is reasonable in terms of its structural integrity. These parameters include the center of gravity, basic spar shaping parameters and the skin thickness. This very accurate geometry model is then passed on to the FEM software (ANSYS). Here a mesh representing the geometry is created and then an analysis with the ANSYS tool SaMaRA is performed. SaMaRA calculates the structural properties of the cross section. The exchange of all data between the different disciplines (e.g. structural and aerodynamic) is performed via CPACS (Common Parametric Aircraft Configuration Scheme) to ensure data integrity and enable modularity of this structural code. The focus in developing this code was on the quick generation of highly accurate structural data for an aerodynamically driven optimization. The meshing automation in Ansys is not yet finished and in ongoing development. Follow up steps will be the extension of modelling options in terms of the inner structural setup and meshing quality