ERF European Rotorcraft Forum
Not a member yet
4279 research outputs found
Sort by
Boundary integral formulations for noise scattered by helicopter fuselage
No full textThe paper deals with a theoretical-numerical comparison among integral formulations for the prediction of noise scattered by moving bodies. Three acoustic scattering integral formulations for the solution of the velocity potential wave equation are considered: a recently proposed linearized boundary-field integral formulation, and two widely applied boundary integral approaches based on Taylor and Taylor-Lorentz transformations. Aim of the work is to highlight their theoretical differences and limits of applicability, while examining their capability of capturing the influence of body motion and corresponding nonuniform mean flow around it on the scattered noise field. Numerical results concern a rigid translating sphere impinged by sound waves emitted by a co-moving pulsating point-source and a helicopter fuselage impinged by noise radiated by main- and tail-rotor
Research on vision system for degraded visual environment
Get PDFJAXA (Japan Aerospace Exploration Agency) has been conducting a research project named SAVERH (Situation Awareness and Visual Enhancer for Rescue Helicopter) since 2008. SAVERH aims at inventing a method of presenting suitable information to pilots to support search and rescue missions in Degraded Visual Environment. An integrated system comprising an Helmet-Mounted Display (HMD) and some vison sensors were installed in JAXA research helicopters and series of flight tests conducted to evaluate the benefit of presenting synthetic and sensor images on the HMD. An effectiveness of images presented on an HMD for road following and landing was evaluated through the series of flight experiments. As results, both synthetic and sensor image were effective for recognizing targets, navigation features such as road and terrain
Estimation of handling quality parameters of a rotorcraft using open-loop linearized and nonlinear flight dynamic models
Get PDFFlight dynamic analysis and estimation of handling quality parameters have become important aspects in the design and development of helicopters. This paper presents a detailed analysis of the procedure for estimating the handling quality parameters such as quickness parameter, bandwidth and phase delay. The flight dynamic model used in this study considers rigid flap model for blade structural dynamics, three states dynamic inflow for inflow calculation and modified ONERA dynamic stall model for sectional aerodynamic loads calculation. The applicability of open loop linearized (uncoupled, and coupled) and nonlinear flight dynamic models in estimating the handling quality parameters is studied. For linearized models, only pulse input is used, whereas in the nonlinear model, two different types of input, namely pulse and step inputs, are used to estimate the attitude quickness parameters. The bandwidth and phase delay are calculated from the frequency responses of helicopter attitude in pitch and roll axes, which are obtained from the time response of nonlinear flight dynamic model for the harmonic excitation of cyclic pitch input. The results show that the attitude quickness parameter depends on the duration of input pulse and the nonlinear open system provides attitude quickness parameter which is different from that of the linearised system. In addition, it is noted that linearized flight dynamic models (8x8) cannot be used for bandwidthphase delay calculations, due to their lower order nature
Experimental studies of non-stationary aerodynamic characteristics of a helicopter airfoil oscillating in the pitch
No full textThe article presents the results of experimental studies of non-stationary integral and distributed aerodynamic characteristics one of the helicopter airfoil in stationary and non-stationary modes. The stationary mode is a fixed airfoil in a uniform steady airflow. The non-stationary mode is an airfoil oscillating in the pitch in a uniform steady airflow. The investigations were carried out in the vertical, closed-circuit TsAGI wind tunnel with an open test section. The tests were carried out at Reynolds numbers Re = 270,000 and 540,000; at reduced frequencies from 0.06 to 0.26. A particular feature of the research was the use of two methods for determining aerodynamic characteristics, namely: a direct method of measuring forces using balance and calculating forces by integrating the pressure distribution along the chord. The obtained results are compared with each other, their satisfactory agreement in the stationary mode is shown. Another feature of the research was the analysis of pulsations of forces and pressures on the airfoil surface. In particular, using the wavelet analysis, a phenomenon called "frequency explosion", specific of dynamic stall of the flow, is demonstrated
Cabin safety sensitivity to the mechanical parameters of the main crashworthy stages
No full textCrashworthy helicopters have energy absorbing concepts introduced into seats, subfloor and landing gears. These stages are always passive systems, usually triggered by a load level, and develop pre-set responses independently from the crash speed. Moreover, the different stages are usually studied as single components, without considering the mutual effects and any possible integration. This study is based on a lumped mass numerical model of a representative, but very simplified, rotorcraft section, including the three crashworthy stages of landing gear, subfloor structure and seat with anthropomorphic dummy. A series of analyses show the advantages, in terms of accident survivability, associated to a seat and landing gear with mechanical characteristics optimised according to varying impact velocities
Shipboard landing period based on dynamic rollover risk prediction
No full textWhile SHOLs (Ship/Helicopter Operating Limitations) provide acceptable wind velocities and orientation and ship motion limits, limited attention has been given to the real-time determination of windows in which ship motions are likely to be safe for helicopter landings and deck handling operations. Existing operational systems developed to indicate periods of quiescence usually combine a specific set of ship motions into a scalar quantity, e.g. an energy index. The contribution of the present paper is to associate forbidden landing windows with the conditions of a control departure when the helicopter landing gear touches the deck of the ship. Among the well-known losses of control, dynamic rollover is particularly critical and hard to recover. A method to determine shipboard landing periods based on dynamic rollover risk prediction is proposed. The objective is to reduce the helicopter hover time and to provide the pilot with a safe go-ahead signal to start the hovering descent to the deck. A simulation tool has been developed, capable of modelling the complex interactions in the dynamic interface between ship and helicopter. Simulation results as well as sensitivity analysis with respect to uncertainties are presented
An experimental investigation of hub drag characteristics on coaxial rotor aircraft
Get PDFA full-scale wind tunnel tests have been conducted to research the hub drag characteristics of combine coaxial rotor aircraft and better understand the aerodynamic interaction between hub and fairings. A hub and fairing drag test was conducted to obtain quantitative drag measurements on multiple fairing geometries, and to get insight into the effect of rotation and the presence of blade stub. There were four interchangeable mid-shaft fairings designed, i.e., optimized fairings F1, F2 based on airfoil and optimized fairing F3, plus a bare shaft(S) for reference. The effect on the hub drag of varying angle of attack, Mach number were investigated. Principal results were that the Mach number had a greater influence on the drag of hub, and the best fairing configuration reduced the drag of coaxial rotor hub by 37%. The test also provided validation data for computational fluid dynamics (CFD), and aerodynamic characteristics for design
Measurement of transient blade passage loads of a coaxial counter-rotating rotor in hover
Get PDFThis study describes the measurement of transient hub loads and blade deformations due to blade passage in a 1x1-bladed, 2m-diameter rigid coaxial counter-rotating rotor system in hover. The experimental results were analyzed and evaluated in combination with a comprehensive analysis model using CAMRAD II. Lower rotor blade deformations were measured using a time-resolved digital image correlation technique. Rotating modal parameters including natural frequencies and mode shapes were identified from measured time histories of rotor blade deformations using the Complexity Pursuit algorithm. Experimentally identified modal characteristics correlated well with numerical results for the first three modes. The numerical model also predicted the vibratory hub and pitch link loads as well as out-of-plane deformations satisfactorily well and within the measurement uncertainties. The2/rev blade tip displacement due to blade passage was found to be 6% of the mean tip displacement, and the transient blade motion of the lower rotor blade was found to be larger than that of the upperrotor blade. Additional numerical studies on the aerodynamic angles of attack, the inflow velocities from rotor�rotor interaction, and sectional lift distributions over the upper and lower coaxial rotor disks provided further insight into the sources of transient loads due to blade passage. For example, it was found that the angle of attack on the lower rotor induced by the upper rotor had a maximum at 15? azimuth before the blade passage
Safety, quality and efficiency in flight data gathering
No full textSafety, quality and efficiency are basic requirements on flight data gathering campaigns. The challenges of meeting all three of them in flight test campaigns planned for the purpose of simulator development are the main subject of the present paper. Specific processes for preparation and conduction of flight test campaigns are discussed according to the challenges of campaigns for simulation compared to those for aircraft certification. A newly developed flight test instrumentation that can be easily adapted for integration in a wide range of helicopter types and fixed-wing aircraft is described. The use of the flight test instrumentation and defined processes lead to convincing results with high safety standards. Thus, the flight test team optimises the process flow allowing the best possible result in terms of quality and completeness of the collected data, with acceptable investment costs for chartering the helicopters. During the data acquisition campaign, the Netherlands Aerospace Centre NLR carried out a substantiation of the data acquisition process through an independent assessment. The goal of this substantiation is to evaluate whether the data acquisition process is capable of delivering accurate data of good quality and is representative of the helicopter type to be modelled
Human biodynamic models for rotorcraft comfort assessment
No full textThis work shows how different occupant biodynamic modeling techniques are integrated in a rotorcraft design environment and discusses the resulting differences in comfort assessment. Three modeling techniques, that are used for biodynamic characterization, are considered: lumped parameter, finite element and multibody dynamics. These models are identified for the same gender, age, weight and height and then integrated into a virtual helicopter environment with a seat-cushion interface. A generic helicopter model is used to demonstrate the approach. For each of the three techniques, the vertical acceleration levels at the human-helicopter interface, as required by vibration regulations, and at the head are evaluated up to 30 Hz. At a first glance, it is observed that in terms of model set-up the lumped parameter is the easiest to implement. However, the use of lumped parameter models is limited to the population groups that they are identi1ed from, and thus are not as flexible as the finite element and multibody ones in developing biodynamic models for individuals of an arbitrary population percentile. Furthermore, through numerical analysis it is found that the differences are not very significant in terms of accelerations at the interface. Therefore, for comfort related issues, the use of more complex models is not justified, unless complicated comfort assessments other than human interface accelerations are required. On the other hand, the spine dynamic can play a significant role when head acceleration is considered; therefore, when the head-neck health of occupants is considered, the sophisticated finite element and multibody dynamics models redeem their higher modeling cost and computation time