ERF European Rotorcraft Forum
Not a member yet
4279 research outputs found
Sort by
Implementation of a comprehensive mathematical model for tilt-rotor real-time flight simulation
No full textThis paper aims at describing the effort performed by the joint research group of Politecnico di Torino and ZHAW (Zurich University of Applied Sciences) in achieving a novel implementation of a mathematical model for real-time flight simulation of tilt-rotors and tilt-wings aircraft. The focus is on the description of the current stage of the project, the achievements of the first version of the model, on-going improvements and future developments. The first part of the work describes the initial development of the overall simulation model: relying on several NASA reports on the Generic Tilt Rotor Simulator (GTRS), the mathematical model is revised and the rotor dynamic model is improved in order to enhance computational performance. In particular, the model uses the conventional mathematical formulation for non-dynamic inflow modelling based on Blade Element Momentum Theory. A novel but simple numerical method is used to ensure the convergence of the non-linear equation in every tested condition. The resulting simulation model and its development and implementation in the MATLAB/Simulink® environment is described. The second part of the work deals with the integration of the model in the ZHAW Research and Didactics Simulator (ReDSim), the replacement of the pilot controls by the introduction of a center stick and the corresponding adjustment of the force-feel system to suitable values for the tilt-rotor model. Subsequently, several pilot tests are carried out and preliminary feedbacks about the overall behaviour of the system are collected. Limits and weaknesses of the first release of the model are investigated and future necessary improvements are assessed, such as the development of a novel generic prop-rotor mathematical model. The third part introduces the novel multi-purpose rotor mathematical model which was developed to improve the overall tilt-rotor simulation model. The multi-purpose rotor model implements non-approximated flapping dynamics and inflow dynamic based on Pitt-Peters formulation. The validation of the nover rotor model is carried out with available data of both the XV-15 Research Aircraft and the UH-60 Helicopter
Helicopter maneuver performance with active load limiting
No full textThis paper expands on a previously developed real-time load limiting for critical helicopter components that are subjected to significant fatigue loading. The (structural) load limiting scheme, which is posed as an optimal control problem where estimate of control margin associated with the component load limit is used to arrive at load limiting, is developed within a Dynamic Inversion control architecture. The integration of the load limiting via Model Predictive Control (MPC) within the Dynamic Inversion environment is described in detail. The developed controller resulting from this integration is evaluated using nonlinear model simulations for its ability to limit harmonic pitch link loads and its direct effect on maneuver performance for test cases including attitude and rate command maneuvers
Wind tunnel test of a rotorcraft with lift compounding
Get PDFA recent doctrine in rotorcraft development is the pursuit of higher flight speeds. Limiting factors are compressibility effects on the advancing blade side and decreasing lift potential on the retreating blade side. It may therefore be beneficial to employ a hingeless rotor to generate additional lift on the advancing blade side and compensate the resulting rolling moment with a fixed-wing on the retreating blade side. This concept is a form of “lift-compounding” that has not been studied in detail yet. The present paper presents results of a wind tunnel test with a slowed, hingeless rotor and single fixed-wing (0.7R span, 0.24R below rotor plane) on the retreating blade side. Based on rotor test stand data and flow field measurements, the impact of operational and rotor parameters on performance and flow field of the system is examined, mutual interaction effects between rotor and fixed-wing are analyzed, and dominant flow structures are characterized in the reverse flow region on the retreating blade side. Flow field analysis reveals a dynamic stall vortex that freely convects through the reverse flow region and rivals the blade tip vortices in strength. Contrary to previous beliefs, this vortex originates from upstream of the reverse flow region and only its detachment from the rotor blade is related to entering this region. Advance ratio and shaft tilt angle are found to have significant and non-linear impact on the dynamic stall vortex and its interactions with rotor blades and other vortices. The rotor downwash reduces fixed-wing lift by up to 23% and increases its vibratory loads, while the fixed-wing is found to influence the effective angle of attack of the retreating rotor blade by up to 2 deg. The combination of finite rolling moment trim and aft shaft tilt increases the rotor lift coefficient by up to about 79% at 6 deg rotor collective and the corresponding peak lift-to-drag ratio of the compound rotorcraft is improved by up to 60% at ? = 0.5. Results are compared with predictions from a comprehensive rotor analysis code that is expanded to cover the main effects of added fixed-wing and is able to reproduce general performance trends of the rotorcraft. The present study highlights that adding a single fixed-wing to a high-speed hingeless rotor could significantly improve its performance
Advanced coupled aeroelastic analysis of helicopter rotor system
Get PDFComparing to other flight vehicles, aerodynamics of helicopter blades is time-periodic. For blade flutter analysis this feature requires development of special tools, taking the flow time-dependency into account. In this study, we develop a framework for the flutter analysis of the full blade model based on Floquet theory. A finite-element beam model governs the blade, whereas the flow is governed by quasi-static aerodynamic functions. An in-house software is developed to integrate the aerodynamics into Nastran finite-element model for solving both static and dynamic aeroelastic problem
Rotor loads reduction by dynamically extendable chord
Get PDFDynamically extendable blade chord sections show promise for reducing helicopter rotor loads. A rotor model based on elastic beam concept, and capable to predict helicopter power, is utilized. A four bladed rigid rotor with the shape similar to the UH-60A rotor, is used as baseline for comparisons. For the control of the 4/rev vertical hub force, it is not beneficial to actuate the extendable chord at hover and low speed flight. At a high speed of 270km/h, the extendable chord, with a width of 10% rotor radius and responded to 10% of chord length, obtained a maximum force reduction of 89.4%. The magnitude of the dynamic chord needs to be optimized according to the flight state. The performance can be enhanced by increasing the extension or width of the dynamic chord. The dynamically extendable chord was not suitable for reducing the 2/rev blade flapwise root bending moment. A 3/rev dynamic chord though showed great potential in reducing the 3/rev flapwise root bending moment and the 4/rev rotor rolling and pitching moments, simultaneously. The effectiveness of a 5/rev dynamic chord in reducing the 4/rev rotor rolling or pitching moment degraded significantly compared with a 3/rev actuated. To control the 4/rev target load originating from the 3/rev flapwise root bending moment, the phase difference for the maximum rotor rolling and pitching moment reduction was 180o for the 5/rev dynamic chord. Based on the analyses, it is recommended to use the 4/rev dynamically extendable chord to reduce the 4/rev vertical hub force, and use the 3/rev dynamic chord to reduce the 3/rev blade flapwise root bending moment and 4/rev rotor rolling and pitching moments
Mid-fidelity analysis of unsteady interactional aerodynamics of complex Vtol configurations
Get PDFThe paper presents a new flexible medium fidelity aerodynamic computational tool, developed from the collaboration between Politecnico di Milano and A3 by Airbus, and tailored to obtain reliable and fast aerodynamic simulations of new aircraft configurations like Vahana, the fully-electric vertical take-off and landing multi-rotor tiltwing aircraft built by A3 by Airbus. The proposed solution, called DUST, relies on the Helmholtz decomposition of the velocity field to recast the aerodynamic problem as a mixed boundary elements-vortex particles method. In DUST different aerodynamic elements can be combined in a single model to best capture the relevant physical phenomena, while an accelerated vortex particle model of the wakes allows for a numerically stable Lagrangian description of the free vorticity evolution. Pressure field evaluation in a rotational flow relies on an integral boundary problem for the Bernoulli polynomial obtained from the Navier-Stokes equation. The code is validated against numerical and experimental data available for conventional vehicle configurations, like airliner and helicopter models, and more complex architechtures, such as a tiltwing-rotor in hover and forward flight. Finally a comparison between flight test data and DUST computations is shown for Vahana
Resonant frequency tuning of a nonlinear helicopter inceptor model: a sensitivity analysis
No full textThe term inceptor refers to the controls pilots use to orientate and manoeuvre an aircraft, applicable to both fixed or rotary-wing aircraft. Active inceptors are unique in that they include the ability to provide tactile force feedback from the aircraft control surfaces to the pilot; the pilot is able to experience the aircraft dynamics. Typical active inceptor anatomies comprise components interconnected through a network of mechanical links and understanding how these individual components behave collectively under the influence of helicopter vibratory loads is crucial in assessing the dynamic response of the entire inceptor. This paper presents an investigation into the mathematical modelling of a candidate inceptor mechanism using a dynamic modelling approach formulated by Udwadia-Kalaba to explore resonance frequencies. Results demonstrate the ability of the Udwadia-Kalaba scheme to model and capture the location of the inceptor mechanism’s resonance frequencies. Sensitivity studies were also conducted on selected inceptor design parameters to demonstrate that system resonance frequencies may be influenced and tuned away from baseline values
Dynamic stall induced by blade vortex interaction in helicopter descending flight
Get PDFIn recent years studies have shown how blade-vortex interaction (BVI) can cause the onset of dynamic stall on helicopter rotors. In order to investigate this phenomenon wind tunnel tests were performed on a rotor model in descent flight conditions. The anaylsis of the rotor global performances indicated a defect of thrust for a particular value of collective pitch angle that can be explained as the occurrence of dynamic stall induced by a perpendicular vortex interaction. This conclusion is supported by evidence from both flapping angle measurements and by the results of numerical simulations performed using a code based on blade-element coupled with a vortex-particle wake model
An experimental investigation of helicopter slipstream in the presence of elevated heliport
Get PDFAn unsteadiness of pressure in a helicopter rotor slipstream may bring a significant problem during operation from the elevated heliports, as the oscillating slipstream acts on the heliport plate and causes vibration of building’s structure. However, still it is an unappreciated issue, discussed mainly in the literature focused on the brownout. In this case researchers usually neglect the loads acting on the ground. On the other hand, investigations of interaction between rotor slipstream and helicopter’s surroundings, e.g. [7], [4], are often limited to a time-averaged case. Meanwhile, results of the investigation presented in the paper show that amplitude of the pressure oscillation cannot be omitted, as it can achieve its value of roughly 50% of the rotor disc load. This value, however, is dependent on thrust coefficient and height above the ground. Presented results have been obtained in an experimental way, using the helicopter with the rotor diameter of 0.7 m and validated by comparison with the full-scale rotor (with its diameter of 8 m)
Implementation of a flight simulation tool into a rotorcraft design environment
Get PDFThe German Aerospace Center (DLR) is currently developing a new integrated design environment called IRIS (Integrated Rotorcraft Initial Sizing). This framework features distributed computation on the servers at different locations using the DLR collaboration software RCE (Remote Component Environment) and the data model CPACS (Common Parametric Aircraft Configuration Schema). The flight performance calculation is one of the main parts within a sizing loop. To compute and analyze the flight mechanic properties the simulation tool HOST (Helicopter Overall Simulation Tool) developed by Airbus was integrated into the process. The purpose of this paper is to provide an overview of the rotorcraft design environment IRIS and the necessary calculations before using a flight performance calculation. Afterwards the implementation of such a complex flight performance calculation tool into the design environment IRIS involving the automatization of the pre- and post-processing procedures will be described. For mission performance calculation, a physics based engine model is integrated and coupled with the trim and performance calculation conducted by HOST. The presented results are considering different requirements like main rotor geometries or mission specifications. Beyond sizing and mission analysis the same tools are used to compute load cases in order to deliver the necessary input for a more sophisticated structural analysis and design