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Real time estimation of VTOL vehicle weight using standard on-board sensors
Get PDFThis paper presents an effective method for real time computation of the gross weight of vertical take-off and landing aircraft (specifically, a tiltrotor). Accurate in-flight estimation of gross weight allows computing fatigue life of vehicle’s components and optimizing inspection or replacement of vehicle’s life-limited parts, in order to reduce operating cost and enhance safety. Several techniques for determining gross weight are available in the literature, which mainly rely on hover performance charts, neural networks, and model based augmented state observers. The method presented in this paper estimates gross weight by solving forces balance equation when vehicle is trimmed in straight and level flight. In this condition, the balance equation depends on few variables, measured by standard on-board avionic sensors. The key innovation of proposed approach is the exploitation of system identification to tune the estimation algorithm parameters, by performing, just once, a calibration flight campaign in which vehicle’s weight is known. After calibration campaign is completed, the proposed method applies very simple relations to estimate the weight every time the vehicle is trimmed in straight and level flight, whatever its configuration is (helicopter or aircraft). Since the weight varies slowly and most of the mission usually takes place in straight and level flight, this approach guarantees a reliable weight estimation during about the whole mission; moreover, it does not require any a priori knowledge of vehicle parameters neither huge dataset for algorithms training. Monte Carlo analysis, employing the FlightLab ERICA tiltrotor model for flight data generation, was used to assess the estimation method performance. Obtained results are very promising in terms of accuracy, precision and robustness to sensors errors
Uncertainty quantification of tiltrotor whirl flutter aeroelastic stability from multibody analysis
Get PDFTiltrotor aircraft maximum horizontal flight speed is limited by whirl flutter. Current research efforts focus on one side on experimentally investigating on the stability margins through specialized wind tunnel test-beds, and on the other side on developing efficient numerical tools, to both guide the development and gain information from experimental efforts. In this work, the development of TiPa, a software package providing a customizable interface to the general-purpose multibody dynamics solver MBDyn to provide a parametric tiltrotor model generation and investigation tool is presented. The tool is combined with DAKOTA, a state of the art Uncertainty Quantification (UQ) tool to form a complete aeroelastic stochastic analysis package. Two strategies for the parametric model generation are presented. One is based on the definition of complete MBDyn tiltrotor models while the other one relies on the generation of two different subsystems to be assembled through a substructuring approach. Some promising early results and assessment are presented, together with the expected future research direction
Wind tunnel test of the performance of coaxial rigid rotor
No full textTests of 2m-diameter rigid coaxial rotor model were conducted in the?3.2m wind tunnel of CARDC to investigate the hovering and forward flight aerodynamic characteristics of rigid coaxial rotor. The aerodynamic data such as rotor lift, drag and power were acquired in the test, and the aerodynamic force of upper and lower rotor were measured individually. The hover test results show that the FM of the upper and lower rotors is lower than that of the isolated single rotor, and the FM of the lower rotor is lower than that of the upper rotor. Increasing lift offset will result in a decrease in the required power of the rotor and an increase in drag. When the effect of reducing power is greater than the effect of increasing drag, the lift-to-drag ratio of the rotor increases as the lift offset. In the forward flight state, the lift-to-drag ratios of the upper and lower rotors are smaller than the isolated single rotor. And the lift-drag ratio of the upper rotor is lower than that of the lower rotor, which is significantly different from the hover state
Simulation of tiltrotor maneuvers by a coupled multibody–mid fidelity aerodynamic solver
Get PDFThe present work proposes a new aeroelastic solution applicable to rotors and tiltrotors configuration by joining the multibody software MBDyn and the mid-fidelity aerodynamic tool DUST. The coupled MBDyn-DUST simulation environment is aimed to be used for the evaluation of the loads and of the vibratory levels of a tiltrotor aircraft during some critical transient maneuvers. The coupling is first validated by modelling the XV-15 equipped with metal blade rotors in hover configuration. Firstly, the dynamic behaviour of the rotor is tested by comparing the MBDyn Campbell collective diagram with the corresponding CAMRAD II and RCAS diagrams. Secondly, the rotor performances in hover are evaluated by using the coupled approach. The structural dynamics is taken from MBDyn whereas the aerodynamic loads are calculated by DUST. This coupled approach shows a good agreement in terms of polar curve and figure of merits when compared to experimental results. These preliminary results encouraged the use of this novel coupled tool for the simulation of tiltrotor flight dynamics and aeroelasticity
Numerical analysis of helicopter’s blade pitch link loads
Get PDFThe industrial process for the design of main rotor blades is more and more challenging. Taking into account the loads aspect in the blade design process became necessary to ensure a blade design that can be relevant with a high-speed usage. This paper presents the last results of recent studies about pitch link loads. Within the framework of the CHAllenge AeRothermoMEchanique project (CHARME) an important study has been made in order to understand and to improve the control loads prediction capability. The first part of this work was to identify the correct model to be used. A large study was done in order to understand different model’s effects, validity domain and relevance. The main goal of this part was to identify the most relevant aerodynamic modeling base to be used for the next step. All the models used are included in our global aeromechanic code. The second part of the work was to use this modeling base to identify the blade’s pitch link load of a state-ofthe-art main rotor blade during a high-speed forward flight
Mechanical performance of high-altitude tilt-rotor based VTOL vehicle based on full fluid-structure coupling method
No full textMechanical performance of high-altitude tilt-rotor based VTOL vehicle based on full fluid-structure coupling method Affected by the distinct structural characteristics, flight and operation conditions, the tilt-rotor system on an airship may endure aeroelastic instability under certain circumstances during actual envelope flight. Two typical configurations, i.e., beam-rotor layout and wing-rotor layout, are considered in this paper, and each physical model of the tilt-rotor system is established by means of fully fluid-structure coupling method. Because of the low-speed flight condition, the strip aerodynamic theory and the linear structural dynamic model are utilized for modelling. The aeroelastic characteristics of the tilt-rotor system are analyzed, in which the effects of rotation speed and distinct parameters on the aeroelastic characteristics of the models are discussed. The occurrence and evolution mechanism of the aeroelastic instability are revealed, which also provides guidance for the overall parameter design of the system
Experimental-numerical investigation of rotor-rotor aerodynamic interactions for eVTOL aircraft configurations
No full textThe paper presents the description of a research activity aimed to the systematic study of the rotor-rotor aerodynamic interaction with application to the flight conditions typical of eVTOL aircraft. The activity considers a dual effort, experimental and numerical, to gather systematic parametric data on different types of rotor-rotor interactions. In particular, the paper describes the planning and set up of a wind tunnel campaign aimed to evaluate the effects of the aerodynamic interactions on the rotor performance and flow field for two propeller models both in side-by-side and tandem configuration. Moreover, the results of numerical simulations performed with a mid-fidelity aerodynamic code on both the planned test configurations are presented showing the main effects of the aerodynamic interactions on the performance of the propeller
Concept of a variable chord extension
Get PDFAmong all kinds of aircraft, helicopters are standing out due to their capability for both forward flight and hovering. This range of flight conditions requires a special blade design, resulting in a rotor blade geometry, which represents a compromise between the different flight conditions. Morphing rotor blades could address this issue, by changing the rotor blade shape according to the demands of the current flight state. From rotor dynamic calculations it is known, that longer chord length at the blade root and increased pre-twist would increase the performance in hover [1,3], whereas shorter chord and less twist are beneficial for fast forward flight. Based on this assumption, a structural concept has been worked out for a blade design with a variable chord length in the rotor root region. The model, which belongs to that concept forms the basis of a performance calculation. The structural concept consists of a pivot point at around 60% R and the chord extension is linearly increasing all the way to the blade root at 22% R. In this region an auxiliary spar is dividing the blade into a conventional rigid front part and a morphing rear part, whose structural design is the main focus of this paper. It consists of two components: a flexible skin made of rubber-like EPDM material, which is reinforced in the spanwise direction by fibers, as well as an inner support structure. The design drivers for the skin thickness are shape accuracy on one end and actuator force to extend the mechanism and stretch the skin on the other end. The underlying support structure consists of vertical GFRP extending in span wise direction. Design parameters for those webs are the distance between webs, which relates to the skin design, as well as the thickness of the members, which influences the overall stiffness of the design. The publication will present a workflow, in which the rotor is being structurally designed coming all the way from a generic CAD model, considering cg location as well as elastic deformation of the elastic skin and calculating the cross section wise stiffness of structure. This section wise approach is followed by the setup of a beam model of the blade for dynamic analysis as well as the setup of a 3D model for strength analysis as well as aeroelastic simulation by fluid structure interaction (FSI), the first results of which are shown as an example. This is followed by a performance calculation in order to evaluate the efficiency of the concept and to provide input for further iteration steps. This includes trim analyzes for various blade loading conditions in hover as well as various forward flight velocities using DLR comprehensive analysis code S4. Chord-extension of up to 100% and chord-extension-deflection of up to 15deg are considered. Results show that the linearly variable chord-extension concept is effective in reducing power requirement in both hover and forward flight. The chord-extension-deflection helps reduce power requirement in hover, especially at higher blade loadings
The use of CFD in the redesign of a model scale rotor for the investigation of stall onset and alleviation for the UKVLN rotor rig
Get PDFAn experimental setup has been designed to example in the effect of rotor blade stall flutter. The blade has to be designed so that it does not exceed the maximum permissible load on the rotor rig to be employed for wind tunnel tests, while maximising the blade loading to allow for the blade to be excited. An original set of blades where first tested to examine the possibility of their reuse. On discovery that they required too much power drive them at the required collective computational fluid dynamics (CFD) was used to aid a new design
Electro-mechanical de-icing system for a non-rotating structure of small and medium sized helicopters synthesis of a helicopter control system using inverse dynamics and its upgrade with the use of a sidestick controller
No full textThe modern trend of developing highly automated aircraft is characterized by a transition from traditional methods and technical solutions to innovative approaches of creating control systems, inceptors and displays. This paper deals with the development of helicopter control systems based on the inverse dynamics and its integration with a novel type of side stick shaping the pilot output signal such that it is proportional to the control force (Force Sensing Control – FSC). The synergetic asset arising from this integration is also evaluated. The evaluation of the effectiveness of the inverse dynamics was carried out through mathematical modeling of the pilot-aircraft system ground based simulations