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CFD analysis of helicopter wakes in ground effect
No full textThe paper presents CFD results for the wake of a helicopter flying a low altitude at different advance ratios. The wakes are assessed in terms of topology and velocity magnitudes. The structure of the wake near ground changes rapidly with the advance ratio and its decay appears to be faster than what is suggested by theoretical analyses. The results show clear the potential of modern CFD for use in helicopter safety and highlights the need for detailed surveys of helicopter wakes using full-scale physical experiment
Numerical-experimental correlation of rotor flowfield in ground effect
No full textThis work presents the comparison between experimental measurements and numerical simulations concerning the flowfield generated by a helicopter rotor operating in ground effect conditions above an inclined plane. Specifically, the capability of a potential-based, three-dimensional, free-wake aerodynamic solver to simulate in-ground-effect problems is assessed in terms of loads and wake inflow field, showing a good agreement with the experimental data
Identification and selection of rotorcraft candidate models to predict handling qualities and dynamic stability
Get PDFCurrent frequency-domain system identification methods require an open-loop experiment design for data collection to identify one model of a vehicle. This makes open-loop system identification for unstable systems like rotorcrafts challenging. The optimized Predictor-Based Subspace Identification method also estimates accurate models from closed-loop data. In this paper, a parameter study is conducted to identify a set of bare airframe models of the ACT/FHS research rotorcraft using this subspace method. A selection method is introduced to chose appropriate candidate models from the identified set. The selected candidate models differ slightly in terms of the model invariants and are all a valid approximation of the rotorcraft dynamics. Consequently, the selected candidate models can be used to predict the possible properties of the system and their uncertainties. Here, the candidate models are employed to estimate the dynamic stability and handling qualities of the ACT/FHS bare airframe and two control system of the ACT/FHS research rotorcraft
BladeSense - a novel approach for measuring dynamic helicopter rotor blade deformation
Get PDFTechnologies that allow accurate measurement of rotorblade dynamics can impact almost all areas of the rotorcraft sector; ranging from maintenance all the way to blade design. The BladeSense project initiated in 2016 aims to take a step in developing and demonstrating such a capability using novel fibre optic sensors that allow direct shape measurement. In this article the authors summarise key project activities in modelling and simulation, instrumentation development and ground testing. The engineering approach and associated challenges and achievements in each of these disciplines are discussed albeit briefly. This ranges from the use of computational aerodynamics and structural modelling to predict blade dynamics to the development of direct fibre optic shape sensing that allows measurements above 1kHz over numerous positions on the blade. Moreover, the development of the prototype onboard system that overcomes the challenge of transferring data between the rotating main rotor to the fixed fuselage frames is also discussed
Evaluation of a slung load control system for piloted cargo operations
No full textHelicopter operations with externally slung loads are highly demanding for the flight crew. Without having a direct view on the load, the pilot requires assistance from an additional crew member for load handling to achieve operational requirements (e.g. precise load positioning). An automatic load stabilization and positioning system for cargo operations has been designed with the aim to reduce pilot workload, damp load pendulum motion and to improve the load positioning performance. This system uses the concept of load- motion feedback to the rotor control. To avoid degradation of Handling Qualities (HQs), as found in previous investigations, a function has been developed that monitors pilot control inputs. Dependent on the amplitude and duration of pilot control stick deflection, the feedback signal for slung load damping is blended between two different gain sets. One set provides improved HQs during piloted control and one set provides good load damping when the pilot is passive. A further novel aspect is the evaluation of an automatic load control system using a Translational Rate Command as method of helicopter control. A piloted simulation study has been conducted using this advanced load control system with automatic load stabilization and positioning. Three test pilots evaluated the system in different control law configurations using a Mission Task Element simulating an external load cargo operation. HQs and pilot workload were evaluated using the Cooper- Harper Rating Scale and NASA Task Load Index respectively. The results of the study show that improved HQs in combination with improved task performance can be achieved with the advanced slung load control system
Unsteady aerodynamic interaction between rotor and ground obstacle
Get PDFThe mutual aerodynamic interaction between rotor wake and surrounding obstacles is complex, and generates high compensatory workload for pilots, degradation of the handling qualities and performance,and unsteady force on the structure of the obstacles. The interaction also affects the minimum distance between rotorcrafts and obstacles to operate safely. A vortex-based approach is then employed to investigate the complex aerodynamic interaction between rotors and ground obstacle, and identify the distance where the interaction ends, and this is also the objective of the GARTEUR AG22 working group activities. In this approach, the aerodynamic loads of the rotor blades are described through a panel method, and the unsteady behaviour of the rotor wake is modelled using a vortex particle method. The effects of the ground plane and obstacle are accounted for via a viscous boundary model. The method is then applied to a �Large� and a �Wee� rotor near the ground and obstacle, and compared with the earlier experiments carried out at the University of Glasgow. The results show that the predicted rotor induced inflow and flow field compare reasonably well with the experiments. Furthermore, at certain conditions the tip vortices are pushed up and re-injected into the rotor wake due to the effect of the obstacle resulting in a recirculation. Moreover, contrary to without the obstacle case, the peak and thickness of the radial outwash near the obstacle is smaller due to the barrier effect of the obstacle, and an up-wash is observed. Additionally, as the rotor closes to the obstacle, the rotor slipstreams impinge directly on the obstacle, and the up-wash near the obstacle is faster, indicating a stronger interaction between the rotor wake and the obstacle. Also, contrary to the case without the obstacle, the fluctuations of the rotor thrust, rolling and pitching moments are obviously strengthened. When the distance between the rotor and the obstacle is larger than 3R, the effect of the obstacle is small
Unified framework for analysis and design optimization of a multirotor unmanned aerial vehicle
Get PDFDesigning a small-scale multirotor UAV is a complicated procedure that requires multi-disciplinary analyses including rotor aerodynamics, structure, and electric propulsion system. However, owing to the complexity of multi-disciplinary analyses, the design of conventional multirotor UAVs heavily relies on the empirical methods through experimental data or legacy selections. These methods not only lack the firm physical basis for selecting the component, but also are extremely time-inefficient, requiring numerously repetitive experiments. In order to establish a systematic design procedure for multirotor UAVs, the unified design optimization framework, titled as Conceptual Layout Optimization for Universal Drone Systems (CLOUDS), was developed in this study. CLOUDS consists of five multi-disciplinary analysis modules including aerodynamics and electric propulsion system. Utilizing these modules, it can accurately estimate the performance of the system in response to the variation of the combination of components, showing high accuracy of predicting the flight time within 10% deviation. As such, the optimal configuration of multirotors could be designed for a specific mission. Based on the developed framework, correlations between the variables are found using Self-Organizing Maps (SOM) and Analysis of Variance (ANOVA). Additionally, design optimizations were conducted for two hover missions with different time as an example. The optimum design solution was presented by analyzing the optimization results
Development of a conceptual design tool for various compound helicopters
Get PDFRecent rotorcraft community has suggested various forms of compound helicopters capable of carrying out a high-speed maneuver. These aircraft have disparate aerodynamic characteristics and propulsion system due to their unique way of generating lift and thrust. In view of the unique features, each concept is adapted with a specific mission profile. To provide an appropriate concept for a specific mission, this study developed a comprehensive conceptual design tool for the three concepts, winged helicopter, tip-jet gyroplane, and fan-in-body concept. This design tool enables sizing of the compound helicopters with comparable analysis fidelity, while considering their distinctive propulsion system at the conceptual design phase. With the developed tool, the design optimizations were conducted for six different mission profiles covering various flight range, hover and loiter time. Subsequently, systematic comparisons and analyses were carried out to deduce the most appropriate configuration for each missio
A generic ground dynamics model for ground handling evaluations
No full textThis paper demonstrates a generic ground dynamics model for modeling and simulating landing gear systems. Physics based model is developed in MATLAB-Simulink® environment and it is integrated to a non-linear 6-DOF helicopter model which is constructed in an in-house comprehensive analysis code, TAI Originated Rotorcraft Simulation (TOROS). Other than simulating the helicopter motion after touchdown, this model is also capable of trimming the helicopter on ground, which is useful for determining landing and take-off capabilities of a helicopter on either a flat or a sloped surface. This method can show whether the control ranges are adequate or not during the design stage, which is a troublesome task during preliminary design. In this study, slope-landing analyses of a light utility helicopter is demonstrated together with dynamics of a generic landing gear. The effect of ground on non-uniform inflow parameters, which is capable of modelling inclined ground effect, is included into the non-linear mathematical model using a finite state approach. Results show that, finite state ground effect model affected the control margins and main rotor flapping during slope landing and take-off analyses. In addition, rotational degree of freedom is added to the wheel component, which can be utilized not only for trimming and linearizing the helicopter on ground with/without airspeed but also for performing different ground-handling evaluations (e.g. high-speed taxiing, rolling take-off etc.). Moreover, by using this mathematical model, spin-up loads during run-on landings can be calculated, landing distance to full stop can be found and failure simulations (e.g. flat tire) can be performe
The Tilt-Quadrotor: modelling and attitude stabilization
Get PDFThis paper presents the study on a new type of aircraft, the Tilt-Quadrotor. This multirotor platform differs from classical quadrotors by having four servo motors that tilt two of its four rotors, in two different directions each, allowing the horizontal motion to be executed without tilting the platform. The derived Tilt-Quadrotor model is explained and implemented in a simulator. LQR controllers are designed for attitude and altitude stabilization, and validated in simulation. An approach based on the linearized model is implemented experimentally in a PixHawk autopilot, achieving the stabilization of all three attitude angles of a Tilt-Quadrotor prototype