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Comprehensive mixed-sensitivity h? on-blade control for vibration reduction of the EC-145 rotor
Get PDFSensitivity H? is an advanced control method developed when reliable Linear-Time-Invariant representations exist and is especially suited for multivariable control problems. The method allows the designer to specify robustness and performance demands and existing optimisation algorithms would provide a controller which optimises over such design objectives. Alotaibi and Morales recently applied the methods to an analytical and validated model available for the EC-145 helicopter. Their work showed that the method is successful in reducing significantly all 4/rev hub loads while controlling directly the rotor thrust only. In this work, we extend this approach to control directly the remaining 4/rev components of the rotor hub loads. This comprehensive approach is compared to the simpler case (thrust control only) and we outweigh benefits and disadvantages. A key outcome from this work is that the performance can be improved by pursuing the comprehensive approach, achieving a further 21% vibration reduction in average across the flight envelope. However the comprehensive approach requires further implementation requirements, such as additional sensors and increased computational power, and more controller parameters to tune which can limit its applications. Both schemes provide the benefit of having a single controller operating over the wide flight envelope, ensuring highe
Inverse simulation of a helicopter-towing cable-sonar system
No full textAn inverse simulation algorithm based on an integration method is applied to a system formed by a submerged vehicle towed by a single main rotor helicopter by means of a massive, elastic cable. The problem is split into two phases: at each discretization time-step of the inverse simulation, the trajectory of the cable suspension point is derived 1rst, which results into the submerged vehicle following the desired pattern in water; then the control variables for the helicopter are determined, which make the suspension point follow the trajectory obtained at the previous step, including cable tension as an additional load. The control action is then integrated forward in time for a fully coupled complete helicopter-cable-vehicle system model. Discrepancies in the results between the inverse solution and the forward simulation at the end of the time-step are compensated by (i) introducing a guidance term, which slightly modi1es the desired variables at the following step, in order to maintain the towed vehicle on the desired trajectory, and (ii) by an attitude control logic for the helicopter, which manages the variation of moments generated by cable tension. The method is demonstrated for a towed vehicle representative of a realistic sonar system
Design study, prototyping and performance evaluation for on-board blade pitch control system of rotorcraft considering high g environment
No full textThe conventional blade pitch control of rotorcraft is performed by a swashplate mechanism driven by the actuators placed on a non-rotating frame. One of the drawbacks of the swashplate mechanism is the high life cycle cost deriving from its mechanical complexity. In order to cope with this problem, an active trailing edge flap based system is proposed and design studied considering an operation in the high centrifugal force acting environment. The proposed drive mechanism consists of a piezoelectric actuator, an amplifying mechanism and a linear/rotary movement converter to satisfy the design target which requires the trailing edge flap to deflect 6deg amplitude at 22Hz with 1,000G centrifugal force. A prototype of the drive mechanism is developed and statically evaluated by a bench test, then dynamically done by a spin test. Both tests demonstrate the enough operability of the developed drive mechanism on the high centrifugal force condition
Analysis of rotorcraft wind turbine wake encounters using piloted simulation
No full textThe use of offshore wind farms in Europe to provide a sustainable alternative energy source is now considered normal. Particularly in the North Sea, a large number of wind farms exist with a significant distance from the coast. This is becoming standard practice as larger areas are required to support operations. Efficient transport and monitoring of these wind farms can only be conducted using helicopters. As wind turbines continue to grow in size, there is a need to continuously update operational requirements for these helicopters, to ensure safe operations. This study assesses German regulations for flight corridors within offshore wind farms. A semi-empirical wind turbine wake model is used to generate velocity data for the full flight simulator AVES. The reference offshore wind turbine NREL 5 MW has been used and scaled to represent wind turbine of different sizes. This paper reports results from a simulation study concerning vortex wake encounter during offshore operations. The results have been obtained through piloted simulation for a transport case through a wind farm. Both subjective and objective measures are used to assess the severity of vortex wake encounters
Numerical and experimental analysis of the helicopter's flotation system
No full textThe paper presents the results of numerical and experimental hydrodynamic analysis of the PZL SW4 helicopter, undergoing the modifications aimed at adopting it for maritime missions. The primary goal of the analysis was to design an effective emergency flotation system, assuring sufficient buoyancy and stability in calm water as well as minimized motion response to waves. The analysis started with an optimization study, based on simplified stability model. The helicopter with designed floats was then widely analysed in respect of buoyancy, stability and motion response to waves, both by means of experimental analysis with scaled physical model, and with numerical models. Such a parallel approach allowed minimizing the uncertainty, as good agreement of the results was confirmed. As a result, satisfactory performance of the emergency flotation system was proved. The paper gives also the details of the development of physical model of the helicopter, as well as the details of experimental methods used in the analysis
Heliwise - tool for helicopter advanced hums data analysis
No full textPurpose of this paper is to describe a new Software tool (Heliwise) based on Web technology (Server-Client architecture) developed by Leonardo Helicopters S.p.A. for the analysis of Health and Usage data, aimed to increase the aircraft availability (reduction of unexpected Aircraft On Ground’s) and to minimize the extraordinary maintenance activities. In this paper will be shown how Heliwise can achieve these results by implementing an architecture which is modular, flexible and suitable to operate in a global environment (so called HUMS technical community) where all data are shared
Experimental study of secondary vortex structures in a rotor wake
No full textThe aerodynamic performance of a helicopter rotor is strongly affected by the structure of its wake. Rotor simulations using modern computational methods have the potential to capture high levels of detail, which recently triggered discussions of secondary vortex braids entangling the primary tip vortices. These structures are highly dependent on the numerical settings and need experimental validation. The current work investigates the wake of a subscale rotor in ground effect by time-resolved and volumetric flow field measurements using the “Shake-The-Box” technique. Both the Lagrangian tracks of the flow tracers and the derived gradient-based vortex criteria clearly verify the existence of secondary vortices. A post-processing scheme is applied to isolate these vortices in larger datasets. No distinct spatial organization of the structures was observed, but a slightly preferred sense of rotation which agrees to the shear of the wake swirl. The secondary structures were created shortly downstream of the rotor blades, starting at wake ages of about 70 degree
Development of practical drag model for multirotor-type unmanned aerial vehicles and its application
No full textApplication area of multirotor-type Unmanned Aerial Vehicles have become popular and diverse in recent years. This trend makes it more important to obtain an optimally designed multirotor for a specific mission in the conceptual design phase. To this end, accurate prediction of a forward flight performance is essential, and one of the most influential factors on forward flight performance is drag force induced by the body frame. In this study, a practical drag estimation model for multirotor-type Unmanned Aerial Vehicles is developed for the conceptual design phase. The drag model is developed based on physical geometry of the body frame of the multirotors considering interference effect between the components. Therefore, the developed model is able to estimate a drag force depending on the variation of the multirotor geometry. The model estimates the drag force through regression equations derived from Computational Fluid Dynamics (CFD) analysis, which makes the model fast and accurate. The drag model is eventually embedded in a design optimization framework. For a generic filming mission, an optimization example is presented with comparative analysis depending on whether the drag model is applied or not. The optimization result shows that the significance of the drag coefficient on the design optimizatio
Thermal management of helicopter sub-system in various states of flight
Get PDFThe paper describes the aerothermodynamic analysis of the conceptual design of the modern helicopter SH09 developed by the Kopter Group AG. For better understanding of the cooling process in the helicopter, Computational Fluid Dynamics tools were used. The object of research was the internal flow in the space under the cowl of a helicopter. The simulation also takes into account the external influence, including the downwash from the main rotor of a helicopter. The CFD analysis of the SH09 helicopter concerned different states of flight and their impact on the cooling process. The results of the helicopter operating in several conditions such as: hover, forward, rearward and lateral flight are presented. The aim of the computational investigation was to find out key parameters of cooling process of the helicopter, in particular: the main directions of flow in different conditions of a helicopter flight, the airflow cooling under normal and extreme conditions, the impact of the flight conditions, ambient conditions and oil cooler fan setting, the efficiency of the cooling system
CFD analysis of a micro-rotor in ground effect
Get PDFIn this work, computational fluid dynamics is used to compare experimental results for a two-bladed small rotor Out of Ground Effect and In Ground Effect conditions. The paper focuses on the evalutation and prediction of the performance of the rotor and investigates the outwash generated in ground effect. Time and phase averaged outflow velocities with two different scaling methods are compared with experiments. The results are also scaled to a full-size rotor, and compared with the PAXman model of crew operating in close rotor proximity. A particle pickup model is also used showing the dust cloud generated by the rotor