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Physics-based detailed design of a ducted-fan driven rotorcraft
No full textA physics-based detailed design approach is suggested for an accurate estimation of a ducted-fan driven rotorcraft. First, classification of the major components is conducted, and the layout of the inner components in both fuselage and the main wing is attempted. Then the equipment and components will be considered as point masses and arranged to locate the center of gravity appropriately. To evaluate the structural integrity, the pertinent aerodynamic loads are applied. The optimization procedure will be established and performed. Finally, the present approach will be capable of estimating a brand-new compound rotorcraft accurately
Investigating power benefits for a helicopter by variation of the anti-torque device
No full textWith the usage of electrically driven devices, the rigid connection between main rotor and tail rotor can be broken up, allowing for a tail section that can possibly be optimized for different operating conditions. This paper presents the results of a study investigating the power benefits of different variations of the electric anti-torque device. The investigations were performed using an engineering model of a main rotor - tail rotor helicopter built up in the Versatile Aeromechanics Simulation Tool (VAST). The studied variations include horizontal and vertical tilting of the tail rotor, changing tail rotor speed and fin angle as well as fin size and geometry. Various flight conditions such as hover, forward flight, quartering flight, climb, and descent have been investigated. The largest power benefits were observed for (1) a combination of reduced tail rotor speed and a fin angle varying between 12 deg for low speed forward flight and 6 deg for high flight speeds and (2) an increased fin area with the tail rotor being shut off for flight speeds above 35m=s
Prediction of helicopter rotor loads and fatigue damage evaluation with neural networks
No full textMachine learning algorithms have undergone rapid growth in recent years thanks to the ever-increasing amount of data and the parallel growth of computational power. Among the machine learning algorithms, one of the most famous and most effective classes for performance and flexibility are artificial neural networks, algorithms capable of learning relations between the data. In this work, neural networks are exploited to infer the relation between flight mechanics parameters and resulting loads of an articulated rotor configuration. The accuracy of these algorithms is closely related to the quality of the dataset used for their training. Since rotor loads are time-periodic signals with a precise harmonic content, a dedicated neural network is trained to predict each harmonic separately. The load time history is then reconstructed a-posteriori by combining all the predictions given by every single network. Different types of network architectures are tested, and a sensitivity analysis is conducted on hyper-parameters to determine the optimal configuration for the specific application. Furthermore, such predictions are then used to feed a fatigue damage calculation algorithm
Manufacturing of a variable chord extension concept for helicopter rotor blades with a flexible EPDM skin
Get PDFIn the SABRE project a new morphing concept, the so-called linear variable chord extension, has been devel-oped. Here, the blade chord length in the root area is changed with the help of an elastic skin to adapt it to the respective flight condition. This paper focuses on the manufacturing process of the technology demonstrator and give a detailed overview about the advantages and disadvantages of handling with EPDM material. This also addresses the challenge of reinforcing the EPDM with CFRP fibers
Rotorcraft conceptual design methodology with commonality constraints
Get PDFThis paper introduces a comprehensive methodology of commonality-based simultaneous design of multiple -different types of- helicopters so that, the time and budget allocated to the research, development, and production can be decreased significantly. In the presented synchronous design process, three levels of commonality are suggested as low, mid, and high-level in which engine; engine and transmission; engine, transmission, and rotor systems of the helicopters are assumed to be identical, respectively. To illuminate the methodology, simultaneous conceptual design studies of two helicopters -a transport and an attack helicopter- with high and mid-level commonality levels are presented. In this design process, fully parametric three-dimensional geometric models with embedded empirical formulations are created in order to increase the accuracy of the estimations in several considerations such as weight, dimensions, and flat plate drag area of the vehicle to be designed. This surrogate model approach is generalized with a response surface to create a design space, which can be analyzed by both designers and decision makers to assess and evaluate possible design scenarios for both helicopters, simultaneously
Aeroelastic dynamic stall computations of a double-swept blade in a four-bladed rotor configuration
Get PDFInnovative helicopter rotor blades with a combined forward-backward double-sweep at the outer part of the blade enable a reduction in noise emission and enhance the overall performance of a rotor. In this context, the influence of the aeroelastic behaviour in connection with the dynamic stall phenomenon is of great importance. It is accompanied by large aerodynamic load peaks, primarily seen in the lift and the pitching moment, impacting the structural integrity of the blades and adjacent control components. Double-swept model rotor blades were developed and investigated experimentally at the DLR Goettingen regarding the dynamic stall behaviour in a four-bladed rotor configuration at the Rotor Test Facility Goettingen. Due to an axial inflow to the rotor disc a sinusoidal variation in pitch angle is introduced to trigger the dynamic stall behaviour once per revolution. The experimental investigations were accompanied by aeroelastic as well as purely aerodynamic numerical simulations which are the main focus in this study. In case of the aeroelastic simulations, a tight coupling scheme was implemented to perform the data exchange between the inhouse CFD solver TAU and the commercial software Simpack as solver for multibody systems with flexible bodies in each time step. Six test cases with a rotational frequency of 23.6 Hz are presented comprising three with solely collective pitch angle and three with a superposed cyclic variation in pitch angle in order to introduce and strengthen the dynamic stall behaviour stepwise for the investigated rotor configuration. As a result, differences arise in the aerodynamic loads between both blade modelling approaches. They are elaborated in order to draw conclusions about the dynamic stall behaviour under consideration of elasticity in the blade modelling
A numerical optimization framework for rotor airfoil design
No full textThe design of new helicopter airfoils is a challenging task. The individual blade sections undergo very different flow conditions during the various flight regimes of the helicopter. In forward flight, the advancing side operates in a transonic regime where potentially shock waves can occur, while on the retreating side little flow velocities at high angle of attacks are seen up to reverse flow. In hover, the oncoming tip vortex of the previous blade drastically influences the inflow on the rotor. Therefore, after a brief review of given design techniques, a novel approach for airfoil designs is put forward. A surrogate based multi-objective approach including constraints is utilized to concurrently optimize an airfoil for hover, retreating and advancing side flow, while also enforcing a certain robustness as to not looking at single design points in these global flow regimes. Along with the estimation of design targets, this 2D flow analysis-based framework allowed to optimize the airfoil design of an existing model rotor blade. A comparison over a range of flight conditions of the rotor with and without the new airfoils proved the validity of this approac
Helicopter blade twist optimization in forward flight
No full textImproving the efficiency of the helicopter is one of the main objectives in helicopter design. Endurance, ceiling and maximum forward flight are strongly connected with the aerodynamic field around the main rotor and its power consumption, in particular the induced power used to generate the thrust needed to fly. It’s possible to minimize this power with the uniformization of the inflow along the blade for all the azimuthal positions. The main objective of this paper is to find for each flight condition the blade twist distribution that minimizes power. The model is based on Blade Element Momentum theory for hovering condition and Blade Element theory for forward flight. It is tested using the flight test data of the UH-60A. The idea is to divide the blade in sections and impose on them a linear or quadratic twist behaviour. The first concept use only a section with linear or quadratic twist distribution. The second concept uses two segments each with a linear twist distribution. In this study different inner segments were analysed corresponding to 40%, 50%, 60% and 70% of the blade length. Finally, the last concept takes in account the main rotor of the Sikorsky UH-60A Black Hawk. It considers three sections and two airfoils and the twist behaviours are linear in each segment
Mixed criticality communication within an unmanned delivery rotorcraft
No full textStand-alone functions additional to a UAV flight-controller, such as safety-relevant flight-path monitoring or payload-monitoring and control, may be SORA-required or advised for specific flight paths of delivery-drones. These functions, articulated as discrete electronic components either internal or external to the main fuselage, can be networked with other on-board electronics systems. Such an integration requires respecting the integrity levels of each component on the network both in terms of function and in terms of power supply. In this body of work we detail an intra-component communication system for small autonomous and semiautonomous unmanned aerial vehicles (UAVs.) We discuss the context and the (conservative) design decisions before detailing the hardware and software interfaces and reporting on a first implementation. We finish by drawing conclusions and proposing future work
Assessment of reduced order fuselage and blade models for rotorcraft interactional aerodynamics
Get PDFThis paper investigates mid-fidelity Cartesian-based CFD tools developed either by the U.S. Army and ONERA for rotorcraft aerodynamics in the framework of the US-France Project Agreement on Rotary Wing Aeromechanics and Human Factors Integration Research. The common test-case is the simulation of the interaction between the rotor and the fuselage of the D365N configuration in forward flight, for which high-fidelity CFD simulations have been conducted in 2009. US Army’s code Helios/ROAM models the fuselage with an immersed boundary method (IBM) and the rotor blades as an actuator line. ONERA’s code FAST also models the fuselage with an IBM representation and the blades using body-fitted overset grids. This work presents a comparison of fuselage loads, rotor loads, and wake between simulations and experiments