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This work describes a model developed to analyze the aerodynamic loads on a helicopter model on conventional configuration implemented with VehicleSim, a multibody software specialized in modelling mechanical systems composed by rigid bodies. The rotors are articulated and the main rotor implementation takes into account flap, lag and feather degre...
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In this paper we propose a novel actuation concept, consisting of a conventional DC motor in series with a compliant element having multiple configurations of equilibrium. The proposed device works similarly to a traditional series elastic actuator, where the elasticity increases safety and force control accuracy, but presents the possibility of ac...
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... The previous studies have ignored the effect of powerful engine suction on the airflow of the MR, and the velocity rate of the engine inlet was ignored or considered constant [16,17]. Since the inlet airflow to the engine can significantly impact the modelling, stability, and efficiency of the compressor, calculating the value and direction of the speed based on the interaction of the engine and the MR is critical. ...
... Since the helicopter is designed to fly in the troposphere layer, and the atmospheric conditions vary in different regions of this layer, flying at different altitudes will significantly affect the rotor and engine performance. As the most critical environmental parameter affecting the rotor, the air density, as a function of flight altitude, can be obtained from Equation 1 [16]. ...
... Eq. (15) where ℬ is the slope of the turboshaft fuel mass flow rate over the power and is the turboshaft fuel mass flow rate at zero power [29]. Rearranging Equations 14 and 15, the new required power corresponding to the weight changes can be obtained from Equation 16. ...
The turboshaft engine performance is closely related to the helicopter's design, and because of its location beneath the helicopter’s main rotor, it has unique features that distinguish it from other families of gas turbine engines. The impact of the engine suction and main rotor’s blow in different flight regimes and climatic conditions lead to variations in speed, pressure, and temperature at the inlet of the turboshaft engines, which, in turn, will affect the design of the engine cycle. Therefore, in this paper, the equations governing the airflow for turboshaft engines are enhanced to incorporate these effects. The equations in this paper are derived using aerodynamics, flight dynamics, helicopter and turboshaft design to lend the inlet velocity of the engine. In order to validate the analytical outcomes of these equations, a computational fluid dynamics analysis is carried out to evaluate the turbulent flow at the T700-GE turboshaft inlet. The analytical and numerical results comparisons show a promising match that would allow future turboshaft engine designs to take advantage of the proposed solution for the turboshaft engine's inlet velocity.
... They allowed calculating positions, velocities and accelerations. In addition, an inverse dynamics problem that estimates feedforward generalised driving forces was taken into consideration [12]. Zupancic and Sodja [13] dealt with some experiences achieved with education and several industrial projects using the Dymola-Modelica environment. ...
... This approach enabled the importation of data from finite elements code to model flexible bodies and the linking of user-written subroutines to the main body of the program. In this way, the applied aerodynamic loads and nonmechanical phenomena were simulated [12]. ...
... These controllers are chosen due to the low level of complexity to be modelled in VS. Their corresponding proportional, derivative and integral gains (different for each controller) are manually tuned [12]. ...
In this work, a tail rotor is modelled with the aid of a multibody software to provide an alternative tool in the field of helicopter research. This advanced application captures the complex behaviour of tail rotor dynamics. The model has been built by using VehicleSim software (Version 1.0, Mechanical Simulation Corporation, Ann Arbor, MI, USA) specialized in modelling mechanical systems composed of rigid bodies. The dynamic behaviour and the control action are embedded in the code. Thereby, VehicleSim does not need an external link to another software package. The rotors are articulated, the tail rotor considers flap and feather degrees of freedom for each of the equispaced blades and their dynamic couplings. Details on the model’s implementation are derived, emphasising the modelling aspects that contribute to the coupled dynamics. The obtained results are contrasted with theoretical approaches and these have displayed to agree with the expected behaviour. This rotorcraft model helps to study the performance of a tail rotor under certain dynamic conditions.
Resumen El presente trabajo muestra el procedimiento seguido para determinar el modelo no lineal de un helicóptero a escala de seis grados de libertad (6DOF) y el sistema de control implementado. Se propusieron dos subsistemas para describir el helicóptero: la dinámica del fuselaje y el acelerador del motor. Para analizar los subsistemas de forma independiente, se analizó el motor utilizando la teoría de identificación de sistemas, por lo que se realizó una experimentación del motor del helicóptero. Para encontrar la dinámica del fuselaje, se utilizaron las ecuaciones de cuerpo rígido, torque, fuerza, empuje, inclinación del rotor y un breve estudio aerodinámico. Se obtuvieron modelos de incertidumbre para cada subsistema. Los subsistemas fueron linealizados en torno a puntos de equilibrio durante la maniobra de vuelo estacionario. El método de matriz de ganancia relativa fue utilizado para desacoplar los sistemas. El controlador H∞ de conformación de bucle fue diseñado para lograr la estabilización del helicóptero y un control PID fue diseñado para controlar el acelerador del motor. Finalmente, se evalúan las estructuras de control y se describen algunas conclusiones. Palabras Clave: Helicóptero, dinámica, H-infinity, optimización, PID, Identificación, Desacople de sistemas, Aerodinámica. 1. Introducción Desde el surgimiento del helicóptero diferentes estudios han sido desarrollados a fin de optimizar el comportamiento de estas máquinas, pues por su versatilidad y su capacidad de vuelo vertical, pueden ser utilizadas en diferentes aplicaciones. Las propiedades aerodinámicas y dinámicas presentes durante el vuelo en este tipo de aeronaves tienen una repercusión directa sobre el espacio seis-dimensional en el que se mueve. Sin embargo, las entradas de control no permiten de manera directa actuar sobre cada coordenada espacial, lo cual significa que el sistema en estudio es altamente subactuado. Adicionalmente, la interactividad entre las variables que intervienen en las dinámicas de vuelo y la dependencia directa con variables externas como la velocidad del viento, su dirección y la densidad de aire, terminan por hacer del helicóptero una aeronave compleja de controlar. En ese orden de ideas, es importante desarrollar modelos que permiten analizar no solo su característica subactuada, sino también aspectos de estabilidad, control, etc. Existen dos perspectivas clásicas para modelar y caracterizar su vuelo: i) el modo crucero; el cual consiste en hacer que el helicóptero siga una trayectoria espacial preestablecida y ii) el modo estacionario (también conocido como "hovering"), y es en este último en el que se concentra este trabajo. El vuelo estacionario permite aplicaciones de alta precisión en las que el helicóptero mantiene fija una posición espacial mientras se encuentra suspendido en el aire. Se propone entonces encontrar un modelo que describa las dinámicas no lineales del helicóptero a escala KDS450SV y diseñar una ley de control robusto que permita estabilizarlo en vuelo estacionario. Se encuentra una aproximación del modelo matemático (figura 1), el cual es una adaptación de los diferentes modelos generales propuestos por al., 2005). El esquema de modelación consiste en dividir un gran modelo en dos submodelos, el fuselaje y el motor. Esto se logra partiendo del principio que, discriminando variaciones abruptas de la densidad del aire, la sustentación de un helicóptero puede ser controlada manipulando el ángulo de paso de las aspas del rotor principal y manteniendo una velocidad angular constante del eje del rotor principal. El presente artículo se realizan aproximaciones físicas a partir de la teoría de momentos, las ecuaciones de movimiento de Newton-Euler y algunas aproximaciones aerodinámicas para determinar el empuje producido por los rotores. Adicionalmente se utiliza la teoría de la identificación de sistemas para determinar un modelo multivariable que define la relación entre el motor, el acelerador y el colectivo con la velocidad angular (Ω) del rotor principal. Como técnicas de control se utilizaron H∞; para el fuselaje, y PID desacople de ganancia relativa para regular la velocidad angular. 2. Estructura del Modelo General La estructura para determinar el modelo no lineal se presenta en Fig.1, donde el modelo del fuselaje del helicóptero se divide en 2 subsistemas, los cuales se subdividen a su vez en 4 modelos más, que determinan las ecuaciones de empuje e inclinación del aspa (M1), las ecuaciones de torque y fuerza (M2), las ecuaciones de cuerpo rígido (M3) y finalmente se realiza una identificación del motor (M4); en la que se relacionan las entradas de colectivo y acelerador.
This article presents the fuselage/main rotor coupling dynamics under a modal analysis to study the modes of oscillation. The authors provide a rotorcraft simulation model that captures complex dynamics, wherein the validation is done with existing theories. The model has been set up by using VehicleSim, software specialized in modelling mechanical systems composed by rigid bodies. It is presented a helicopter simulation framework, that allows to study the impact of the main rotor varying angular speed on the system. Moreover, the generated heterodyning behaviour and harmonics can be analysed on the fuselage. The detection of this performance is not a simple task, and this helicopter model provides an accurate system for its study using a short-time Fourier transform processing. The coupled dynamics observed between the fuselage and the main rotor indicate that the model can be a suitable tool to detect this type of performance.
For the integrated stealth issue of ducted tail rotor noise radiation and radar scattering, a comprehensive optimization method based on high frequency electromagnetic calculation theory and boundary element method is introduced. The radar cross section of the rotor, radiated noise and radar cross section of the ducted tail rotor are designed as optimization goals under the constraints of geometric parameters and aerodynamic force. The model of the ducted tail rotor is established by using the full factorial design and the flow field is constructed by high-precision unstructured grid technology. The aerodynamic characteristics of the ducted tail rotor is simulated by the computational fluid dynamics method based on Navier–Stokes equations and k–ε standard viscous model. The noise radiation is solved by boundary element method and the radar cross section value is calculated by physical optics method and physical theory of diffraction. On the basis of these calculation results, the optimization model of the ducted tail rotor is obtained and generated by comprehensive optimization method based on Pareto solution. The final scheme has been satisfactorily improved in terms of noise suppression, radar cross section reduction and aerodynamic lifting. The proposed approach is very effective and efficient for the acoustic/radar comprehensive stealth design of the ducted tail rotor.
This work presents a helicopter dynamic model that captures the fuselage vibrations for an accelerated main rotor. Some rotor parameters are modified with the purpose of study their impact on the rotorcraft. Being this, a tool that allows to predict vibrations on the helicopter. The rotorcraft model has been built up by using VehicleSim, software specialized in modelling mechanical systems composed by rigid bodies. The rotors are articulated, the main rotor takes into account flap, lag and feather degrees of freedom for each of the equispaced blades and their dynamic couplings. The dynamic performance and the control action are embedded in a single code, thereby VehicleSim does not require external connection to other software package. This generates some advantages such as to reduce the compilation time. The control methodology makes use of PID controllers (Proportional, Integral, Derivative), which allows to use VehicleSim commands exclusively. The state space matrices have been obtained in order to analysis the uncoupled main rotor flap and lag modes. The detection of vibrations from the offset flap hinge as well as the lag hinge are not straightforward tasks and this helicopter model provides an accurate tool to study these. A short time Fourier transform processing is used to analysis the vibrations and these have shown to agree with the expected behaviour.
