Helicopter Model Research Articles

Ejector-type heat exchangers in the air conditioning in transport

In the modern world, the air conditioning systems have become the most widespread application and have become an everyday part of everyday life. However, due to the complexity of the construction during the designing of the air conditioning systems and the development of modern technologies, there are still many system’s assemblies that can be upgraded and improved. Along with such parameters as ergonomics and weight and size characteristics, a significant role is played by such parameters of the operation of the air conditioning systems as efficiency, reliability, resource. These parameters are particularly relevant in the context of miniaturization and work on a closed cycle in mobile transport vehicles (automotive, aircraft and ship equipment), since efficiency, mass and resource exert a determinative influence on the total cost of vehicles and the costs of its maintenance and operation. The main parameters that regulate the air conditioning systems are the temperature, flow rate and humidity of the supplied air. The article studies and compares the methods of primary cooling of hot air supplied to the helicopter's air conditioning systems, when the cabin is heated at low temperatures. Often this is done using air-to-air heat exchangers. In the materials of the article, it is proposed to consider the option of replacing one of such heat exchanger with an ejector-type heat exchanger, a description and comparison of the existing and proposed options for the modernization of the air conditioning system’s schemes, and estimate the acceptability of their implementation on the helicopter. Also, a comparative work was conducted to estimate the advantages and disadvantages of such a replacement. The primary estimated calculations of the change in the system’s parameters were implemented in the case of introduction of a replacement in all conventional load modes of a typical helicopter model. Specific features of the application of this replacement are given and additional innovations which are necessary for its implementation are pointed out. For calculations, the software complex ANSYS CFX, MathCAD, Solid Edge ST8 was used. In the course of the work, a construction and a method were revealed that provided the optimal parameters and method of implementation for the introduction of the ejector into the composition of the air conditioning system.

Event-driven PID control of autonomous quadrotor helicopters

This paper proposes an event-driven PID control mechanism for autonomous quadrotor helicopters that will reduce the usage of communication channels. Compared to traditional PID controller, the event-driven PID controller can maintain the satisfactory stabilization effect with the ability of reducing the number of transmissions significantly. The simplified dynamics model of quadrotor helicopter is also established. Finally, the improvements realized by the developed method are verified in the computer simulations.

Trajectory control of aggressive maneuver by agile autonomous helicopter

In this paper, a new state-dependent coefficient parameterization of an agile helicopter dynamics is derived to deal effectively with the optimal trajectory control of aggressive maneuver such as the infinity maneuver with agility. The angular velocity of the main rotor and engine throttle as state and input, respectively, are involved in the dynamic model to improve the maneuvering capability of helicopter. Since the presented six degrees-of-freedom helicopter model is highly nonlinear and nonaffine, particularly nonlinear in actuator, the state-dependent Riccati equation is implemented in the presence of saturation bounds for actuators to achieve precision trajectory control and conquer the challenge of aggressive maneuver tracking control. In addition, new helicopter dynamic representation results in the conventional state-dependent Riccati equation to be applied without prevalent simplifications within dynamic and actuators and also certain augmentations on controllers such as trim or feedforward compensators. Indeed, the proposed controller structure is verified by simulations for both regulation and trajectory tracking problem.

Reinforcement Q-learning based on Multirate Generalized Policy Iteration and Its Application to a 2-DOF Helicopter

In this paper, we propose a novel Q-learning method based on multirate generalized policy iteration (MGPI) for unknown discrete-time (DT) linear quadratic regulation (LQR) problems. Q-learning is an effective scheme for unknown dynamical systems because it does not require any knowledge of the system dynamics to solve optimal control problems. By applying the MGPI concept, which is an extension of basic GPI with multirate time horizon steps, a new Q-learning algorithm is proposed for solving the LQR problem. Further, it is proven that the proposed algorithm converges to an optimal solution i.e., it learns the optimal control policy iteratively using the states and the control-input information. Finally, we employ the two degree-of-freedom helicopter model to verify the effectiveness of the proposed method and investigate its convergence properties.

Accuracy–simplicity trade-off for small-scale helicopter models: A comparative study based on flight data

A good model is a trade-off between simplicity of the model structure and accuracy of the prediction. Higher accuracy is generally expected from more complex models, but at the cost of higher computational burden, more complex handling and potential identifiability issues. Depending on the targeted use, assumptions and simplifications are made to find the simplest model still capturing the important phenomena. These choices are not straightforward and, to this end, the paper gives a comparison of miniature helicopter models often found in the literature. The contribution of the paper is thus twofold. A time-domain identification procedure for parametric models of miniature helicopters is first described and applied to four different models with increasing complexity. The procedure is based on flight data obtained during a manual slow-speed flight. Secondly, the accuracies of these models are evaluated and compared, which highlights the main differences and improvements brought by the differences in the aerodynamic model equations and allows the selection of a relevant model structure depending on the target application.

Doppler spectrum analysis of helicopter for an active seeker head

The pulsed Doppler of a helicopter as the angle between a seeker line of sight (LOS) and the plane of rotor varied is explored. A special emphasis is placed to determine the variation of the Doppler strength and frequency from the main rotor blades. This paper also reviews some literatures related to helicopter detection. An experiment consisting a model helicopter, radar and some measuring equipment is described. The result shows that the strength of the Doppler signal increases as the angle increases. On the other hand, the Doppler frequency from the rotating blades reduces as the angle increases. The analysis of the results indicates that MMW radar is very suitable to be used as an active seeker head especially if the missile is used to attack a hovering helicopter.

Neural network disturbance observer-based distributed finite-time formation tracking control for multiple unmanned helicopters

The distributed finite-time formation tracking control problem for multiple unmanned helicopters is investigated in this paper. The control object is to maintain the positions of follower helicopters in formation with external interferences. The helicopter model is divided into a second order outer-loop subsystem and a second order inner-loop subsystem based on multiple-time scale features. Using radial basis function neural network (RBFNN) technique, we first propose a novel finite-time multivariable neural network disturbance observer (FMNNDO) to estimate the external disturbance and model uncertainty, where the neural network (NN) approximation errors can be dynamically compensated by adaptive law. Next, based on FMNNDO, a distributed finite-time formation tracking controller and a finite-time attitude tracking controller are designed using the nonsingular fast terminal sliding mode (NFTSM) method. In order to estimate the second derivative of the virtual desired attitude signal, a novel finite-time sliding mode integral filter is designed. Finally, Lyapunov analysis and multiple-time scale principle ensure the realization of control goal in finite-time. The effectiveness of the proposed FMNNDO and controllers are then verified by numerical simulations.

Prediction of Aerial Spray Release from UAVs

Abstract. This article summarizes the ability of CHARM+AGDISP to predict the drift and deposition of sprays released from rotary wing unmanned aerial vehicles (UAVs). This predictive capability results from merging algorithms for spray transport, as found in AGDISP (AGricultural DISPersal), with CHARM (Comprehensive Hierarchical Aeromechanics Rotorcraft Model). The resulting software tracks the release of spray droplets from nozzles on the UAV to deposition on the ground. To date, both AGDISP and CHARM, a code that provides a complete representation of the time-varying, unsteady flow field surrounding a helicopter during transient maneuvering flight near the ground, have been extensively validated. The CHARM+AGDISP software is applied to two UAVs to explore the flow field regimes that present challenges for effective UAV operations. The simulations undertaken indicate flight conditions that yield acceptable deposition levels and minimize drift; inversely, conditions are also identified that result in off-target drift that may be problematic. Keywords: Aerial application, AGDISP, CHARM, Helicopter modeling, Unmanned aerial vehicle (UAV).

Controller Development for a Rotary UAV using Physics Based Non-Linear Helicopter Model

Unmanned aerial vehicles are rapidly changing the rules of modern day war. Unmanned helicopters are a recent entity in this league and have a promising future in military as well as in civil applications. However, due to various non-linear phenomenon and effects, the helicopter dynamics are well known to be complex to model mathematically and hence controlling rotary air vehicle is far more challenging than fixed wing platforms. Under the present work, a physics based model of a mini helicopter has been developed and used to design the controller. This paper presents the modelling aspects for the candidate vehicle, preliminary validation using experimental RC flying, overview of controller design based on chosen specifications and few typical results of simulations including the waypoint navigation.

Experimental study of a helicopter rotor model in hover

This paper presents the results from an experimental study of the aerodynamic performance and efficiency of a model helicopter rotor in steady hover at Reynolds numbers below 70000. Results are shown for a two-, three- and four-bladed rotor configuration for various pitch angles and speeds of rotation. The influence of the rotor solidity on the aerodynamic efficiency in terms of the Figure of Merit is highlighted. The profile drag component is evaluated as a function of the Reynolds number. The internal friction losses of the test stand are estimated and taken into account in all measurements. A brief description of the designed test stand is provided. The experimental setup allows for the measurement of thrust and torque of helicopter rotors with diameters of up to 1 meter, for pitch angles varying from -12° to +24° and for rotational speeds of up to 3000 RPM. Conclusions are drawn about the aerodynamic performance and efficiency of the studied rotor configurations. This experimental study provided a significant database, which will serve for validation purposes.

Speed control and force-vectoring of bluebottle flies in a magnetically levitated flight mill.

Flies fly at a broad range of speeds and produce sophisticated aerial maneuvers with precisely controlled wing movements. Remarkably, only subtle changes in wing motion are used by flies to produce aerial maneuvers, resulting in little directional tilt of the aerodynamic force vector relative to the body. Therefore, it is often considered that flies fly according to a helicopter model and control speed mainly via force vectoring by body pitch change. Here, we examined the speed control of bluebottle flies using a magnetically levitated (MAGLEV) flight mill, as they fly at different body pitch angles and with different augmented aerodynamic damping. We identified wing kinematic contributors to the changes of estimated aerodynamic force through testing and comparing two force-vectoring models - a constant force-vectoring model and a variable force-vectoring model - while using Akaike's information criterion for selection of the best-approximating model. The results show that the best-approximating variable force-vectoring model, which includes the effects of wing kinematic changes, yields a considerably more accurate prediction of flight speed, particularly in higher velocity range, as compared with those of the constant force-vectoring model. Examination of the variable force-vectoring model reveals that, in the flight mill tethered flight, flies use a collection of wing kinematic variables to control primarily the force magnitude, while the force direction is also modulated, albeit to a smaller extent compared with those due to the changes in body pitch. The roles of these wing kinematic variables are analogous to those of throttle, and collective and cyclic pitch of helicopters.

Artificial bee colony optimised controller for small-scale unmanned helicopter

ABSTRACTIn this paper, an efficient approach to design and optimize a flight controller of a small-scale unmanned helicopter is proposed. Given the identified helicopter model, the Linear Quadratic Gaussian/Loop Transfer Recovery (LQG/LTR) robust control method is applied for trajectory tracking and attitude control of the helicopter with a two-loop hierarchical control architecture. Since the performance of the controller extremely depends on its weighting matrices, the Artificial Bee Colony (ABC) algorithm is introduced to automatically select the parameters of the matrices. Comparative studies between optimal algorithms are also carried out. A series of flight experiments and simulations are conducted to investigate the effectiveness and robustness of the proposed optimised controller.

Development of Approximate Prediction Model for 3-DOF Helicopter and Benchmarking with Existing Controllers

<p>Recent trend of living is getting modernized rapidly by the involvement of automatic systems. Within the aviation industry, automatic systems had become heavily reliable by the end of the nineteen centuries. The systems usually require controllable devices with desired control algorithm known as controller. Controllers can be replaced with, almost every mechanical automation aspect where, safety is a serious issue. But it is not easy to adapt a controller with a specific model at the beginning. It is important to predict the model before a controller works on the model and the controller parameters need to be adapted to get maximum efficiency. A 3-DOF (Three Degrees of Freedom) airframe model is an advanced benchmark model of real 3-DOF helicopter. It has the same uncommon model dynamics with nonlinearities, strong duel motor cross coupling system, uncertain characteristics, disturbances dependent, unmodeled dynamics and many more. The 3-DOF airframe model is a well-known platform for controller performance benchmarking. This research paper shows the development of an approximate prediction model of a Three Degrees of Freedom helicopter model and uses the proposed approximate model to observe the performance of an existent hybrid controller. The hybrid controller is the combination of two different controllers named Quantitative Feedback Theory (QFT) controller and Adaptive controller. To achieve the research objective, the proposed mathematical model of this airframe was used to develop transfer function and simulate with the hybrid controller in MATLAB. The performance of the controller based on the proposed heliframe model of 3-DOF helicopter have also been reported added within this paper.</p>

Flapwise Vibration Computations of Coupled Helicopter Rotor/Fuselage: Application of Multibody System Dynamics

Natural vibration characteristics of rotating blades are of fundamental importance from the viewpoint of maneuvering, blade life, vibration levels, aeroelastic, and stability. Helicopters may have serious resonant vibration problems when the excitation frequencies are equal to some multiple of the rotational speed. To ensure that conditions susceptible to resonance do not exist within the range of operating speeds, it is necessary that the natural frequencies and mode shapes be determined accurately. On one hand, as the complexity of multibody systems and the methods used for their design and control increases, the need for more elegant formulations of the equations of motion becomes an issue of paramount importance. On the other hand, although processor speed has increased dramatically over the last decade, development of computationally efficient algorithms is still a major issue in multibody dynamics. The transfer matrix method for multibody systems (MSTMM) accounts for both aspects. Based on many advantages of MSTMM in studying multibody system dynamics, a scenario of dynamics coupling between the flexible twin blade rotor and flexible fuselage of a typical helicopter model is proposed. The dynamical model of the coupled system, its topological figure, the overall transfer equation, and the characteristics equation are developed. The flapwise vibrations characteristics are carried out to obtain uncoupled/coupled twin blade/fuselage system natural modes and frequencies as a function of rotor speed. Examples are performed to validate with those published in the literature and produced by Workbench ANSYS.

Stochastic Control of the External Sling of a Fire Helicopter

The paper describes the motion modeling of a fire helicopter with an external sling and a spillway device. The mathematical model of the fire helicopter with an external sling takes into account the effect of the stochastic disturbances for the sling caused by the rotor vibrations, gusts of wind and convection flows in the fire zone. The stochastic optimal control is synthesized with minimal sling oscillations and control power for its implementation. The solution is obtained due to dynamic programming. The resulting optimal control does not depend on the mass of a spillway device, but it is a function of a sling length. Thus, because of the changing sling length during motion, the length should be measured together with the sling deviation angle and the intensity of the stochastic disturbances. The temporal evolution of the system solution is done for various disturbance intensities. The computer calculation results are presented as a function of the suspension length and the intensity of the stochastic disturbances. Analysis of the results shows that the sling length affects significantly the value of the control signal, especially at high levels of the disturbances. A structure of the helicopter stochastic control system is proposed. It makes it possible to control oscillation of the external sling within an acceptable range. The system includes an oscillation angle, a sensor of the stochastic disturbance intensity and the sling length sensor. Thus, the helicopter control can be obtained through changing the thrust magnitude of the main and tail helicopter rotors.

Helicopter modelling and study of the accelerated 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.

Lightning Indirect Effects on Helicopter: Numerical Simulation and Experiment Validation

When lightning strikes an aircraft, the electromagnetic (EM) field penetrates inside the aircraft, and induces currents and voltages on the onboard cables, resulting in the risk of equipment failure, which is a serious safety hazard to the flight safety. With the wide use of low-conductivity composite materials in aircraft manufacturing, the EM shielding effectiveness of the aircraft is weakened. As for the helicopter, the proportion of windows and doors is relatively larger than the fixed-wing aircraft, thus the EM shielding effectiveness is much weaker. Proper lightning protection design must be validated to eliminate the risk of electrical and electronic equipment failure. This paper describes the lightning indirect effects related to the modeling and simulation process of the composite UH-60 helicopter. The external and internal EM field environment together with the induced currents and voltages on cables are discussed. Moreover, in order to validate the simulation, an iron helicopter model was tested and the comparison between simulated and measured waveforms was carried out.

On the observer matching condition and unknown input observer design based on the system left-invertibility concept

This paper considers the problems of unknown input observer (UIO) designs when the so-called observer matching condition (OMC) is not satisfied. Firstly, the system left-invertibility (SLI) concept is investigated in detail and some new criteria are given. Secondly, based on the SLI concept, an augmented output vector formed partly by the original measurable output and partly by the auxiliary output is obtained. By this constructed output vector, the new system is allowed to be transformed into an equivalent linear dynamic system which contains no unknown input, and thus a simple Luenberger observer can be constructed to simultaneously estimate the original states and unknown inputs. Compared with the existing results, the present UIO design can be taken under the single strong detectability condition and the OMC is not needed any more. Finally, the simulations of a single-link flexible joint robotic model and a linearized vertical take-off and landing helicopter model are given to show the effectiveness of our method and its superiority over existing ones.

Thermal characteristics of helicopters based on integrated fuselage structure/engine model

Although the temperature distributions and infrared characteristics on the helicopter fuselage and in the exhaust plume have been great investigated in previous literatures, most of them are only in hover condition. In order to extend these models to any flight condition, a new integrated methodology is proposed considering the construction coupling and energy transfer relation of the helicopter. In this integrated methodology, we put forward a helicopter model to estimate the flight performance, including required power and attitude of the rotor, and a component-based model of the engine to evaluate the working performance of engines and exhaust plume parameters under various symmetrical steady level flight conditions. After this analysis of coupled working performance, the characteristics of flow and temperature fields are investigated through computational fluid dynamics. Subsequently, infrared radiation characteristics of helicopters are analyzed by a ray tracing method. This work can provide useful information for the energy management design and infrared radiation suppression of helicopters.

Nonlinear Modeling of Miniature Helicopters - A Comparative Study Based on Flight Data

Mathematical models of a flight vehicle can take various forms. Physics-based phenomenological models are often preferred for aircrafts, because their parameters usually have a physical meaning, the underlying physics and aerodynamic effects are well-known, and, as the resulting structure is linked to physical phenomena, they generally offer large validity domain. During the modeling process, a trade-off has to be made between high accuracy and identifiability. This paper presents a methodology for selecting a model of adequate complexity for miniature helicopters. To this end, three models with increasing complexity, typically used for such systems, are considered. The parameters of the models are estimated from flight datasets and the models are compared in terms of accuracy and complexity, thus highlighting the relevant physical effects. The fidelity of the models on both rotational and translational dynamics is evaluated. The contribution of the paper is thus twofold: an identification procedure for a nonlinear parametric model of a miniature helicopter is first described and applied on the three aforementioned models (flight data collection and preprocessing, structural analysis, estimation technique). Secondly, prediction capability of these models is evaluated using flight data and compared, which allows the selection of a relevant model structure depending on the target application.