Helicopter Model Research Articles

Simulation of a Light Aircraft Encountering a Helicopter Wake

Different methods of modeling helicopter wakes are presented and compared with available wind-tunnel and flight-test data. A free-wake model was then used to generate the wake vortices of a helicopter hover-taxiing over an airport runway. A hybrid wake model, with a wake decay law, was also used to generate the far wake of a helicopter in level flight. The wake-induced velocity fields were integrated into an aircraft flight dynamics model, and piloted flight simulations were carried out to study a light aircraft encountering a helicopter wake during landing and level flight. It was found that, for the current landing wake-encounter scenario, the existing wake-encounter criteria and severity metrics for the determination of the hazardous distance might not be appropriate if the wake encounter occurs close to the ground. The landing simulation results suggest that, for a helicopter in low-speed hover-taxiing (less than 40 kt airspeed), the wake-encounter detectable horizontal distance is about three times the diameter of the rotor, which coincides with the current safety guidelines of the Civil Aviation Authority of the United Kingdom. The level-flight simulations revealed the effects of the vertical separation distance and of the wake decay on the encounter severity.

Nonlinear Control for a Model-scaled Helicopter with Constraints on Rotor Thrust and Fuselage Attitude

A nonlinear control is proposed for trajectory tracking of a 6-DOF model-scaled helicopter with constraints on main rotor thrust and fuselage attitude. In the procedure of control design, the mathematical model of helicopter is simplified into three subsystems: altitude subsystem, longitudinal-lateral subsystem and attitude subsystem. The proposed control is developed by combining the sub-controls for the corresponding subsystems. The sub-controls for altitude subsystem and longitudinal-lateral subsystem are designed with hyperbolic tangent functions to satisfy the constraints; the sub-control for attitude subsystem is based on backstepping technique such that fuselage attitude tracks the virtual control for longitudinal-lateral subsystem. It is proved theoretically that tracking errors are ultimately bounded, and control constraints are satisfied. Performances of the proposed controller are demonstrated by simulation results.

Experiment demonstration of micro-Doppler detection of rotor blades with passive coherent location based on digital video broadcast

We propose a realtime passive coherent location (PCL) system based on digital video broadcast (DVB) for the detection of the micro-Doppler (m-D) signature induced by the blades of a helicopter. In this paper, the detailed demonstration of the hardware system, signal processing and field experiment is presented. The m-D parameters of the model helicopter in the experiment are accurately estimated by means of cross ambiguity function (CAF). This paper contributes additional experimental m-D data and analysis, and the effectiveness of micro-motion detection by PCL system is well proved. The attractive merits of DVB based PCL make it more feasible to be widely deployed in urban environment for homeland security purpose. The present work is the first reported realtime system of DVB based PCL for the m-D detecting purpose.

Identification method for helicopter flight dynamics modeling with rotor degrees of freedom

A comprehensive method based on system identification theory for helicopter flight dynamics modeling with rotor degrees of freedom is developed. A fully parameterized rotor flapping equation for identification purpose is derived without using any theoretical model, so the confidence of the identified model is increased, and then the 6 degrees of freedom rigid body model is extended to 9 degrees of freedom high-order model. Bode sensitivity function is derived to increase the accuracy of frequency spectra calculation which influences the accuracy of model parameter identification. Then a frequency domain identification algorithm is established. Acceleration technique is developed furthermore to increase calculation efficiency, and the total identification time is reduced by more than 50% using this technique. A comprehensive two-step method is established for helicopter high-order flight dynamics model identification which increases the numerical stability of model identification compared with single step algorithm. Application of the developed method to identify the flight dynamics model of BO 105 helicopter based on flight test data is implemented. A comparative study between the high-order model and rigid body model is performed at last. The results show that the developed method can be used for helicopter high-order flight dynamics model identification with high accuracy as well as efficiency, and the advantage of identified high-order model is very obvious compared with low-order model.

Decentralized fuzzy-integral-sliding control for a class of TITO uncertain nonlinear systems with application to a 2-DOF helicopter model

In this paper, a novel fuzzy-integral-sliding controller (FISC) is designed for coupled nonlinear two-input two-output (TITO) systems. Decomposing the original system into two subsystems, the coupling effects are modelled as uncertainties. In order to ensure the robustness properties with respect to system uncertainties and external disturbances, the sliding mode technique with a proportional integral (PI) sliding surface is adopted. On the other hand, to avoid the chattering phenomenon, the Takagi-Sugeno fuzzy rules are incorporated into the control algorithm, which forms a fuzzy sliding controller. The stability analysis is also presented based on the Lyapunov stability theorem. The proposed FISC is then applied to control the elevation and azimuth angles of Humusoft CE150, as a two degree of freedom (DOF) laboratory helicopter model with highly cross-coupled dynamics. The simulation results are also presented to demonstrate the performance of the proposed control scheme.

System Identification Modeling and Flight Characteristics Analysis of Miniature Coaxial Helicopter

This paper describes the identification modeling and analysis of a miniature coaxial helicopter. The first part of the paper focuses on the development of the parameterized model with an emphasis on the coaxial rotor configuration. The model explicitly accounts for the dynamics of the lower rotor and uses an implicit lumped parameter model for the upper rotor and stabilizer bar. The parameterized model was identified using frequency domain system identification. The flight data collection experiments were performed in an indoor flight-test facility built around a commercial vision-based tracking system. The second part of the paper focuses on the verification of the model's accuracy, the consistency of the identified parameters, and the analysis of the flight dynamics. The accuracy was verified by comparing model-predicted responses with flight experimental responses. The identified parameters and model's physical consistency were examined using experiments in which specific aspects of the dynamics were isolated. For example, we used video images from a high-speed camera to verify the rotor and stabilizer bar time constants. Finally, the identified derivatives were verified based on first principles to demonstrate that the derivatives are physically meaningful.

Dynamic Stability of a Helicopter with an External Suspended Load

A simplified but comprehensive model for helicopter and external suspended load, based on the linear superposition of effects, is defined. The coherence of the external load modal response and of the helicopter response to control input is verified through available reference data. Finally, the impact of the slung load on the overall system dynamic stability, on the helicopter response to control input, and on flight qualities is assessed.

Experimental investigation on the aerodynamic interaction between a helicopter and ground obstacles

In this study, experiments were performed to investigate the aerodynamic interaction between a helicopter and ground obstacles. A new experimental set-up was realised and validated. The motorised helicopter model, which included the fuselage, was positioned in different positions relative to a model building in order to replicate different hovering configurations. The use of a helicopter model with a six-component balance and a building model with several pressure taps allowed a database to be compiled for the loads on the helicopter and obstacle. First several tests were performed without the building in order to develop a reference database and assess the experimental set-up through a comparison with results in the literature. The measured loads were analysed to investigate the interference effects of the building model on the helicopter performance. A physical interpretation of the flow phenomena was obtained through analysis of the obstacle pressure measurements and particle image velocimetry surveys of relevant configurations.

Novel adaptive bacterial foraging algorithms for global optimisation with application to modelling of a TRS

In this paper, adaptive bacterial foraging algorithms and their application to solve real world problems is presented. The constant step size in the original bacterial foraging algorithm causes oscillation in the convergence graph where bacteria are not able to reach the optimum location with large step size, hence reducing the accuracy of the final solution. On the contrary, if a small step size is used, an optimal solution may be achieved, but at a very slow pace, thus affecting the speed of convergence. As an alternative, adaptive schemes of chemotactic step size based on individual bacterium fitness value, index of iteration and index of chemotaxis are introduced to overcome such problems. The proposed strategy enables bacteria to move with a large step size at the early stage of the search operation or during the exploration phase. At a later stage of the search operation and exploitation stage where the bacteria move towards an optimum point, the bacteria step size is kept reducing until they reach their full life cycle. The performances of the proposed algorithms are tested with various dimensions, fitness landscapes and complexities of several standard benchmark functions and they are statistically evaluated and compared with the original algorithm. Moreover, based on the statistical result, non-parametric Friedman and Wilcoxon signed rank tests and parametric t-test are performed to check the significant difference in the performance of the algorithms. The algorithms are further employed to predict a neural network dynamic model of a laboratory-scale helicopter in the hovering mode. The results show that the proposed algorithms outperform the predecessor algorithm in terms of fitness accuracy and convergence speed.

Set-Membership Identification Method for Helicopter Flight Dynamics Modeling

A new method based on the theory of set-membership estimation for time-domain identification of helicopter flight dynamics model has been developed. The parameters in most helicopter flight dynamics models are generally coupled, and it is difficult to obtain an explicit-function relationship between an identification model and the parameters to be identified. An indirect-identification algorithm should be established. The concept of generalized noise is introduced to solve the problems using the set-membership-identification method to construct a helicopter flight dynamics model. The identification of a six-degree-of-freedom linear flight dynamics model of the BO-105 helicopter in hover condition based on the new method is implemented. A comparative study of the new method with the maximum-likelihood method is also performed. The obtained results show that the new method increases the identification accuracy, efficiency, and robustness to noise by comparison with a conventional statistic-based identification method.

Comprehensive kinematic modeling and analysis of a coaxial helicopter’s swashplate mechanism

A comprehensive mathematical model of a coaxial helicopter’s swashplate mechanism is established, analyzed and verified in this paper. The mechanism widely used in helicopters to manipulate blade pitch angles is complex because of its configuration of multi closed-loop kinematic chains, especially for coaxial layout. First, geometrical method is used in determining the direct and inverse position kinematics. Based on that model, an approach of differentiation on spatial vectors is adopted to induce the relative velocity and acceleration matrices of every part of the system. The influence of rotors’ rotation is also considered in the modeling of velocity and acceleration kinematics to obtain a comprehensive model. The workspace and dexterity characteristics are analyzed in detail under the constraint of actuators’ inputs. After that, the complete direct kinematic model is simulated with consideration of control allocation and actuator dynamics. Finally, an integrated verification approach is designed based on experimental and simulative method to validate the established model. The work is concluded with an application prospect in future.

Modeling and Simulation of the Helicopter Control System Based on the Flight Qualities

Helicopter is a strong coupling and instability nonlinear system, of which the inherent flight qualities are poor. Helicopter model following control technology can make four control channels of helicopter with excellent tracking and decoupling characteristics. This paper applied the control method of model following control combining eigenststructure assignment to the helicopter control system. The results of simulation show that the helicopter flight qualities meet the requirements of ADS-33, the helicopter has excellent tracking and decoupling characteristics. Thus it proves that this control method is of great effectiveness.

Unmanned coaxial rotor helicopter dynamics and system parameter estimation

A numerical model that estimates the parameters of a small, unmanned coaxial rotor helicopter with a takeoff mass of 11.9 kg was developed. The modeled coaxial rotor helicopter did not have any additional damping to its dynamics such as a stabilizer bar or external gyro, which are common in commercial hobby helicopter models. Therefore, any sinusoidal actuator input from manual flight led to a large deviation of attitude rates, resulting in uncontrollable situations. A feedback attitude controller was included during test flights and parameter estimation to address this problem. Time domain experimental data were used to help estimate and validate the parameters of the helicopter. Attitude responses predicted by the model show extremely small discrepancies with experimental data. Therefore, the developed numerical model can be used for coaxial rotor helicopter controller design and other simulation purposes.

Hybrid DE-PEM algorithm for identification of UAV helicopter

Purpose – The purpose of this paper is to develop a hybrid algorithm using differential evolution (DE) and prediction error modeling (PEM) for identification of small-scale autonomous helicopter state-space model. Design/methodology/approach – In this study, flight data were collected and analyzed; MATLAB-based system identification algorithm was developed using DE and PEM; parameterized state-space model parameters were estimated using the developed algorithm and model dynamic analysis. Findings – The proposed hybrid algorithm improves the performance of the PEM algorithm in the identification of an autonomous helicopter model. It gives better results when compared with conventional PEM algorithm inside MATLAB toolboxes. Research limitations/implications – This study is applicable to only linearized state-space model. Practical implications – The identification algorithm is expected to facilitate the required model development for model-based control design for autonomous helicopter development. Original...

Tyre model development using co-simulation technique for helicopter ground operation

This paper describes the development of a new aircraft tyre model applied using a co-simulation approach for the multibody dynamic simulation of helicopter ground vehicle dynamics. The new tyre model is presented using a point follower approach that makes a novel contribution to this area by uniquely combining elements of two existing tyre models used by the aircraft industry, namely the NASA R64 model developed by Smiley and Horne and the Engineering Sciences Data Unit (ESDU) Mitchell tyre model. Before the tyre model was used with a full helicopter model, a virtual tyre test rig was used to examine the tyre and to predict the tyre forces and moments for a range of tyre states. The paper concludes by describing the successful application of the new tyre model with a full helicopter model and the simulation of representative landing, take-off and runway taxiing manoeuvres. The predictive capability of the model is demonstrated to show the open-loop ground vehicle dynamics response of the helicopter and also the ground load predictive capability for the distribution of loads through the tyres, wheels and landing gears.

An Effective System Identification Method of Small-Scale Unmanned Helicopter

In order to control an unmanned helicopter accurately and reliably, it is necessary to have a precise mathematical model of its dynamics. This paper presents a new timedomain identification method and process for full state space model of small-scale unmanned helicopters. The identification method is called ISAcwPEM (Improved Simulated Annealing combined with Prediction Error Method), which is not sensitive to initial point selection and doesn’t require frequency-sweeping inputs. Firstly, the primary parameters to be identified are selected by model sensitivity analysis. After that, the improved simulated annealing algorithm runs in a distributed computing platform to figure out a 13-order state space model of the SJTU T-REX700E small-scale unmanned helicopter (consisting of a cruise modal and a hover modal). Then the iterative Prediction Error Method (PEM) is used to optimize the model. In addition, the time-delay term and the trim term are estimated and added to the model. Finally, the effectiveness of the identification method is well validated by real outdoor flight experimental results.

Estimates of hover aerodynamics performance of rotor model

Hover computations were undertaken for a helicopter model rotor using Computational Fluid Dynamics (CFD). The influence of CFD mesh construction peculiarities and mesh parameters on the results was considered. Aerodynamics performance of the rotor were obtained including the rotor polar, loads per unit length, and vortical flow below the rotor disk was also visualized.

UAV path planning using artificial potential field method updated by optimal control theory

The unmanned aerial vehicle (UAV) path planning problem is an important assignment in the UAV mission planning. Based on the artificial potential field (APF) UAV path planning method, it is reconstructed into the constrained optimisation problem by introducing an additional control force. The constrained optimisation problem is translated into the unconstrained optimisation problem with the help of slack variables in this paper. The functional optimisation method is applied to reform this problem into an optimal control problem. The whole transformation process is deduced in detail, based on a discrete UAV dynamic model. Then, the path planning problem is solved with the help of the optimal control method. The path following process based on the six degrees of freedom simulation model of the quadrotor helicopters is introduced to verify the practicability of this method. Finally, the simulation results show that the improved method is more effective in planning path. In the planning space, the length of the calculated path is shorter and smoother than that using traditional APF method. In addition, the improved method can solve the dead point problem effectively.

Calculation of One-dimensional Forward Modelling of Helicopter- borne Electromagnetic Data and a Sensitivity Matrix Using Fast Hankel Transforms

The helicopter-borne electromagnetic (HEM) frequency-domain exploration method is an airborne electromagnetic (AEM) technique that is widely used for vast and rough areas for resistivity imaging. The vast amount of digitized data flowing from the HEM method requires an efficient and accurate inversion algorithm. Generally, the inverse modelling of HEM data in the first step requires a precise and efficient technique provided by a forward modelling algorithm. The exact calculation of the sensitivity matrix or Jacobian is also of the utmost importance. As such, the main objective of this study is to design an efficient algorithm for the forward modelling of HEM frequency-domain data for the configuration of horizontal coplanar (HCP) coils using fast Hankel transforms (FHTs). An attempt is also made to use an analytical approach to derive the required equations for the Jacobian matrix. To achieve these goals, an elaborated algorithm for the simultaneous calculation of the forward computation and sensitivity matrix is provided. Finally, using two synthetic models, the accuracy of the calculations of the proposed algorithm is verified. A comparison indicates that the obtained results of forward modelling are highly consistent with those reported in Simon et al. (2009) for a four-layer model. Furthermore, the comparison of the results for the sensitivity matrix for a two-layer model with those obtained from software is being used by the BGR Centre in Germany, showing that the proposed algorithm enjoys a high degree of accuracy in calculating this matrix.

Nonlinear identification of a small scale unmanned helicopter using optimized NARX network with multiobjective differential evolution

The need for a high fidelity model for design, analysis and implementation of an unmanned helicopter system (UHS) in various emerging civil applications cannot be underestimated. However, going by a first principle approach based on physical laws governing the dynamics of the system, this task is noted to be highly challenging due to the complex nonlinear characteristics of the helicopter system. On the other hand, the problem of determining network architecture for optimal/sub-optimal performances has been one of the major challenges in the use of the nonparametric approach based on Nonlinear AutoRegressive with eXogenous inputs Network (NARX-network). The performance of the NARX network in terms of complexity and accuracy is largely dependent on the network architecture. The current approach in the literature has been largely based on trial and error, while most of the reported optimization approaches have limited the domain of the problem to a single objective problem. This study proposes a hybrid of conventional back propagation training algorithm for the NARX network and multiobjective differential evolution (MODE) algorithm for identification of a nonlinear model of an unmanned small scale helicopter from experimental flight data. The proposed hybrid algorithm was able to produce models with Pareto-optimal compromise between the design objectives. The performance of the proposed optimized model is benchmarked with one of the previously reported architectures for a similar system. The optimized model outperformed the previous model architecture with up to 55% performance improvement. Apart from the effectiveness of the optimized model, the proposed design algorithm is expected to facilitate timely development of the nonparametric model of the helicopter system.