Main Rotor Research Articles

Active Surge Control for Magnetically Suspended Centrifugal Compressors Using a Variable Equilibrium Point Approach

Surge is one of the main rotor dynamic instabilities limiting the operation of centrifugal compressors. This paper proposes an active surge control scheme for magnetically suspended centrifugal compressors using a variable equilibrium point approach. Multiple uncertainties caused by magnetic air gap adjustment are considered for the active magnetic bearing (AMB) control systems. By using the combination of an analytical model and a finite-element method, the perturbation of bearing force parameters, including the force-current factor and the force-displacement factor, is analyzed. The model uncertainties caused by the perturbation of the power amplifier parameters are identified through the online frequency sweep excitation. Based on the uncertainty analysis of the AMB control system, a μ-synthesis-based controller is designed for the axial magnetic bearing system to suppress the vibration caused by surge. The experiments demonstrate that the proposed method can suppress surge and improve the reliability of the system by using automatic magnetic air gap adjustment of the AMB-rotor system.

Designing and FEM simulation of the helicopter rotor and hub

The paper presents a preliminary design of the three-blade rotor. The geometric model was prepared in the Siemens NX 12.0 programme. After the preparation of the model and kinematic analysis, the structure was checked for strength by means of NX Nastran software. In addition, structural solutions of bearing rotors currently used in the construction of helicopters were discussed and a comparative analysis of the developed rotor design with other rotors was carried out in order to define the basic advantages and disadvantages of each solution. The main rotor of a helicopter is considered the most important component of the rotorcraft, which determines its performance. Rotating blades generate the resultant forces and moments in the rotor hub that allow the helicopter to fly. In the case of a single-rotor helicopter design, a tail rotor must be added to obtain directional control. Cyclic and collective control of blade inclination influences the generation of aerodynamic and inertial loads, which depend on the azimuthal position of the blade on the rotor disc. The number of rotor blades and the properties of the blade-hub connections strongly influence the level of load transfer from the blades through the hub to the helicopter fuselage. By incorporating a set of hinges, it is possible to reduce the component loads of the rotor, tilt and rolling moments transferred to the hull. A conventional articulated rotor head with built-in hinges requires frequent maintenance, which increases helicopter operating costs. Furthermore, a complex structure with a large number of components increases the weight of the articulated rotor.

Processing of videos of the fatigue cracks propagation in the rotor blades of the helicopter

The article describes the processing of videos of growing fatigue cracks in the main rotor blades of a helicopter, which are formed during their fatigue tests on the stand. A specially created computer program allows to determine the geometrical parameters of a crack based on video recording (length, width, extreme points, center of gravity). Each frame of the video is binarized, after which a binary matrix is created on its basis, which is subject to element-by-element processing. The obtained data are presented in the form of a graph showing the dependence of the crack growth rate on the time of its growth. The graph is traced in the Mathcad program, as a result, two data vectors are created — the time and crack growth rate, which undergo an interpolation procedure with the construction of a third-degree polynomial. According to the results of the integration of the polynomial, the critical length of the crack is determined, after reaching which its rapid growth begins.

Design and performance comparison of different adaptive control schemes for pitch angle control in a twin – rotor – MIMO – system

The Twin Rotor MIMO System is a higher order non-linear plant and is inherently unstable due to cross coupling between tail and main rotor. In this paper only the control of main rotor is considered which is non-linear and stable by using adaptive schemes. The control problem is to achieve perfect tracking for input reference signals while maintaining robustness and stability. Four adaptive schemes were implemented, two using Model Reference Adaptive Control under which MIT rule and Modified MIT rule are used. The other two using Adaptive Interaction, namely, Adaptive PID and Approximate Adaptive PID. It is observed that adaptive schemes fulfill all the three system performance requirements at the same time. Modified MIT rule was found to give superior performance in comparison to other controllers. Also Approximate Adaptive PID was able to stabilize the main rotor and cancel the effect of cross coupling between tail rotor and main rotor when operating simultaneously without the need for designing decouplers for the system. Thus the main rotor can be made independent from the state of the tail rotor by using Approximate Adaptive PID.

Distributed Turbulence Model with Rigorous Spatial Cross-Correlation for Simulation of Helicopter Flight in Atmospheric Turbulence

This paper presents a distributed turbulence model with rigorous spatial cross-correlation for helicopter flight simulation in atmospheric turbulence and for future handling-quality analysis. First, digital filters with longitudinal correlations of the von Kármán turbulence are developed to generate discrete turbulence velocity components. Meanwhile, transverse turbulence correlations are considered by relating the filters in different positions with mathematically rigorous spatial cross-correlation. Then, the distributions of the related filters on the transverse plane in front of helicopter and their velocity components in the longitudinal direction of airspeed, as well as turbulence models of helicopter aerodynamic surfaces, are established. Finally, a flight dynamics model coupled with the turbulence model is developed and validated against the flight-test data. The proposed model can achieve accurate real-time simulations of helicopter response to atmospheric turbulence in the frequency range of interest of handling qualities. The effect of transverse turbulence correlations on helicopter frequency response is also analyzed. The results show that the simulation model regardless of transverse turbulence correlations would aggravate the "rotor-to-body attenuation" effect of the main rotor and therefore underpredict the helicopter roll, pitch, and heave rate responses to atmospheric turbulence in the frequency range of interest.

The effect of inner blade position on the performance of the Savonius rotor

In this study, the effect of the inner blade position on the performance of the Savonius rotor has been investigated numerically to determine the best position of the inner blade. Five values of inner blade angles are adopted (180°, 160°, 140°, 120°, and 100°). Two-dimensional simulation is performed for the conventional rotor, rotor with the inner blade tip parallel with rotor tip, and rotor with the inner blade parallel with rotor root keeping the main rotor diameter constant in each case. The simulation has been achieved using the k-ε/realizable turbulence model with the assist of the ANSYS-Fluent solver. The torque coefficient (Ct) and power coefficient (Cp) are estimated as a function of tip speed ratio (TSR) for each case. Finally, the total pressure, velocity, and streamlines are obtained and analyzed. The numerical results demonstrated the maximum Cp to be 0.1885 at TSR equal to 0.5 when the inner blade is placed parallel with rotor tip with inner blade angle of 120°. Moreover, results found that the maximum Ct is 0.407 at TSR = 0.4 for the rotor with 180° inner blade. Furthermore, the peak value of the torque found to be generated at the azimuth position of (θ = 105°).

Design and Performance Analysis of Dual-Stator Brushless Doubly-Fed Machine With Cage-Barrier Rotor

This paper proposes a novel dual-stator brushless doubly-fed machine (DSBDFM) with cage-barrier rotor structure for torque density improvement in application of wind power generation. The torque density of electrical machine mainly relates to machine main dimensions and rotor coupling capability (CC). Therefore, optimizing the DSBDFM, especially the machine power distribution and rotor, affects machine torque density and rotor CC. At first, several rotor topologies are proposed and analyzed to strengthen rotor CC. Then, design principles and methods in deciding the main dimensions and power distribution for the developed DSBDFM are analyzed and illustrated in detail. Based on the machine structure and design methods, a 50-kW DSBDFM is designed, with outer and inner unit electrical machine power distribution, rotor CC, slot-pole combinations, and non-magnetic ring considered. The design example with detailed design procedure in this study provides designers a practical method in initial estimation of the dimensions and parameters for the designed DSBDFM. Meanwhile, a finite-element method is used to analyze performances of DSBDFM with winding series connection, which are verified by the experimental test. Through the results analysis, it is found that the designed DSBDFM satisfies the requirements with desirable performances, indicating the validity and rationality of design methods.

Helicopter Flight Simulation based on URANS Solver and Virtual Blade Model

Abstract The methodology of simulation of a rotorcraft flight has been developed and applied to simulate several stages of flight of light helicopter. The methodology is based on coupling of several computational models of Computational Fluid Dynamics, Flight Dynamic. The essence of the methodology consists in calculation of aerodynamic forces acting on the flying rotorcraft by solving during the simulation the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. In this approach, the rotorcraft is flying inside the computational 3D mesh modelling the space filled with the air. The flight simulation procedure is completely embedded in the URANS solver ANSYS FLUENT. Flow effects caused by rotating blades of main or tail rotor are modelled by application of the developed Virtual Blade Model (VBM). In this approach, real rotors are replaced by volume discs influencing the flow field similarly as rotating blades. Time-averaged aerodynamic effects of rotating blades are modelled using momentum source terms placed inside the volume-disc zones. The momentum sources are evaluated based on the Blade Element Theory, which associates local flow parameters in the blade sections with databases of 2D-aerodynamic characteristics of these sections. Apart of the VBM module, two additional UDF modules support the simulation of helicopter flight: the module responsible for modelling of all kinematic aspects of the flight and the module gathering the momentary aerodynamic loads and solves 6 DOF-Equations describing a motion of the helicopter seen as solid body. Exemplary simulation of helicopter flight, starting from a hover, through an acceleration and fast flight until a deceleration and steep descent, has been discussed.

Gyroplane Rotor Hubs Strength Tests

Abstract In this article a review of rotor, hub constructions were presented. Discussed rotor’s hub is made of composite or aluminum alloys materials. Two types of rotor hub were presented (four-blades and two-blades teetering rotor hub), each of them are dedicated to gyroplanes. Typical gyroplane main rotors are characterized by simple design, especially in case of rotors for light gyroplanes. In the following part of the article the type of strength tests required by certification process were shown. The test programs based on legal aspects of admission to the flight tests taking into account legislation such as CS 27 (Subpart C – Strength Requirements), CAP 643 British Civil Airworthiness requirements Section T Light gyroplanes, ASTM F2972. Furthermore, this article discusses strength tests of gyroplane rotor hub such as measured parameters, methodology of measurement, types of sensors, course of test, test stands, and limit loads. The loads during “pull-up from level flight” manoeuvre are limit loads during tests. Required additional processes, like a verification the same parameters by two types of method were shown i.e. deformation of structure were tested by strain gauges and reverse engineering. Strength tests had to be made before flight test, based on results of them aircrafts are flight authorized. In conclusion, the results of tests were presented and fulfilment of legal assumptions and requirements were shown.

헬리콥터 주로터 블레이드의 동적밸런싱 시험에 대한 데이터베이스 설계 및 적용

헬리콥터 주로터 블레이드의 동적 밸런싱 시험은 헬리콥터의 비행시험 전 각 블레이드의 트랙과 피치로드 하중을 동일한 수준으로 조절하기 위해 수행되는 지상회전시험이다. 이러한 동적밸런싱 시험의 목적은 블레이드 간 특성차이로 인해 나타나는 주로터 시스템 진동을 감소시키기 위함이다. 고흥 항공센터의 훨타워 시험설비에서는 오랜 기간에 걸쳐 수리온 주로터 블레이드에 대한 동적밸런싱 시험을 수행하고 데이터를 축적해 왔다. 이에 데이터양이 점차 방대해짐에 따라 시험결과를 효율적으로 관리하기 위한 데이터베이스 프로그램의 개발의 필요성이 제기되어 왔다. 본 연구에서는 훨타워 시험설비에서 수행한 동적밸런싱 시험결과를 바탕으로 구축한 데이터베이스 시스템에 대해 기술하였다. 본 연구에서 구현된 데이터베이스 시스템은 동적밸런싱 시험 결과를 각 정보별로 논리적으로 모델링하고 각각의 데이터가 상호 관계를 이룰 수 있도록 연결하여 관계형 구조를 이루도록 설계되었다. 아울러 본 논문을 통해 기 설계된 데이터베이스 시스템이 동적밸런싱 시험 결과의 축적과 시험 결과 분석에 효과적으로 활용될 수 있음을 보였다.

System identification and robust attitude control of an unmanned helicopter using novel low-cost flight control system

In recent years, unmanned aerial systems have attracted great attention due to the electronic systems technology advancements. Among these vehicles, unmanned helicopters are more important because of their special abilities and superior performance. The complex nonlinear dynamic system (caused by main rotor flapping dynamics coupled with the rigid body rotational motion) and considerable effects of ambient disturbance make their utilization hard in actual missions. Attitude dynamics have the main role in helicopter stabilization, so implementing proper control system for attitude is an important issue for unmanned helicopter hovering and trajectory tracking performance. Besides this, experimental utilization of low-cost flight control system for unmanned helicopters is still a challenging task. In this article, dynamic modeling, system identification, and robust control system implementation of roll and pitch dynamics of an unmanned helicopter is performed. A TRex-600E radio-controlled helicopter is equipped with a novel low-cost flight control system designed and constructed based on Raspberry Pi Linux-based microcomputer. Using Raspberry Pi makes this platform simpler to utilize and more time and cost-effective than similar platforms used before. The experiments are performed on a 5-degree-of-freedom testbed. The robust control system is designed based on [Formula: see text] method and is evaluated in real flight tests. The experiment results show that the proposed platform has the ability to successfully control the roll and pitch dynamics of the unmanned helicopter.

Research of Methodological Errors of the Air Data System of Aircraft with Stationary Included Receiver of Incoming Air Flow

It is shown that the known limitations on the measurement of air parameters on board the helicopter due to significant aerodynamic disturbances introduced by inductive flows of vortex column of main rotor. This determines the need to create the means of measurement, taking into account the aerodynamics and dynamics of the helicopter flight. The known direction of overcoming these limitations is the use for measuring the information of aerodynamic field of vortex column of main rotor and its perception by means of the stationary multi-functional aerometric receiver. However, the need to protect a large number of full-pressure tubes installed in the flow channel of the multifunctional aerometric receiver, strict requirements for the identity and stability of the characteristics of the large number aerometric channels, complicate the design, reduce reliability, increase cost, inhibit the use of the air parameters measurement system on helicopters of various classes and purposes. Principles of construction, functional scheme, features of perception of primary information of measuring system of air parameters of the helicopter with the stationary receiver of a stream, ion-label and aerometric measuring channels are showed. Algorithms for processing primary information at various stages and flight modes, including: in the parking lot before the launch of the power plant and when rotating the rotor, when taxiing and maneuvering on the earth’s surface, on takeoff and landing modes and when flying at low speeds, at flight speeds, when the stationary receiver of primary information leaves the zone of the vortex column of the rotor using ion-label and aerometric measuring channels, are presented. It is shown that the proposed approaches to the construction, models and algorithms for processing the primary information of the measuring system air parameters of helicopter with ion-label and aerometric measurement channels allow to determine the speed and direction of the wind vector, altitude-velocity parameters of motion relative to the environment and atmospheric parameters in a wide range of helicopter operation, which determines its competitive advantages in solving problems of piloting and provide the flight safety of helicopters of different classes and purposes.

Влияние несущего винта и других элементов конструкции вертолета на качество функционирования размещаемой на нем аппаратуры потребителей спутниковых радионавигационных систем

We analysed how signal diffraction caused by the main rotor, signal reflection from helicopter components, and receiver antenna shielding by the main rotor blades affect the signal-to-noise ratio in the correlator band of satellite radionavigation system user equipment for GLONASS and GPS, its navigation precision and error probability when transmitting overhead information from navigation spacecraft to the helicopter. The investigation showed that the effect of helicopter design on the performance of user equipment mounted on it manifests as antenna shielding and diffraction waves appearing at the edges. The presence of diffraction waves and reduction in the original signal amplitude as a result of shielding the user equipment antenna leads to the Bit Error Rate in the overhead information transmission channel increasing by one or two orders of magnitude. Effect on navigation accuracy is negligible.

Design and Physical Prototyping of a Novel Braking System for a Helicopter Rotor

The aim of this paper was to demonstrate the improved functionality and performance of an electromechanical brake for a helicopter main rotor, which to date has been hydraulically actuated using a disc brake and caliper arrangement. Increasingly, designers seek higher performing solutions to traditional problems through the integration of modern actuation and control strategies. This electromechanical device is required to constrain the helicopter tail rotor shaft protruding from the main rotor gearbox to allow safe taxiing and storage of the helicopter. A systematic and rigorous design methodology was used to converge on an effective solution which satisfied a very demanding specification. The design was further detailed and optimized, leading to the development of a prototype at a high technology readiness level that was tested within a bespoke rig, simulating the torque requirements found on a helicopter main rotor using the torque and position control. The design was shown to meet the required holding torque whilst providing additional functionality of continuous holding capability and meeting the challenging volumetric constraints.

MATHEMATICAL MODELS OF THE RADAR SIGNAL REFLECTED FROM A HELICOPTER MAIN ROTOR IN APPLICATION TO INVERSE SYNTHESIS OF ANTENNA APERTURE

Introduction. The basis for solving the problem of aircraft recognition is the formation of radar portraits, reflecting the constructive features of aerial vehicles. Portraits, which are radar images of the propellers of aerial vehicles, have high informativeness. These images allow us to distinguish the number and relative position of the propeller blades, as well as the direction of its rotation. The basis for obtaining such images are mathematical models of reflected signals. Objective. The aim of this paper is to develop mathematical models of the radar signal reflected from the helicopter main rotor applied to inverse synthetic aperture radar (ISAR). Methods and materials. ISAR processing is used to produce a radar image of a propeller in a radar with a monochromatic probing signal. The propeller blades in the models are approximated by different geometric shapes. The models used to describe the reflection from the propellers of helicopters and fixed-wing aircraft have significant differences. In the process of moving each blade of the helicopter main rotor makes characteristic movements (flapping, dragging, feathering), as well as bends in a vertical plane. Such movements and bendings of the blades are influence the phase of the signal reflected from the main rotor. It is necessary to take the phase change of the reflected signal into account as accurately as possible when developing an ISAR algorithm for imaging the main rotor. Results. We found that in the centimeter wavelength range the mathematical model of the signal reflected from the helicopter main rotor as a system of blades is most accurately described by representing each blade with a set of isotropic reflectors located on the main rotor’s blade leading and trailing edges. Taking into account the flapping movements and curved shapes of the blades in the model allows you to get as close as possible to the features of the real signal. Conclusion. The developed model which takes into account the flapping movements and bends of the helicopter main rotor blades can be used to improve the ISAR algorithms providing the radar imaging of aerial vehicles.

КОНСТРУКТИВНО-ТЕХНОЛОГІЧНІ ОСОБЛИВОСТІ НЕСУЧИХ ПОВЕРХОНЬ ВЕРТОЛЬОТА З ПОЛІМЕРНИХ КОМПОЗИЦІЙНИХ МА-ТЕРІАЛІВ

The analysis of both foreign and domestic experience in the use of polymer composite materials in the structures of the lifting surfaces of a helicopter (blades, wing, stabilizer, fin), as well as the technological features of the manufacture of such structures is performed. The design and technological and operational advantages and disadvantages of composite blades compared to all-metal blades are noted. The load-carrying structures of the composite main rotor blades of a helicopter, as well as the schemes of special joints of the MR blade and the polymer composite materials package are considered. The route scheme for manufacturing of the composite blade of a helicopter is presented. The technological features of manufacturing the composite spar of a blade are analyzed by the methods of lay-up and winding-on. The scheme and route technology for manufacturing the tail section of a blade, including the scheme of lay-up and molding of composite covers and ribs, are presented. The efficiency of the equipment for automatic cutting of the roll prepreg and manual lay-up of the prepreg layers with the help of a laser projector is noted. The technological tasks of special software for lay-up CNC equipment are given. The technological transitions of the general assembly-bonding of a helicopter composite blade in the assembly jig are presented. Recommendations are given on the method of manufacturing a monoblock lifting surfaces of type of a wing, tail pylon and helicopter stabilizer from polymer composite materials using automated winding-on. A scheme of surface reinforcement is proposed. It allows to obtain a variable wall thickness from the root rib to the end rib. The trajectories of movement of the working bodies of a three-coordinate CNC winding machine for their implementation are determined. A variant of a computer simulation of the stages of lay-up of a reinforcing tape on a technological mandrel is shown. The technology of manufacturing a low aspect wing made of polymer composite materials by the method of automated winding is presented.

Coupled and Trimmed Aerodynamic and Aeroacoustic Simulations for Airbus Helicopters' Compound Helicopter RACER

In recent years, various helicopter manufacturers increasingly have been focusing on the development of new high-speed rotorcraft configurations, one of them being the compound helicopter RACER (rapid and cost-efficient rotorcraft) of Airbus Helicopters (AH). However, these new configurations encounter new aeromechanic challenges, in terms of aerodynamic interactions, flight mechanics stability, rotor dynamics, or aeroacoustic noise emission, to name only a few. To support AH at the minimization of risk of RACER's first flight, the Institute of Aerodynamics and Gas Dynamics provides high-fidelity coupled and trimmed aerodynamic and aeroacoustic simulations of the complete helicopter by the application of a multidisciplinary tool chain. In its first part, the work focuses on the description of this advanced tool chain and on important features for the analysis of this new configuration. In the second part, exemplary simulation results for a hover and a high-speed cruise flight condition are shown, and the main aerodynamic interactions between the different components are identified. As expected for this configuration, numerous interactions are found for both flight cases, e.g., main rotor–propeller interaction in hover or main rotor–wing interaction in high-speed flight. Finally, aeroacoustic results are shown for hover with a close look at the propellers' contribution.

Design of Composite Gyrocopter Main Rotor Blade Involving Rib and Spar Elements

Abstract Gyrocopter or gyroplane is a type of rotorcraft that uses an unpowered main rotor in free autorotation to develop lift. Gyrocopter rotor blades have smaller cord length and longer span compared to helicopters blades. National Advisory Committee for Aeronautics (NACA) 8-H-12 gyrocopter rotor blade profile, unsymmetrical airfoil sections were used for this research. An attempt has been made in this work to investigate the effect of ribs and spar elements in response to applied load. Three possible modeling alternatives were studied to predict the actual induced stress and deformation of the blade: Model I is by considering the blade shell part only, Model II is blade shell with 25 numbers of ribs and without the spar element and Model III is blade shell with 25 numbers of ribs and with spar element. The rotor blade was sized based on single seat open frame and high-wind-start gyrocopter. Structural static analysis has been carried out to evaluate the strength of composite rotor blade using ANSYS Workbench 15. The results show that among these three proposed models; Model III had registered minimum Von Mises stress and deformation. Also the result reveals that by considering ribs and spar element during analysis of gyrocopter blade is crucial because, it will help to know the actual induced stress and deformation. The predicted value of induced stress and deformation is closer to the actual values will help the designer not to overdesign the parts. Consequently, the main drawbacks related to overdesign increase in weight and cost will be minimized; thereby the product operational efficiency will be improved.

Investigating the impact of wakes on single turbine availability

The current trend in wind energy leads to closely packed wind farms. These short distances result in a higher turbulence and consequently higher loads. In this paper an approach is proposed to evaluate single turbine availability losses due to the wake effect by modeling material fatigue behavior of selected turbine components. First, a characteristic wake scenario is defined: While one turbine is exposed to a wind field conforming to wind class IIB, another turbine experiences higher turbulence intensities according to Frandsen’s wake model. Using a dynamic multibody simulation, turbine loads are calculated which then are analyzed using the rainflow counting algorithm (giving load range and cycle counts) before being extrapolated to design lifetime of 20 years. Subsequently, artificial material curves are estimated representing the minimum load cycles to withstand during design lifetime. The slope of these curves is determined using the slope of a representative S-N-curve for each component. Position is then determined applying Miner’s rule with unity damage at the end of design lifetime. Lastly, failure behavior is approached by using a lognormal probability distribution. As a result increased failure probabilities for the rotor hub unit (main bearing and rotor hub) are found in the wake case. First results for an annual time in wake fraction of 20 % show an increase in total failure probability from 2.30 % to up to 41.85 % at a distance between the two turbines of 3D. Applying a mean down time per failure from literature (based on modern EU wind farms) finally leads to an overall technical availability decrease due to hub unit failure of 0. 035 % in the wake case compared to the free stream case.

Recent Experiences of Helicopter Main Rotor Blade Damage

Results of a survey investigating commonly occurring minor rotor blade damage incidents are presented in this paper. Over 100 participants worldwide ranging from test pilots to commercial pilots and licensed engineers answered the survey. The focus of this work was to provide a user-oriented context that can inform the decision-making process for integrating state-of-the-art instrumentation systems for rotor blade health monitoring onboard operational helicopters. This paper highlights the dichotomy faced by designers who have a choice to follow either a reactive strategy based on operational experience or a preventative approach based on technological trends.