Helicopter Main Rotor Research Articles

On the use of strain sensor technologies for strain modal analysis: Case studies in aeronautical applications.

This paper discusses the use of optical fiber Bragg grating (FBG) and piezo strain sensors for structural dynamic measurements. For certain industrial applications, there is an interest to use strain sensors rather than in combination with accelerometers for experimental modal analysis. Classical electrical strain gauges can be used hereto, but other types of strain sensors are an interesting alternative with some very specific advantages. This work gives an overview of two types of dynamic strain sensors, applied to two industrial applications (a helicopter main rotor blade and an F-16 aircraft), FBG sensors and dynamic piezo strain sensors, discussing their use and benefits. Moreover, the concept of strain modal analysis is introduced and it is shown how it can be beneficial to apply strain measurements to experimental modal analysis. Finally, experimental results for the two applications are shown, with an experimental modal analysis carried out on the helicopter main rotor blade using FBG sensors and a similar experiment is done with the aircraft but using piezo strain sensors instead.

Aerodynamic and acoustic analysis of helicopter main rotor blade tips in hover

Purpose The design of main rotor blade tips is of interest to helicopter manufactures since the tip details affect the performance and acoustics of the rotor. The paper aims to discuss this issue. Design/methodology/approach In this paper, computation fluid dynamics is used to simulate the flow around hovering helicopter blades with different tip designs. For each type of blade tip a parametric study on the shape is also conducted for comparison calculations were performed the constant rotor thrust condition. The collective pitch and the cone angles of the blades were determined by at an iterative trimming process. Findings Analysis of the distributed blade loads shows that the tip geometry has a significant influence on aerodynamics and aeroacoustics especially for stations where blade loading is high. Originality/value The aeroacoustic characteristics of the rotors were obtained using Ffowcs Williams-Hawkings equations.

Student research highlights: MACHe — Model-based algorithm for classification of helicopters

Secondary motions of a target, such as rotating blades of a helicopter's main rotor, induce a Doppler modulation around the main Doppler shift. This represents a unique feature of the target itself, known as micro-Doppler signature, and can be used for classification purposes. In this student research highlight a model-based automatic helicopter classification algorithm is presented. It is a parametric classification approach based on a sparse signal recovery method and it is independent of both the initial position of the blades and the aspect angle. The algorithm is tested on simulated and real data.

Calculation of a safety factor of damaged composite main rotor blade according to limit equilibrium theory

Safety factors of the Ansat helicopter main rotor blade are determined in the root section at various flight modes with taking into account the possible damages.

Spectral-Boundary-Integral Compact-Source Formulation for Aero-Hydroacoustics of Rotors

This paper presents an aeroacoustic compact-source formulation for predicting tonal noise generated aerodynamically by rotors that is applicable to hydroacoustic problems as well. Based on the knowledge of blade sectional loads, it is suitable for reducing the amount of aerodynamic data required (particularly relevant, for instance, in maneuvering motion) and is applicable also when detailed blade pressure is not available. The Küssner–Schwarz airfoil aerodynamics theory is applied to derive the chordwise pressure jump equivalent to the sectional loads provided (either by measurements or computational tools). A zeroth-order boundary element method is applied for spanwise integration of the resulting compact-source, spectral-integral formulation. Numerical investigations concern a helicopter main rotor in descent flight and a marine propeller in nonuniform inflow. They demonstrate that, increasing the number of spectral coefficients (and corresponding sectional loads), this compact-source formulation converges toward solutions providing accurate noise predictions, even for rotors with irregular blade pressure distributions.

Monitoring the Dynamics of a Helicopter Main Rotor With High-Speed Stereophotogrammetry

Monitoring the Dynamics of a Helicopter Main Rotor With High-Speed Stereophotogrammetry

Vibration-based damage detection for a composite helicopter main rotor blade

This work presents experimental results of two damage detection techniques based on modal properties, with the application on a full-size composite helicopter main rotor blade. The damage detection methods used in this study are the coordinate modal assurance criterion (COMAC) and the modal strain energy method, which are respectively based on the comparison of vibration modes and on the comparison of the modal strain energy of a beam. Modal parameters were obtained with experimental modal analysis and damage was introduced artificially on the blade by attaching a small mass to it, changing its global properties in this way. Finally, experimental results for the damage detection technique are shown for both methodologies, and remarks concerning sensitivity and robustness of the methods are discussed.

Computational modeling of interference between helicopter main and tail rotors based on nonlinear blade vortex model

The Mi-2 helicopter was taken as an example for modeling the main and tail rotors operation with account for the interference at low speed sliding flight. Aerodynamic characteristics were calculated. The form of nonlinear vortical wake was obtained.

Computational analysis of helicopter main rotor blades in ground effect

Computational analysis of helicopter main rotor blades in ground effect

Identification of aeroelastic parameters for helicopter tail rotor limit cycle oscillation monitoring

The aeroelastic parameters of helicopter main rotor and tail rotor are required in the monitoring and evaluation of rotor aeroservoelastic instability incidents such as limit cycle oscillations. However, in situ measurement of these parameters on helicopters is generally difficult due to the need to transfer vibration data across a rotating interface. This article presents a novel center frequency scaling factor relationship of the aeroelastic parameters between the rotating and stationary frames. Together with the stochastic parameter identification technique, this methodology enables real-time estimation and tracking of the critical aeroelastic parameters in the rotating frame during limit cycle oscillation events based on vibration information measured exclusively in the stationary frame. The methodology has been validated using flight vibration data measured from both the rotating and stationary frames of a helicopter tail rotor system during a limit cycle oscillation event. Moreover, this methodology has been applied to the analysis of vibration data measured from the teeter tail rotor system on the Canadian CH-149 Cormorant helicopters to derive the critical aeroelastic parameters during several limit cycle oscillation events.

Combined passive and active helicopter main rotor morphing for helicopter energy save

In this article, passive morphing and active morphing approaches are combined to save more helicopter flight control system (i.e., FCS) energy. For this purpose complex, physics-based, control-oriented nonlinear helicopter models are benefited. A specific variance-constrained control strategy, namely Output Variance-Constrained Control (i.e., OVC) is applied for helicopter FCS. Control energy savings using passive, active and combined morphing approaches are examined. Parameters of helicopter FCS and combined morphing helicopter design parameters are simultaneously optimized using a stochastic optimization method, namely simultaneous perturbation stochastic approximation (i.e., SPSA). To observe energy save, closed-loop analyses are done. Finally, robustness of combined morphing helicopter with respect to (w.r.t.) the modeling uncertainties is examined.

Damage tolerance approach for analyzing a helicopter main rotor blade

In this article, damage tolerance approach is used for life estimation of the main rotor blade of a helicopter under random loading. At first, fatigue crack growth properties and threshold stress intensity range of the spar is obtained based on ASTM E647 test method. Then, crack growth analysis is done using Zencrack software. In order to calculate the length of the smallest growing cracks and their fatigue crack growth life, no crack growth and slow crack growth approaches were used. A comprehensive investigation was carried out on the effect of initial crack length on growth or no growth of cracks.

Monitoring the Dynamics of a Helicopter Main Rotor With High-Speed Stereophotogrammetry

Stereophotogrammetry in conjunction with three-dimensional point tracking (3DPT) algorithms has proven to be a highly robust dynamic measurement technique on small, rotating bladed systems. This measurement technique can be scaled up to much larger systems and has several desirable features for helicopter and wind turbine structural health monitoring (SHM) applications that include: (1) it is noncontact and does not require the use of roll/slip rings for signal transmission; (2) the applied measurement targets negligibly affect the aerodynamics or structural mass/stiffness; and (3) position data can be collected on many hundreds of points over what is capable using conventional multichannel data acquisition (DAQ) systems. A field test was conducted in which operating data were collected on the main rotor of a helicopter in both grounded and hovering operating conditions. Part 1 of this work describes the experimental setup and DAQ process of the test performed and part 2 of this work presents some of the results including blade dynamics and extracted operating deflection shape information for the helicopter. The promising results presented in this work will serve as the foundation for the development of noncontacting SHM techniques that can be applied to large, rotating bladed structures while in operation.

Helicopter Vibratory Loads Alleviation through Combined Action of Trailing-Edge Flap and Variable-Stiffness Devices

The aim of this paper is the assessment of the capability of controllers based on the combined actuation of flaps and variable-stiffness devices to alleviate helicopter main rotor vibratory hub loads. Trailing-edge flaps are positioned at the rotor blade tip region, whereas variable-stiffness devices are located at the pitch link and at the blade root. Control laws are derived by an optimal control procedure based on the best trade-off between control effectiveness and control effort, under the constraint of satisfaction of the equations governing rotor blade aeroelastic response. The numerical investigation concerns the analysis of performance and robustness of the control techniques developed, through application to a four-bladed helicopter rotor in level flight. The identification of the most efficient control configuration is also attempted.

Review of the design of the helicopter rotor

This article - paper presents the design of the main rotor of the helicopter supported by the patent documents, as a very useful tool (instrument) to reach the specific ideas and design in order to find the most economical way for the quality solution for a certain technical problem present in the process of design (construction). A large amount of technical information first appears in patent documents and about two thirds of this information cannot be found on any other site. The structure of patent documents is presented with an emphasis on the elements that relate to technical information with the detailed explanation of the possibilities of the application of the patent documentation during the process of design of the main helicopter rotor. The procedure and methods of research of the related patent documents are presented on a specific example of helicopter rotor design. The Espacenet database of patent documents was used as the most comprehensive and the most frequently used database containing over eighty million different patent documents about inventions and technical improvement (advancement) from all over the world. The crucial part of the paper relates to the presentation of a patent search method in order to find a technical solution for the structures of the main helicopter rotor which relates to the provision of the required casting and rapid response changes of accommodation angle (step) of the rigid rotor blades of helicopters.

Parallel Blade-Vortex Interaction Modelling for Helicopter Rotor Noise Control Synthesis

The present work deals with a methodology for the alleviation of loads and corresponding emitted noise generated by blade-vortex interaction (BVI) phenomena occurring on helicopter main rotors in low-speed, descent flight. It consists of a multi-cyclic, optimal control approach driving higher harmonic blade pitch actuation. First, for the specific flight condition to be examined, the BVI phenomena are simulated as equivalent two-dimensional, multi-vortex, parallel BVI problems and then a local controller methodology is applied for the efficient identification of the closed-loop control algorithm. In order to assess the capability of the proposed control approach to alleviate rotor blade loads and emitted noise, the results of a numerical investigation concerning a realistic helicopter main rotor in descent flight are presented and discussed.

Numerical Simulation and Investigation of Transonic & Symmetrical Airfoil for Helicopter Main Rotor Blade Application

Helicopter rotor aerodynamics is prognosticated to be one of the most perplexing and enigmatic affliction encountered by both researchers and aviators throughout the ages. The bewilderment of the flow field around the main rotor blade ceaselessly remains unrequited in tangible flight environments. Appalling calamities repeatedly befall owing to these unforeseen and equivocal instances. In order to extricate these impediments, one must go back to the brass tacks and apprehend the cause. However, it is every so often exceedingly disconcerting to obtain experimental data due to intricacy, perplexity and substantial price tag. Subsequently, computational simulation is progressively becoming more of a preferred choice in recent times. Bearing this in mind, this study intended to simulate and visualize the air flow configuration of the main rotor blade using symmetrical and transonic airfoils to demarcate their physiognomies and behavior. Results have revealed that the transonic airfoil has a higher lift coefficient (Cl) than the symmetrical airfoil. Contrariwise, if used in an actual rotorcraft, the transonic airfoil can cause stern apprehension in terms of stability and control.

Implementation of artificial neuron networks for the simulation of loads generated by the helicopter main rotor

The possibility of applying the mathematical apparatus of artificial neural networks for simulating the loads, created by the helicopter rotors, is investigated. The effect of the network characteristics on the calculated root-mean-square error of parameters being simulated is evaluated on examples. The future prospect of this simulation method in the flight dynamics mathematical models of a helicopter flight simulator is demonstrated.

State-Space Rotor Aeroelastic Modeling for Real-Time Helicopter Flight Simulation

This paper introduces a new approach for the identification of linear state-space models of dynamical systems of arbitrary complexity. The identification procedure is described and applied for modeling aeroelastic response of helicopter main rotors. With the aim of developing a tool that might be conveniently applied for real-time simulations of helicopter flight dynamics, the state-space model considered is a reduced-order description of loads transmitted to the airframe due to hub motion and blade pitch controls. In order to validate the proposed approach, loads from the state-space, reduced-order model are compared with those predicted by the complete full-state, nonlinear rotor model for prescribed helicopter maneuvers.

Numerical Study of Helicopter Rotors in a Ship Airwake

Operating helicopters in a naval environment is challenging because it imposes a pilot workload significantly higher than that during land-based operations. The aerodynamic interaction between the aircraft and the ship wake is known to play an important role in increasing the pilot workload, hence reducing the aircraft capability as a result of maintaining safety. As a further step toward numerical prediction of ship/helicopter operational limitations, computational-fluid-dynamics simulations are conducted for the Canadian Patrol Frigate. The effect of the rotor is included in the simulation, first using an actuator-disc method together with steady calculations, then using rotor blades and the unsteady Reynolds-averaged Navier–Stokes equations. Results using the actuator-disc method demonstrate the importance of coupling effects on the wake and rotor inflow when the rotor is operating close to the ship and therefore the invalidity of superposition methods. The case of a Sea King helicopter main rotor hovering above the deck just before touchdown is reproduced to overcome the limitations of steady calculations and the actuator-disc method. Predictions of rotor thrust compare well with the experimental data available and give confidence in the results. The findings highlight the differences in rotor loading between forward flight and near-deck operation. The possibility of using such simulations for determining safe flight envelopes is discussed as part of the future work.