Helicopter Main Rotor Research Articles

Fuel consumption of rotorcrafts and potentiality for hybrid electric power systems

The paper proposes a simulation approach to evaluate the power required by a rotorcraft in standard flight missions and in emergency landing maneuvers, and the corresponding fuel consumption, in order to compare the feasibility and potential fuel savings for different hybrid power systems. More in detail, three options are analyzed, namely electrification of the tail rotor, fully hybrid electric propulsion and electric emergency landing. Weight penalty and potential fuel saving for the proposed hybridization schemes are evaluated for an Agusta-Westland A109 twin engine helicopter model. Nonetheless the discussed methods of analysis have general validity for single main rotor helicopter configurations.Two different scenarios are considered in this investigation: current technologies for batteries and motors and improved electrical components, with performance projections as of 2040. According to this analysis, electrification of the tail rotor and parallel hybridization are feasible with available technology, whereas a fully electrical power system for emergency landing could be developed only in the future. Finally, a parallel hybrid electric power system is sized according to the analysis of power request over four different missions. Fuel savings are evaluated for different energy management strategies. According to the results of this investigation, the parallel hybrid electric power system with present-day and future technologies can save fuel up to 5% and 12%, respectively, with an appropriate energy management strategy.

A Comparison of Helicopter Main Rotor Features Due to Stiffness of Rotor Blade-Hub Connection

Abstract The paper presents results of simulation calculations concerning an influence of stiffness of blade-hub connection on rotor loads and blades deflections in hover, level flight and pull up maneuver. The three versions of rotor are considered with articulated, elastic and stiff connections of blades and hub. The blades with the same distributions of stiffness, mass and the same aerodynamic characteristics are applied for all rotor cases. The rotor loads are calculated applying Runge-Kutta method to solve the equations of motion of deformable blades. According to the Galerkin method, the parameters of blades motion are treated as combination of considered blade bending and torsion eigen modes. The results of calculations indicate for possibility to generate the greater rotor control moments and to improve helicopter maneuverability in the case of applying the non-changed blade of articulated rotor combined with elastic rotor hub.

Helicopter Main Rotor Blade Root End under High Velocity Bird Impact

A numerical simulation methodology has been successfully developed to model the bird strike on the innovative helicopter main rotor blade root end under high velocity bird impact. This paper demonstrates the state-of-the-art composite modelling methodology of main rotor blade and numerical bird models through experimental tests and simulation tools. The present work is based on the application of non-linear explicit finite element analysis to simulate the response of main rotor blade root end. The damage behavior under soft body impact depends upon bird size, blade size, blade span wise location of impact and bird orientation with respect to hitting location, blade rotational speed and rotorcraft cruise speed. Bird model is considered as hydrodynamic with length to diameter ratio of 2. A bird strike event is characterized by loads of high intensity and short duration. A transient explicit non-linear finite element based impact analysis using Autodyn has been carried out to predict bird strike resistance to withstand 1.0 kg bird at critical flight condition. The numerical simulation results are compared to experimental bird strike test data, leading to conclusions about the success of both the design concept and the simulation methodology. The comparison shows a very good agreement between experimental and simulated damage evolution during impact.

Wavelet-Based Sparse Representation for Helicopter Main Rotor Blade Radar Backscatter Signal Separation

Sparse signal representation is used to coherently separate the main rotor blade components of a helicopter from the composite data of complex time series radar returns. Received signals of this type typically consist of returns from the rotating main and tail rotor blades, the helicopter body, and other residual components which may overlap in time and frequency, thus making it difficult for conventional time–frequency separation techniques to be applied for the signal separation. In the proposed algorithm, a sparse signal representation is applied with the use of tunable Q wavelet transform to construct the dictionary, and basis pursuit denoising is used for the signal reconstruction of the component of interest. The algorithm shows very effective separation of the main rotor blade component from the composite radar returns, which is demonstrated using both simulated and real radar data at X -band.

Helicopter noise in hover: Computational modelling and experimental validation

The aeroacoustic characteristics of a helicopter rotor are calculated by a new method, to assess its applicability in assessing rotor performance in hovering. Direct solution of the Euler equations in a noninertial coordinate system is used to calculate the near-field flow around the spinning rotor. The far-field noise field is calculated by the Ffowcs Williams–Hawkings (FW–H) method using permeable control surfaces that include the blade. For a multiblade rotor, the signal obtained is duplicated and shifted in phase for each successive blade. By that means, the spectral characteristics of the far-field noise may be obtained. To determine the integral aerodynamic characteristics of the rotor, software is written to calculate the thrust and torque characteristics from the near-field flow solution. The results of numerical simulation are compared with experimental acoustic and aerodynamic data for a large-scale model of a helicopter main rotor in an open test facility. Two- and four-blade configurations of the rotor are considered, in different hover conditions. The proposed method satisfactorily predicts the aerodynamic characteristics of the blades in such conditions and gives good estimates for the first harmonics of the noise. That permits the practical use of the proposed method, not only for hovering but also for forward flight.

Method for the Extraction of Helicopter Main and Tail Rotor Noise

In this paper a method for the extraction of main and tail rotor noise from an acoustic pressure time history of a helicopter is described. The method is based on the classic Fourier series; however, modifications are made to account for nonperiodic and nonstationary data. Convergence of the method is demonstrated by the application of the method to artificial data. Thereafter the method is applied to wind tunnel data and flight test data for two different helicopters, one with a traditional tail rotor (Bo105) and one with a modern Fenestron (EC135). The results illustrate that a traditional tail rotor displays a rather tonal noise signature very similar to that of the main rotor, only smaller in amplitude and on a shorter time scale. The Fenestron displays a more chaotic noise signature with both a tonal and a broadband noise characteristic.

Numerical Modeling of Helicopter Main Rotor Behavior near a Small-Scale Helideck by the Vortex Method

A mathematical model and numerical scheme of the method being used are described. The results of calculating the helicopter main rotor aerodynamic performance in hover mode above a helideck are compared to the known wind tunnel test data.

Influence of the Air Viscosity on the Induced Power of a Helicopter Main Rotor in Hover and Vertical Takeoff Modes

The paper presents a method of calculating the main rotor's inductive velocities considering the influence of nonlinear air stream on ejection of air masses contiguous to it.

Parametric analysis of a hybrid power system for rotorcraft emergency landing sequence

The use of a hybrid powertrain for a conventional single main rotor helicopter is investigated, with the objective of assessing its feasibility and its potential impact on improving safety, especially for single-engine rotorcraft. The study is focused on the characteristics of the powertrain and required battery pack. It is based on a simple analysis of power required in forward flight and the estimate of the total energy required for a powered landing manoeuvre after thermal engine failure. Current technologies are considered as well as expected improvements, especially as far as energy density and power density of the battery are concerned. The latter analysis is based on current trends for battery and motors technologies, in order to determine the technological breakthrough limit.

Main Rotor Trimming Using CFD Method in Forward Flight

In this paper a CFD trimming method was proposed and compared with wind tunnel experiment and blade element method. NASA’s generic ROBIN helicopter model was adopted for transient simulations to get the final main rotor trimming condition. Totally three steps were applied to CFD method, one being no cyclic pitch motion, one being pure longitudinal cyclic pitch motion and the other one being pure lateral cyclic pitch motion. At the same time, a simple linear equation system between the roll and pitching moment was adopted to get the final longitudinal and lateral cyclic pitch angles for the main rotor through these three steps. An overset grid approach was used where the volume around each blade was modeled in an individual overset grid region. The rotor rotation was resolved with 3 degree per time-step. Turbulence was modeled with the well known SST K-omega model with 2nd order convection. The helicopter was in straight forward flight with an advance ratio of μ=0.151. Three sources of stick angles, which are also calling rotor trimming angles, were shown and compared with each other. And the corresponding results were also plotted with type of history plot in CFD condition. In the simulations the results became quasi periodic after about 1.5 rotations and 4 rotor rotations were simulated for each case. The pitch moment coefficient and roll moment coefficient were all trimmed to zero by CFD trimming method while moments were not be removed thoroughly in other two sources condition. So, it is concluded that CFD trimming method has an ability to trim helicopter main rotor in forward flight.

Coupled CFD/CSD simulation of the helicopter main rotor in high-speed forward flight

The helicopter main rotor in forward flight is considered in this paper. The results for rigid blades and elastic blades are compared by the method of coupled simulation. The influence of the structural damping coefficient on the blade in-flight deformation is also considered.

Optimally weighted recursive median filters for denoising vibration signals used in health monitoring of rotating systems

A novel weighted recursive median (WRM) filter for denoising vibration signals is presented in this paper. Vibration signals emanating from rotating systems are typically periodic as the transients die out with time due to damping. The weights of this nonlinear filter are optimized for typical vibration signals encountered in helicopter main rotor vibration such as multi-frequency sinusoids. The resulting filter removes outliers and reduces noise to a considerable extent when compared to a baseline noisy signal. FFT results show that the WRM filter is able to perform the noise removal while causing no change to the underlying frequencies in the ideal signal. The integer design space for the filter is multimodal with several local minima and the filter design problem presents a benchmark problem for testing integer programming algorithms. An exhaustive search of the design space ensures that all the local minimum points are found and the global minimum is identified. The 5-point median filter with weights [2 1 2 1 2] is found to be good choice for denoising vibration signals. The WRM filter can be used as a data preprocessor before subjecting the vibration signals to fault detection and isolation algorithm.

Design and Development of Main Helicopter Rotor Blade

Design and Development of Main Helicopter Rotor Blade

Helicopter flap/lag energy exchange study

This paper presents a study on the energy exchange taking place on articulated helicopter main rotor blades. The blades are hinged, and the flap/lag modes are highly coupled. These dynamical couplings existing between the two degrees of freedom are clearly identifiable as the nonlinear terms that appear in the equations of motion are key to understand the energy exchange process. The work here conducted is carried out using VehicleSim, a multibody software specialized in modelling mechanical systems composed by rigid bodies. A spring pendulum system is also studied in order to examine its nonlinear behaviour and to establish existing analogies with the rotor blade nonlinear dynamics. The nonlinear couplings of both systems are compared to each other, and commensurability condition is analysed by means of short-time Fourier transform methods as well as the flap and lag amplitudes spectrum. Simulations are carried out, and the obtained results show clear analogies in the energy exchange process taking place in both systems. The stability of these modes is also studied using Poincare’ map method.

CAA modeling of helicopter main rotor in hover

In this work rotor aeroacoustics in hover is considered. Farfield observers are used and the nearfield flow parameters are obtained using the in house HMB and commercial Fluent CFD codes (identical hexa-grids are used for both solvers). Farfield noise at a remote observer position is calculated at post processing stage using FW–H solver implemented in Fluent and HMB. The main rotor of the UH-1H helicopter is considered as a test case for comparison to experimental data. The sound pressure level is estimated for different rotor blade collectives and observation angles.

Mathematical description of the interaction between a probing microwave signal and the helicopter main rotor blade

The paper deals with the non-contact method of monitoring the integrity of the main rotor blades of a helicopter. The available methods of monitoring the integrity of the main rotor blades of the helicopter are labor-intensive to implement, their reliability is low and they do not allow drawing a general picture of the state of rotor blades in flight. To solve this problem a method based on illumination of the blades by a probing microwave signal is proposed. Particular attention is given to the calculation of the power of the signal reflected from the helicopter main rotor blades. In deriving analytic equations it is assumed that a rotor blade is an undeformed flat metal surface. As a result, a spatial-temporal model of a probing SHF signal reflected from a helicopters main rotor blade has been obtained and the parameters of the model make it possible to assess the operational status of the main rotor of the helicopter.

헬리콥터 주로터 블레이드 동적밸런싱 시험을 위한 조절변수 최적화 연구

헬리콥터 주로터 블레이드 동적밸런싱 시험을 위한 조절변수 최적화 연구

On determining the acoustic properties of main helicopter rotor models on an open test bench

The paper presents the results of experimental studies on developing a technique to determine the acoustic properties of models of main helicopter rotors on an open test bench. The method of maximum length sequences is used to choose the optimum arrangement of microphones for an open test bench that would minimize the influence of parasitic echo. The results of processing the data of an acoustic experiment with a model rotor are detailed.

Main helicopter rotor trimming using computational fluid dynamics method in forward flight

In this paper, a computational fluid dynamics trimming method is proposed and compared with wind tunnel experiment and the blade element method. The NASA’s generic ROBIN helicopter model is adopted for transient simulations to obtain the final main rotor trimming conditions. Totally three steps were applied to the computational fluid dynamics method. The first step is associated with no cyclic pitch motion, the second is regarding pure longitudinal cyclic pitch motion and the last is concerning with pure lateral cyclic pitch motion. At the same time, a simple linear equation system between the roll and pitching moment was established to get the final longitudinal and lateral cyclic pitch angles for the main rotor through the above three steps. An overset grid approach was used where the volume around each blade was modeled in an individual overset grid region. The rotor rotation was resolved with three degrees per time-step. Turbulence was modeled with the well-known SST K-omega model with second-order convection. The helicopter was in straight forward flight with an advance ratio of [Formula: see text]. Three sources of stick angles, which are also called rotor trimming angles, were shown and compared with each other. And the corresponding results were also plotted with a type of history plot in the computational fluid dynamics condition. In the simulations, the results became quasi periodic after about 1.5 rotations and four rotor rotations were simulated for each case. The pitch moment coefficient and roll moment coefficient were all trimmed to about zero by the computational fluid dynamics trimming method while moments were not removed thoroughly in the other two source conditions.

Effect of surface roughness on helicopter main rotor blade

This paper describes the effect of surface roughness when applied on helicopter main rotor blade. The aim is to prove that surface roughness can be used as a simple and inexpensive method to achieve better flight performance such as enhanced thrust and/or reduced power requirement. The research was done experimentally, using scaled model of Eurocopter AS350 Ecureuil. Smooth profile of the main rotor blade was modified by applying surface roughness on the upper and lower camber in transition and turbulent boundary layer region, starting from 25% of chord length and extending up to the trailing edge (TE). This study was conducted with the conditions of a vertical flight (particularly in hover condition) since this is a high powerconsuming flight regime for helicopter. The experiment resulted in lower power requirement but at the expense of reduced thrust at the middle collective pitch level. At upper range of the collective pitch level, surface roughness was seen to delay the stall angle as well as increase the lift in the stall region. Meanwhile, at lower pitch level, there was an increase in thrust-to-power ratio.