Tail Boom Research Articles

Research on the Propagation of AE Signals in Helicopter Structural Components

Abstract The paper contains results of experimental research carried out helicopter bench. In order to create an attenuation chart for AE signal amplitude in helicopter fuselage, a number of experiments were performed on the frame and stringers, inside the fuselage. Later helicopter test bench was used to develop defect localization methodology of helicopter structure fatigue damage technical diagnostics. Analysing helicopter structural defects for different helicopters types it is concluded that the joint elements of helicopter tail boom are still exposed to fatigue crack formation. AE method shows highly effective results predicting fracture of helicopter joint elements.

Pulsed Actuation Control of Flow Separation on a ROBIN Rotorcraft Fuselage

Separation control of the three-dimensional flow over the aft segment of a NASA Rotor-Body-Interaction (ROBIN) rotorcraft fuselage is investigated in wind-tunnel experiments using arrays of miniature combustion-based actuators. Successive pulsed actuation is effected by momentary jets each having a characteristic time scale that is an order of magnitude shorter than the convective time scale of the flow. The actuators are placed upstream of the transition ramp between the ROBIN’s fuselage and the tail boom. The jet-induced interactions with the massively separated crossflow over the ramp and their effects on the global aerodynamic forces and moments are investigated using high-resolution particle image velocimetry that is acquired phase-locked to the actuation waveform in conjunction with simultaneous force and moment measurements using an onboard load cell. The present investigations show that symmetric actuation about the model’s centerline can significantly mitigate separation, lead to a reduction in drag and lift, and alter the pitching moment. Asymmetric actuation, and consequently nonuniform attachment, can induce significant side forces as well as roll and yaw moments that may be exploited for steering and improved flight maneuverability.

Fatigue Cracks Detection using PZT Transducers under the Influence of Uncertain Environmental Factors

Abstract This paper presents technique for qualitative assessment of fatigue crack growth monitoring, utilizing guided elastic waves generated by the sparse PZT piezoelectric transducers network in the pitch – catch configuration. Two Damage Indices (DIs) correlated with the total energy received by a given sensor are used to detect fatigue cracks and monitor their growth. The indices proposed carry marginal signal information content in order to decrease their sensitivity with respect to other undesired non-controllable factors which may distort the received signal. The reason for that is to limit the false calls ratio which besides the damage detection capability of a system, plays a crucial role in applications. However, even such simplified damage indices can alter over a long term, leading to the misclassification problem. Considering a single sensing path, it is very difficult to distinguish whether the resultant change of DIs is caused by a damage or due to decoherence of these DIs. Therefore, assessment approaches based on threshold levels fixed separately for DIs obtained on each of the sensing paths, would eventually lead to a false call. An alternative approach is to compare changes of DIs for all sensing paths. Developing damage distorts the signal only for the sensing paths in its proximity. In order to decrease the misclassification risk, a method of compensating such DIs drift is proposed. The main features and damage detection capabilities of this method will be demonstrated by conducting a laboratory fatigue test of an aircraft panel. The proposed approach has been verified on a real structure during fatigue test of a helicopter tail boom.

New Modular Product-Platform-Planning Approach to Design Macroscale Reconfigurable Unmanned Aerial Vehicles

The benefits of a family of macroscale reconfigurable unmanned aerial vehicles to meet distinct flight requirements are readily evident. The reconfiguration capability of an unmanned-aerial-vehicle family for different aerial tasks offers a clear cost advantage to end users over acquiring separate unmanned aerial vehicles dedicated to specific types of missions. At the same time, it allows the manufacturer the opportunity to capture distinct market segments, while saving on overhead costs, transportation costs, and after-market services. Such macroscale reconfigurability can be introduced through effective application of modular product-platform-planning concepts. This paper advances and implements the Comprehensive Product Platform Planning framework to design a family of three reconfigurable twin-boom unmanned aerial vehicles with different mission requirements. The original Comprehensive Product Platform Planning method was suitable for scale-based product-family design. In this paper, important modifications to the commonality matrix and the commonality constraint formulation in Comprehensive Product Platform Planning are performed. These advancements enable the Comprehensive Product Platform Planning to design an optimum set of distinct unmanned-aerial-vehicle modules, different groups of which could be assembled to configure twin-boom unmanned aerial vehicles that provide three different combinations of payload capacity and endurance. The six key modules that participate in the platform planning are 1) the fuselage/pod, 2) the wing, 3) the booms, 4) the vertical tails, 5) the horizontal tail, and 6) the fuel tank. The performance of each unmanned aerial vehicle is defined in terms of its range per unit fuel consumption (miles/gallon). It is found that, when the average unmanned-aerial-vehicle performance (miles/gallon) and the commonality among the unmanned-aerial-vehicle variants are simultaneously maximized, a one-third reduction in the number of unique modules is accomplished at a 66% compromise in performance. On the other hand, when simultaneously maximizing performance and minimizing costs, the best tradeoff unmanned-aerial-vehicle-family designs provide a remarkable 26% reduction in cost for a 6% compromise in performance. In this case, the cost savings are attributed to both material reduction and increased module sharing across the three unmanned-aerial-vehicle variants. It is also observed that, among the best tradeoff unmanned-aerial-vehicle families, the individual unmanned aerial vehicles are most likely to share the horizontal tail and tail booms, and are least likely to share the wing.

Semi-empirical modeling of fuselage–rotor interference for comprehensive codes: influence of angle of attack

The flow field around the isolated Bo105 fuselage including the tail boom and empennage is computed by an unsteady panel code. Velocities normal to the rotor rotational plane are extracted in a volume around the rotor as a data base. A simple semi-empirical analytical formulation of the fuselage-induced velocities, based on parameter estimation from the panel code data, is extended to include rotor shaft angles of attack from $$\alpha =-90^{\circ }$$ (hover, vertical climb) to +90° (vertical descent) for use in comprehensive rotor codes. This model allows the computation of fuselage–rotor interferences on the rotor blade element level in a simplified form, thus eliminating the need for costly CFD computation (of this effect). It also allows the prediction of the rotor wake geometry deformation due to the presence of the fuselage in both prescribed wake and free-wake codes. Its impact on rotor thrust, power and trim is estimated analytically using blade element momentum theory.

Theoretical Analysis and Experimental Researches regarding the Asymmetrical Fluid Flow Applied in Aeronautics

The current paper has been written in order to find the best solutions to replace the antitorque rotor of single-rotor helicopters, with removal of its disadvantages through the Coandă Effect. This would significantly increase the flight performance. The research mainly aims at obtaining a controlled lateral force due to Coandă flows through the tail boom, a force which would be useful for the stabilization needed because of the lifting rotor during the flight of single-rotor helicopters.

A Numerical Method for Blast Shock Wave Analysis of Missile Launch from Aircraft

An efficient empirical approach was developed to accurately represent the blast shock wave loading resulting from the launch of a missile from a military aircraft to be used in numerical analyses. Based on experimental test series of missile launches in laboratory environment and from a helicopter, equations were derived to predict the time- and position-dependent overpressure. The method was finally applied and validated in a structural analysis of a helicopter tail boom under missile launch shock wave loading.

Static and Dynamic Balancing of Helicopter Tail Rotor Blade Using Two-Plane Balancing Method

Balancing is a rotating component is critical in any mechanism. Devoid of proper balancing, any vehicle - be it in air, land or sea, it will affect stability, control and safety. The same goes for rotor crafts. Imbalance of the helicopter tail rotor system leads to vibrations in the entire vehicle and may cause accident. Typically, for the tail rotor of a helicopter, the blade is a source of vibration on the tail boom. This not only causes inconvenience to the pilot but also reduces the life span of the helicopter. There is a certain amount of vibration in the helicopter rotor systems especially the tail rotor. Hence, balancing procedure for rotating mass was conducted to reduce the vibration. This research focuses on balancing of the tail rotor for UTM Single Seat Helicopter. Experiments have been conducted in order to study the vibration level of the tail rotor. Adding and removing masses separately on the tail rotor exhibited different vibration levels. The responses were analyzed and used for balancing the tail of rotor system. The balancing effort was considered successful, although there was still some residual unbalance in the tail rotor.

Coal-gangue interface detection based on Hilbert spectral analysis of vibrations due to rock impacts on a longwall mining machine

Coal-gangue interface detection during top-coal caving mining is a challenging problem. This paper proposes a new empirical approach to detect the coal-gangue interface based on vibration signal analysis of the tail boom support of the longwall mining machine. Due to nonstationary characteristics in vibration signals in this complicated environment, the empirical mode decomposition is used to decompose the original vibration signals into intrinsic mode functions. The associated Hilbert transform calculates the instantaneous frequency and amplitude of the selected intrinsic mode functions, providing a novel Hilbert spectrum in the time-frequency domain. The distribution of the Hilbert spectrum of top-coal caving is found to be more uniform than that of coal-gangue caving. A method of vibration feature extraction based on the information entropy of the Hilbert spectrum is presented. The Mahalanobis distance function is used to classify the caving states. Experimental results show that the Mahalanobis distance measure applied to the information entropy of the Hilbert spectrum of vibration signals from the tail boom support of a longwall mining machine is effective for coal-gangue interface detection.

Application of EMD-Based SVD and SVM to Coal-Gangue Interface Detection

Coal-gangue interface detection during top-coal caving mining is a challenging problem. This paper proposes a new vibration signal analysis approach to detecting the coal-gangue interface based on singular value decomposition (SVD) techniques and support vector machines (SVMs). Due to the nonstationary characteristics in vibration signals of the tail boom support of the longwall mining machine in this complicated environment, the empirical mode decomposition (EMD) is used to decompose the raw vibration signals into a number of intrinsic mode functions (IMFs) by which the initial feature vector matrices can be formed automatically. By applying the SVD algorithm to the initial feature vector matrices, the singular values of matrices can be obtained and used as the input feature vectors of SVMs classifier. The analysis results of vibration signals from the tail boom support of a longwall mining machine show that the method based on EMD, SVD, and SVM is effective for coal-gangue interface detection even when the number of samples is small.

Integral structural health monitoring of helicopter tail booms by guided acoustic waves

The general principles of structural health monitoring by ultrasonic waves with high resolution monitoring of the time dependence of the transport properties are presented. Reported are essential aspects of the theoretical background together with the results of modeling relating to the developed monitoring scheme and the experimental findings. The presented applications of the developed integral structural health monitoring concentrate on examples involving helicopter tails booms. These include conventional aluminum based bolted frame and stringer constructions as well as fiber compound structural components with foam inlays, in both cases for helicopter tail booms. The presentation includes experimental demonstrations on samples suitable for transport.

Production of a Helicopter Tail Boom and Associated Mechanical Tests

The lightweight materials such as composites are often used for the aerospace structures. One of the uses of these materials is for the tail boom of helicopters. Tail booms are the structures connecting the tail rotor to the fuselage. It is mainly subjected to the pitching moment and torsion. Because it is long to obtain the enough distance between the tail rotor and the main rotor, the materials used for manufacturing the tail boom needs to be a lightweight material. The structural optimization of the tail boom is also necessary. In this study, two different tail booms are manufactured by using laminated composites. The tail booms considered in this study are a semi-monocoque structure consisted of skins and stiffeners. These skins and stiffeners are made of carbon/epoxy. One is produced by using 3-ply carbon/epoxy and it is strengthened using stiffeners. The other is produced by using honeycomb between 2-layers of carbon/epoxy. A hand lay-up technique is used for the manufacturing of the tail booms. The vacuum bagging and a moderate heat are used to cure the composite structure. The bending and bending with torsion tests are performed to determine the structural performance of the tail booms. The tail boom is also modeled using the finite element method and analyses are performed. The results are presented and discussed.

Production of a Helicopter Tail Boom and Associated Mechanical Tests

Production of a Helicopter Tail Boom and Associated Mechanical Tests

Eigenvalue density of linear stochastic dynamical systems: A random matrix approach

Eigenvalue problems play an important role in the dynamic analysis of engineering systems modeled using the theory of linear structural mechanics. When uncertainties are considered, the eigenvalue problem becomes a random eigenvalue problem. In this paper the density of the eigenvalues of a discretized continuous system with uncertainty is discussed by considering the model where the system matrices are the Wishart random matrices. An analytical expression involving the Stieltjes transform is derived for the density of the eigenvalues when the dimension of the corresponding random matrix becomes asymptotically large. The mean matrices and the dispersion parameters associated with the mass and stiffness matrices are necessary to obtain the density of the eigenvalues in the frameworks of the proposed approach. The applicability of a simple eigenvalue density function, known as the Marenko–Pastur (MP) density, is investigated. The analytical results are demonstrated by numerical examples involving a plate and the tail boom of a helicopter with uncertain properties. The new results are validated using an experiment on a vibrating plate with randomly attached spring–mass oscillators where 100 nominally identical samples are physically created and individually tested within a laboratory framework.

Simulation of a complete helicopter: A CFD approach to the study of interference effects

Computations performed with the RANS solver ROSITA are compared with the experimental data gathered for the GOAHEAD full helicopter model. The tested configuration is made of a scaled NH90 fuselage, the ONERA 7AD rotor with a simplified rotor hub and a scaled BO105 tail rotor. The model is mounted on a support to match the wind tunnel conditions of the experiments. The considered flow conditions correspond to a cruise level flight. The general agreement between numerical and experimental results can be judged satisfactory, such as to validate the use of the ROSITA code for aerodynamic interference studies.In the second part of the study, numerical simulations of the 7AD isolated rotor, the NH90 isolated fuselage and the full GOAHEAD helicopter configuration are compared to analyze the interference effects between the rotor wakes and the fixed components of the fuselage and the influence of the fuselage on the rotor loads. The unsteadiness of the fuselage loads, especially on the tail boom and vertical fin, due to a highly turbulent wake is put in evidence, as well as the average incidence variation experimented by the horizontal tail plane. The influence of the fuselage on the main rotor loads appears to be localized.

Visualisation of guided wave propagation by ultrasonic imaging methods

Structural health monitoring (SHM) with Lamb waves (LWs) principally enables an in-service damage detection of large aircraft components without time-consuming scanning. Piezoelectric elements can be effectively used as senders and receivers for LWs. However, the complex interaction between defects and Lamb waves – especially for composites, the presence of two wave modes in minimum and its dispersive behaviour and reflections from all structure elements contribute to receiver signals which are very difficult to predict and to evaluate. Ulltrasonic imaging technique (UIT) can also be used for the visualisation of LW propagation in composites especially using air-coupled techniques. Out of the recorded full-wave data calculations of Lamb wave A-, B-, C- and D-scans and video animations can be carried out. Examples of visualisation in composites such as monolithic specimens, a stringer stiffened laminate and a sandwich tail boom which impressively show the Lamb wave propagation and also their interaction with defects.

An analysis of the efficiency of Coanda - NOTAR anti-torque systems for small helicopters

The use of jet thrust for anti-torque for monorotor small helicopters is based on the circulation control concept, which result in a distributed side force along the entire tail boom assembly. High velocity jets of air from a pressurized tail boom is blown tangential to the surface out of narrow slots that run lengthwise on the side of the tail boom. In combination with the downstream velocity produced by the main rotor, Coanda jets cause the flow to remain attached to the tail boom surface. The anti-torque NOTAR system is in fact the result of Coanda effect and the interest is to analyze the efficiency of replacing the tail rotor on a small monorotor helicopter.

Coaxial Rotor Helicopter in Hover Based on Unstructured Dynamic Overset Grids

C OAXIAL rotor configuration is one of the technological solutions for increasing helicopter forward speed, maneuverability, and load-carrying ability. Since two rotors produce the net thrust instead of a single rotor in the conventional design, the diameter of the rotors can be reduced to carry the same amount of weight. Themost attractive feature of a coaxial design is the resulting compactness and safety of the vehicle. Second, the antitorsional moment generated by the two rotors would be canceled due to the opposite rotational directions, and the tail rotor and tail boom can be eliminated, resulting in a smaller and lighter vehicle. Compared to the individual-rotor helicopter, the aerodynamics and flow physics of coaxial rotor helicopter are relatively less studied and understood. The method of slipstream theory was first used to study the coaxial rotor, and then the predicted wake vortex model [1,2], free wake vortex model [3], and vorticity transport model [4,5] were applied to the coaxial rotor analysis. All the methods above carry out some approximations to the rotor, and the detailed flow feature near the blades and blade vortex in the wake cannot be simulated. Recently, the unsteady Navier–Stokes equations were used to simulate the coaxial rotor flows [6–8] to provide a detailed understanding of the flow physics of coaxial rotor. In the present Note, the three-dimensional unsteady Euler equations were solved to simulate the unsteady flows around coaxial rotor helicopter and individual-rotor helicopter in hover based on the unstructured dynamic overset grids. The aerodynamic interaction property of the coaxial rotor helicopter in hover and the effect of fuselage on the unsteady performance were studied.

Fatigue Life Estimation of the Tail Boom and Vertical Stabilizer of MI-24 Helicopter

Fatigue Life Estimation of the Tail Boom and Vertical Stabilizer of MI-24 HelicopterThe aim of this work was to estimate fatigue life of the Mi-24 helicopter tail boom and vertical stabilizer sheathing. The analysis was based on a numerical model of the helicopter airframe crucial to obtain stress fields under defined loads and to estimate fatigue life.In order to do so, the load spectrum, specific for Polish army helicopters, was obtained by means of strain gauge measurements during a series of experimental flights. Data collected during flights was post-processed to create a characteristic ten hour spectrum that would statistically represent the flight profile for Polish Army Mi-24 helicopters.The third crucial element of the analysis was the safe S-N curve that was created on the basis of 2024-T3 aluminum S-N curve. Two factors were introduced in order to change the curve in a way that would guarantee a higher level of certainty that the outcome is not overrated.As a result of this analysis the total fatigue life was estimated including the list of critical locations in which fatigue damage is prone to occur. These regions are going to be carefully examined during scheduled inspections.

System Analysis and Optimization of the CIRSTEL Tail Boom

System Analysis and Optimization of the CIRSTEL Tail Boom