Helicopter Body Research Articles

Design of a Functional Active Epoxy Coating for Anticorrosion Performance Using SiO2 Nano-Conductive Polyaniline Nanoparticles in Aluminum Blends of Helicopters

In this study, polyaniline (PANI) nanocomposites/silica (SiO2) nanoparticles are used in epoxy to create smart anticorrosive coatings for the alloy used in helicopters. SiO2 was synthesized by a sol–gel method with tetraethyl orthosilicate. Then, PANI/SiO2 nanocomposites were formed by the electrostatic method. Various tests, including Fourier-transform infrared, ultraviolet–visible spectroscopy, x-ray diffraction, thermo-gravimetric analysis and field-emission scanning electron microscopy, have been performed for characterization of the nanocomposites, and the results indicate that the synthesis of these nanocomposites has been completed. Then, 1 wt.% of PANI/SiO2 nanocomposite was added into epoxy resin and cured by polyamine hardener. Epoxy/PANI/SiO2 coatings with 30-µm thickness were tested on the alloy of the helicopter body. The atomic weight fraction of the helicopter alloy was determined by the inductively-coupled plasma emission test. The results indicate that aluminum constitutes 98% of the alloy. Finally, the analysis of the sealed coatings by electrochemical impedance spectroscopy and salt spray tests have demonstrated that epoxy/polyaniline/silica nanocomposites significantly increase the anticorrosive properties of the epoxy.

Failure Analysis of Weldment Crack in Body Structure of a Helicopter

Leak of nitrogen gas was noticed from a helicopter body structure in-service. Inspection showed that the leak was from a crack located at the end of the welded joint between the parts tube and gusset of the body structure. Scanning electron microscopy showed that the weldment crack was a fatigue crack that had originated at multiple locations from the weld bead. At the end of the weldment between tube and gusset, overlap/overwelding was observed toward the tube side of the weldment. The leg size of the weldment was excessive, and it also showed lack of fusion and penetration. Lack of fusion is discontinuity between weld and base metals, so there is no path for stress to transfer through the weld into the adjoining member. Thus, the stress axis got shifted toward the overlap/overwelded region resulting in bending moment on the weldment and making it vulnerable to fail by fatigue. As an outcome of this investigation, it was recommended to alter the welding sequence of the body structure to avoid any blind welds that can result in lack of fusion and overwelding.

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.

Evaluation of Microphone Array for Multirotor Helicopters

[abstFig src='/00290001/16.jpg' width='300' text='UAV with a microphone array whose performance is evaluated' ] High expectations are placed on the use of unmanned aerial vehicles (UAVs) in such tasks as rescue operations, which require a system that makes use of visual or auditory information to recognize the surrounding environment. As an example of such a system, this study examines the recognition of the environment using a helicopter mounted with a microphone array. Because the rotors of a helicopter generate high noise during operation, it is necessary to reduce the effects of this noise and those from other sources to record the audio signals coming from the ground with onboard microphones. In particular, because of helicopter body control, the rotor speed changes continuously and causes an unsteady rotor noise, which implies that it would be effective to arrange the microphones at a sufficient distance from the rotors. When a large microphone array is employed, however, the array weight may alter the helicopter’s flight characteristics and increase the noise, presenting a dilemma. This paper presents a model of rotor noise that takes into account the effect of the microphone array on the helicopter’s dynamic characteristics and proposes a method of evaluating the optimality of the array configuration, which is necessary for design. The validity of the proposed method is investigated using a multirotor helicopter mounted with a microphone array previously developed by the authors. In addition, an application example for locating sound sources on the ground using this helicopter is presented.

Understanding pilot biodynamical feedthrough coupling in helicopter adverse roll axis instability via lateral cyclic feedback control

The paper reassesses the mechanism of biodynamical feedthrough coupling to helicopter body motion in lateral-roll helicopter tasks. An analytical bio-aeroelastic pilot–vehicle model is first developed and tested for various pilot's neuromuscular adaptions in the lateral/roll axis helicopter tasks. The results demonstrate that pilot can destabilize the low-frequency regressing lead-lag rotor mode; however he/she is destabilizing also the high-frequency advancing lag rotor mode. The mechanism of pilot destabilization involves three vicious energy circles, i.e. lateral-roll, flap-roll and flap-lag motions, in a very similar manner as in the air resonance phenomenon. For both modes, the destabilization is very sensitive to an increase of the steady state rotor coning angle that increases the energy transfers from flap to lag motion through Coriolis forces. The analytical linear time-invariant model developed in this paper can be also used to investigate designs proneness to lateral/roll aeroelastic rotorcraft–pilot couplings.

Direct and indirect lightning tests to the Z11 helicopter radome in China

A 4.8 MV impulse voltage generator and impulse current generators are used to perform lightning simulation on the Z11 helicopter radome. The radome system is composed of lightning diverter strips, air data probe and a 0.5 m long metal structure attached to the radome to simulate the helicopter body. The test facilities, process and the results are presented according to the Chinese CCAR27 standard. This test improved considerably the lightning protection performance of the Z11 radome system by optimizing the diverters. This resulted in successful passing of ground simulated lightning test requirements.

Fuzzy-Genetic Identification and Control Stuctures for Nonlinear Helicopter Model

The paper exploits advantages of the genetic algorithm and fuzzy logic in identification and control of 2DOF nonlinear helicopter model. The genetic algorithm is proposed for identification of the helicopter system, which contains a helicopter body, main and tail motors and drivers. The quality of helicopter model achieved was validated through simulation and experimental modes. Then, this model is used to design of elevation and azimuth Mamdani type fuzzy controllers. The main objective of the paper is to obtain robust and stable controls for wide range of azimuth and elevation angles changing during the long time flight. The robustness and effectiveness of both fuzzy controllers were verified through both simulations and experiments. Also, a comparative analysis of proposed fuzzy and traditional PID controllers is performed.

Demonstrating the conservation of angular momentum using model cars moving along a rotating rod

We have developed an exciting non-traditional experiment for our introductory physics laboratories to help students to understand the principle of conservation of angular momentum. We used electric toy cars moving along a long rotating rod. As the cars move towards the centre of the rod, the angular velocity of this system increases. Alternatively, when the cars move away from the axis of the rotating rod, the angular velocity of the system decreases. This allows the students to grasp the striking effects of the conservation of the system’s angular momentum. The experiment illustrates the physical laws underlying fascinating natural phenomena and processes such as the origin of neutron star rotation, the motion of planets and the reaction of a helicopter body to the rotation of its blades. In addition, the effect of air resistance on the angular velocity is measured and discussed in detail, as it adds a significant component of realism to the experiment. Realism is often ignored in traditional experiments of this kind. Even though the air resistance effect is minor, we tackled it in our experiment and found it too substantial to be ignored. It is very enlightening for the students to see the reality of air resistance and it will help them to develop a critical approach to the idealized pictures often used in physics. Our experiment is simple and can be implemented in any introductory physics laboratory at little cost.

365 RX CPUを用いた自律型Quadrotorヘリコプタのホバリング

In this research project the developed an autonomous quadrotor helicopter is used for in indoor search applications. The helicopter body weighs 0.83 kg and can carry a payload weighing 0.4 kg. It is equipped with MEMS sensors (gyro, acceleration, magnetic, and pressure), a PSD unit, an ultrasonic sensor, and an optical position sensor. The control system employed an RX CPU. To measure the attitude angle, the output signal of the gyro sensor is passed through a filter to eliminate vibration components and then integrated. Correction based on the acceleration sensor is applied to suppress the drift of integration. Position calculation is performed by the optical position sensor, which is observed infrared LEDs placed on the floor. As a result, hovering was achieved with an accuracy of ±0.3 meter.

Signal Processing Algorithm to Reduce RWR Electro-Magnetic Interference with Tail Rotor Blade of Helicopter

In the environment where various and complicated threat signals exist, RWR (Radar Warning Receiver), which can warn pilot of the existence of threats, has long been a necessary electronic warfare (EW) system to improve survivability of aircraft. The angle of arrival (AOA) information, the most reliable sorting parameter in the RWR, is measured by means of four-quadrant amplitude comparison direction finding (DF) technique. Each of four antennas (usually spiral antenna) of DF unit covers one of four quadrant zones, with 90 degrees apart with nearby antenna. According to the location of antenna installed in helicopter, RWR is subject to signal loss and interference by helicopter body and structures including tail bumper, rotor blade, and so on, causing a difficulty of detecting hostile emitters. In this paper, the performance degradation caused by signal interference by tail rotor blades has been estimated by measuring amplitude video signals into which RWR converts RF signals in case a part of antenna is screened by real tail rotor blade in anechoic chamber. The results show that corruption of pulse amplitude (PA) is main cause of DF error. We have proposed two algorithms for resolving the interference by tail rotor blades as below: First, expand the AOA group range for pulse grouping at the first signal analysis phase. Second, merge each of pulse trains with the other, that signal parameter except PRI and AOA is similar, after the first signal analysis phase. The presented method makes it possible to use RWR by reducing interference caused by blade screening in case antenna is screened by tail rotor blades.

Layout Optimization of Mooring Base of the Ship-Based Helicopter Based on FEM

The ship-based helicopter is always dangling in the sea because of winds and waves. It is necessary to analyze and calculate the mooring of helicopter. In order to void the complex derivation of mathematical formulas, the parameterized finite element method (FEM) model about the ship-based helicopter body, mooring cable and mooring base is established with the software ADAMS. This model is used to calculate the mooring tension and optimize the locations of the mooring bases. In the various layouts of the mooring bases, the minimal mooring tension is the layout optimization object. After some added constraint conditions are considered, the mooring point coordinates are searched and calculated in the standard and nonstandard parking positions with subproblem approximation method. Through the comparison and analysis of the relative changing ratio of the position coordinates, the final optimization layout scheme is obtained.

An accelerated life test approach for aerospace structural components

In this article, analysis and testing processes of the prototype of a helicopter’s mission system sensor (MSS)-cowling assembly is described. MSS is an add-on unit which is mounted on the helicopter body. In order to ensure that the attached unit functions for a specified life without structural failure, a careful analysis and testing program had been implemented. The approach described here which involves accelerated life testing (ALT) establishes an appropriate methodology for such “integration” projects. The expected mode of failure for the MSS-cowling assembly was metal fatigue under random vibrations. Operational flight tests were performed for obtaining the loading data (accelerations) at the analyzed location. This data was utilized both in the numerical simulation (vibration fatigue analysis through finite element modeling) and in the actual testing of the assembly. In order to qualify the design life in the laboratory, ALT profiles were created by synthesizing the collected data. Fatigue test of the assembly was executed by using these profiles. At the same time strain gage data was collected at the critical locations. Representative alternating stress values were obtained by processing this strain data. By changing the test durations and accordingly the mission profile amplitudes a simple equation is proposed which relates ALT durations with the equivalent alternating stresses. The laboratory testing of the assembly was continued until failure. Results of numerical simulations and testing are discussed.

スティンガー式ヘリコプター磁気探査システムの開発とその磁気センサーに対する機体磁気補償

A helicopter-borne magnetic survey system was developed in use of a nose boom magnetic sensor, which enables safe and practical operation of low-altitude high-resolution survey even in mountainous regions of very steep topography and high elevation. The system consists mainly of airborne Cesium magnetometer, 3-axis fluxgate magnetometer, GPS receiver, navigation unit, data-acquisition PC, etc., incorporating with other equipment on the ground including base station magnetometer and reference station GPS receiver.The nose boom magnetic sensor is situated rather near the helicopter body and cannot be free from its magnetic noise, though the boom itself is made non-magnetic. The 3-axis fluxgate magnetometer is the equipment to compensate aircraft's magnetic noise field. Theoretical consideration for passive magnetic compensation and the method of actual data processing for it are discussed. Then the software for magnetic compensation was developed and applied to the data of actual verification survey, and the procedure was proven to accomplish post-flight magnetic compensation properly.

Field tests of an experimental helicopter time‐domain electromagnetic system for unexploded ordnance detection

Field trials of a low‐flying time‐domain helicopter electromagnetic system designed for detection of unexploded ordnance have yielded positive and encouraging results. The system is able to detect ordnance as small as 60‐mm rounds at 1‐m sensor height. We examined several transmitter and receiver configurations. Small loop receivers gave superior signal‐to‐noise ratios in comparison to larger receiver loops at low heights. Base frequencies of 90 Hz and 270 Hz were less affected than other base frequencies by noise produced by proximity to the helicopter and by vibration of the support structure. For small ordnance, a two‐lobed, antisymmetric transmitter loop geometry produced a modest signal‐to‐noise enhancement compared with a large single rectangular loop, presumably because the antisymmetric transmitter produces smaller eddy currents in the helicopter body, thereby reducing this source of noise. In most cases, differencing of vertically offset receivers did not substantially improve signal‐to‐noise ratios at very low sensor altitudes. Signal attenuation from transmitter to target and from target to receiver causes signals from smaller ordnance to quickly become indistinguishable from geological background variations, so that above a sensor height of about 3 m only large ordnance items (e.g., bombs and large caliber artillery rounds) were consistently detected.

Numerical Study of Interaction between Vortex and Helicopter Rotor Blades by the Three-Dimensional Discrete Vortex Method. 2nd Report.

The blade-vortex-interaction (BVI) of a helicopter's two-blade rotor is analyzed by the three-dimensional discrete vortex method for various conditions including the helicopter's body. The rotor is represented by source panels and the decent vortices are shed from the tips and the trailing edges of the blades as vertex rings and a part of each vortex ring is kept within the blades. The body is also expressed by source panels. It is found that the thrust fluctuation on the blade occurs rather randomly in the region of the azimuth angle 0 to 180 degrees. The fluctuation is stronger in descending case than in horizontally flying case, and the fluctuation occurs even in the region of azimuth angle larger than 320 degrees in the descending case. The helicopter's body does not affect the characteristics of the rotor aerodynamics, but the disturbance in the wake slightly glows. It is also shown that combinations of the vortices is effective for decreasing the number of vortices without affecting the computing results.

A nonlinear inverse simulation technique applied to coaxial rotor helicopter maneuvers

As compared with the maneuvering flight studies for single main rotor helicopters, the corresponding studies for coaxial rotor helicopters are relatively poor. In this paper, the maneuvering flight governing equations for coaxial rotor helicopters is established. By introducing induced velocity interference factor analysis, the coaxial rotor aerodynamic interference can be taken into account. With the combination of coaxial rotor helicopter control features and nonlinear inverse simulation technique, the governing equations for maneuvering flight can be solved so as to determine helicopter control input, control force and moment, and helicopter body attitudes which are needed for performing a specified maneuver. Good results of the sample calculations of level turn and lateral jink maneuvers are obtained and simply analyzed.

Low cost L‐band mobile terminal antennas for helicopters

AbstractThe feasibility of using a low‐gain antenna (LGA) as a mobile terminal antenna for helicopers is described in this article. The objectives are (a) to select the lowest cost antenna system which can be easily mounted on a helicopter and capable of communicating with a satellite, and (b) to determine the best antenna position on the helicopter to mitigate the signal blockage due to rotor blades and the multipath effect from the ehlicopter's body. The omnidirectional low gain antenna (LGA) is selected because it is simple, reliable, and low cost. The helix antenna is selected among the many LGAs because it is the most economical and has the widest elevation beam‐width. Both two‐ and four‐arm helices are studied experimentally to determine the antenna's performance and the scattering effects from the helicopter's body. It is found that the LGA should be located near the tail section and at least 8 in. above the helicopter.

Computation of three-dimensional boundary layers on fuselages

A new approach is developed to construct boundary-layer coordinates, and to handle metric properties, transformations, and so forth on realistic configurations. The approach, which employs tensorial concepts, is discussed in its major steps. Results of boundary-laye r computations on a helicopter body, a car body, and on a supersonic fighter nose found with the integral method of COUSTEIX are then used to show the potential of the approach. Special attention is given to the interpretation of the boundary-layer results with regard to possible separation patterns. The results may be used in order to model separated flow. ETHODS for the computation of laminar or turbulent three-dimensional boundary layers have been available for several years. Comparisons of integral and finite- difference methods, as well as applications to test cases organized for instance by the EUROVISC-Working Party on Three-Dimensional Shear Layers,1'2 have established an acceptable level of confidence for applications in design aerodynamics. Boundary-layer computations on simple wing geometries are made routinely today. The computation of boundary layers on general configurations, especially fuselage con- figurations, has been hampered because of the problems connected with the creation of boundary-laye r coordinates on the surfaces of such configurations. Recently, means have been developed for the definition of general, nonorthogonal, curvilinear boundary-layer coordinates,3'4 so that boundary- layer theory can now be applied in design aerodynamics to flows on rather complicated shapes. In the present paper a brief description is given of some of the concepts obtained in Ref. 3 with regard to boundary-layer problems on fuselages. Results of boundary-laye r studies on a helicopter fuselage, a car body, and on a supersonic fighter nose are discussed in order to show the value of the approach. Because three-dimensional boundary-layer separation is difficult to detect in computations, some ad hoc criteria are applied: \T - minimum criterion,5 convergence of skin- friction lines, and bulging of boundary-laye r thickness and displacement-thickness contours.6 Special attention is given to the interpretation of the boundary-layer results with regard to possible separation patterns, which may be used in order to model separated flow. The above separation criteria, together with topological laws and details of the skin-friction distribution, allow one in many cases to sketch the skin- friction line topology beyond the region where boundary- layer results were found; that is, the separation region. The boundary-layer method used for the studies is the integral method of COUSTEIX 7 in the form of COUSTEIX- AUPOIX. In this method a mixing length model is used together with similarity solutions to find families of both main-flow and cross-flow profiles. The continuity equation is applied as an entrainment equation. The surface is assumed to be insulated. The method is formulated for arbitrary boundary-layer coordinates and can be applied to flows with

Orthogonal multiblade coordinates

Introduction T method of multiblade coordinates introduced by Coleman is a powerful technique for describing the motion of a multibladed helicopter rotor. Multiblade coordinates describe the overall rotor motion in a nonrotating coordinate frame fixed in the helicopter body. This provides advantages over individual blade coordinates which describe the motion of the individual blades in a frame rotating with the rotor. Some advantages are 1) the overall rotor motion, which includes the motion of all the blades, is intuitively easier to understand because it is described in terms of the collective mode and the periodic longitudinal and lateral modes in the nonrotating frame; 2) fuselage motion and active controls couple with the rotor motion in the form of nonrotating feedback effects; and 3) the transformation to multiblade coordinates replaces some harmonic terms in the equations of motion by constants and higher frequency terms. This last property results in the time-averaged constant coefficient approximation being valid for higher advance ratios compared with the individual blade equations. It also reduces the computation time necessary for a stability analysis using Floquet theory in the case that periodic terms are not time aver aged. The method of multiblade coordinates has been applied by Hohenemser and Yin, Biggers, Gaonkar and Peters,' Hodges, Briczinski and Cooper, and others to analyze various aspects of the motion of multibladed rotors. In this Note a modified set of multiblade coordinates is introduced for which the transformation between individual blade coordinates and mutiblade coordinates is orthogonal, hence the name orthogonal multiblade coordinates. This property results in simplifications in the transformations of the equations of motion and their solutions.