• Journal of the Korean Society for Aviation and Aeronautics
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• v.15 no.4
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• pp.33-37
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• 2007

In this paper, a dynamic analysis of a helicopter landing gear with considering flexible structural modes has been investigated. The main body of the helicopter has been modeled as a flexible body using FEM code, then a few selected vibration modes of the helicopter main body have been used as basis for the dynamic analysis of the helicopter landing gear. The simulation of dynamic analysis was carried out on the base of ADAMS aircraft module. It has been found by a series of simulation that the flexible structural modes has a significant effect on the dynamic characteristics of helicopter landing gear as the flexibility of the main body is increased.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.383-389
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• 2013

Rotor system is a very important part which produces lift, thrust and control force in helicopter. Component of rotor system must endure various flight load for the required life. In helicopter rotor system, bearingless rotor system is the highest technology rotor system compare with articulated and hingeless rotor system. Baaringless rotor system is not include mechanical flap hinge, lag hinge and pitch bearing. Bearingless rotor component flexbeam which made by composite material has conduct hinge and bearing role instead of mechanical flap hinge, lag hinge and pitch bearing. These characteristics has less part number and lass weight than others. In this paper, conduct safe life analysis of bearingless composite component flexbeam and torque tube applying to utility helicopter load condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.132-137
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• 2005

This paper addresses what amount of whole-body vibration is exposed to pilots of UH60 helicopters during flight. To measure the whole-body exposed from the feet and seat, the 12-axis vibration measurement system was used. It enables simultaneous measurement of vibration exposure from the body contact area of the feet, hip and back. The measured 12-axis vibration signals are exploited to the comfort level of UH60 helicopters during flight. It is shown that the evaluated ride value is close to $0.74{\sim}0.79m/s^2$ and that it is equivalent to the semantic scale of 'fairly uncomfortable'. To assess the health effects of whole-body vibration exposed to pilots of UH60 helicopters during their flight, the rms-based and VDV(vibration dose value)-based evaluation results of measured four-axis vibration signals are shown in this work. The fatigue-decreased proficiency limit, whose level is half of the exposure limit, is expected to come after the two-hour flight. The exposure limit is shown to reach after the 10-hour flight.

• Transactions of the KSME C: Technology and Education
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• v.2 no.2
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• pp.113-124
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• 2014

In developing an aircraft, configuration determination and requirement proofing depend on flight test results. Since the flight tests require much time and high cost, systematic flight test planning and analysis are needed to reduce cost and development time. This paper presents a desirability function approach to present an integrative measure of vibration levels at important positions and suggests a fractional factorial design which is one of the experimental design methods to help perform systematic flight tests. A method to perform flight tests in stages is also suggested to further reduce the number of flight tests.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.6
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• pp.63-69
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• 2011

This study analyzes stress, fatigue and vibration on main rotor and body of helicopter. The maximum stress is shown on adjoint part between body and main rotor at the lower position of main rotor. As the maximum displacement amplitude is happened at 4000Hz, there is no resonance and the state of helicopter becomes safe at hovering without the abnormal air current and the disabled rotor. Among the cases of nonuniform fatigue loads, 'SAE bracket history' with the severest change of load becomes most unstable but 'Sample history' becomes most stable. In case of 'Sample History' with the average stress of 0MPa to $-10^5MPa$ and the amplitude stress of 0MPa to $8.539{\times}10^5MPa$, the possibility of maximum damage becomes 3%. This stress state can be shown with 5 times more than the damage possibility of 'SAE bracket history' or 'SAE transmission'. The structural result of this study by using the analysis of vibration and fatigue can be effectively utilized for safe and durable design of helicopter.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.653-655
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• 1999

카메라 영상을 통하여 무인 헬리콥터 동작을 추정하기 위해 적응형 가중치를 사용한 새로운 Ego-Motion을 검출 기법을 제안하였다. 무인 헬리콥터 동적 특성은 비선형이며, 심한 진동 발생으로 영상 번짐(blur) 현상이 나타나기 때문에 상관 값만을 고려한 정합 방법으로는 빈번히 오차가 발생한다. 본 논문에서는 가속도, 각 가속도 및 제어입력 값에 의한 위치 추정 값과 상관 값 및 에지 강도를 가중치에 의해 융합하여 정확한 Ego-Motion을 계산할 수 있는 기법을 제안하였다. 또한 무인 헬리콥터의 가속도, 각 가속도, 상하 속도에 따라서 영상의 번짐 정도가 달라 이들 같이 크면 위치오차에 가중을 크게 주고, 작으면 상관 값에 가중치를 적게 주는 적응형 가중치 결정 알고리즘을 적용하였다. 제안한 적응형 가중치 기법을 무인 헬리콥터에 실험한 결과 카메라에 포착된 영상에 의해 무인헬기의 동작을 정확히 추정 할 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.159-166
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• 2018

In this study, the internal structural design, dynamic characteristics and load analyses of the small scaled rotor blade required for LCH(Light Civil Helicopter) main rotor wind tunnel test were carried out. The test is performed to evaluate the aerodynamic performance and noise characteristics of the LCH main rotor system. Therefore, the Mach-scale technique was appled to design the small scaled blade to simulate the equivalent aerodynamic characteristics as the full scale rotor system. It is necessary to increase the rotor speed to maintain the same blade tip speed as the full scale blade. In addition, the blade weight, section stiffness, and natural frequency were scaled according to the Mach-type scaling factor(${\lambda}$). For the design of skin, spar, torsion box, which are the main components of the blade, carbon and glass fiber composite materials were adopted, and composite materials are prepreg types that can be supplied domestically. The KSec2D program was used to evaluate the section stiffness of the blade. Also, structural loads and dynamic characteristics of the Mach scale blade were investigated through the comprehensive rotorcraft analysis program CAMRADII.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.8
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• pp.759-769
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• 2013

Electronic equipment has been applied to virtually every area associated with commercial, industrial, and military applications. Specifically, electronics have been incorporated into avionics components installed in aircraft. This equipment is exposed to dynamic loads such as vibration, shock, and acceleration. Especially, avionics components installed in a helicopter are subjected to simultaneous sine and random base excitations. These are denoted as sine on random vibrations according to MIL-STD-810F, Method 514.5. In the past, isolators have been applied to avionics components to reduce vibration and shock. However, an isolator applied to an avionics component installed in a helicopter can amplify the vibration magnitude, and damage the chassis, circuit card assembly, and the isolator itself via resonance at low-frequency sinusoidal vibrations. The objective of this study is to investigate the dynamic characteristics of an avionics component installed in a helicopter and the structural dynamic modification of its tray plate without an isolator using both a finite element analysis and experiments. The structure is optimized by dynamic loads that are selected by comparing the vibration, shock, and acceleration loads using vibration and shock response spectra. A finite element model(FEM) was constructed using a simplified geometry and valid element types that reflect the dynamic characteristics. The FEM was verified by an experimental modal analysis. Design parameters were extracted and selected to modify the structural dynamics using topology optimization, and design of experiments(DOE). A prototype of a modified model was constructed and its feasibility was evaluated using an FEM and a performance test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.7
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• pp.489-498
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• 2019

The airloads and structural loads of Light Civil Helicopter (LCH) rotor are investigated using a loose CFD/CSD coupling. The structural dynamics model for LCH 5-bladed rotor cwith elastomeric bearing and inter-bladed damper is constructed using CAMRAD-II. Either isolated rotor or rotor-fuselage model is used to identify the effect of the fuselage on the aeromechanics behavior at a cruise speed of 0.28. The fuselage effect is shown to be marginal on the aeromechanics predictions of LCH rotor, though the effect can be non-negligible for the tail structure due to the prevailing root vortices strengthened by the fuselage upwash. A lifting-line based comprehensive analysis is also conducted to verify the CFD/CSD coupled analysis. The comparison study shows that the comprehensive analysis predictions are generally in good agreements with CFD/CSD coupled results. However, the predicted comprehensive analysis results underestimate peak-to-peak values of blade section airloads and elastic motions due to the limitation of unsteady aerodynamic predictions. Particularly, significant discrepancies appear in the structural loads with apparent phase differences.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.32-41
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• 2009

In this study, scale-down design of full-scale Korean Utility Helicopter (KUH) main rotor blade has been investigated. The scaled model system were designed for the measurement of aerodynamic performance, tip vortex and noise source. For the purpose of considering the same aerodynamic loads, the Mach-scale method has been applied. The Mach-scaled model has the same tip Mach number, and it also has the same normalized frequencies. That is, the Mach-scaled model is analogous to full-scale model in the view point of aerodynamics and structural dynamics. Aerodynamic scale-down process could be completed just by adjusting scaling dimensions and increasing rotating speed. In the field of structural dynamics, design process could be finished by confirming the rotating frequencies of the designed blade with the stiffness and inertial properties distributions produced by sectional design. In this study, small-scaled blade sectional design were performed by applying domestic composite prepregs and structural dynamic characteristics of designed model has been investigated.