• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 춘계학술대회 논문집
• /
• pp.340-346
• /
• 2013

This paper describes a helicopter vibration induced by main rotor in forward flight. The hub loads in the fixed frame, which are dominant source of helicopter vibration, are obtained by multi-blade summation of rotating blades loadings. The components of 3/rev, 4/rev, and 5/rev blades loadings are transmitted by blades to 4/rev hub loads in the fixed frame. The vertical vibrations of helicopter at pilot seat and copilot seat are calculated through rigid body transfer functions considering airframe to be rigid body. The blades are assumed to be elastic and undergo the flap, lag, and torsion motion and free wake aerodynamic model is used to calculate the precise blade loadings in the analysis. The 4/rev vertical vibration responses are analyzed from rotating blade loadings and fixed hub loadings.

• 한국정밀공학회지
• /
• 제28권8호
• /
• pp.951-958
• /
• 2011

In this paper, the purpose is to investigate the vibration characteristics and the design of resonance avoidance of the unmanned helicopter master. Based on the Euler-Bernoulli beam theory for helicopter master, the equation of motion is derived by using extended Hamilton's principle. It was studied about the natural frequency of helicopter master as the design variances(tip mass, length and diameter of master). Also, it was compared the theoretical results for natural frequency with the results of FE analysis. The results of this study showed the vibration characteristics of helicopter master for the design of resonance avoidance.

• 한국소음진동공학회논문집
• /
• 제14권11호
• /
• pp.1129-1136
• /
• 2004

The structural modification to install a heavy sensor was made at the front extremities of the foreign-produced helicopter operated in the Korea Navy Mounting the sensor directly to the nose structure is unlikely to be practical because it lowers a dynamic mode of the airframe close to rotor blade passing frequencies, leading to increased helicopter vibration. Unfortunately we have no information on dynamic characteristics of the imported helicopter. So the experimental modal model derived from shake testing on the overall airframe of a working helicopter was used to solve the sensor Installation problems. The sensitivity analysis was done to evaluate what the best of modification woo)d be. Simple ID model and experimental modal data for mount system with sensor were Incorporated into overall dynamic model to assess the effects of the sensor installation on helicopter. Modal testing for the modified helicopter shows that the airframe modes are sufficiently displaced from rotor passing frequencies. The mount system has been proven fight to be sufficiently stable to meet vibration-level requirement for all required operational profiles.

• 항공우주산업기술동향
• /
• 제9권1호
• /
• pp.77-89
• /
• 2011

헬리콥터는회전하는구동시스템에의해추력및비행제어력을발생하기때문에회전체에서기체로전달되는 진동 및 소음을 줄이는 것이 아주 중요하다. 과거에는 수동적 방법으로 특정주파수에 해당하는 진동 및 소음을 줄였지만, 기술이 발달함에 따라 주파수를 변동시킬 수 있는 장치를 적용할 수 있는 능동적 진동 및 소음 제어방법이 개발되었다. 본 논문에서는 이러한 헬리콥터 진동 및 소음을 제어하는 능동적 방법에 대한 세계적인 기술동향 및 사례를 기술하였다. 서론에서는 헬리콥터 진동 및 소음을 제어하는 일반적인 방법론을 소개하고, 본론에서는 능동적으로 제어하는 사례 및 동향을 중심으로 기술하였다. 현재 가장 활발하게 진행되고 있는 능동적 플랩구동장치 및 비틀림장치 등을 중심으로 소개하였다.

• 한국항공운항학회지
• /
• 제15권4호
• /
• pp.33-37
• /
• 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.

• 소음진동
• /
• 제10권2호
• /
• pp.229-239
• /
• 2000

To reduce the drag rise on the advancing helicopter rotor blade tips, the tip of the blade is modified to have sweep, anhedral and pretwist. The equations of motion of rotor blade with these tip angles were derived using Hamilton principle, programmed using FORTRAN and named as ARMDAS(Advanced Rotorcraft Multidisplinary Design and Analysis System). Rotating frequency analysis of rotor blades with swept tipe was performed that is necessary in conceptual and preliminary design phases of the helicopter design. Vibration analysis of non-rotating blades was also accomplished and compared with MSC/NASTRAN resutls for the basis of comparison with the vibration test data. The rotating frequency analysis of blades with an actual rotor blade data was also performed to verify coded program and to check the possibility of a resonance of an actual rotor blade at the specific rotating speed.

• International Journal of Aeronautical and Space Sciences
• /
• 제1권1호
• /
• pp.48-61
• /
• 2000

Korea Aerospace Research Institute (KARI) have gained experience with Helicopter Vibration Health Monitoring (VHM) System technology with the help of UK GKN-WHL. GKN-WHL have had many years of experience with the research and development of vibration analysis techniques to improve the health monitoring of helicopter transmissions. This activity was targeted at transmission rig testing at first, but the techniques have been progressively developed where they are now used as a part of integrated Health and Usage Monitoring (HUM) systems on many types of in-service and new helicopters. The technique development process has been considerably aided by an ever expanding database of transmission monitoring experience from both the rig testing and aircraft operations. This experience covers a wide range of failure types from naturally occurring faults to crack propagation studies and covering a wide range of transmission configurations. Primarily based on accelerometer signals GKN-WHL's vibration analysis methods have also been applied to a variety of other sensor types. The transition from an experimental environment to operational VHM systems has been a lengthy process, there being a need to demonstrate technique reliability as well as effectiveness to both regulatory (Airworthiness Authority) and commercial organizations. Another important feature of this process has been the development of close relationships with a number of VHM system hardware and software suppliers. Such an experienced GKN-WHL provides various raw vibration data which was acquired from transmission ground test rig and allow KARI to develop it's own analysis program. KARI made a program and then analyzed the data to coma pre with the results of GKN-WHL. The KARI's results both time domain signals and statistical values show comparable to GKN's.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2005년도 추계 학술대회논문집(수송기계편)
• /
• pp.41-44
• /
• 2005

This paper described improvement and operation of a 'Tail-Fan' anti-torque performance test system KARI (Korea Aerospace Research Institute) developed a 'Tail-Fan' anti-torque system of a helicopter and a performance test-rig to test the performance of the Tail-Fan. The test-rig was improved for full rotating test in 4300rpm(100%). Machinery and hydraulic parts ware changed to reduce vibration and to increase safety. To find the operation rotating speed for the performance test, vibration test were carried out rising accelerometers on tail gear box. The performance test conditions of the Tail-Fan to avoid a resonance were found from vibration test results. The Tail-Fan operation tests were performed safely frier to carry out performance test.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2006년도 춘계학술대회논문집
• /
• pp.300-303
• /
• 2006

The rotor blade of a helicopter is the key structural units and provides three components such as vertical lifting force, horizontal propulsive force and control force. With advancements in aerospace technology, composite materials have been widely used in lightweight structures. In addition, composites show great potential on the design of rotor blades due to the advantages of strength, durability and weight of the materials. In the operational condition of a helicopter, it is required the vibration characteristics of the rotating blades for avoiding resonance and analysis of efficient performance prediction et al. In this study, the CAMRAD-II is used for analyzing the vibration characteristics of rotating composite blades. The effects of rotating speed and collective angles are investigated. Also, the numerical results are compared with experimental data.

• 한국항공우주학회지
• /
• 제50권11호
• /
• pp.791-800
• /
• 2022

능동 진동 제어 시스템(Active vibration control system, AVCS)을 이용하여 헬리콥터 기체의 능동 진동 제어 시 우수한 진동 제어 성능을 얻기 위하여서는 진동 상쇄 하중 발생기의 개수, 위치 및 하중 방향의 조합의 최적화가 중요하다. 따라서 고려 가능한 모든 하중 발생기의 조합에 대하여 헬리콥터 기체에 대한 AVCS의 진동 제어 성능을 조사하기 위해 Exhaustive 시험 기법을 적용한 AVCS 프레임워크를 구축하였다. 로터 진동 하중 해석, 기체 진동 응답 해석 및 AVCS 시뮬레이션 연구를 수행하기 위해 DYMORE II, MSC.NASTRAN 및 MATLAB Simulink 등 다양한 프로그램을 사용하였다. 이를 이용하여 비행 속도 158 knots의 UH-60A 헬리콥터에 대한 AVCS 적용을 위한 CRFG 조합을 최적화하였다. 최적의 CRFG 조합이 적용된 AVCS를 통해 UH-60A 헬리콥터의 4P 기체 진동 응답을 능동 제어한 결과, 기체의 주요 위치에서 4P 기체 진동 응답이 19.35~98.07%만큼 감소될 수 있었다.