Taejoo Kim

Hub Parametric Investigation of Main Rotor Stability of Bearingless Helicopter

This paper describes a stability and dynamic characteristics of bearingless helicopter main rotor in hover. Baseline rotor configuration is defined and modal analysis for the configuration is taken to verify the dynamic characteristics. The kinematic pitch-lag couplings through ways of pitch link installation are analyzed to know effects on loads, frequencies and stability. The effects of pitch link attachments in spanwise direction and chordwise direction as well as pitch link inclination on thrust, power, flpa-lag-pitch mode frequencies and inplane damping are examined. Pitch link at trailing edge location in chordwise direction has influence on aeroelastic stability of the rotor. Also, the pitch link with negative inclination angle makes inplane damping increase.

Test and Simulation of an Active Vibration Control System for Helicopter Applications

A significant source of vibration in helicopters is the main rotor system, and it is a technical challenge to reduce the vibration in order to ensure the comfort of crew and passengers. Several types of passive devices have been applied to conventional helicopters in order to reduce the vibration. In recent years, helicopter manufacturers have increasingly adopted active vibration control systems (AVCSs) due to their superior performance with lower weight compared with passive devices. AVCSs can also maintain their performance over aircraft configuration and flight condition changes. As part of the development of AVCS software for light civil helicopter (LCH) applications, a test bench is constructed and vibration control tests and simulations are performed in this study. The test bench, which represents the airframe, is excited using a pair of counter rotating force generators (CRFGs) and a multiple input single output (MISO) AVCS that consists of three accelerometer sensors and a pair of CRFGs; a filtered-x least mean square (LMS) algorithm is applied for the vibration reduction. First, the vibration control tests are performed with uniform sensor weights; then, the change in the control performance according to changes in the sensor weight is investigated and compared with the simulation results. It is found that the vibration control performance can be tuned through adjusting the weights of the three sensors, even if only one actuator is used.

Manufacturing Process and Basic Property Tests of Composite Helicopter Rotor Hub System

를 통해 복합재료로 제작된 플렉스빔과 토크튜브가 구조적인 강성 요구도를 만족함을 확인할 수 있었다. Abstract: This paper describes the manufacturing processes for a flexbeam and torque tube made of composite materials, along with the procedures for testing their basic properties. A flexbeam and torque tube can be considered to be key structural components of a bearingless rotor hub system. A hinge offset effect can be realized by a large elastic deformation and twist of the flexbeam, and the blade pitch control forces are transferred by the rotation of the torque tube. The basic property tests included bending and twist tests to determine the flap stiffness, lag stiffness, and torsion stiffness of the flexbeam, torque tube, and blade, and these tests were performed prior to starting the whirl tower test. In addition, the estimated results were compared with experimental data, and the calculations were found to be a good match for the analysis results and had a similar tendency. Through these results, we could confirm that a flexbeam and torque tube made of composite materials satisfied the structural stiffness requirements.

Hingeless Blade Flexure Bending Stiffness Reinforcement for Whirl Tower Test

BO-105 helicopter applies hingeless rotor hub system and blade root uses a flexure of hingeless rotor hub system. So bending stiffness reinforcement for flexure was conducted for preparation of whirl tower test using BO-105 blade. Bending moment of flexure area was calculated with FE modeling of section shape for stiffness reinforcement of flexure and thickness of composite material for reinforcement was chosen. Flexure bending stiffness reinforcement was conducted and bending stiffness measurement test was performed before and after bending stiffness reinforcement. And the test data are compared with analysis results.

Fatigue Safe Life Analysis of Helicopter Bearingless Rotor Hub Composite Flexbeam

After we designed Bearingless rotor hub system for 7,000lb class helicopter, flexbeam fatigue analysis was conducted for validation of requirement life time 8,000 hours. sectional structural analysis method applying elastic beam model was used. Fatigue analysis for two sections of flexbeam which were expected to weak to fatigue damage from result of static analysis was conducted. Extension, bending and torsion stiffness of flexbeam section shape was calculated using VABS for structure analysis. S-N curve of two composite material which composed flexbeam was generated using wohler equation. Load analysis of bearingless rotor system was conducted using CAMRAD II and load analysis result was applied HELIX/FELIX standard load spectrum to generate bearingless rotor system load spectrum which was used flexbeam fatigue safe life analysis.

Ground Resonance Instabilities Analysis of a Bearingless Helicopter Main Rotor

The ground resonance instability of a helicopter with bearingless main rotor hub were investigated. The ground resonance instability is caused by an interaction between the blade lag motion and hub inplane motion. This instability occurs when the helicopter is on the ground and is important for soft-inplane rotors where the rotating lag mode frequency is less than the rotor rotational speed. For the analysis, the bearingless rotor was composed of blades, flexbeam, torque tube, damper, shear restrainer, and pitch links. The fuselage was modeled as a mass-damper-spring system having natural frequencies in roll and pitch motions. The rotor-fuselage coupling equations are derived in non-rotating frame to consider the rotor and fuselage equations in the same frame. The ground resonance instabilities for three cases where are without lead-lag damper and fuselage damping, with lead-lag damper and without fuselage damping, and finally with lead-lag damper and fuselage damping. There is no ground resonance instability in the only rotor-fuselage configuration with lead-lag damper and fuselage damping.

Dynamic Characteristic Analysis of Active Gurney Flap Considering Rotational Effect

Abstract : In this study, the finite element analysis was carried out to investigate dynamic characteristics of the AGF(Active Gurney Flap) which is under development for reducing vibration and noise of the helicopter rotor system. The Gurney flap is a kind of small flat plate, mounted normal to the lower surface of the airfoil near to the trailing edge. An electric motor, L-shaped linkages and flap parts were integrated into a rotor bade, and 3~5/rev control was given to the AGF to reduce the vibration in the fixed frame. Thus, an explicit time integration method was adopted to investigate the dynamic response of the AGF with considering both centrifugal force due to the rotor rotation and active control input, and it can be seen that the vertical displacement of the AGF was satisfied to meet the design requirement. § 이 논문은 대한기계학회 2014년도 추계학술대회(2014. 11. 11-14., 김대중컨벤션센터) 발표내용을 토대로 한 논문임. † Corresponding Author, naltlguy@kari.re.kr Ⓒ 2015 The Korean Society of Mechanical Engineers

Active Gurney Flap Design Modification for High Speed Operation and Natural Frequency Estimate

ABSTRACT Working displacement variation by elastic deformation of active Gurney flap which was operated on high frequency was observed. Flap-wise natural frequency was lower than mode analysis result and hinge boundary condition was identified to be the cause through the simple modal test. Design modification for increasing natural frequency was conducted for minimizing the elastic deformation at maximum 35 Hz operating condition which was design requirement condition. Brass bushing was ap-plied instead of rotating bearing for gap minimization and Gurney flap design modification was con-ducted to increase of the flap-wise natural frequency. Design modification effect was validated by natural frequency comparison with mode analysis result and modal test result of design modification model. * 기 호 설 명 ue00b ue004 : 편심축 길이(mm)ue00b ue034 : 거니플랩 높이(mm)ue00b ue035 : 거니플랩 길이(mm)ue003: AGF 작동기 작동 길이(mm)ue0b4 ue0f2 : 고유 회전 주파수(rad/sec)ue0ea : 고유진동수(Hz)ue0ad : 단위 길이 당 질량(kg/m)ue0a7 : 모드 상수 1. 서 론 거니플랩(Gurney flap)은 미국 자동차 경주 드라이버인 Dan Gurney가 고안한 것에서 유래한다. Dan Gurney는 본인의 경주용차가 운행 중 낮은 자세를 유지시킬 수 있도록 하방력(down force)을 증가시키기 위해 자동차 후방 스포일러에 조그마한 탭을 적용하였다. 이 조그마한 탭은 중량 증가를 최소화하면서 에어포일의 양력계수 및 최대양력계수를 증가시키고, 동시에 항력계수의 증가를 상대적으로 작게 하여 양항비를 증가시키는 효과를 가져오게 된

Dynamic Characteristic Study of Hingeless Blade Stiffness Reinforcement for Bearingless Rotor Whirl Tower Test

Whirl tower test is conducted basically during helicopter rotor system development process. And for whirl tower test of rotor hub system, new design blade or existing blade which is remodeled for new rotor hub system is used. Because of simple shape and efficient aerodynamic characteristic, BO-105 helicopter blade is used for helicopter rotor hub development project widely. Originally BO-105 blade is used for hingeless hub system and blade root is used to flexure. So flap stiffness and lag stiffness at blade root area is relatively low compare with airfoil area. So, in order to apply the BO-105 blade to bearingless hub, blade root area have to be reinforced. And in this process, blade root area`s section property is changed. In this paper, we suggest reinforcement method of BO-105 blade root area and study dynamic characteristic of bearingless rotor system with reinforcement BO-105 blade.

An Efficient Triangular Mesh Generation Algorithm using Domain-wise Hash Structure

In this work, a domain-wise hash structure is developed for efficient data handling, and by using the developed domain-wise hash structure, an automatic triangular mesh generation algorithm is proposed. To generate the optimal nodal points and triangles efficiently, the advancing layer method and Delaunay triangulation method are utilized. To investigate the performance of the proposed algorithm, benchmarking tests are carried out for various models including convex, concave and complicated shapes through the developed object oriented C++ mesh generation code.