• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.10
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• pp.928-935
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• 2015

This paper presents low temperature structural tests of a UAV wing which has room temperature-curing adhesive bond. The wing structure is made of carbon fiber reinforced composites, and the skins are bonded to the inner structures (such as ribs and spars) using room temperature-curing adhesive bond. Also, to verify damage tolerance design of the wing structure, barely visible impact damages are intentionally created in the critical areas. The attachment fittings of the wing are fixed in a specially designed chamber which can simulate the low temperature environments of the operating altitudes. The test load is applied by hydraulic actuators which are placed outside the chamber. The structural tests consist of strain survey tests and a durability test for 1-life fatigue load spectrum. During the tests, strains of major parts are measured by strain gauges and FBG sensors. The change of the initial impact damages is also monitored using piezoelectric sensors. The 1-life damage tolerance of the composite structure is verified by the structural tests under the simulated environments.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.287-294
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• 2007

A static aeroelastic analysis for supersonic aircraft wing equipped with external store under the wing lower surface is performed using computational fluid dynamics (CFD) and computational structural technology(CST) coupling methodology. Two mapping algorithms, which are the pressure mapping algorithm and the displacement mapping algorithm, are used for CFD/CST coupling. A three-dimensional unstructured Euler code and finite element analysis program are used to calculate the flow properties and the structural displacements, respectively. The coupling procedure is repeated in an iterative manner until a specified convergence criterion is satisfied. Static aeroelastic analysis for a typical supersonic flight wing is performed and final converged wing configuration is obtained after several iterations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.396-404
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• 2015

The UAV's wing has high aspect ratio that is suitable for the high altitude and long endurance. Knowing the real-time deformation of wing structure in flight, it can be utilized in structural health and loading status monitoring, improvement of control effectiveness and extraordinary vibration phenomena using displacement-strain relationship. In this paper, nonlinear displacement prediction algorithm was developed for prediction of large structural deflection in flight. The algorithm was validated through the comparison with finite element analysis results and also experimental results for several large tip displacements of cantilever beam. The predicted displacements using strains are agreed well with the measured values from laser displacement sensor.

• Journal of KSNVE
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• v.6 no.1
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• pp.11-19
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• 1996

지금까지의 항공기 날개에 공력 탄성학적 제어를 위해 압전재료를 작동기로 사용하는 연구는 아직은 완전하지 못하지만 실용화 가능성을 조사하기 위해 집중적인 투자가 행해지고 있다. 본 글에서 언급한 예 외에도 압전재를 이용 날개의 익형을 능동적으로 조절함으로써 천음속에서의 저항을 줄이기 위한 연구(transonic drag reduction with piezos), 압전재로 작동하는 제어면을 부착하여 헬리쿱터 블레이드 의 진동을 제어하기 위한 실험적 연구, 항공기 외부 장착물에 의해 발생되는 불안정 성을 제어하기 위한 압전작동기를 사용한 pylon decoupler 설계 등 다양한 분에에서 연구가 되고 있다. 하지만 아직까지는 제어에 필요한 충분한 제어력을 얻는 문제, 주 구조물과 압전재료의 강성도의 차이, 가용한 압전재의 실용화, 내구성 문제 등 항공 기에의 응용을 위한 새로운 재료의 개발이 요구되고 있다. 그리고 사용에 필요한 전력을 공급하는 문제는 지상에서 작동되는 시스템과는 달리 항공기에서는 해결해야 될 큰 문제점이며, 이에 대한 연구가 요구되고 있으며, 실용 가능성이 보일 경우 재료의 내구성, 제어 성능, 번개 등 외력에 대한 손상 예측 등 광범위한 연구가 이어 질 것으로 예측된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.8
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• pp.699-705
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• 2015

Aircraft needs high lift-to-drag ratio and weight reduction of the structure for long endurance flight with a small power. Generally high aspect ratio wing is applied to HALE(High Altitude Long Endurance) aircraft. Also high modulus, and high strength CFRP(Carbon Fiber Reinforced Plastic) has been used in primary structures. and thin mylar(membrane material) film has been applied to skin of wing. As a result, wing is more flexible than the other structures. and the stiffness of thin mylar film has an affect on dynamic stability. In this study, the membrane characteristic of mylar film has been simulated using nonlinear gap elements. And equivalent modeling method using shell elements is presented using the nonlinear simulation result. The linear equivalent model has verified using the results of nonlinear membrane method. Proposed linear equivalent shell model has applied to mode analysis for estimate the effect of mylar mechanical properties on natural frequency.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.687-694
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• 2019

A circular composite spar in the wing of ultra-light aircraft is subjected to both bending moment and transverse shear loads. However, the beam being used in the aircraft may be inefficient because the design would not take into account the characteristics of the circular tube that supports the bending moment in top and bottom arc parts and the transverse load in left and right ones. Therefore, it is necessary to efficiently fabricate the circular tube beam by properly selecting the stacking sequences or the laminated composite structure. In order to increase both bending and transverse shear strengths of the beams, in this study, a cross-section of circular tube is divided into four arcs: top, bottom, left and right ones. The commercial program, MSC/NASTRAN is used to calculate vertical displacement and the normal and shear strains with variation of parameters such as division angle of arc and fiber orientation. Based on the results, the effective parameters for the new circular composite beam are presented to increase its bending and shear strengths.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.57-58
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• 2011

• 대한공업교육학회지
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• v.31 no.2
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• pp.364-380
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• 2006

This paper presents a procedure for designing command to maneuver flexible structure with very little residual vibration, even in the presence of modeling errors. For the open loop maneuver, the various shaped profiles using multiple step inputs delayed in time are considered for robustness and compared with the responses of rigid body and flexible body in virtue of simulations and experiments. Input shaping generates vibration-reducing shaped commands through convolution of an impulse sequence with the desired command. A flexible model with a cylindrical hub and four symmetric appendages is considered to examine the responses to real plant, and to illustrate the effectiveness of the proposed shapers. The appendages are long and flexible, leading to low frequency vibration under any control action. It is shown by a series of simulation that a properly designed feedback controller with input shaper performs well, as compared with open loop controller with input shaper. The control objective is to achieve a fast settling time of residual vibration to flexible structure and robustness (insensitivity)to plant uncertainty, to eliminate residual vibration.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.12
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• pp.9-17
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• 2005

An experimental study of the vortical flow over a yawed delta wing with leading edge extension(LEX) was conducted to investigate the effects of the existence of a centerbody configuration on the flow characteristics of the wing and LEX vortices using off-surface visualization and PIV measurements. The qualitative investigation using these two techniques indicated that the effect of the centerbody existence on the vortex formation was minimal at somewhat low range of angles of attack and sideslip angles. However, the quantitative analysis of the surface pressure measurements revealed the effect of centerbody existence to be prominently increased for the cases with higher angles of attack and sideslip angles. It was also found that the centerbody effect was not significant compared to the effect of sideslip for the present LEX-delta wing configuration.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.345-352
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• 2016

As aircrafts are being operated at high altitude, wing structures experience various fatigue loadings under cryogenic environments. As a result, fatigue damage such as a crack could be develop that could eventually lead to a catastrophic failure. For this reason, fatigue damage monitoring is an important process to ensure efficient maintenance and safety of structures. To implement damage detection in real-world flight environments, a special cooling chamber was built. Inside the chamber, the temperature was maintained at the cryogenic temperature, and harmonic fatigue loading was given to a wing structure. In this study, piezoelectric active-sensing based guided waves were used to detect the fatigue damage. In particular, a beamforming technique was applied to efficiently measure the scattering wave caused by the fatigue damage. The system was used for detection, growth monitoring, and localization of a fatigue crack. In addition, a sensor diagnostic process was also applied to ensure the proper operation of piezoelectric sensors. Several experiments were implemented and the results of the experiments demonstrated that this process could efficiently detect damage in such an extreme environment.