• 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.32 no.3
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• pp.74-81
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• 2004

In this study preliminary structural design has been performed to develop an all composite wing box for experimental aircraft(classified in FAR Part 21). Considerations on composite materials and their manufacturing process were taken into account throughout the design phase. Aerodynamic loads were estimated by using Shrenk method(NACA TM No 948) and FAR Part 23 Appendix A. The structural layout has been determined to carry effectively the critical loads and to maximize the benefit of composite structure. Maximum strain failure allowable and first ply failure criteria were applied for the sizing of major structural members. Finally, the designed composite wing box structure is presented in the form of drawings, which include material specifications, stacking sequences and joint design.

• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.123.2-123
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• 2002

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.647-654
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• 2010

In this study, an efficient ornithopter aerodynamic model, which is applicable to ornithopter wing design considering fluid-structure interaction or ornithopter flight dynamics and control simulation, was proposed and experimentally validated through the wind tunnel experiments. Due to the ornithopter aerodynamics governed by unsteady low Reynolds number flow, an experimental device was specially designed and developed. A part of the experimental device, 2-axis loadcell, was situated in the non-inertial frame; the dynamic calibration method was established to compensate the inertial load for pure aerodynamic load measurements. The characteristics of proposed aerodynamic model were compared with the experimental data in terms of mean and root-mean-square values of lift and drag coefficients with respect to the flow speed, flapping frequency, and fixed angle of attack.

• Transactions of the KSME C: Technology and Education
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• v.2 no.1
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• pp.29-37
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• 2014

In this study, analyzed the aerodynamic characteristics of Kline-Fogleman airfoils and wings with those more efficiency at low Reynolds number. It was found that lift to drag ratio is enhanced in the range of Reynolds number below $2.4{\times}10^5$, especially, can be improved up to 26% at Reynolds number is $1{\times}10^4$. It was confirmed that the most advantage case in terms of lift-to-drag ratio is Middle case and lift-to-drag ratio is improved to 20% at 80% of the wing area is Kline-Folgeman airfoil. At this time, endurance time increase to 12%. Also taking the structural stability of the wing and lift-to-drag improvement into account, designed to be from 50% to 80% the size of the Kline-Fogleman Airfoil would be advantageous.

• Aerospace Engineering and Technology
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• v.7 no.1
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• pp.24-29
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• 2008

Aircraft fuel efficiency is one of main concerns to aircraft manufacturers and to aviation companies because jet fuel price has tripled in last ten years. One of simple and effective methods to increase fuel efficiency is to reduce aircraft induced drag by using of wingtip devices. Induced drag is closely related to the circulation distribution, which produces strong wingtip vortex behind the tip of a finite wing. Wingtip devices including winglets can be successfully applied to reduce induced drag by wingtip vortex mitigation. Winglet design, however, is very complicated process and has to consider many parameters including installation position, height, taper ratio, sweepback, airfoil, toe-out angle and cant angle of winglets. In current research, different shapes of winglets are compared in the view of vortex mitigation. Appropriately designed winglets are proved to mitigate wingtip vortex and to increase lift to drag ratio. Also, the results show that winglets are more efficient than wingtip extension. That is the reason B-747-400 and B-737-800 chose winglets instead of a span increase to increase payload and range. Drag polar comparison chart is presented to show that minimum drag is increased by viscous drag of winglet, but at high lift, total drag is reduced by induced drag decrease. So, winglets are more efficient for aircraft that cruises at a high lift condition, which generates very strong wingtip vortex.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.8
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• pp.41-46
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• 2006

The capability for reconstructing impact forces of an aircraft wing using impact response functions and regularization methods were examined. The impact response function which expresses the relation between the structure response and the impact force was derived using the information on mass and stiffness data of a finite element model for the wing. Iterative Tikhonov regularization method and generalized singular value decomposition method were used to inverse the impact response function that was generally ill-posed. For the numerical verification, a fighter aircraft wing was used. Strain and deflection histories obtained from finite element analysis were compared with the results calculated using impact response functions. And the impact forces were reconstructed with the strain histories obtained from finite element analysis. The numerical verification results showed that this method can be used to monitor impact forces on aircraft structures.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.66-66
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• 2004

중량은 항공기의 성능을 좌우하는 주요 변수로써, 최소의 중량 달성이 100여 년 전 라이트 형제가 최초의 비행을 성공한 후, 항공기 개발자들의 주요 관심사였다. 일반 구조물의 최적화를 통한 설계는 구조물의 강도를 유지하면서 중량절감, 비용절감을 위해 널리 사용되고 있다. 하지만, 현재 항공기 구조물에 대해서는 아직 최적화론 통한 설계가 널리 적용되지 않고 있다. 그래서, 항공기에서는 중량절감을 위해 가벼우면서 강도를 큰 알루미늄이 주재료로 사용되고 있다.(중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.20-27
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• 2002

Aircraft design requires the intergration of several disciplines, inculding aerodynamics, structures, controls. To achieves advances in performance, each technology, or discipline must be more accurate in analysis and must be more highly intergrated. One of the important interdisciplinary interactions in mordern aircraft design is that of aerodynamics and structures. In this study, for increasing accuracy in each discipline's analysis, CFD for aerodynamic analysis and FEM for structurral analysis was used and, for considering important interdisciplinary interactions, aeroelastic effect was considered. As optimization algorithm, PBIL algorithm was used for global optima and was parallelized to alleviate the computational burden. The efficiency and accuracy of the present method was assesed by range maximiziation of reference of reference wing.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.1
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• pp.80-87
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• 1998

This paper deals with the evaluation of structural safety to fatigue strength of marine propeller blades having high skew angle and operating in irregular wake field. The determination of the optimum skew angle of a propeller blade is one of the important task at the initial design stage especially in the case of high speed vessel such as container ships. A computer program system has been developed to evaluate the structural safety to fatigue strength and has been applied to several propeller blades with varying skew angle within a wide range. In the parametric study the pressure acting on the blade surface is calculated using the non-lineal lifting surface theory and the structural analysis is performed using MSC/NASTRAN. The relationship between skew angle and structural safety to fatigue strength is investigated and this paper ends with describing the optimum skew angle of a propeller blade.