• 항공우주기술
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• 제7권1호
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• pp.24-29
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• 2008

최근의 유가인상과 관련하여 상업용 및 군용 항공기 운용시의 연료 효율을 높이고자 하는 노력이 가속화되고 있다. 관련 연구에 의하면 수송기와 비즈니스 젯 항공기에 있어서 윙렛은 공력/구조적 효율성을 향상시키고, 적은 중량 증가로 저속 수송기의 상승 성능을 향상시킨다고 보고된 바 있다. 윙렛은 일반적으로 날개 끝에 장착되는 작은 공력면이며, 날개에 수직에 가깝게 장착되어 날개 끝단 와류의 순환 유동장내에서 작용한다. 윙렛의 설계는 위치, 높이, 테이퍼비, 후퇴각, 익형, toe-out 및 켄트각 등 많은 요소를 고려해야 하는 매우 복잡한 과정이다. 최근에는 미국 보잉사의 B737-800과 B787 등의 최신 기종에서 Blended 윙렛을 성공적으로 적용하여 날개끝의 길이를 늘리는 것(Wing Tip Extension) 보다 적은 추가 중량으로 같은 순항 성능을 도출하는데 성공하였다. 윙렛의 점성저항으로 인하여 최소항력은 증가하지만 높은 양력계수에서는 유도항력의 감소로 전체 항력이 감소하게 됨을 알 수 있다. 따라서, 윙렛은 강한 날개끝 와류를 발생시키는 높은 양력계수에서 순항하는 항공기에 더욱 적합하다.

• 한국항공우주학회지
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• 제47권6호
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• pp.422-428
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• 2019

수직미익이 없는 전익기 형상은 낮은 레이더반사면적(RCS) 특성으로 인해 최근 UCAV를 위한 대표적인 형상으로 대두되고 있다. 무미익 전익기 형상은 방향축 관점에서 보면 정적으로 불안정하면서도 이를 효과적으로 제어하기 위한 수직 조종면이 없다는 두 가지 난제를 모두 갖고 있다. 이같은 형상을 제어하기 위해서는 추력 벡터링을 적용하거나 날개의 항력차이를 이용하는 드래그 러더(Drag Rudder) 형태의 에일러론 또는 스포일러 등을 적용할 수 있다. 본 논문에서는 전익기 형상의 횡방향축 공력특성 및 드래그 러더 중 스포일러 형태의 조종면에 대한 공력특성을 설명한다. 또한, PI 구조의 제어설계 기법을 사용하여 전익기의 횡방향축 운동을 효과적으로 제어할 수 있음을 제시하고, 비행시험을 통하여 설계된 제어기로 안정적인 비행이 가능함을 보였다.

• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.215-221
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• 2017

An electromagnetic (EM) wave absorber reduces the possibility of radar detection by minimizing the radar cross section (RCS) of structures. In this study, a radar absorbing structure (RAS) was applied to the leading edge of a blended wing body aircraft to reduce RCS in X-band (8.2~12.4GHz) radar. The RAS was composed of a periodic pattern resistive sheet with conductive lossy material and glass-fiber/epoxy composite as a spacer. The applied RAS is a multifunctional composite structure which has both electromagnetic (EM) wave absorbing ability and load-bearing ability. A two dimensional unit absorber was designed first in a flat-plate shape, and then the fabricated leading edge structure incorporating the above RAS was investigated, using simulated and free-space measured reflection loss data from the flat-plate absorber. The leading edge was implemented on the aircraft, and its RCS was measured with respect to various azimuth angles in both polarizations (VV and HH). The RCS reduction effect of the RAS was evaluated in comparison with a leading edge of carbon fabric reinforced plastics (CFRP). The designed leading edge structure was examined through static structural analysis for various aircraft load cases to check structural integrity in terms of margin of safety. The mechanical and structural characteristics of CFRP, RAS and CFRP with RAM structures were also discussed in terms of their weight.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권4호
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• pp.439-449
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• 2018

In this paper, multi-objective optimization of a multi-bubble pressure cabin in the underwater glider with Blended-Wing-Body (BWB) is carried out using Kriging and the Non-dominated Sorting Genetic Algorithm (NSGA-II). Two objective functions are considered: buoyancy-weight ratio and internal volume. Multi-bubble pressure cabin has a strong compressive capacity, and makes full use of the fuselage space. Parametric modeling of the multi-bubble pressure cabin structure is automatic generated using UG secondary development. Finite Element Analysis (FEA) is employed to study the structural performance using the commercial software ANSYS. The weight of the primary structure is determined from the volume of the Finite Element Structure (FES). The stress limit is taken into account as the constraint condition. Finally, Technique for Ordering Preferences by Similarity to Ideal Solution (TOPSIS) method is used to find some trade-off optimum design points from all non-dominated optimum design points represented by the Pareto fronts. The best solution is compared with the initial design results to prove the efficiency and applicability of this optimization method.

• 천문학회지
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• 제36권2호
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• pp.55-60
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• 2003

In Lee, Kang & Byun (2001) the discovery of Raman scattered 6545 A feature was reported in symbiotic stars and the planetary nebula M2-9. The broad emission feature around 6545 A is formed as a result of Raman scattering of He II n = 6 $\to$ n = 2 photons by atomic hydrogen. In this paper, we introduce a method to compute the equivalent width of He II $\lambda$ 1025 line and present an optical spectrum of the symbiotic star RR Telescopii as an example for a detailed illustration. In this spectrum, we pay attention to the broad H$\alpha$ wings and the Raman scattered He II 6545 feature. The broad Ha wings are also proposed to be formed through Raman scattering of continuum around Ly$\beta$ by Lee (2000), and therefore we propose that the equivalent width of the He II $\lambda$ 1025 emission line is obtained by a simple comparison of the strengths of the 6545 feature and the broad H$\alpha$ wings. We prepare a template H$\alpha$ wing profile from continuum radiation around Ly$\beta$ with the neutral scattering region that is supposed to be responsible for the formation of Raman scattered He II 6545 feature. Isolation of the 6545 feature that is blended with [N II] $\lambda$ 6548 is made by using the fact that [N II] $\lambda$ 6584 is always 3 times stronger than [N II] $\lambda$ 6548. We also fit the 6545 feature by a Gaussian which has a width 6.4 times that of the He II $\lambda$ 6527 line. A direct comparison of these two features for RR Tel yields the equivalent width $EW_{Hel025} = 2.3{\AA}$ of He II $\lambda$ 1025 line. Even though this far UV emission line is not directly observable due to heavy interstellar extinction, nearby He II lines such as He II $\lambda$ 1085 line may be observed using far UV space instruments, which will verify this calculation and hence the origins of various features occurring in spectra around H$\alpha$.