LESSON 10 Airfoil I 1 Aerospace Engineering Lesson

LESSON 10 Airfoil I 공군사관학교 항공우주공학과 1 Aerospace Engineering

Lesson Outcomes 1. Viscous Flow Review 2. Airfoils : Definitions 3. NACA Series 4. AOA 2 항공공학개론

에어포일 (Airfoil)이란? - Cross cut of a wing - 2 -D Wing - Infinite wing 5 항공공학개론

Examples : A-10 7 항공공학개론

Eagle and Viper Airfoil NACA 64 A 204 (Mod on F-15) 8 항공공학개론

B-52 “Buff” Airfoil NACA 63 A 219. 5 9 항공공학개론

Airfoil Geometry Definitions Chord Line: straight line from leading edge to trailing edge (length = c) Mean Camber Line: curved line midway between upper and lower surfaces of airfoil Camber: Max distance between camber line and chord line (no camber if symmetric) Thickness: Distance between uppzer and lower surfaces 10 항공공학개론

Airfoil Geometry Definitions 시위(chord) : 시위선의 길이 중요한 요소 : Max Camber와 Max Thickness(chord 대비) - max camber : 에어포일의 곡률 척도 (대칭 에어포일은 0) - max thickness(chord 대비) : 날씬비 척도 11 항공공학개론

4 -Digit NACA Nomenclature NACA 2421 Airfoil: 1 st: Max camber (in % chord) 2 nd: Location of max camber (in tenths of chord) 3 rd and 4 th: Max thickness (in % chord) 4/10 c 21% of chord 2% of chord ※ 대칭형 에어포일 - 캠버가 없으며 시위선을 기준으로 윗면과 아랫면의 형태 동일 예) NACA 0012 13 항공공학개론

Definitions (중요) Span (b) – Width of a wing section Planform Area (S) – Area of the projection of an airfoil onto a surface (“shadow”) 15 항공공학개론

Definitions (중요) Lift Moment + Drag Relative wind v Relative Wind – Direction of incoming flow (freestream velocity) or 항공기 전진 방향 v Angle of Attack (α, AOA) – Angle between relative wind and chord line v Lift – Force perpendicular to freestream velocity v Drag – Force parallel to freestream velocity v Moment – 회전하려는 힘 (nose-up 방향이 positive) 16 항공공학개론

Definitions (중요) § Why Moment on airfoils? - 에어포일 윗면의 공력분포와 아랫면의 공력분포 비대칭 돌아가려는 경향성 발생 - cambered airfoils : m ≠ 0 - symmetric airfoils : m = 0 18 Cambered airfoil produces a negative moment (nose-down). 항공공학개론

에어포일 양력/항력/모멘트 발생에 영향을 미치는 요소는? ? ? LIFT, DRAG, MOMENT : change with shape (camber, change with angle of attack change with Re thickness…) Airfoil Charts : 형상, 받음각, Re에 따른 Cl, Cd, Cm 경향성에 대한 실험 결과를 그래프로 정리 Ex) NACA 2421 airfoil chart 자세한 내용은 Next Lesson에서 22 항공공학개론