항공공학 (Aeronautical Engineering) 메카트로닉스전공 4 학년 1 학기 전공선택과목 http ://yoo2.kangwon.ac.kr/lecture

1. 항공공학 (Aeronautical Engineering) 메카트로닉스전공 4학년 1학기 전공선택과목 http ://yoo2.kangwon.ac.kr/lecture NASA : National Aeronautics and Space Administration NACA : National Advisory Committee for Aeronautics TEXT : Aircraft Flight 2nd Ed. by R. H. Barnard & D. R. Philpott “항공기 어떻게 나는가?” 경문사 Since 2005.3.1

7. CH.1 Lift(양력) 1./ Lift ▶ Forces on an aircraft in steady level flight(정상 수평비행) : Fig. 1.1 (p1)  Lift = Weight, Thrust = Drag ▶ Direction of the aerodynamic forces : Fig. 1.2 (p2) ▶ Lift : a force at right angles to the direction of flight

9. 2./ Conventional (=Classical) Wing

10. (지주) (동체세로뼈대)

11. 3./ Moving Aircraft and Moving Air 4./ Generation of Lift

13. The lift is defined as the force normal to the free-stream direction and the drag parallel to the free-stream direction. For a planar airfoil section operating in a perfect fluid, the drag is always zero no matter what the orientation of the airfoil is. This seemingly defies physical intuition and is known as D'Alembert's paradox. It is the result of assuming a fluid of zero viscosity. The components of the static-pressure forces parallel to the free-stream direction on the front surface of the airfoil always exactly balance the components of the pressure forces on the rear surface of the airfoil. • The lift is determined by the static-pressure difference between the upper and lower surfaces and is zero for this particular case since the pressure distribution is symmetrical. If, however, the airfoil is tilted at an angle to the free stream, the pressure distribution symmetry between the upper and lower surfaces no longer exists and a lift force results. This is very desirable and the main function of the airfoil section. 

15. 2. Kutta Condition

16. Martin Wilhelm Kutta * Born: 3 Nov 1867 in Pitschen, Upper Silesia (now Byczyna, Poland)* Died: 25 Dec 1944 in Fürstenfeldbruck, German Martin Kutta studied at Breslau from 1885 to 1890. Then he went to Munich where he studied from 1891 to 1894, later becoming an assistant to von Dyck at Munich. During this period he spent the year 1898-99 in England at the University of Cambridge. Kutta held posts at Munich, Jena and Aachen. He became professor at Stuttgart in 1911 and remained there until he retired in 1935. He is best known for the Runge-Kutta method (1901) for solving ordinary differential equations and for the Zhukovsky - Kutta aerofoil. Runge presented Kutta's methods.

17. (inviscid flow) (viscous flow)

18. 5./ Aerofoil Section ▣익형 (翼型, airfoil)이란, 날개의 단면 형상을 뜻하며 항공기의 날개(wing), 보조익(aileron), 승강타(elevator), 방향타(rudder)와 같은 것들의 단면(section)을 말한다. 공기보다 무거운 항공기를 비행시키기 위해서 공기 역학적인 효과, 즉 양력은 크고 항력은 작은 익형이 요구된다. 양력을 크게 하기 위해서 익형은 상면을 둥글게 해주고 뒤를 뾰족하게 하여 유선형으로 한다. ▣ 평균 캠버선: (Mean Camber Line): 위면과 아래면의 평균선으로 두께의 중심선이다. 평균 캠버선의 앞끝을 앞전(前緣, leading edge), 뒤 끝을 뒷전(後緣, trailing edge)이라 부른다. ▶ 캠버 또는 최대 캠버 (Camber or Maximum Camber): 시위선에서 평균 캠버선까지의 최대 거리 ▶시위 (Chord): 앞전과 뒷전을 잇는 직선. 평균 캠버선의 양끝. ▶ 두께 (Thickness): 시위선에 수직방향으로 잰 윗면과 아랫면까지의 높이. 즉, 에어포일의 최대 두께.

27. 7./ Pressure and Speed 6./ Air Pressure Density and Temperature

28. 8. / Dynamic Pressure 9./ Unexpected Effects 10./ Wing Circulation ▣ Circulation ▣ Kutta-Joukowski Theorem : The faster the flight speed (at a fixed altitude), the less will be the circulation required to generate a given amount of lift.

30. Nikolai Egorovich Zhukovsky Born: 17 Jan 1847 in Orekhovo, Vladimir gubernia, RussiaDied: 17 March 1921 in Moscow, USSR

31. Nikolai Egorovich Zhukovskii (or Zhukovsky or Joukowski) was the son of Egor Zhukovskii who was a communications engineer. Nikolai Egorovich attended the Fourth Gymnasium(고등학교) for Men in Moscow, completing his secondary education there in 1864. He then entered the Faculty of Physics and Mathematics at Moscow University where he studied applied mathematics. He graduated in 1868 and from 1870 he taught at the Second Gymnasium for Women in Moscow. After two years teaching at the Gymnasium, Zhukovskii received an invitation to teach mathematics at Moscow Technical School then, from 1874, he also taught theoretical mechanics there. While he was teaching these courses, Zhukovskii was also studying for his Master's Degree and in 1876 he was awarded this degree for a thesis on the kinematics of a liquid. It is worth pointing out that the Russian Master's Degree is essentially the equivalent of a British/American Ph.D. today while the Russian doctorate at this time was essentially the equivalent of the German Habilitation. After being awarded his Master's Degree,

32. a special chair of mechanics was created for Zhukovskii at Moscow Technical School. Zhukovskii obtained a doctorate from Moscow University in 1882 for a dissertation on the stability of motion. He worked at the university, becoming the Head of the Department of Mechanics in 1886. By this time he had begun to receive awards for his outstanding work, having been awarded the N D Brashman prize for theoretical work in fluid dynamics in 1885. During 1890-91 he experimented with disks placed in currents of air and, in 1891, he began to study the dynamics of flight. In 1895 he visited Lilienthal in Berlin. Lilienthal was selling gliders produced in his factory in Berlin. Zhukovskii [2]:- Perhaps Zhukovskii is most famous, however, as the founder of the Russian schools of hydromechanics and aeromechanics. For his work in these areas he became known as the Father of Russian Aviation. Zhukovskii [1]:-

33. Zhukovskii purchased one of the eight gliders which Lilienthal sold to members of the public. In 1906 Zhukovskii published two papers in which he gave a mathematical expression for the lift on an airfoil. Today it is known as the Kutta-Joukowski theorem, since Kutta pointed out that the equation also appears in his 1902 dissertation. Zhukovskii was concerned both with theoretical and with experimental aspects of the subject. His theoretical work concentrated on lift, high-speed aerodynamics, vortex theory, longitudinal and cross stability but he complemented this work with appropriate experimental observations in every case. With this twin approach he became the Russian pioneer on both aspects of aviation. He went on to establish an aerodynamics laboratory and to teach courses on his theories of aerodynamics [1]:- During World War I Zhukovskii taught a special course for pilots and he was the first person in Russia to study the theory of bombing from aeroplanes in 1915. In 1918 he organised the Central Aerohydrodynamic Institute and

34. became its first head. The Institute was renamed the N E Zhukovskii Academy of Military and Aeronautical Engineering in 1922 following Zhukovskii's death. Zhukovsky also worked on hydrodynamics and hydraulics, in particular shock waves in water pipes. In particular he solved problems concerning the bursting of pipes with his studies of hydraulic shock. Other problems he considered were the formation of river beds and the construction of dams, where again his expertise was invaluable in constructing power stations.

35. 11./ Wing-Bound Vortex (날개 속박와류 , 束縛渦流 ; Wing= Lifting Line)

36. 12./ Magnus Effect : Any object rotated so as to produce a vortex or circulation, will generate lift when placed in a stream of air. This is known as the Magnus effect. downwash

37. Magnus, Heinrich Gustav 1802–70, German chemist, physicist, and educator. In 1831 he became lecturer and in 1834 professor of physics and technology at the Univ. of Berlin. A brilliant and highly popular teacher, Magnus introduced the seminar and the teaching laboratory and was influential in the science of his time. The scope of his interests was broad; he was the first to prepare a platino-ammonium compound (Magnus’s green salt) and several acids and their salts. From his study of projectiles was developed the theory of the “Magnus effect,”(1853) the lateral force on rotating cylinders in air currents. His other investigations included studies in thermoelectricity, electrolysis, and vapor pressure.

40. 13./ Air Flow around an Aerofoil Section downwash

41. 14./ Stagnation(정체 停滯)

42. 15./ Pressure and Lift

44. 16. / Direction of the Resultant Force due to Pressure

45. 17./ Lift Coefficient(양력계수, 揚力係數) 1. where : flight speed, : wing plan area : lift coefficient 2. Lift force is directly related to the dynamic pressure. 3. Lift : a measure of the lifting effectiveness of the wing lift = f [wing planform, section shape, angle of attack, compressibility, viscosity]

46. 18. / Variation of Lift with Angle of Attack and Camber • curve (Fig. 1.17) • ▶ The influences of angle of attack and camber are largely independent: that is, the increase in lift coefficient due to camber is the same at all angles of attack. : • ▶ • ▶ zero-lift angle : • ▶ stall angle

47. stall zero-lift angle