Why Airplanes Fly

1. Why Airplanes Fly Aerodynamics Institute of Computational Fluid Dynamics

2. Aerodynamics? • Aero – means Air • Dynamics – means Motion • Aerodynamics – the study of air in motion • Important Point: Air is “Viscous” Uh, that means it’s Sticky

3. Forces and Vectors • A force may be thought of as a push or pull in a specific direction. • A force is a vector quantity so a force has both a magnitude and a direction. • When describing forces, we have to specify both the magnitude and the direction.

4. Airplane Parts Empennage(Tail) Vertical Stabilizer Wing Horizontal Stabilizer Engine Fuselage (Body)

5. 4 Forces of Flight

6. Center of Gravity (CG) Weight

7. Drag Newton’s 1st Law Applies

8. Thrust Newton’s 3rd Law Applies

9. Lift Thrust Drag Weight Lift Newton’s 3rd Law Applies

10. Think About ItIt’s “Tug-a-War” The motion of the airplane through the air depends on the relative strength and direction of the forces we’ve discussed. If the 4 forces are balanced, the aircraft cruises at constant velocity and altitude. If the forces are unbalanced, the aircraft accelerates in the direction of the largest force.

12. More on Lift … Lift in Depth

13. Streak Lines 10° AOA AOA: Angle Of Attack - the angle that the wing meets the oncoming air. Note: Downwash Air Accelerated Down Newton’s 2nd and 3rd Laws Apply

14. Circulation Pattern“Bound Vortex” Airflow Around a Wing AOA Notice that: • Air on top arrives well before air below. “accelerated” (stretched in the diagram) • Air below decelerated (arrives after “free stream”)(compressed in the diagram) 0° 3° 8°

15. Pressure Field Result of the accelerated flow on top and decelerated flow on bottom.

16. Forces on the Airfoil Forces act along the entire surface.

17. Which way does the liftingforce actually work? Net Force Combining all the forces.

18. Lift Relates to AOA Zero Lift at Zero AOA

19. 2D Airflow Over an Airfoil Institute of Computational Fluid Dynamics

20. AOA: 0° AOA: 8° AOA: 20° Airflow at Selected AOA Institute of Computational Fluid Dynamics

21. Wrapping Up Forces & Lift • Lift = Pressure * Wing Area • Pressure is dependant on: • Airfoil Shape • Wing Velocity through the air • Angle that wing meets air (AOA) • Air density (more dense = more pressure) • Newton’s 3rd Law? “For every Action there is and Equal and Opposite Reaction” The more air moved down by the wing (Action)the more lift is generated (Reaction) “Equal and Opposite”

22. Flight Without Thrust? • Lift is dependant on Velocity • Velocity is generated by Thrust • Lift is dependant on Thrust • No Thrust = No Lift If Thrust is so critical to generate Velocity Then … How do GLIDERS FLY

23. Rising Air 500’ per minute Gliders Glider Climbing 400’ per minute Glider Descending 100’ per minute Due to Gravity Air Rising: 500’ per minute Glider Descending: 100’ per minute -------------------------------------------------- Glider Climbing: 400’ per minute

24. Stability and Control • Add cool graphics

25. Stability and Control

26. Aircraft Motion Aircraft move in 3D (dimensions) (Cars move in just 1D) • Pitch (up and down) • Yaw (left and right) • Roll (well uh, roll) • ALL motion occurs around the balance point, called the Center of Gravity (CG)

27. Glider Demonstration • Fly gliders • Observe difference in flight • Find physical differences in planes • Explore why they work

28. The Gliders What are the differences?

29. Dihedral Balanced Forces Unbalanced Forces Plane slips towards low wing, increasing lift on that wing.

30. Lift Lift Lift Lift Lift Lift Down Down Down CG CG CG CG CG CG Lift Lift Lift Lift Lift Lift Lift Lift Lift Unstable Down Down Down Down Down CG CG CG CG CG CG Location Stable Unstable

31. Stable vs. Unstable • Stability is not always desirable. • Why? • Where would you want: • Stable airplanes? • Unstable airplanes?

32. Control • A simple matter of affecting the forces that we have just discussed! • Control results from manipulating various control surfaces on the plane to change the forces.

33. Rudder (Yaw) Elevators (Pitch) Spoilers (Decrease Lift Increase and Drag) Ailerons (Roll) Slats (Increase Lift) Flaps (Increase Lift and Drag) Control Surfaces

34. Aerodynamic Myths • Biplanes have 2 wings to get twice the lift. • “Air Pockets” cause airplanes to drop suddenly while flying. • Lift is generated by the wing’s top, curved, surface which causes low pressure. • Bumblebees can’t fly.

35. Russian Helicopter

36. Questions?

37. References • “The Beginner’s Guide to Aeronautics”, NASA http://www.grc.nasa.gov/WWW/K-12/airplane/ • “IRROTATIONAL PLANE FLOWS OF AN INVISCID FLUID”; Colombini, Marco; UNIVERSITY OF GENOA http://www.diam.unige.it/~irro/ • Institute of Computational Fluid Dynamicshttp://www.icfd.co.jp/index-e.htm • See How It Flies; Denker, John S.http://www.av8n.com/how/#mytoc • “Bumblebees finally cleared for takeoff”; Wang, Z. Jane; Cornellhttp://www.news.cornell.edu/releases/March00/APS_Wang.hrs.html • DNS of Separated Flow around NACA0012 Airfoil; Shih, et al. (1992, 1995); University of Texashttp://www.uta.edu/faculty/hshan/research/gallery.shtml

38. Bumblebees Do Fly

39. BACKUP MATERIAL

40. FoilSim

41. Items to Bring • Gliders • Glue • Demo plane • Propellers

42. Vortex Generation DNS of Separated Flow around NACA0012 Airfoil

43. Stream Lines

44. Streak Lines -12° AOA

45. Streak Lines 0° AOA

46. Velocity Vectors

47. 2D Airflow Over an Airfoil

48. CG Location Lift Down Stable CG Lift Unstable Down CG