1. Aero Engineering 315 Lesson 12 Airfoils Part I

2. First things first…  Recent attendance  GR#1 review  Pick up handout

3. Airfoil lesson objectives  Define: thickness, camber, mean camber line, symmetrical airfoil, relative wind, angle of attack, center of pressure and aerodynamic center  Identify forces and moments acting on an airfoil

4. What is an airfoil?

5. Chord line: straight line connecting leading and trailing edges of airfoil (length = chord) Thickness: Distance between upper and lower surfaces of airfoil measured in % chord (max thickness is max distance in % chord) Camber: Distance between camber line and chord line measured in % chord (Max camber is max distance in % chord) Mean Camber line: curved line midway between upper and lower surfaces of airfoil (same as chordline for a symmetric airfoil) Airfoil Geometry

8. NACA Nomenclature NACA 2421 c = 1 m 2 nd Digit: Location of maximum camber is at 4/10ths (or 40%) of the chord line, from the LE. 0.40 m 4 1 st Digit: Maximum camber is 2% of 2D airfoil chord length, c. 0.02 m 2 3 rd & 4 th Digits: Maximum thickness is 21% of c. 0.21 m 21

9. NACA Nomenclature  Example: NACA 2412 with a chord of 4 feet Max camber: Location of max camber: Max thickness: 0.08 ft (2% x 4 ft) 1.6 ft aft of leading edge (0.4 x 4 ft) 0.48 ft (12% x 4 ft)

10. A-10 Airfoil Example

11. Planform Area (S) S = b * c Chord (c) Span (b) Airfoil Geometry

12. Airfoil Forces and Moments 3) moment is positive nose-up Aerodynamic Force Lift Drag Moment + Relative wind Angle of attack (  : angle between relative wind and chord line Note: 1) lift is perpendicular to freestream velocity 2) drag is parallel to freestream velocity

14. Where does the moment come from? P U = Upper surface pressure distribution P L = Lower surface pressure distribution F net M Note: M is negative for this example In general: M is < 0 for positive camber M is = 0 for symmetric airfoils M is > 0 for negative camber Note: Shear Stress also contributes to moment in the same manner…

15. Center of Pressure M = 0

16. Forces and Moments + The force and moment system can be represented anywhere on the free body diagram; forces don’t change with location but the moment does! M1M1 x y F1F1 + M2M2 F2F2 F 2   F 1 BUT M 2 does not equal M 1

17. Center of Pressure Aerodynamic Force Lift Drag Moment = 0 + Center of Pressure: the point on the airfoil where the total moment due to aerodynamic forces is zero (for a given  and V  )

18. Aerodynamic Center + M ac x y Aerodynamic Center : The point on the airfoil where the moment is independent of angle of attack. Fixed for subsonic flight  c/4. Fixed for supersonic flight  c/2. The moment has a nonzero value for cambered airfoils (negative for positively cambered airfoils). Moment is zero for symmetric airfoils.  Aerodynamic Force

19. Next Lesson (T13)…  Prior to class Finish airfoil reading (3.5.1 – 3.5.8)  In Class Airfoil data