Aero Engineering 315

Lesson 12

Airfoils Part I

First things first…

Recent attendance GR#1 review Pick up handout

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

What is an airfoil?

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)

NACA 6716

-0.06

-0.01

0.04

0.09

0.14

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x/c

y/c

A-10 Airfoil Example

Planform Area (S)S = b * cChord (c)

Span (b

)

Airfoil Geometry

Where does the moment come from?

PU = Upper surface pressure distributionAupper

dAP force surfaceUpper U

PL = Lower surface pressure distribution lower

L

A

dAP force surfaceLower

Fnet

M

Note: M is negative for this exampleIn general:

M is < 0 for positive camberM is = 0 for symmetric airfoilsM is > 0 for negative camber

Note: Shear Stress also contributes to moment in the same manner…

Center of Pressure

M = 0

Center of Pressure

Aerodynamic ForceLift

Drag

Moment = 0

V

+

Center of Pressure: the point on the airfoil where the total moment due to aerodynamic forces is zero (for a given and V )

Aerodynamic Center

V

+

Macx

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

Next Lesson (T13)…

Prior to class Finish airfoil reading (3.5.1 – 3.5.8)

In Class Airfoil data