Aero Engineering 315 Lesson 12 Airfoils Part I. First things first… Recent attendance GR#1...
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Transcript of Aero Engineering 315 Lesson 12 Airfoils Part I. First things first… Recent attendance GR#1...
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
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
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
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