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## Airfoil%20Terminology%20and%20Pressure%20Distribution

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### Cambered, meaning there is more cross-sectional area above the chordline than below. ... The amount of camber is a measure of the overall curvature of the airfoil. ... – PowerPoint PPT presentation

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Title: Airfoil%20Terminology%20and%20Pressure%20Distribution

1
Airfoil TerminologyandPressure Distribution
• Lecture 3
• Chapter 2

2
Airfoil Terminology
• Review from handout

3
Typical Airfoil Shape
• Cambered, meaning there is more cross-sectional
area above the chordline than below. (it is not
symmetrical)
• The amount of camber is a measure of the overall
curvature of the airfoil.
• Cambered airfoils are normally used to more
effectively provide lift in a given direction.
(this direction is usually up)

4
Symmetrical Airfoil
• A symmetrical airfoil has no camber.
• The meanline and the chordline coincide.
• All Airfoils are either cambered or symmetrical.

5
Upper/Lower Camber
• Upper Camber- curvature of the upper surface of
the cambered airfoil
• Lower Camber- curvature of the lower surface of
the cambered airfoil
• A symmetrical airfoil has equal curvature of
upper and lower surface, yet it technically has
no camber.

6
Lift on Cambered Airfoils
• A cambered airfoil at zero degrees angle of
attack will produce some lift at this angle
because there is more cross-sectional area above
the chordline than below.
• This causes a greater reduction in the area
available for the airflow.
• At this angle of attack, the flow will divide

7
What if the angle of attack is increased?
• The flow no longer divides at the leading edge,
but a point farther down the nose of the airfoil.
• The stagnation point is the dividing point for
the flow to go above or below the airfoil.
• It is called the stagnation point because the
flow is stagnate at this point. (the flow either
goes above or below this point)

8
The effective upper cross sectional
• A cambered airfoil at a moderate angle of attack
(fig. 2-15,p.22) has increased effective area due
to the location of the stagnation point.
• This area of the airfoil is therefore increased
and the effective lower area is decreased.

9
Back to Continuity Bernoulli
• Lower area higher velocity lower pressure
• There is a greater effective upper surface area
and leads to a greater lowering of pressure on
the top of the surface.
• The reverse is true on the lower surface.
• The reduction in effective cross-sectional area
has reduced the airflow area and resulted in less
lowering of pressure on the bottom surface.

10
Figure 2-16 p. 23
• An airfoil showing the change in pressure forces
of the top and bottom surfaces when the angle of
attack is increased above zero.
• Angle of attacked increased
• Stagnation point moves back
• this causes a greater lowering of pressure on top
rather than bottom resulting in greater lift.

11
Symmetrical Airfoils
• This airfoil at zero angle of attack have equal
upper and lower surfaces (fig.2-17,p.23)
• If the angle of attack is increased, the
stagnation point moves below the leading
edge(just like a cambered airfoil)
• The effective upper lower cross-sectional areas
are then different (just like a cambered airfoil)

12
Symmetrical airfoils
• However, a greater angle of attack is required to
get the same amount of lift as the cambered
airfoil.
• Therefore, the symmetrical airfoil is not as
efficient in this respect.
• So what is the advantage of a symmetrical airfoil?

13
• The fact that it can produce an equal amount of
lift in either direction at the same positive or
negative angle of attack.
• Negative lift can also be obtained with a
cambered airfoil but at a very great negative
angle. (this means you can fly a cambered airfoil
inverted)

14
A Cambered Airfoil Inverted
• The inverted angle must be great enough, though,
that the effective lower area of the airfoils
(which is now, in reality, the upper)