Airfoil Aerodynamics

1
Lecture 3

• Airfoil Aerodynamics

2
Aerodynamic Coefficients

• Cl (Lift force/unit span)/(q c)
• Cd (Drag force/unit span)/(q c)
• Cm (Pitching moment/unit span)/(q c2)
• where
• q is the dynamic pressure, q 0.5 r V2,
  and c is the airfoil chord

3
Some Questions

• What is an airfoil?

4
Some Questions

• What is an airfoil?
• What aerodynamic characteristics are we
  interested in knowing?

5
Some Questions

• What is an airfoil?
• What aerodynamic characteristics are we
  interested in knowing?
• What are the geometric parameters that describe
  an airfoil?

6
Some Questions

• What is an airfoil?
• What aerodynamic characteristics are we
  interested in knowing?
• What are the geometric parameters that describe
  an airfoil?
• What are the factors that influence the
  aerodynamic characteristics?

7
Airfoil Geometry
8
Geometric Construction of an Airfoil
From NASA Sp-367 by Taly
9
Airfoil Camber line Variations
From NASA Sp-367 by Taly
10
Lift Coefficient versus angle of attack
From Introduction to Flight by Anderson
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(No Transcript)
12
Drag Bucket
13
Influence of Airfoil Geometry on airfoil
aerodynamics

• What are some of the geometric factors that
  influence the aerodynamic performance of an
  airfoil?
• Thickness to chord ratio, t/c
• Location of max t/c
• Nose radius
• Camber
• Maximum camber
• Location of max camber

14
Aerofoil Thickness

• What is the influence of thickness?

15
Aerofoil Thickness

• What is the influence of thickness?
• Influence of t/c on lift coefficient
• Clmax increases with increasing t/c up to t/c in
  the order of 13-15 at t/c gt 15 begins to Clmax
  decrease.

16
Aerofoil Thickness

• What is the influence of thickness?
• Influence of t/c on lift coefficient
• Clmax increases with increasing t/c up to t/c in
  the order of 13-15 at t/c gt 15 begins to Clmax
  decrease.
• Influence of t/c on drag coefficient
• Cdmin increases with increasing t/c

17
Leading edge nose radius

• What is the major effect of the leading edge
  radius on airfoil performance?

18
Leading edge nose radius

• What is the major effect of the leading edge
  radius on airfoil performance?
• Effects airfoil stall characteristics
• Small leading edge radius has a sharp stall break
• Large leading edge radius has a gentle stall
  break

19
Camber

• What is the influence of camber on the
  aerodynamic characteristics?

20
Camber

• What is the influence of camber on the
  aerodynamic characteristics?
• Increasing camber increases zero lift angle of
  attack.

21
Camber

• What is the influence of camber on the
  aerodynamic characteristics?
• Increasing camber increases zero lift angle of
  attack.
• Camber can be used to get a low drag coefficient
  at the designed lift coefficient.

22
Camber

• What is the influence of camber on the
  aerodynamic characteristics?
• Increasing camber increases zero lift angle of
  attack.
• Camber can be used to get a low drag coefficient
  at the designed lift coefficient.
• The maximum lift coefficient of moderately
  cambered airfoil sections increase with
  increasing camber.

23
Camber

• What is the influence of camber on the
  aerodynamic characteristics?
• Increasing camber increases zero lift angle of
  attack.
• Camber can be used to get a low drag coefficient
  at the designed lift coefficient.
• The maximum lift coefficient of moderately
  cambered airfoil sections increase with
  increasing camber.
• Camber can effect the stall behavior.
• For airfoil sections that have the maximum camber
  far forward the stall is very abrupt

24
What other factors besides geometry influence the
aerodynamic characteristics?
25
What other factors besides geometry influence the
aerodynamic characteristics?

• Aerodynamic coefficients are a function of
• Geometry
• Angle of attack
• Reynolds number
• Mach Number

26
Maximum Lift Coefficient
27
Minimum Drag Coefficient