Airfoil Geometry & Nomenclature

Chord, camber, thickness, and NACA 4-digit series

Aerospace EngineeringAirfoilsFree preview
⏱️ About 15 min
Airfoil Geometry & Nomenclature — illustration
Decorative illustration.

An airfoil is the fundamental shape that generates lift. Understanding its geometry is the first step in aerodynamics.

💡
The big idea: Airfoil performance is dictated by geometric parameters: camber, thickness distribution, and angle of attack.
🎯 By the end, you'll be able to
  • Identify the chord line, mean camber line, and thickness distribution of an airfoil.
  • Decode NACA 4-digit airfoil designations.
  • Differentiate between symmetric and cambered airfoils.

Airfoil Anatomy

An airfoil is a 2D cross-section of a wing. Key geometric features include the leading edge (LE), trailing edge (TE), chord line (straight line from LE to TE), and chord length (c). The mean camber line is the locus of points halfway between the upper and lower surfaces. Camber is the max distance between the chord line and camber line. Thickness is the distance between upper and lower surfaces.

\[ \text{camber ratio} = \frac{z_{c,max}}{c} \]
\[ \text{thickness ratio} = \frac{t_{max}}{c} \]
🔑 Angle of Attack

The angle of attack (alpha) is the angle between the chord line and the freestream velocity vector (V_inf). It is a primary control of lift.

NACA 4-Digit Series

The NACA 4-digit series describes airfoil geometry. For a NACA XYZZ: X is max camber as % of chord, Y is position of max camber in tenths of chord, and ZZ is max thickness as % of chord.

📝 Worked example: Decode "NACA 2412" and calculate its dimensions for a chord c = 1.5 m.
  1. 1. Camber: 2% of chord = 0.02 * 1.5 m = 0.030 m.
  2. 2. Position: 4 tenths of chord = 0.4 * 1.5 m = 0.60 m aft of LE.
  3. 3. Thickness: 12% of chord = 0.12 * 1.5 m = 0.18 m.
✓ Max camber is 0.030 m at 0.60 m from the LE; max thickness is 0.18 m.
✏️ Practice: Decode "NACA 0012".
Solution
  1. Hint: Leading two digits are zero => no camber.
  2. Answer: Symmetric airfoil (0% camber), 12% thick.

Check your understanding

1. What does the first digit in a NACA 4-digit airfoil represent?
The first digit is the maximum camber as a percentage of the chord length.
2. An airfoil with zero camber is called:
If the mean camber line coincides with the chord line (zero camber), the airfoil is symmetric.
🔎 Related lessons
Pressure Coefficient · soon
✅ Key takeaways
  • Airfoil geometry is defined by chord, camber, and thickness.
  • NACA 4-digit series encodes camber, position of max camber, and thickness.
  • Symmetric airfoils have zero camber.
➡️ Now that we understand the shape, let's look at how pressure forms over this shape to create lift.
Want to test yourself on this? Try the Aerospace Engineering Aptitude test →
🎓 Go deeper: external courses & trusted references
Foundational aerospace courses (OpenCourseWare)

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