An airfoil is the cross-sectional profile of a wing — the shape you see if you slice a wing perpendicular to the span. Its geometry determines how the wing converts forward motion into lift, how much drag it produces, and how it behaves as angle of attack increases toward stall.
An airfoil is described by:
- Chord — the straight-line distance from leading edge to trailing edge.
- Camber — the curvature of the mean line between upper and lower surfaces. Positive camber produces lift at zero angle of attack. Symmetric airfoils (zero camber) produce no lift at zero AoA.
- Thickness — maximum distance between upper and lower surfaces, expressed as a percentage of chord. Typical values: 6–8% for high-speed sections, 12–18% for low-speed, high-lift sections.
- Thickness distribution — where the maximum thickness falls along the chord. Forward (20–30% chord) promotes laminar flow; rearward (40–50%) provides more volume.
Airfoil selection for UAVs is complicated by Reynolds number. Small UAVs (chord < 200 mm, speed < 20 m/s) operate at Reynolds numbers of 50,000–200,000, where the boundary layer is predominantly laminar and prone to separation bubbles that dramatically increase drag. Airfoils designed for full-scale aircraft (NACA 2412, Clark Y) perform poorly at these scales. Specialized low-Reynolds-number airfoils (Selig S1223, Eppler 387, AG-series) use specific camber and thickness distributions to manage the laminar-turbulent transition.
For 3D-printed wings, airfoil selection also interacts with manufacturing constraints: thin trailing edges are difficult to print accurately, and surface roughness from layer lines affects boundary layer behavior. Many printed-wing designers use slightly thicker trailing edges (1–2 mm rather than knife-edge) and accept the small drag penalty.
Related terms
- Chord — the characteristic length of the airfoil
- Camber — the curvature that generates lift at zero angle of attack
- Reynolds Number — the flow parameter that determines which airfoils work at a given scale
- Boundary Layer — the thin air layer whose behavior the airfoil shape is designed to control