An airfoil is the cross-sectional shape of a wing, propeller blade, or similar lifting surface. Cut a wing perpendicular to the span: the outline you see is the airfoil.
Why airfoils matter
Aircraft, UAVs, gliders, and many wind-turbine blades depend on section shape. Camber, thickness, and leading-edge radius strongly influence performance. Choosing the wrong section early can force expensive planform or structure changes later.
The main geometric words
Chord
Distance from leading edge to trailing edge.
Camber
Curvature of the mean line between upper and lower surfaces.
Thickness
Local distance between surfaces — often as % of chord.
Leading-edge radius
How blunt or sharp the nose is — strongly affects stall.
How an airfoil works (without myths)
Lift comes from a net pressure difference between the lower and upper surfaces. Angle of attack and camber both change that pressure field.
Myth to retire
“Equal transit time” (air parcels must meet at the trailing edge together) is not how lift works. Prefer pressure — or circulation — language instead.
2D section vs 3D wing
A 2D airfoil polar assumes infinite span. Real wings have tips, induced drag, and spanwise loading. Section analysis is still the right first step before vortex-lattice or lifting-line wing studies.
Student checklist
- Name chord, camber, thickness, and leading edge on a sketch
- State the mission Reynolds number
- Ask what Cl and L/D you need at cruise
- Only then pick a library family — then practise in HFOIL
Next: read How Airfoils Create Lift or Parts of an Airfoil Explained.