Airfoil fundamentals
What Is an Airfoil? A Complete Guide to Airfoil Geometry and Aerodynamics
HENDOI · 27 October 2026
Chord, camber, thickness, leading edge and trailing edge — the geometry that lets a wing, blade or fin make lift with controlled drag.
The short definition
An airfoil is the cross-section of a wing, propeller blade, wind-turbine blade, fin or fan, shaped so that moving air (or water) produces a useful force. In aircraft work that force is mostly lift, perpendicular to the oncoming flow, bought with as little drag, parallel to the flow, as the mission allows. The same idea appears as a hydrofoil in water. The outline is two-dimensional: it describes the shape at one station along the span. A real wing is a stack of those sections, usually twisted, tapered and swept.
People say “airfoil,” “aerofoil” and “section” for the same object. HENFOIL treats the section as the decision you make before you lock a three-dimensional wing.
The geometry you should be able to name
| Name | What it is | Why it matters |
|---|---|---|
| Chord | The straight line from the leading edge to the trailing edge. Length c is the chord length. Coordinates are usually written as x/c and y/c, so the chord runs from 0 to 1. | Chord sets the Reynolds number with speed, and it is the ruler for every other length. |
| Leading edge | The front of the section, where the flow splits onto the upper and lower surfaces. Its radius is a local bluntness. | A sharp leading edge stalls abruptly at low speed. A large radius is kinder at high angle of attack and usually costs a little cruise drag or cruise Mach. |
| Trailing edge | The back, where the upper and lower surfaces meet. It may be sharp, blunt, or open by a small gap in the coordinate file. | Thickness here changes base drag, manufacturing, and how cleanly the wake leaves. Analysis codes are sensitive to a messy trailing edge. |
| Camber line | The mean line halfway between the upper and lower surfaces. Camber is how much that line bends away from the chord. | Camber is the main reason a section can lift at zero geometric angle of attack. It also sets the pitching moment the tail or the structure must balance. |
| Thickness | The distance between upper and lower surfaces, measured perpendicular to the camber line (or, loosely, to the chord). Quoted as a fraction of chord, for example 12%. | Thickness carries structure, fuel or a spar. More thickness usually softens stall and lowers the Mach number where compressibility drag rises. |
A symmetric airfoil has a straight camber line: the upper surface is a mirror of the lower. A cambered airfoil is bent. Both are still “an airfoil.” The next lesson compares them directly.
What the flow does
In ordinary flight the air arrives along a direction called the freestream. The angle between that direction and the chord is the geometric angle of attack. The section turns the flow. Over the upper surface the streamlines crowd, the speed rises, and the pressure falls. Under the lower surface the pressure is often higher. The imbalance, integrated over the whole skin, is lift and drag. Skin friction adds drag even when pressure drag is small. A moment remains: the forces do not act through an arbitrary point, so the section wants to pitch nose-up or nose-down.
Coefficients remove size and speed so two sections can be compared:
- CL — lift coefficient, lift divided by dynamic pressure times chord (per unit span).
- CD — drag coefficient, the same idea for drag.
- CM — pitching-moment coefficient about a stated point, usually the quarter-chord.
Those three curves, plotted against angle of attack, are the airfoil polar. Reading them is its own lesson.
Two-dimensional is a model, not a wing
A 2D result assumes an infinite wing: no tips, no trailing vortices, no induced drag. A finite wing pays extra drag that depends on aspect ratio and lift distribution, and its stall can start at one station and spread. A good section is necessary. It is not a sufficient description of the airplane. The last lesson in this series connects the section to the wing on purpose.
Where airfoils are used
- Wings, canards, horizontal tails and vertical fins
- Control surfaces: aileron, elevator, rudder and flap sections, often with a different camber from the cruise wing
- Propellers, rotors and fans
- Wind-turbine blades, which change thickness from a structural root to a thin, quiet tip
- Hydrofoils, keels and underwater control surfaces
- UAV and model wings, where the Reynolds number is low and a section that looks fine at airliner scale can disappoint
A practical check before any plot
If the coordinates are upside down, the chord is not 1, the trailing edge is a scribble, or the leading edge has a dent from a bad digitizer, every CL and CD that follows is fiction. Name the geometry first. Then ask for forces. HENFOIL’s geometry gate exists for that reason: thickness, camber, leading-edge radius and trailing-edge state are inspected before a polar is trusted.
Where this sits in the series
These pages teach the ideas. They are not wind-tunnel data and not a certification analysis. When a number matters, compute it at a stated Reynolds number, Mach number and transition setting, and keep the method label on the result. In HENFOIL that production polar is a VIC polar — see the analysis ladder and the polar field guide.
In simple words: what this page is for
Chord, camber, thickness, leading edge and trailing edge — the geometry that lets a wing, blade or fin make lift with controlled drag.
This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. What Is an Airfoil? A Complete Guide to Airfoil Geometry and Aerodynamics helps you keep a clean trail from shape to polar to choice.
Why the topic matters
Engineers lose time when a title sounds clear but the page only sketches the idea. This article expands What Is an Airfoil? A Complete Guide to Airfoil Geometry and Aerodynamics so you can answer three questions without jargon: what is the idea, when do you use it, and how do you check it in a HENDOI product.
Read the sections above for the core definitions. Use the steps below to move from reading into a real project trail you can share with a teammate.
How to apply this in HENDOI
In practice: create a HENDOI account or log in, open HENFOIL, bring a section in (create, import DAT, or digitize), pass the geometry gate, climb the analysis ladder only as far as the decision needs, then compare and archive. Every calculated number should keep its method label.
When the section choice is ready for the aircraft, continue in HENSYNTH for mission, compliance and trades. Same account. Same plans.
What this page will not claim: a teaching polar or geometry note is not a flight-Re certificate. HENFOIL labels methods so you know what you bought. Tunnel data and professional judgement still sit outside any single software run.
Checklist before you leave this page
- Can you state the idea of What Is an Airfoil? A Complete Guide to Airfoil Geometry and Aerodynamics in one sentence?
- Do you know which product owns the next action — HENFOIL or HENSYNTH?
- Will every number you keep carry a method label or a stored-run source?
- If you are new here, have you opened Register or Login?
Related reading on this site
Both products live
Use this lesson in the HENDOI workspace
This page sits in Airfoil fundamentals. HENFOIL and HENSYNTH are both live on one account. These articles are screening lessons — not certification reports.
Live · section
HENFOIL
Turn this lesson into a section you can draw, check, analyse and compare. Run the polar at the Reynolds number of the vehicle. The method name stays on the result.
To Know MoreLive · aircraft
HENSYNTH
After the section is chosen, set geometry and mission requirements, run screening, read compliance, synthesize candidates and download or mail the report.
To Know MoreAerospace industry collaboration
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Related articles
- Symmetric vs Cambered Airfoils: Differences, Advantages and Applications
A symmetric section lifts only when it is at an angle. A cambered section lifts at zero chord angle — and it brings a pitching moment with it.
- How to Read NACA 4-Digit Airfoil Designations: NACA 2412 Explained
The four digits are maximum camber, where that camber sits, and thickness. NACA 2412 is 2% camber at 40% chord and 12% thick.
- How Angle of Attack Affects Airfoil Lift, Drag and Stall
Geometric angle of attack tilts the chord to the freestream. Lift rises almost linearly, drag rises faster, and then the section stalls.