Lift and drag
Maximum Lift Coefficient (CLmax): Factors That Determine Airfoil Performance
HENDOI · 27 October 2026
CLmax is the highest section lift coefficient on the polar before stall wins. It moves with Reynolds number, nose shape, camber, roughness and Mach number.
One point on one polar
CLmax is the maximum of section CL versus angle of attack at a stated Reynolds number, Mach number and surface condition. The angle where it occurs is the stall angle for that same condition. Neither number is a property of the NACA digits alone. A 2412 at Re = 3×10⁶ with a clean nose and a 2412 at Re = 1×10⁵ with a tripped nose do not share a CLmax, and a viscous panel method may not be equally right about either of them. Read CLmax off a curve you trust, and write the condition beside it.
What moves it
| Factor | Usual direction |
|---|---|
| Reynolds number, upward, attached-type sections | CLmax tends to rise, and the stall type can change. The low-Re value is the conservative one if that is where you fly. |
| Leading-edge radius | A larger radius usually delays leading-edge stall and raises usable CL. A very sharp nose does the opposite. |
| Camber and flaps | More camber, and especially a trailing-edge flap, raises CLmax and shifts the whole lift curve. The moment rises with it. A flap is a second geometry. Analyse the deflected shape. |
| Thickness | Very thin sections tend toward thin-airfoil stall and a soft, sometimes disappointing maximum. Moderate thickness with a decent nose is often kinder. Very thick sections pay in cruise. |
| Roughness, insects, ice | All of these cut CLmax and often cut the stall angle more than they change the linear slope. The clean CLmax is not the landing CLmax. |
| Mach number | As shocks appear, the lift curve breaks earlier. A low-speed CLmax is not a transonic CLmax. |
Stall type matters as much as the peak. A gentle trailing-edge stall and an abrupt leading-edge stall can share a similar CLmax and feel nothing alike. The stall-type lesson is the companion to this number.
How to take the number from a computation
- Sweep angle finely enough that the peak is not hidden between two points. A 2° step can miss the top or place it on a single unconverged sample.
- Check that the solver converged at the points around the peak. A spike from a failed iteration is not CLmax.
- Treat deep stall from an integral boundary-layer method as a screen. The peak can be in the right neighbourhood and the post-stall branch can still be wrong.
- Repeat with a trip if the vehicle will not stay clean. Report both.
- Do not convert section CLmax into a stall speed by itself. Stall speed needs weight, area, density and the wing’s maximum lift coefficient, which is lower than a naive section value once planform and twist are included, and different again with flaps and ground effect.
Where this sits in the series
In simple words: what this page is for
CLmax is the highest section lift coefficient on the polar before stall wins. It moves with Reynolds number, nose shape, camber, roughness and Mach number.
This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. Maximum Lift Coefficient (CLmax): Factors That Determine Airfoil Performance 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 Maximum Lift Coefficient (CLmax): Factors That Determine Airfoil Performance 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 Maximum Lift Coefficient (CLmax): Factors That Determine Airfoil Performance 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
- How to Determine the Best Angle of Attack for Maximum Airfoil Efficiency
- How Leading-Edge Slats Delay Airfoil Stall and Increase Maximum Lift
- Maximum Camber vs Maximum Thickness: Understanding Airfoil Geometry
- All HENDOI blog articles
- HENFOIL product page
- HENSYNTH product page
- Pricing — Student, Professional & Team
- FAQ
- Login · Register now
- Previous: Zero-lift angle of attack
- Next: Airfoil efficiency at different angles of attack
- Index: all HENFOIL airfoil lessons
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.
Both products live
Use this lesson in the HENDOI workspace
This page sits in Lift and drag. 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.
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