Airfoil Sensitivity Analysis: Measuring the Effect of Geometry Changes on Performance

One change, one rerun

A sensitivity answers “if this geometric number moves a little, what happens to the polar at the design lift?” Change one parameter. Keep the Reynolds number, Mach number, transition setting and solver settings identical. Subtract the coefficients at the same lift coefficient, not at the same geometric angle, unless the angle is what the vehicle holds. Camber changes the lift at a fixed angle, so an angle-matched difference mixes a lift change with a drag change. The geometry-modification lesson is how to make the edit without a crossed curve. This lesson is how to score it.

Parameters worth differencing

• Maximum thickness, with the thickness distribution’s shape held as still as the family allows.
• Maximum camber, or the design lift of a mean line, with thickness held.
• Leading-edge radius, when you can change it without also changing maximum thickness. If you cannot, say so. The two are coupled in the four-digit equation.
• Trailing-edge gap, because manufacturing will not hit zero and the base drag is the sensitivity you are buying insurance against.

Report the step size. A difference across a 4% thickness change is not a derivative, and a difference across a 0.01% change can be solver noise. Repeat at a second step. If the sign flips, you are in the noise or in a separated region where the polar is not smooth. The robust-optimization lesson is what to do when the condition is uncertain as well as the shape. Sensitivity to geometry at one flight condition does not replace that. Keep the baseline hash and the perturbed hash. A slope without the two polars cannot be audited.

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Where this sits in the series

In simple words: what this page is for

Sensitivity is the change in CD, CL or CM when you change one geometric quantity and rerun the same case. It is a local slope. It is not an optimum, and it is not a license to stack several changes and add the slopes.

This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. Airfoil Sensitivity Analysis: Measuring the Effect of Geometry Changes on 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 Airfoil Sensitivity Analysis: Measuring the Effect of Geometry Changes on 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 Airfoil Sensitivity Analysis: Measuring the Effect of Geometry Changes on 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

• Active Flow Control on Airfoils: Suction, Blowing and Synthetic Jets
• What Is the Aerodynamic Center of an Airfoil? Location, Meaning and Applications
• How to Identify Numerical Convergence Problems in Airfoil Analysis
• How to Build an Airfoil Analysis Database with Consistent Simulation Conditions
• All HENDOI blog articles
• HENFOIL product page
• HENSYNTH product page
• Pricing — Student, Professional & Team
• FAQ
• Login · Register now

• Previous: An analysis database with consistent conditions
• Next: Outliers and unphysical polar data
• 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.