How to Measure Airfoil Lift and Drag in a Wind Tunnel

Two instruments, one coefficient

A force balance measures the load between the model and the tunnel. Resolve that load into lift and drag using the geometric angle, and divide by dynamic pressure times area. A wake rake measures the momentum missing downstream and converts it to profile drag by a momentum integral. Lift is almost always the balance. Drag may be either, and the two drags do not have to agree: the rake sees the wake of the section, while a balance can also see end effects, a leak at the wall, and the drag of whatever holds the model. The wind-tunnel lesson is when to trust a published test. This lesson is what the test was physically doing.

A measurement that can become a coefficient

1. Record total and static pressure and temperature, and compute dynamic pressure and Reynolds number from them. A fan RPM is not a q.
2. Set the angle from a known geometric zero, and record where that zero came from. A shifted zero looks exactly like camber.
3. Read the balance, or traverse the rake across the whole wake, including the thin edges of the defect.
4. Apply the tunnel’s solid blockage, wake blockage and streamline-curvature corrections. An uncorrected lift slope is a property of the test section as much as of the airfoil.
5. Repeat at least one angle. A single sweep with no repeat has no scatter to quote.

Write CL, CD, CM, α, Re, Mach, trip location and “corrected” on the same line. A plot with only CL and α is a picture, not a measurement you can put next to a computation.

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Where this sits in the series

In simple words: what this page is for

Lift is usually a balance reading. Drag is a balance reading or a wake survey. Both are useless until dynamic pressure, angle and the wall corrections are part of the same record.

This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. How to Measure Airfoil Lift and Drag in a Wind Tunnel 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 How to Measure Airfoil Lift and Drag in a Wind Tunnel 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 How to Measure Airfoil Lift and Drag in a Wind Tunnel 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
• How Adverse Pressure Gradients Affect Airfoil Boundary Layer Separation
• What Is the Aerodynamic Center of an Airfoil? Location, Meaning and Applications
• What Is Airfoil Aerodynamic Efficiency Across a Range of Flight Conditions?
• All HENDOI blog articles
• HENFOIL product page
• HENSYNTH product page
• Pricing — Student, Professional & Team
• FAQ
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• Previous: Spanwise flow and three-dimensional effects
• Next: Instrumentation and data reduction
• 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.