How to Choose the Right Airfoil for a Fixed-Wing UAV

Start from the flight, not from a famous name

A fixed-wing UAV section is chosen at a Reynolds number the wing will actually see. That number is speed times chord divided by viscosity. Small electric aircraft often live between about 10⁵ and 5×10⁵. A larger tactical UAV with a longer chord moves toward 10⁶. A section celebrated at Re = 3×10⁶ can carry a laminar bubble, extra drag and an early stall at the lower figure. Compute Re for cruise and for loiter before you open a catalog.

The second number is the lift coefficient the wing must fly. From weight W, wing area S and dynamic pressure q, the airplane lift coefficient is W/(q S). Wing loading W/S is the design driver people feel in the air: heavier loading means faster flight or a higher CL. The section only has to supply the CL the wing asks for at that speed, with margin for gusts and for the turn.

Mission first

Practical filters

• Thickness. A spar, a servo wire and a battery bay need depth. Very thin low-Re sections look fast and arrive fragile. Many small UAVs end up around 10–14% thick as a compromise, and the root can be thicker than the tip.
• Camber. Enough to put the design CL near the best L/D, not so much that the moment demands a large tail download. Check CM, not only CD.
• Leading-edge radius. Too sharp at low Re invites an abrupt stall. Too blunt can cost the drag you were counting.
• Stall shape. Read the lift curve at the right Re. A rounded top is usually kinder to an automatic landing than a cliff.
• Contamination. Run a tripped polar. A UAV that only works with a laboratory leading edge will lose its range after the first insect season or the first taped repair.
• Tip versus root. Taper lowers the tip Reynolds number. The tip section is often the one that stalls first if you copied the root section outboard. Twist and a different tip section exist for that reason.

A selection sequence

1. Freeze speed, chord, altitude and an estimate of wing loading.
2. Build a short list of sections that have been used at a similar Re, plus one or two you generate with the thickness and camber you need. Famous is not a requirement.
3. Analyse them all at the same Re, Mach (usually small) and transition setting.
4. Score design-CL drag, moment, CL max and thickness. Then score the tripped case.
5. Only then draw the wing. The section decision is allowed to change when the spanwise Re and the stall pattern are visible.

HENFOIL’s selection flow is this sequence with the weights written down, so “why this section” survives the next design review. Pair it with the comparison lesson so the Reynolds number stays honest.

---

Where this sits in the series

In simple words: what this page is for

Cruise speed, chord, endurance and how gently it stalls decide the section. A name that worked on a light aircraft is not automatically a UAV section.

This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. How to Choose the Right Airfoil for a Fixed-Wing UAV 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 Choose the Right Airfoil for a Fixed-Wing UAV 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 Choose the Right Airfoil for a Fixed-Wing UAV 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

• Airfoil Design Considerations for Flying-Wing UAVs
• How to Select an Airfoil for High-Altitude Long-Endurance UAVs
• Who HENSYNTH is for: OEMs, UAV teams, labs and students
• HENSYNTH electric UAV mission screening loop
• All HENDOI blog articles
• HENFOIL product page
• HENSYNTH product page
• Pricing — Student, Professional & Team
• FAQ
• Login · Register now

• Previous: How to compare two airfoils
• Next: Airfoil optimization explained
• 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.