Airfoil Design for Solar-Powered UAVs: Endurance and Low-Speed Efficiency

The energy balance is an airfoil problem

A solar aircraft collects power on the wing and spends power overcoming drag. Endurance through the day, and through the night if there is a battery, improves when the drag at the loiter lift is low and the wing area that carries cells is large. Area and aspect ratio are planform choices. The section choice is the profile drag and the thickness that lets that huge, light wing exist. The HALE lesson covers the thin air at altitude. A solar airplane adds a surface constraint: solar cells, cover glass and joints are roughness and steps on the very surface you wanted laminar.

What the section owes the airplane

• Efficiency at a high loiter CL and a modest Reynolds number. Wing loading is very low and speed is low, so Re is often a few hundred thousand even when the chord is not tiny. Score CL^3/2/CD as well as CL/CD. The first is the endurance leaning of a propeller-driven loiter. The second is still the glide and the range leaning.
• A laminar bucket that survives cell edges, or a section that was never depending on a long laminar run. A trip at the first cell joint is an honest case. A clean Ncrit of 14 with no joint in the model is not.
• Thickness for a spar that is almost the whole weight budget. A thinner section with a slightly better clean CD can lose once the spar gets heavier and the induced drag rises with weight.
• A gentle stall. These wings are flexible and fly with little margin in gusts. An abrupt leading-edge stall at low Re is a poor match.
• A small pitching moment. Tail download is extra lift the wing must carry, and extra lift is extra area or extra speed, both of which fight the energy budget.

A selection cut

Analyse candidates at the loiter Re, clean and with a trip at a plausible cell-joint location. Keep the section whose tripped endurance parameter is still high and whose thickness closes the spar. Then check a faster recharge climb if the mission has one. The array layout and the airfoil coordinates should be drawn together. A cell map added after the polar is a new roughness distribution, and it deserves a new polar.

---

Where this sits in the series

In simple words: what this page is for

A solar UAV spends the day’s collected energy on drag. The section has to be efficient at low speed and low Reynolds number, and the upper surface is also a solar array that must stay smooth.

This lesson exists because section decisions fail when geometry, method labels and selection reasons are scattered. Airfoil Design for Solar-Powered UAVs: Endurance and Low-Speed Efficiency 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 Design for Solar-Powered UAVs: Endurance and Low-Speed Efficiency 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 Design for Solar-Powered UAVs: Endurance and Low-Speed Efficiency 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
• Login · Register now

• Previous: Finite-wing effects and induced drag
• Next: Airfoils for human-powered aircraft
• 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.