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I'm a member of a student competition team, we design light aircraft (total airplane overhead area is limited to 0.9 m²) capable of carrying higher payload. The competition also limits the takeoff distance (this year's limit was 70 m).

Coming from the last event, we decided that winglets are probably a great introduction to the project, but we have no idea how to design one.

My question is basically: with this kind of aircraft (weighs about 2.3 kg empty, carries about 13 kg, wingspan is 2.8 m), what should we look for in a winglet design?

We are mostly in doubt about what kind of airfoil should we use. Should we look for less drag? More efficiency? How can we maximize the traction vector, and should we do that in first place?

We have been reading papers on the subject, but with little luck. We also don't think it would be wise to just randomly test things until we get right, so a little bit of direction would help a lot, even if it's an article that we should work around.

Thanks in advance!

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    $\begingroup$ Are you looking for a winglet design or airfoil design? Your title and question don't really match. $\endgroup$ – SMS von der Tann Nov 23 '15 at 22:36
  • $\begingroup$ I'm unsure if the teminology is correct, in portuguese it's the same. But what I meant with airfoil is winglet airfoil selection. $\endgroup$ – Caio Guimarães Nov 24 '15 at 4:18
  • $\begingroup$ What are the constraints? Winglets would make sense if you have limit on wingspan and not much otherwise. $\endgroup$ – Jan Hudec Nov 24 '15 at 8:14
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    $\begingroup$ @JanHudec The total airplane overhead area is limited to 0,9m^2, as of this year's rules. $\endgroup$ – Caio Guimarães Nov 24 '15 at 11:36
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    $\begingroup$ The efficacy of winglets in large(r) aircraft is not recognized universally. Many engineers are of the opinion that they are nothing more than a salesman's gimmick. Just my opinion, but you might consider letting go the thought that winglets will be anything but a time-waster, from design to implementation, and just "build a better plane" $\endgroup$ – CGCampbell Nov 24 '15 at 14:29
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For best results, put good flaps on the wing and forget using a winglet.

If you insist on bending the wing up at its end, just continue with the tip airfoil and select the incidence such that your circulation distribution over the wing and winglet will become elliptical when you plot it in a straight line. The small size of your airplane implies that you will not need to unload the tips to reduce root bending moment.

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  • $\begingroup$ Ah, I think I got that. I'm gonna bring this up with the other members, let's see what happens. Also, flaps are on our minds. On the current project, we had bad results with them because the wing airfoil had a lot of camber and deploying flaps were adding very little to lift while increasing too much drag. An aerodynamicist suggested us to look into multi-element airfoils, if we are to use flaps. Thanks for the tips! $\endgroup$ – Caio Guimarães Nov 24 '15 at 4:25
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    $\begingroup$ @CaioGuimarães: If your airfoil has what is called "rear loading" (high camber at the rear), it is ideal for slotted Fowler-type flaps. The best flap is thin and highly cambered. You will need to rejuvenate the boundary layer, so simple camber flaps will not help. Also, make sure to combine them with slats, especially at the outer part which have no slotted flaps. $\endgroup$ – Peter Kämpf Nov 24 '15 at 21:29

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