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What are typical naca foils for winglets for ultralights?

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    $\begingroup$ There are ultralights with winglets? They are only really effective on airplanes that cruise at low indicated airspeed where the vortices are strong enough to give an energy recovery benefit that exceeds the weight/drag penalty of the winglet itself. Which is, mostly, airplanes that cruise above 30000ft And maybe, gliders. $\endgroup$
    – John K
    Commented Jun 15, 2019 at 0:10
  • $\begingroup$ Winglets are used on hangliders, trikes, the original ultralight - the lazier, velocity pusher aircraft, and most of all: birds, which is where the idea came from in the first place. I'm thinking a NACA 009, although I've seen lot's of winglets that don't seem to be foils, just plates. $\endgroup$
    – Fred
    Commented Jun 15, 2019 at 15:11
  • $\begingroup$ The Lazair has a kind of turned up wing tip, no so much a winglet. The velocity and it's kin are using them as yaw stability surfaces (tip rudders) more than winglets. Some hang gliders and sailplanes use them, because they fly in a speed range that is able to exploit the energy in the vortice. Remember that a winglet is a sail. It makes lateral lift, producing an outwash that weakens the circulation around the tip and also generates a forward thrust component. Winglets on a jet point outboard slightly to optimize AOA. Since they are sideways lift makers, you need to use a cambered airfoil. $\endgroup$
    – John K
    Commented Jun 15, 2019 at 16:10
  • $\begingroup$ They are only worth using when induced drag is the dominant factor. As soon as you speed up, other types of drag predominate and the induced drag benefit is cancelled out by the form drag of the winglet. Unless you are optimizing your ultralight/LSA for best L/D close to the stall, which is desirable for soaring aircraft, they are a waste of time because you pay for it at the high speed range. $\endgroup$
    – John K
    Commented Jun 15, 2019 at 16:24
  • $\begingroup$ Winglets are very common on ultralights and trikes, and have been so for more than a decade. airtrikes.net/wings.shtml They have been found to improve longitudinal stability in straight and level flight, much as the effect of dihedral aeros.com.ua/news.php?lang=english&id=144. For winglet airfoils used it's a challenge to find out. You might have to email individual manufacturers. $\endgroup$ Commented Jun 16, 2019 at 19:41

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The information I have, is that you would want to have the thinnest symmetrical airfoil, that will work in the specified Re range, eg. NACA009

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