Comment by kqr
2 years ago
Huh, odd. I was under the impression that for swept/delta winged paper airplanes one wants a smooth top surface to encourage attachment and any steps on the bottom to provide decalage. (I.e. the area ahead of the step acts as a canard-like surface.)
Is this an airfoil that works for tailed aircraft but not tailless ones, perhaps?
Edit: I just skimmed the book on paper planes by KF and indeed they are using the variation with the step on the bottom for their paper planes.
I'm actually even more surprised now. How on Earth did they manage to patent the idea of reflex on a delta wing to give a tailless plane stability? This seems like the thing that (a) was known since early human-carrying gliders, and (b) implicitly discovered by anyone that folds a lot of paper airplanes. I will definitely read their book in more detail.
Attachment isn't as much of an issue with paper planes since the small size and low speed give much more favorable Reynolds numbers.
Could you elaborate on that, please? This is just at the edge of my understanding and I'd like to learn more.
You can see the effect in the second animation of the linked page, but the basic idea is the lower the Reynolds number, the less likely for flows to separate and become turbulent. Shrinking the scale and slowing the airspeed both lower the Reynolds number, so paper planes have vastly different aerodynamics to full size aircraft.
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