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Most airplanes of its days had a Dihedral, or a wing thickness tapering with a 'V' shape, this one is the opposite, hints exist as done to avoid: 'Dutch Roll', or that the ordinary way will impair performance. What is it?? Hoffman all-wing airplane
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Johnson 1931 Round Wing airplane

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This plane is very interesting as it highlights a few design options. Firstly, in seems to have neither significant dihedral nor anhedral, but it does have landing gear underneath it, lowering its CG for stability. Being low aspect ratio, the builder probably decided to forego dihedral as cross wind gusts could make for a rolly, uncomfortable ride. A slight sweep in the leading edges of the wing would provide some "dihedral effect" when rudder was applied.

Now for the wing itself, not albatross or eagle, we'll go flying squirrel here. But notice how low the landing speed is. This is a virtue of lower AR wings, though not as efficient as high AR (albatross) wings, they do stall at significantly lower speeds. This design was also applied to the Navy "flying flapjack" and it performed well.

And thanks for the article, the ads made good reading too!

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  • $\begingroup$ Send me everything listed -- look at those balsa prices! $\endgroup$ – amI Oct 8 '18 at 1:18
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I don't think it's a deliberate anhedral. It's just a geometrical consequence of having an airfoil with flatter bottom. If you imagine a plane connecting the leading edge and the trailing edge, it will be flat. Or likewise, if the airfoil had a completely flat bottom, the lower surface would be flat, and the top one sloping down.

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  • $\begingroup$ The question focuses on inferior side of Hoffman wing being flat, upper side thinning from root to tips, opposite as the Johnson Circular Wing plan, that probably never flew. In YouTube: 'Wingless wonders'; the Hoffman flies. Johnson's has a flat upper wing side, some kind of a dihedral in the inferior side, close to NASA 'Flying bathtub' lifting body. This dihedral-like, besides providing stability, if too much, it could induce 'Dutch Roll', raise drag, decreases chances of noxious Ground effect on landing, more possible with the flat bottom approach [![R B Johnson Round Wing 1931][1]][1] $\endgroup$ – Urquiola Oct 10 '18 at 18:59
  • $\begingroup$ Raoul J Hoffman was the engineer who changed the concepts of the podiatrist Snyder into the well flying Arup line of airplanes. No 'visibility' problems exist today for Short AR designs as cost of a TV camera and screen is below that of a full gas tank $\endgroup$ – Urquiola Oct 10 '18 at 19:09
  • $\begingroup$ These low aspect ratio wings had a vertical speed at landing higher than more common designs, but speed respect to ground was low, this can help in aircraft carriers and some dangerous airports, landing is along an inclined line, not a curve tangent to ground. $\endgroup$ – Urquiola Oct 30 '18 at 21:10

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