NACA 4 series aerofoil/airfoil generator
(by Gareth)
Create NACA 4 series aerofoil/airfoil sections on the fly
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A GH definition embodying the equations and methods set out in Abbot and von Doenhoff’s classic student aerodynamicists’ text, Theory of Wing Sections.

Although NACA's 4 Series aerofoils are now rather old (they were developed in the thirties), they are still useful for low-speed applications such as wind turbines or velomobile fairings. They are also tolerant of innacuracies in construction, dirt and insect accumulation, and real-world conditions generally.

I’ve improved on the methods described in the book by using Cosine spacing of the samples along the Thickness Distribution, working from Trailing Edge to Leading Edge so that there are more samples in the critical Leading Edge area, as well as wrapping it around the Mean Line as a single curve from Trailing Edge to Trailing Edge. The Mean Line was cleaned up by running it through a Fit Curve component, to smooth out the bump that inevitably occurs (with Abbot and von Doenhoff’s method) when the equation for the front portion and rear portion of the Mean Line meet. Finally, a Flow component was used to map the Thickness Distribution onto the Mean Line: a lot less fuss than using the mathematical approach that was necessary in the 1930s!

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