Aero parts

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hippy in reply to @umop3pisdn

Any idea re: existing tubes though? I don't recall seeing many frames with an airfoil that severe.

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wjrh in reply to @hippy

Yeah that aerofoil has a fair bit of camber, so it produces lift at zero incidence hence wouldn't be a good choice for a a bicycle.

It wouldn't be surprised if the aerofoil section used on bicycle frames is one of the NACA 4-digit aerofoils, so NACA 00XX range, probably a NACA 0012, where the '12' is the percentage of max. thickness to chord length.

airfoiltools.com has a decent database of aerofoil properties here is the NACA 0012: http://airfoiltools.com/airfoil/details?airfoil=n0012-il
Alpha represents angle of attack, which for a bicycle would be the yaw angle. If you assume the Reynolds number on the headtube of a bicycle is roughly 5x10^4, it should give you a good good idea of the aero properties of the section. You can also assume the CD of a cylinder is around 1 at this Reynolds number (CL is obviously 0).

Should also remember the tubing on bicycles is three dimensions this isn't ideal and distributions of the aero coefficients over the span of the tubes will change. Also once the air reaches places like the downtube the air is already really turbulent and messy, so it's not quite this simple.

If you want to work out the actual drag force that you need to overcome, you just multiply the drag coefficient by 0.5*1.225*velocity^2*surface area
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Ptown in reply to @hippy

Not as sciencey but maybe more applicable info? Nice bit of analysis here from Specialized's steel Allez vs Venge video (including other aero-road frames).