# Aerodynamics drag of hollow cylinder vs solid cylinder of the same cross area?

I wonder how a hollow cylinder at the same cross area perform vs a solid one, i.e the hollow cylinder has larger radius? I guess they have a similar drag, is that true?

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I don't have answer right now, but there is more surface for a hollow cylinder, so maybe more drag? –  fffred Jun 3 at 7:05
I didnt get the question. Are you comparing two identical cylinders wherein the dimensions are identical but one is hollow, and the other is closed? –  Saurabh Raje Jun 3 at 7:54
@fffred, I would say the excess area hypothesis is true only for the initial fraction of seconds –  Saurabh Raje Jun 3 at 7:56
By hollow, do you mean that there are no circular faces. i.e. air can flow through the cylinder? –  user80551 Sep 19 at 17:55

If the flow is perpendicular to the cylinders axis of symmetry as long as the two cylinders have the same radius, length and are made of the same material, then the drag on them will be the same.

If the flow is parallel to the axis of symmetry then you are right to suggest that (assuming the radius, length and material of the two cylinders are the same) the larger surface area of the hollow cylinder will cause more drag.

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