Aerodynamics of a thick airfoil?

[D-Fens 0]

Hi,

So I was thinking why some parachutes have a thicker airfoil than others, and what the thickness means in terms of aerodynamics.

So accuracy and seven-cell canopies are usually thicker than high performance nine cells.

Can anyone explain the science here?

I was thinking (or, guessing) that the increased thickness will increase drag ("bad") however it may (?) also increase lift because the air has to travel further above the wing than below it ("good")? The canopies with a low aspect ratio need this thickness out of necessity to create lift.

Enlightenment appreciated :-)

Cheers,
D

[polarbear 1]

Aerodynamics can be a little tricky and deceptive. However, generally speaking, thicker airfoils are used in low-speed applications. You are correct that the thickness tends to increase both lift and drag, however, at lower speeds the extra drag isn't a problem. With a high-speed airfoil, the extra drag from the increased thickness becomes so dominate that it is too hard to get the wing flying fast, so a thinner section becomes necessary.

Generally speaking, if you look at low speed parachutes (accuracy canopies, student canopies, etc) they will have much thicker airfoils than high speed canopies (X-braces).

Likewise, in the airplane world, you will see similar trends...lower speed airplanes tend to have airfoils a little thicker and perhaps a little more cambered then high-speed airplanes.

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