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Originally Posted by ebacherville
very cool.. however to spendy for me .. I'll wait for mother nature to give me a windy day and break ou tthe tufts and smoke..lol
However wouldn't a mini wind tunnel be pretty easy to construct and use models for some testing be far cheaper and decently accurate for us "tinkerers".. Thats what the write brothers did for there airplane design.
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For a full-size car,drag coefficients become stable at about 20-mph,so your tuft-testing at 20 or above would give you an accurate representation of your car's aero.In wind tunnels,they like to keep the percent blockage( the ratio of the frontal area of the vehicle,to the area of the test section of the tunnel)to about 4-percent.For a NASCAR at around 22 square-feet of area,you'd need a tunnel with a test section of 550-square-feet .When you start to get into models you run into scaling factors,as Reynolds numbers have to do with size as a function of velocity.So lets say your going on the cheap,and you're gonna target the 20-mph minimum for full-scale.With models,you'd have to have tunnel velocities at the following relationships to maintain appropriate Reynold's numbers and meaningful results :
1/2-scale = 40-mph
---------------------- 1/4-scale = 80-mph
-------------------1/8-scale = 160-mph
-------------------------1/16-scale = 320-mph
---------------and so on.
I discovered that I could duct-tape cardboard to the vehicle and test it in full-scale cheaper and quicker than by building models.It's a choice everyone will have to sort out for themselves.I have a small a small tunnel for public demonstrations and its dramatic what it can reveal to people who've never seen such a thing,however it does nothing really meaningful as a development tool. Just my two-cents.