Cross wind drag and side skirts / 'tails

[tasdrouille]

Say you're going 60 mph and you're getting a 60 mph crosswind at 90 degrees. What I called the flow vector is going to be 45 degrees.

[puddleglum]

Originally Posted by BamZipPow

Fixed yer links...

Thanks. What did I do wrong?

[BamZipPow]

Originally Posted by puddleglum

Thanks. What did I do wrong?

I think you clicked on the "Insert Link" button and when you pasted yer link, you had copied the "http://" part which the link button already added in.

[aerohead]

EPA published a chart in 1970s.
An 18-mph crosswind reduces mpg by 2%.
----------------------------------------------------------------------------
From Bain Dayman,Jr.,Jet Propulsion Lab,Cal Tech Univ.,SAE Paper 780337:

Annual mean wind spectra effect on zero-yaw Cd

Annual Mean Wind Speed,mph

5.8 10 15

Highway + 4.5% +12.0% +33.0%

This is not targeted specifically to crosswind,but will give you a feel to effect on Cd.


With respect to skirts,I've never come across any research which suggested that a skirt should be any lower than the bottom of the floorboard.

For a ground-effect racing car there would be a very carefully designed intake at front,then the rest of the car would be sealed all the way around until the very rear,where the low-pressure wake could communicate under the car, inducing downforce.

[moonmonkey]

then its front and rear strakes aka tire boattails. instead for me,, the rocker panels are even with my belly pan already.

[aerohead]

Originally Posted by moonmonkey

then its front and rear strakes aka tire boattails. instead for me,, the rocker panels are even with my belly pan already.

Yes,the leading and trailing fairings really help for the wheel drag.
Ford found that a trailing fairing after the front tires was not necessary on it's Probe-IV.The MG EX-181,Sunraycer,and Honda Dream-2 all employed complete fore and aft fairings for their tires.GM did delete theirs' for the trans-Australian Solar Challenge so they could survive 40-mph crosswinds,a strategy which allowed them to out run storms and get to sunshine.

[orange4boy]

I have Hucho's "bible" here with some data on side skirts and yaw in semi trailers and they improve the CD. At a yaw of 25˚ the cd is .15 better with fully skirted wheels.

CD @ 25˚ yaw faired: 1.0
CD @ 25˚yaw open wheeled: 1.15

Amen.