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Old 12-15-2010, 10:38 AM   #309 (permalink)
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Join Date: Feb 2008
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vectra a - '95 Opel Vectra GLS
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Why would Jim consider adding area to the rear, while the centre of pressure is obviously still forward enough not to cause handling issues in sidewind conditions ?
A tail wouldn't cure an aft shift in CoP, it'd make it worse.
first of i'm no expert so i might be wrong about any number of things, and i'm just trowing in an idea for what it's worth and to perhaps learn what such mods would actually do in reality to both handling and FE.

But it's my understanding that a forward Cop is bad for sidewind handling, since the front will be pushed out more than the back, sidewinds effectively "steering" the vehicle of the road, where a more aft COP, as can be achieved with adding a rear fin, will cause the rear of the vehicle to be pushed out more than the front, thus "steering" the vehicle into the wind, countering the outward force. as long as this fin does not projects above or below the vehicle no frontal area is added although the fin can change the Cd.

looking at the shape if the tail i'm wondering if it isn't perhaps produceing downforce behind the rear axle, esicially when the air is passing over it sideways and the elitical cross section starts looking a lot like an (inverted in the case of downforce)airfoil to the airflow. if this is the case this could unload the front tires and cause more oversteer (especially in conditions where traction is at it's limit) a fin underneath the tail (or above, this is speculation) could have a dual function, shifting the center of pressure back, but also working as a spoiler when the airflow becomes more sideways and thus canceling any undesirable downfoce that might exist. thus putting more waight on the front wheels and curing understreer

again, i'm mostely interested in actual experiments because airflow is so complex that some things are really counter intuitive, and as stated above i'm no expert
aer·o·dy·nam·ics: the science of passing gass

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