Jim;
A vertical fin on the back will not generate any lateral force until the
car starts to yaw; if tire forces are neglected (can't really do this in
practice), the car will rotate around its CM but the aerodynamic force
generated by the fin running at an angle to the airstream (angle of
attack) tries to push the rear end back in line, again rotating it
around the CM. If the CP is ahead of the CM, the situation is hopeless.
As Rex pointed out, putting the tire forces back into play greatly
complicates the question. The yaw rotation axis is then determined by a
combination of the tire forces and the CM.
Regards, Neil Tucson, AZ
-----Original Message-----
From: owner-land-speed@autox.team.net
[mailto:owner-land-speed@autox.team.net] On Behalf Of J I Waldron
Sent: Friday, April 22, 2005 4:46 AM
To: land-speed@autox.team.net
Subject: RE: Center of pressure?
Would a fin actually move the CP when the car was running
straight? Or do they only change the CP should the car get
a little sideways? (Which, of course, is the point)
Thanks,
Jim W.
Snip>
>
>Date: Thu, 21 Apr 2005 16:17:17 -0500
>From: "Albaugh, Neil" <albaugh_neil@ti.com>
>Subject: RE: Center of pressure?
>
>Tom;
>
>As an example of moving the CP rearward to enhance high-speed
stability,
>take a look at Rex Svoboda's beautiful blue McLaren modified sports.
The
>additional rear fins move the CP further to the rear, particularly
>important with a mid- engine configuration since its CM is so far aft.
>Rex reported that his car was quite stable at 200, even running "wide
>tires."
>
>Regards, Neil Tucson, AZ
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