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Re: center of pressure vs c.g. (again)

To: Benn <karhu@california.com>
Subject: Re: center of pressure vs c.g. (again)
From: "Thomas E. Bryant" <saltracer@awwwsome.com>
Date: Wed, 20 Apr 2005 08:21:56 -0700
Benn,

I guess I should weigh in on this subject. Up until we had our handling 
problems in '97,  I had not even considered the terms "center of 
pressure" and "center of gravity". It had been my experience that unless 
there were traction problems, handling was not a prominent issue. 
Conventional wisdom said if it gets loose add weight to the rear. Which 
of course just added to the already unbalanced condition of the car.

As built, our car's center of gravity was about a foot behind the center 
of pressure. By adding enough weight to the front of the car (500 lbs. 
just behind the front axle) to move the center of gravity to about even 
or slightly ahead of the center of pressure, the rear did not try to 
lead when we broke traction.

Personally, I don't think that handling will be greatly affected by 
cross-winds other than moving the car across the course unless there are 
traction issues. My advice, however, is don't move the center of 
pressure ahead of the center of gravity if you have a choice.

At present, we carry no extra weight. I have not weighed or checked the 
balance of the car (something I plan to do before running this year) 
since we moved the engine ahead 5 1/2" and added a spoiler with side 
plates. (We have both added weight to the head of the arrow and feathers 
to the tail). The car is handling well as has been shown by two novice 
drivers setting records over 240 MPH last year.

I am still not completely satisfied that the changes in the car are 
totally responsible for our success, however, since we are running on 
much better salt than at the time we were having our problems. So, I 
repeat...if you have a choice, don't build an unbalanced car!

Tom, Redding CA - #216 D/CC

Benn wrote:

> So does anyone have any qualitative handling results with changing the center
> of (side-view) pressure from, say, 0-3" inches behind the c.g. to moving the
> c.of p. say 10-14" in front of the c.g.?  Is the former really dicey in a mild
> crosswind?
> Benn






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