Cd and blunt front ends

[Cd]

I'm bringing up an old topic again due to my lack of understanding on something :

How can a car with a flat front end attain the same .Cd as one shaped like a bullet ?

I would guess that due to the increased pressure* at the front of the object with a blunt front end, that the object would have a higher drag.
Apparently this is not the case though.

*( I'm assuming that when air piles up upon itself it creates pressure ... which I again assume creates drag. )

I keep looking back at the Hot Rod Camaro, which had a .201 .Cd using nothing more than a flat piece of metal as a grill block and a small spoiler modification.

It would be hard for us to match that .Cd figure even with our 'jelly bean ' cars, yet these guys did it without even trying ( no belly pan, wheel skirts, extended nose cones / boat tails /..... etc.

The article stated that they tried a huge windshield extention to 'lay back' the angle of the windshield, yet it did nothing to lower the .Cd in the wind tunnel.

Please explain how that this can be.

Perhaps I should contact the folks at the A2 wind tunnel ( the testing took place there ) and ask them these questons.

Wouldn't that be cool if we could get one them onto this forum to answer some of our questions ?

[Cd]

[TheDon]

I need to do the coast down test on my brick and let you know what the .cd is...

[Cd]

Just think - the EV1 had a drastic tear drop shape from not only the sides , but the top as well, a full belly pan, no grill opening, wheel skirts ..etc, yet was only slightly sleeker than this old beat up* '79 Camaro.

* Just look at how rough the edges are below the 'bumper'.

I just don't get it.

[Cd]

Originally Posted by TheDon

I need to do the coast down test on my brick and let you know what the .cd is...

If a Lexus ls400 can break .26 and a Lexus LS430 break .25 ... it might be easier than we all would think to make your 'brick' a 'missile'.

[Cd]

Originally Posted by Frank Lee

The key is attached airflow along the length of the object, or the avoidance of turbulence.

You recall that the optimal aero shape- a falling drop- has a hemisphere for a leading edge, not a bullet. That is how it is for the very subsonic speeds we operate in.

So a blunt leading edge is OK so long as the flow doesn't go turbulent as it transitions to flow along the sides.

Right. Well I meant bullet shaped / egg shaped .... you know ... anything but a flat plate like they have on that Camaro.

[Duffman]

You guys are being harsh, the Gen2 Camaros have a good basic shape. They did quite a bit to the front of that car and probably did a bunch of clean up on the details to get where they are.

[Cd]

Speaking of falling rain drops and such, in real life, they just look like a blob and rarely take on a teardrop shape.

[Duffman]

Originally Posted by Frank Lee

And speaking of the front of that Camaro, it is a 'glass front end with none of the seams, openings, gaps, or even accurate shape of a stocker.

Exactly on the 'glass, there is no headlights, but the stock shape is there. Its like a NASCAR style front.

[Cd]

Yes, but still flat.