Quote:
Originally Posted by MetroMPG
I've always thought this is the case with GM's EV1 as well (Cd 0.195). The rear glass angle is quite a lot steeper than the generally accepted angles on current aerodynamic production cars. It's something like 18 degrees, if I recall (hoping that's right).
The major difference being that the EV1 from the driver's door back to its trailing edge has a pronounced conical shape which interestingly isn't always apparent in profile photos. The plan taper is quite dramatic, and the car lacks the typical defined "shoulders" at the transition from "side" to "top" surfaces. All of which likely lets it get away with a steeper profile taper (roof through to trunk) because proportionately more pressure recovery is happening along the side of the vehicle.
Of course, this is all topside related.
Back to the bottom taper issue: personally, I'll be sticking closer to 4 degrees.
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I spent some time with an enlargement of the EV1 speed record vehicle photo which appeared in the cars brochure.
The image is shot telescopically and looks close to true length/dimensions,as we'd see on a blueprint.Here's what I measured with squares and protractor:
(1) The angle described by a straight-edge laid across the roof and tail edge of tailcone comes out at 15-degrees.
(2) The original angle of the backlite is 20.5-degrees.
(3) The angle of the top of the boat tail cone itself is 9.5-degrees.
This racer is lowered although there id no mention whether or not it is "raked".I don't believe that it is.
Where the wind tunnel smoke trace over the backlite of the stock EV1 clearly separates,I suspect the flow completely recovers with the very conservative curvature of the cone,helping towards that 183-mph record speed.