GM EV1 LSR was Cd 0.137

[aerohead]

GM reported Cd 0.137 for it's modified EV1 which set a closed-course, United States Auto Club ( USAC ), land speed record of 183.8-mph in 1993, at the Bridgestone / Firestone Proving Grounds, Fort Stockton, Texas.
This car had been previously reported with Cd 0.14, in Goro Tamai's, book, 'The Leading Edge,' with the data attributed to Bart Hibbs of AeroVironment, if memory serves me.
Cd 0.137 ties Ford's 1985 PROBE-V concept car.

[JulianEdgar]

Originally Posted by aerohead

GM reported Cd 0.137 for it's modified EV1 which set a closed-course, United States Auto Club ( USAC ), land speed record of 183.8-mph in 1993, at the Bridgestone / Firestone Proving Grounds, Fort Stockton, Texas.
This car had been previously reported with Cd 0.14, in Goro Tamai's, book, 'The Leading Edge,' with the data attributed to Bart Hibbs of AeroVironment, if memory serves me.
Cd 0.137 ties Ford's 1985 PROBE-V concept car.

Interesting, but I wouldn't get too excited by Cd figures to three decimal places. A top aerodynamicist suggested to me that taking three decimal place Cd figures as gospel was basically a fool's errand. (As in, test in different wind tunnels and you'd likely get a larger variation than this.)

[The Toecutter]

I've known about this.

I remember seeing the video of this record being achieved:

https://www.youtube.com/watch?v=699MzSBIcO4

If the production car were this slippery, it would have needed roughly 100 Wh/mi to do 70 mph on the highway, and would have been a 150 mile range car with the Panasonic PbA batteries and a 250 mile range car with the Ovonic NiMH, at least on the freeway, without drawing the batteries down too low to the point of damaging them. City driving range with these changes versus the original wouldn't have been impacted much, but it is highway driving where long range matters most anyway. The production model needed about 150 Wh/mi to do 70 mph on the highway.

[aerohead]

Originally Posted by JulianEdgar

Interesting, but I wouldn't get too excited by Cd figures to three decimal places. A top aerodynamicist suggested to me that taking three decimal place Cd figures as gospel was basically a fool's errand. (As in, test in different wind tunnels and you'd likely get a larger variation than this.)

A very curious comment considering that wheel rotation drag, side mirrors, and cooling system phenomena occur within a three decimal place environment.

[JulianEdgar]

Originally Posted by aerohead

A very curious comment considering that wheel rotation drag, side mirrors, and cooling system phenomena occur within a three decimal place environment.

You seemed to have missed my point.

My point is that comparing Cd figures of cars to three decimal places is rather moot, when the variation between different wind tunnels is likely to be greater than that.

Your point appears to be that the development of aero on a specific car in a specific wind tunnel involves measurement down to three decimal places.

Two different ideas - one absolute, one relative.

[aerohead]

Originally Posted by JulianEdgar

You seemed to have missed my point.

My point is that comparing Cd figures of cars to three decimal places is rather moot, when the variation between different wind tunnels is likely to be greater than that.

Your point appears to be that the development of aero on a specific car in a specific wind tunnel involves measurement down to three decimal places.

Two different ideas - one absolute, one relative.

If doing development work on a specific vehicle, you'd be advised to stick with the same tunnel.
If doing development work on a specific vehicle, Cd 0.299 would be significantly different than Cd 0.290.
The rotating wheel drag on the Tesla Model S was delta- Cd 0.009.

[JulianEdgar]

Originally Posted by aerohead

If doing development work on a specific vehicle, you'd be advised to stick with the same tunnel.
If doing development work on a specific vehicle, Cd 0.299 would be significantly different than Cd 0.290.
The rotating wheel drag on the Tesla Model S was delta- Cd 0.009.

Yes that's right.

But that's not the point you were making in the original post. You were comparing the drag figures of two different cars, measured in two different wind tunnels, to three decimal places. You said:

"Cd 0.137 ties Ford's 1985 PROBE-V concept car."

Interesting, but I wouldn't get too excited by Cd figures to three decimal places. A top aerodynamicist suggested to me that taking three decimal place Cd figures as gospel was basically a fool's errand. (As in, test in different wind tunnels and you'd likely get a larger variation than this.)

[aerohead]

Originally Posted by JulianEdgar

Yes that's right.

But that's not the point you were making in the original post. You were comparing the drag figures of two different cars, measured in two different wind tunnels, to three decimal places. You said:

"Cd 0.137 ties Ford's 1985 PROBE-V concept car."

Interesting, but I wouldn't get too excited by Cd figures to three decimal places. A top aerodynamicist suggested to me that taking three decimal place Cd figures as gospel was basically a fool's errand. (As in, test in different wind tunnels and you'd likely get a larger variation than this.)

Perhaps he's never been interested in low drag.
Perhaps when he's investing $billions on Wall Street he can't be bothered by decimal places.