What Do These Numbers Mean?

[slinches]

While C_d is a great design parameter for a single vehicle, it's not an intuitive unit for comparison between vehicles of different sizes/shapes. It would make more sense to compare the flat plate drag area (C_d*A_ref). Assuming the frontal area of the Elio is ~2/3 or less of a similarly sized 4-wheel vehicle, to get the same flat plate drag as an Elio, that competing vehicle's C_d would need to be less than 0.2.

 

[Karnaj]

While C_d is a great design parameter for a single vehicle, it's not an intuitive unit for comparison between vehicles of different sizes/shapes. It would make more sense to compare the flat plate drag area (C_d*A_ref). Assuming the frontal area of the Elio is ~2/3 or less of a similarly sized 4-wheel vehicle, to get the same flat plate drag as an Elio, that competing vehicle's C_d would need to be less than 0.2.

Forget the numbers...what do those words mean!!!

 

[Kuda]

0.3 isn't bad, but it's hard to believe the BMW 3-Series has better aero than Elio. I would've expected a bit better with the "half the car/twice the mileage" credo.

0.21 Tesla Model 3 , 2017

 

[Ty]

Okay... Cd is Coeficient of Drag... that's the average drag that your vehicle creates as a function of it's frontal area. Frontal area? Yeah... imagine a wet tissue that's really big... drive your car through it. The shape that's cut out is the frontal area. I picture a cartoon character who is thrown through a wall and it leaves their shape there.

Well, Cd is definitely important... The Elio has a higher Cd than a Tesla. How is that? What about that half as wide stuff? Well, that's the fun part... Cd, by itself doesn't mean all THAT much. It's when it is multiplied by the Area that it matters. That's why someone asked about the CdA during the interview. Since the Elio is so much smaller in the front than the Tesla (for instance), the CdA really comes into play.

Fun with numbers time.

IF the Elio has 66% as much frontal area as a Tesla, we can make a comparison.

Since I don't know the frontal area, I'll make one up. The Tesla, for this comparison (and it doesn't matter what unit I use as long as I'm consistent) is 1 Tesla of frontal area. The Elio is 1 Tesla * 66%.

Tesla CdA is then 0.21 * 1 = 0.21. Yay, Tesla!

Elio CdA is then 0.3 * .66 = .19 Whoa... Way to go, Elio.

In this case, even though the Tesla has a lower Cd, it has a higher CdA than the Elio. The CdA is what really matters at highway speeds.

 

[RUCRAYZE]

Not a clue, but you guys are (I think- if it ain't all B.S.) just amazing-
I never saw a slippery barn, I never want to see one, but this I tell you anyhow.......

 

[wizard of ahs]

Wouldn't the Elio CdA be 1 Tesla * .66 = .13 ???
(Just to be consistant?) I don't know........just asking.........where did .3 come from ?????

 

[wizard of ahs]

DUH...., you're right, found it

 

[Karnaj]

Okay... Cd is Coeficient of Drag... that's the average drag that your vehicle creates as a function of it's frontal area. Frontal area? Yeah... imagine a wet tissue that's really big... drive your car through it. The shape that's cut out is the frontal area. I picture a cartoon character who is thrown through a wall and it leaves their shape there.

Well, Cd is definitely important... The Elio has a higher Cd than a Tesla. How is that? What about that half as wide stuff? Well, that's the fun part... Cd, by itself doesn't mean all THAT much. It's when it is multiplied by the Area that it matters. That's why someone asked about the CdA during the interview. Since the Elio is so much smaller in the front than the Tesla (for instance), the CdA really comes into play.

Fun with numbers time.

IF the Elio has 66% as much frontal area as a Tesla, we can make a comparison.

Since I don't know the frontal area, I'll make one up. The Tesla, for this comparison (and it doesn't matter what unit I use as long as I'm consistent) is 1 Tesla of frontal area. The Elio is 1 Tesla * 66%.

Tesla CdA is then 0.21 * 1 = 0.21. Yay, Tesla!

Elio CdA is then 0.3 * .66 = .19 Whoa... Way to go, Elio.

In this case, even though the Tesla has a lower Cd, it has a higher CdA than the Elio. The CdA is what really matters at highway speeds.

Amazing explanation...thank you.

 

[outsydthebox]

Okay... Cd is Coeficient of Drag... that's the average drag that your vehicle creates as a function of it's frontal area. Frontal area? Yeah... imagine a wet tissue that's really big... drive your car through it. The shape that's cut out is the frontal area. I picture a cartoon character who is thrown through a wall and it leaves their shape there.

Well, Cd is definitely important... The Elio has a higher Cd than a Tesla. How is that? What about that half as wide stuff? Well, that's the fun part... Cd, by itself doesn't mean all THAT much. It's when it is multiplied by the Area that it matters. That's why someone asked about the CdA during the interview. Since the Elio is so much smaller in the front than the Tesla (for instance), the CdA really comes into play.

Fun with numbers time.

IF the Elio has 66% as much frontal area as a Tesla, we can make a comparison.

Since I don't know the frontal area, I'll make one up. The Tesla, for this comparison (and it doesn't matter what unit I use as long as I'm consistent) is 1 Tesla of frontal area. The Elio is 1 Tesla * 66%.

Tesla CdA is then 0.21 * 1 = 0.21. Yay, Tesla!

Elio CdA is then 0.3 * .66 = .19 Whoa... Way to go, Elio.

In this case, even though the Tesla has a lower Cd, it has a higher CdA than the Elio. The CdA is what really matters at highway speeds.

Thank you! (I think) I actually understand.

 

[slinches]

Thanks for rephrasing that in more approachable terms, Ty. Sometimes I forget that not everyone speaks Engineer (it's a separate dialect in the same way as legalese).