CdA list

[ryannoe]

Hey guys, I see some of you are concerned about digitally finding your frontal area and looking up your Cd values so you can calculate your CdA but why?

CdA is what we call Flat plate Drag (FPD) in the field. FPD is simple to use and is the coefficient needed to calculate drag (or vise versa in our situation). It produces easy to compare values for your baseline and modification data.

Flat Plate Drag uses the same equation we are already familiar with:

Drag = 0.5*density*velocity^2*FPD

(honestly, what it does is set Cd to 1.0 to remove it from the equation, then your comparisons are in fictional areas with a Cd of 1.0)

Do you guys have a test methodology for determining drag?

Is there a standard for testing yet? Is that something I could help put together?


-Ryan

[Blue Angel]

Hi all, first post here. I have a '12 Chevy Cruze Eco MT and so far I am very impressed with the mileage as well as the car. For a car used ~95% for commuting it is really working out well.

I looked through your list here and didn't see any info for the Cruze so I thought I'd make a contribution:

Width = 1796mm/70.7in
Height = 1476mm/58.1in
Height = 1466mm/57.7in (Eco/RS*)
Cd = 0.331**
Cd = 0.298 (Eco)

Doing the math I get a CdA of 7.649 for the standard Cruze, and 6.839 for the Eco.

*- Eco height is standard car height -10mm; I couldn't find a spec for the Eco height but it uses the RS package springs making it 0.4in/10mm lower than the standard car.

**- Eco Cd is 0.298, according to GM this is a 10% improvement over the regular Cruze, so 0.298/0.9 = 0.331

EDIT: Added 0.81 correction factor to calculations

[NeilBlanchard]

The VW XL1 frontal area is 1.50 sq m which is 16.146 sq ft. The Cd is 0.189, so the CdA is just 3.05 sq ft.

[Vekke]

Is this mentioned already?
Ilmanvastuskertoimia

[aerohead]

Originally Posted by ryannoe

Hey guys, I see some of you are concerned about digitally finding your frontal area and looking up your Cd values so you can calculate your CdA but why?

CdA is what we call Flat plate Drag (FPD) in the field. FPD is simple to use and is the coefficient needed to calculate drag (or vise versa in our situation). It produces easy to compare values for your baseline and modification data.

Flat Plate Drag uses the same equation we are already familiar with:

Drag = 0.5*density*velocity^2*FPD

(honestly, what it does is set Cd to 1.0 to remove it from the equation, then your comparisons are in fictional areas with a Cd of 1.0)

Do you guys have a test methodology for determining drag?

Is there a standard for testing yet? Is that something I could help put together?


-Ryan

Road vehicle coefficients of aerodynamic drag,as a convention,are always presented as pertaining to frontal projected area.
If we know the original Cd,if only the shape of the vehicle is modified,and a change in mpg shows up,there is a metric by which we can reverse-engineer the new Cd.
The best method to measure drag will remain the full-scale wind tunnel.At $435-$2,000 an hour,they're kind of pricey (and if you can book time in one).
Coast-down testing is so problematic,that while not 'impossible' to pull off,most auto makers have gone to the wind tunnel for results instead.
Computational Fluid Dynamics,while better than ever,is so expensive that it remains within the domain of universities and auto makers.

[euromodder]

VW up!
Cd = 0.32
Frontal area = 22.28 sq.ft.
CdA = 7,13

That's not too bad for such a small car - 3.54m or just under 12 ft.

[GeekForLife]

Either I am misunderstanding the formula or the numbers on the chart are wrong.

Someone check my math here I may be suffering from slept through math-atitis

The first car on the list
Acura CL 1997-1999 Height = 54.7 Width = 70.1
frontal area = 21.6 ft^2

My math

54.7*70.1*.84/144=22.37 ft^2
Am I daft or is the page wrong????

[Coroner]

2011 Kia Forte Hatchback:

cd: .29 - Edmunds
Height: 57.5"
Width: 69.9"
Frontal Area: 23.45 sq ft (includes .84 correction)
cdA: 6.8009


I didn't see any Kia's, so here's one.

[Frank Lee]

Originally Posted by GeekForLife

Either I am misunderstanding the formula or the numbers on the chart are wrong.

Someone check my math here I may be suffering from slept through math-atitis

The first car on the list
Acura CL 1997-1999 Height = 54.7 Width = 70.1
frontal area = 21.6 ft^2

My math

54.7*70.1*.84/144=22.37 ft^2
Am I daft or is the page wrong????

Looks to me like .81 was the frontal area "correction factor" used.

[Jack-Lee]

Hello,

VW Polo 2F (BJ 1991-1994) Coupe :
cw= 0,36
A=1,84m²

Not bad for this "coalbox"

Greetings,
Patrick