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 01-01-2013, 10:29 AM #111 (permalink) Not Ordinary Engineering   Join Date: May 2011 Location: Alabama Posts: 57 Thanks: 9 Thanked 27 Times in 14 Posts 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
 The Following User Says Thank You to ryannoe For This Useful Post: aerohead (12-09-2021)
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 02-21-2013, 03:11 PM #112 (permalink) EcoModding Apprentice     Join Date: Feb 2013 Location: Ottawa, ON, Canada Posts: 190 Previous Car - '12 Chevrolet Cruze Eco MT Team Chevy 90 day: 44.29 mpg (US) 535d XDrive - '16 BMW 535d M-Sport Thanks: 17 Thanked 59 Times in 38 Posts 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 Last edited by Blue Angel; 02-21-2013 at 03:19 PM.. Reason: Added 0.81 factor to FA
 The Following User Says Thank You to Blue Angel For This Useful Post: aerohead (02-23-2013)
 03-07-2013, 01:57 PM #113 (permalink) Master EcoModder     Join Date: May 2008 Location: Maynard, MA Eaarth Posts: 7,897 Mica Blue - '05 Scion xA RS 2.0 Team Toyota 90 day: 42.48 mpg (US) Forest - '15 Nissan Leaf S Team Nissan 90 day: 156.46 mpg (US) Number 7 - '15 VW e-Golf SEL TEAM VW AUDI Group 90 day: 155.81 mpg (US) Thanks: 3,459 Thanked 2,933 Times in 1,836 Posts 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. __________________ Sincerely, Neil http://neilblanchard.blogspot.com/
 The Following User Says Thank You to NeilBlanchard For This Useful Post: aerohead (08-06-2016)
 04-02-2013, 02:45 AM #114 (permalink) Mechanical engineer     Join Date: Jan 2009 Location: Kitee (Finland) Posts: 1,168 Siitin - '98 Seat Cordoba Vario 90 day: 58.56 mpg (US) VW Lupo 3L --> 2L - '00 VolksWagen Lupo 3L Diesel 90 day: 104.94 mpg (US) A8 luxury fuel sipper - '97 Audi A8 1.2 TDI 6 speed manual 90 day: 64.64 mpg (US) Audi A4B6 Avant Niistäjä - '02 Audi A4b6 1.9tdi 96kW 3L 90 day: 54.57 mpg (US) Tourekki - '04 VW Touareg 2.5TDI R5 6 speed manual 90 day: 32.98 mpg (US) A2 1.4TDI - '03 Audi A2 1.4 TDI 90 day: 45.68 mpg (US) A2 1.4 LPG - '02 Audi A2 1.4 (75hp) 90 day: 24.67 mpg (US) Thanks: 240 Thanked 712 Times in 334 Posts Is this mentioned already? Ilmanvastuskertoimia __________________ https://www.linkedin.com/in/vesatiainen/ Vesa Tiainen innovation engineer and automotive enthusiast
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flat plate drag coefficient

Quote:
 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.
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 04-04-2013, 07:22 AM #116 (permalink) Master EcoModder     Join Date: Jul 2010 Location: Belgium Posts: 4,683 The SCUD - '15 Fiat Scudo L2 Thanks: 178 Thanked 651 Times in 516 Posts 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. __________________ Strayed to the Dark Diesel Side Last edited by euromodder; 07-07-2013 at 06:32 PM..
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 04-04-2013, 05:44 PM #117 (permalink) EcoModding Lurker     Join Date: Dec 2012 Location: Richmond Texas Posts: 25 White Elephant - '07 Toyota Tundra SR5 90 day: 19.27 mpg (US) Thanks: 34 Thanked 9 Times in 4 Posts 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????
 04-13-2013, 06:13 PM #118 (permalink) Slow steppin'     Join Date: Mar 2013 Location: Bryan, Ohio Posts: 30 2013 Coachman 21QBC - '12 Chevy Express 4500 RV Thanks: 5 Thanked 2 Times in 2 Posts 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. __________________ If you pay for my gas, I'll go faster... I brake for tailgaters... Poop management professional, it seems... Last edited by Coroner; 04-13-2013 at 06:18 PM.. Reason: added .84
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Quote:
 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.
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 06-16-2013, 07:26 PM #120 (permalink) EcoModding Apprentice     Join Date: Jun 2013 Location: Germany Posts: 126 Partygurke - '90 VW Polo 2F TEAM VW AUDI Group Rodi - '04 Smart Roadster Coupe Thanks: 2 Thanked 60 Times in 38 Posts Hello, VW Polo 2F (BJ 1991-1994) Coupe : cw= 0,36 A=1,84m² Not bad for this "coalbox" Greetings, Patrick
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