Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 12-07-2009, 03:58 PM   #41 (permalink)
Master of 140 hamsters
 
superchow's Avatar
 
Join Date: May 2008
Location: Lacey, WA
Posts: 183

Hamster - '07 Honda Civic EX
90 day: 29.41 mpg (US)

Whooshy Wagon - '04 Volvo V40
90 day: 23.33 mpg (US)

Minotaur - '09 Ford Taurus X SEL
90 day: 19.05 mpg (US)
Thanks: 1
Thanked 8 Times in 7 Posts
Quote:
...but we have to protect our styling flexibility.
Basjoos had some styling flexibility - not this Viridian Joule colored greenwashing-mobile. The more I hear about this car, the more I am tempted to seriously mod my Civic.

__________________
  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 12-10-2009, 11:21 AM   #42 (permalink)
EcoModding Lurker
 
Join Date: Nov 2008
Location: Annapolis, MD
Posts: 27

Mom's Taxi - '05 Toyota Sienna LE 8-passenger
90 day: 22.59 mpg (US)

Diesel - '09 VW Jetta TDI
Thanks: 0
Thanked 0 Times in 0 Posts
Hi- great site!

I question the validity of the statement regarding the Volt's superior aerodynamics.

CdA= Cd * wetted area

Dubious claims of Cd aside... let's focus on frontal area.

Without taking into account side mirror area (btw GM's claim of "drag neutral" mirrors is ridiculous)- the Volt is supposedly 70.8 wide by 56.3 inches high while the Prius is 68.7 inches wide by 58.7 inches high. However, the Prius does not have as deep an airdam as that which is installed on the Volt.

Assuming an average ground clearance of 5.5 inches for the Prius and 3.0 inches for the Volt- frontal area would be 25.4ft^2 and 26.2ft^2 respectively. Advantage: Prius.

Yes, the airdam serves to direct high speed flow away from the vehicle's relatively "dirty" underbody. It's an easy/cheap fix that GM is exploiting to help earn impressive EPA hwy fuel economy ratings with their latest crossovers and SUV's.

However, deep airdams also increase frontal area. (Cd of an object is measured as the fraction of its drag when compared to the drag from an equivalent flat plate area.) Of course, with a larger equivalent flat plate area, GM should possess a lower Cd.

This would help explain GM's claimed low Cd of 0.28, vs. the Prius Cd of 0.30.

Careful shaping of a vehicle's underside or underside fairings can reduce drag better than an airdam- whose increase in frontal area may mask an overall potential drag reduction. Reference Aptera's lack of an airdam as an example.

An early morning coast-down test with each vehicle would help dispell all the aerodynamic conjecture.

Finally, in the absence of independent testing, I would not place much faith on any manufacturer's claims.
  Reply With Quote
Old 12-10-2009, 01:39 PM   #43 (permalink)
Master of 140 hamsters
 
superchow's Avatar
 
Join Date: May 2008
Location: Lacey, WA
Posts: 183

Hamster - '07 Honda Civic EX
90 day: 29.41 mpg (US)

Whooshy Wagon - '04 Volvo V40
90 day: 23.33 mpg (US)

Minotaur - '09 Ford Taurus X SEL
90 day: 19.05 mpg (US)
Thanks: 1
Thanked 8 Times in 7 Posts
Ah... a refreshing approach: A coast-down test. My mind is reeling with the excuses Chevy could come up with to discredit cold hard evidence...
__________________
  Reply With Quote
Old 12-10-2009, 04:34 PM   #44 (permalink)
EcoModding Apprentice
 
JackMcCornack's Avatar
 
Join Date: Mar 2008
Location: Southern Oregon
Posts: 179
Thanks: 5
Thanked 39 Times in 23 Posts
I'm with you in concept, DieselHybrid (though I differ on a few details). The Cd thing can indeed be 'spun' to give higher drag vehicles nicer numbers than they deserve--if one is manufacturing cars, the easiest way to get a lower Cd is to make the car bigger. Hucho has a drawing showing how cambering a roof can increase drag, because the frontal area goes up faster than the Cd comes down. Open cockpit racers nearly always have higher Cd than their closed cockpit counterparts, but don't always have less drag (the Bristol 450 is a case in point) because they have more frontal area.
__________________
Modding MAX, a Kubota-powered classic sports car
http://www.kineticvehicles.com
  Reply With Quote
Old 12-10-2009, 07:55 PM   #45 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,272
Thanks: 24,394
Thanked 7,363 Times in 4,763 Posts
Cd's

there is an SAE paper which deals with "scatter" based on a single vehicle or standardized calibration models when tested in 6-or 8 different wind tunnels.
GM and Lockheed ( closed return ) results are the most conservative as far as Cd.
Ford publishes a yaw-averaged Cd ( they'll yaw the car up to 8-degrees in the tunnel )when they claim a Cd.
Is anyone saying if a uniform procedure was followed,to arrive at these latest numbers?
The mean standard deviation between GM,Ford,Chrysler,JARI,MIRA,Pininfarina,Canadian National Labs,etc., was only about 2.2%.
  Reply With Quote
Old 12-10-2009, 10:27 PM   #46 (permalink)
Banned
 
Join Date: Feb 2008
Location: california
Posts: 1,329
Thanks: 24
Thanked 161 Times in 107 Posts
I'm willing to bet the total drag (CD x frontal area) is lowest for the Insight, then the Prius then the Volt. The devil is always in the details.
  Reply With Quote
Old 12-11-2009, 09:07 AM   #47 (permalink)
Master EcoModder
 
tasdrouille's Avatar
 
Join Date: Jan 2008
Location: Mirabel, QC
Posts: 1,672

The Guzzler - '08 Hyundai Elantra GL
90 day: 33.12 mpg (US)

Got Soul? - '11 Kia Soul 2U
Thanks: 35
Thanked 86 Times in 57 Posts
You might very well be right.

Volt: ((70.8 * 56.3 * .85) + 240 (airdam)) / 144 = 25.19 sq ft -> * 0.28 = 7.055 CdA
Prius: (68.7 * 58.7 * .85) / 144 = 23.8 sq ft -> * 0.3 = 7.141 CdA
Insight: (66.7 * 56.1 * .85) / 144 = 22.09 sq ft -> * 0.32 = 7.068 CdA

This is all just approximations, but in the end it looks like the total drag for all those cars is going to be within a 2-3% range.
__________________



www.HyperKilometreur.com - Quand chaque goutte compte...
  Reply With Quote
Old 12-11-2009, 12:22 PM   #48 (permalink)
Master EcoModder
 
NeilBlanchard's Avatar
 
Join Date: May 2008
Location: Maynard, MA Eaarth
Posts: 7,907

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: 3,475
Thanked 2,950 Times in 1,844 Posts
We did the math on the Aptera 2e PP6, and the CdA came in just under 3. The "production" version lowers the Cd from 0.15 down by ~9%, and the frontal area increases a bit, so we'll find out (hopefully) later what it is.
__________________
Sincerely, Neil

http://neilblanchard.blogspot.com/
  Reply With Quote
Old 12-11-2009, 01:39 PM   #49 (permalink)
Master EcoModder
 
Join Date: Jun 2008
Location: Earth
Posts: 5,209
Thanks: 225
Thanked 811 Times in 594 Posts
Quote:
Originally Posted by aerohead View Post
Ford publishes a yaw-averaged Cd ( they'll yaw the car up to 8-degrees in the tunnel )when they claim a Cd.
This is a good point. In these parts, it's not at all unusual to have a 40 mph or so crosswind - and anyone who's flown small planes into tight fields knows that a bit of slip is a darned good way to bleed off altitude/airspeed in a hurry. So I wonder what that 0.28 Cd straight into the wind becomes when the effective wind's at 30 degrees?
  Reply With Quote
Old 12-11-2009, 01:58 PM   #50 (permalink)
Master EcoModder
 
Join Date: Nov 2009
Location: Leadville, CO
Posts: 509

Maroon Ballon - '98 Chrysler Town & Country LXI
90 day: 26.42 mpg (US)

MaEsTRO - '95 Geo Metro 5spd hatch, 3 cyl
Thanks: 47
Thanked 54 Times in 38 Posts
The EV1 had a nice clean underside, but since the wheels weren't inline, it had 4 wheeltracks instead of 2. The narrowing of the rear must have aerodynamically outweighed this penalty in frontal area and drag, but what if it had 3 wheels and an even narrower stern?

  Reply With Quote
Reply  Post New Thread






Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com