2012 Toyota Prius v

[Fuel Miser]

Toyota took the wraps off its long-awaited second Prius model, the upcoming Prius v (for “versatility”) at the 2011 Detroit auto show.

Scheduled to go on sale this summer as a 2012 model, this most practical of Priuses is measurably larger than the familiar hatchback—the v is 6.1 inches longer, 1.2 inches wider, 3.3 inches taller, and rides on a wheelbase stretched by 3.1 inches.

Still, in spite of the larger frontal area and longer roof, the Prius v’s coefficient of drag is claimed to be a low 0.29.

Thanks to more mass and different aerodynamics, however, the Prius v is expected to achieve EPA ratings of 42 mpg city, 38 mpg highway, and 40 mpg combined versus 51/48/50 for the Prius hatch.


Pricing has yet to be formally established, but Toyota executives said that we should expect a slight premium over the hatchback

http://www.caranddriver.com/news/car...nfo-auto_shows

[JanGeo]

Having recently driven a 2007 model in an ice storm I can say that the nice big sloping windshield can really ice up and it takes all of the defroster heat set way up to melt it. Not too impressed with those mileage numbers either.

[Fuel Miser]

Yes, I might imagine that sloping windshield stands out when compared to an xB. Of course that slope is an important design element resulting in the 0.29 drag coeffifient.
I too was initially disappointed with the mileage numbers, on consideration of the vehicle's size they're quite impressive.

[theholycow]

Still, in spite of the larger frontal area and longer roof, the Prius v’s coefficient of drag is claimed to be a low 0.29.

I would not say "in spite of the longer roof"; extra length makes lowering the coefficient of drag easier.

Also, frontal area is not part of coefficient of drag.

[Fuel Miser]

Originally Posted by theholycow

I would not say "in spite of the longer roof"; extra length makes lowering the coefficient of drag easier.

Also, frontal area is not part of coefficient of drag.

The drag coefficient is a common metric in automotive design, where designers strive to achieve a low coefficient.

The average modern automobile achieves a drag coefficient of between 0.30 and 0.35. SUVs, with their typically boxy shapes and larger frontal area, typically achieve a Cd of 0.35?0.45

A very gently inclined windshield gives a lower drag coefficient

While designers pay attention to the overall shape of the automobile, they also bear in mind that reducing the frontal area of the shape helps reduce the drag.

http://en.wikipedia.org/wiki/Automob...ag_coefficient

[dieselbenz]

Originally Posted by Fuel Miser

Still, in spite of the larger frontal area and longer roof, the Prius v’s coefficient of drag is claimed to be a low 0.29.

This is backwards. Given the same shape, a longer roof (and longer overall lenght) will reduce drag.

And thumbs up to toyta for making a more practical prius. This should capture a ton of new sales.

[Fuel Miser]

NASA provides a wonderfully entertaining Java Applet, FoilSim III, one may use to investgate the various factors that affect drag. It's also available for download at no charge.
Do be sure to heed the warning:
Please do not attempt to design, build, or fly a full scale aircraft using data from FoilSim. It is fine for models, but be careful.

http://www.grc.nasa.gov/WWW/K-12/airplane/foil3.html

[theholycow]

Originally Posted by Fuel Miser

The drag coefficient is a common metric in automotive design, where designers strive to achieve a low coefficient.

The average modern automobile achieves a drag coefficient of between 0.30 and 0.35. SUVs, with their typically boxy shapes and larger frontal area, typically achieve a Cd of 0.35–0.45

A very gently inclined windshield gives a lower drag coefficient

While designers pay attention to the overall shape of the automobile, they also bear in mind that reducing the frontal area of the shape helps reduce the drag.

http://en.wikipedia.org/wiki/Automob...ag_coefficient

I don't disagree that frontal area is an extremely important part of drag, but it is not part of the drag coefficient. In fact, to calculate total drag you need both drag coefficient and frontal area. If you have two cars with the same drag coefficient but different frontal areas, the one with more frontal area has more drag.

At least, that's what I've always been told.

Edit: While in the shower I remembered why it makes sense.
http://en.wikipedia.org/wiki/Automob...g_coefficients
While designers pay attention to the overall shape of the automobile, they also bear in mind that reducing the frontal area of the shape helps reduce the drag. The combination of drag coefficient and area is CdA (or CxA), a multiplication of the Cd value by the area.

Some drag coefficients from that article:
0.9 -a typical bicycle plus cyclist
0.57 Hummer H2
0.42 Lamborghini Countach
0.29 2005 Chevrolet Corvette
0.29 1969 Dodge Charger Daytona
0.29 2010 Ford Escape
0.29 2001 Toyota Prius
0.28 Honda Civic Hybrid
0.27 1997 Volkswagen Passat B5 (sedan)
0.26 Chevrolet Volt
0.26 2009 Toyota Prius
0.25 2010 Toyota Prius
0.24 Mercedes E 220 CDI Blue Efficiency European version only, other E-Class Coupe 0.28
0.212 1935 Tatra T77A
0.195 General Motors EV1

Eh, didn't need to include such a long list to show that a bicycle with tiny frontal area has a huge cD but I was having fun.

[VetteOwner]

either way it still looks like a big ol plastic easter egg like 99.9% of the cars out there nowadays...

gimmie the 2011 dodge charger or challenger anyday haha even tho they arent too fuel friendly

[Fuel Miser]

Originally Posted by theholycow

Edit: While in the shower I remembered why it makes sense.

I found this drag issue bouncing around my (otherwise empty) head as well. It required a climb into the very cold attic for some ancient textbooks before I got my mind wrapped around it. Yes, you've got it nailed down, my confusion was tied more to language than science.
Shakespeare wrote, "What's in a name?..." Well, plenty, William, it's the difference between Cd and CdA.
Now I find it rather odd that the automotive press has adopted the Cd as definitive of a particular design. It may speak to the efforts of the design engineers within a particular parameter but without additional data and some math it's hardly the whole story. Two cars with identical Cd values may experience very different total drag loads.
I may recall a total drag value specific to autos. I believe, as in aircraft, it was expressed in pounds (or newtons.)
Back to the attic, talk about a total drag!