GM describes 2013 Chevy Malibu ECO aerodynamic tweaks (Cd ~0.28)

[lunarhighway]

i wonder how usefull drag coeficients really are for comparison ....
i assume that with more accurate testing these days...such as spinning wheels, etc, drag coeficient would come out higher, because more detailed testing will reveil more drag.
i've heard they're also dependant on the actual wind tunnel used.

so how comparable are drag coeficients of something that was tested 20 years ago in a different wind tunnel with something tested today. or two current cars tested in different wind tunnels, wich they very likely will be if they're different brands.

that said, the lower is obviously the better, and 0.28 is not something to brag about... the opel insignina/buick regal is build on the same platform ...the the ecoflex has a claimed 0.26Cd!

than again drag coeficient seems very dependent on things like tire width and engine choise, different (bigger)engines needing more cooling = less factory grill blocking
this combined easily changes the Cd by 0.02, without any visible external changes.

the good thing in all this is aerodynamics is back in the marketing talk...

[mort]

Hi lunarhighway,
Before 1974 there were no full size automotive wind tunnels. Before then and still today published drag figures for real cars are derived from coast down tests. The drag numbers should be exactly comparable. Some prototype work publishes drag numbers based on wind tunnel tests on models.
-mort

Originally Posted by lunarhighway

i wonder how usefull drag coeficients really are for comparison ....
i assume that with more accurate testing these days...such as spinning wheels, etc, drag coeficient would come out higher, because more detailed testing will reveil more drag.
i've heard they're also dependant on the actual wind tunnel used.

[aerohead]

Originally Posted by lunarhighway

i wonder how usefull drag coeficients really are for comparison ....
i assume that with more accurate testing these days...such as spinning wheels, etc, drag coeficient would come out higher, because more detailed testing will reveil more drag.
i've heard they're also dependant on the actual wind tunnel used.

so how comparable are drag coeficients of something that was tested 20 years ago in a different wind tunnel with something tested today. or two current cars tested in different wind tunnels, wich they very likely will be if they're different brands.

that said, the lower is obviously the better, and 0.28 is not something to brag about... the opel insignina/buick regal is build on the same platform ...the the ecoflex has a claimed 0.26Cd!

than again drag coeficient seems very dependent on things like tire width and engine choise, different (bigger)engines needing more cooling = less factory grill blocking
this combined easily changes the Cd by 0.02, without any visible external changes.

the good thing in all this is aerodynamics is back in the marketing talk...

I'd like to see them listed on the new car window sticker along with the frontal area.
It would be to the consumer,as square footage and thermal insulation ratings would be for a home.
The Cd would be the equivalent of the heat transfer coefficient of the home which is the inverse of its composite R-Factor.
And the frontal area would suggest the CFM/CMM in which your going to push that R-Factor.
Driving speed would be the same as design indoor temp..

[superchow]

Why does the "face" of the new Malibu remind me of a transformer... ? Anyway: what manufacturers forget to mention is the frontal area? SUVs now can have drag coefficients in the sub-0.30 range if I'm not mistaken. Everything helps, but as mentioned above, .29 is not THAT great.

[cfg83]

aerohead -

Originally Posted by aerohead

I'd like to see them listed on the new car window sticker along with the frontal area.
It would be to the consumer,as square footage and thermal insulation ratings would be for a home.
The Cd would be the equivalent of the heat transfer coefficient of the home which is the inverse of its composite R-Factor.
And the frontal area would suggest the CFM/CMM in which your going to push that R-Factor.
Driving speed would be the same as design indoor temp..

110% agreement. Published info like that should also increase the competition to have better numbers.

CarloSW2

[Peter7307]

[QUOTE=mort;256699]Hi lunarhighway,
Before 1974 there were no full size automotive wind tunnels. Before then and still today published drag figures for real cars are derived from coast down tests. The drag numbers should be exactly comparable. Some prototype work publishes drag numbers based on wind tunnel tests on models.
-mort[/Q


Sorry but not so.

The St Cyr wind tunnel in Paris was in use in the 1920's and is still used today especially by Citroen and Peugeot.

Coast down tests are probably still used by some makers but most have moved on the CFD and wind tunnel data.

German universities also had auto wind tunnels in the 1930's to help with the aero work on the Audi and Mercedes cars of the mid and late 1930's (usually referred to as Silver Arrows)

Peter.

[mort]

Originally Posted by Peter7307

Sorry but not so.

The St Cyr wind tunnel in Paris was in use in the 1920's and is still used today especially by Citroen and Peugeot.

Coast down tests are probably still used by some makers but most have moved on the CFD and wind tunnel data.

German universities also had auto wind tunnels in the 1930's to help with the aero work on the Audi and Mercedes cars of the mid and late 1930's (usually referred to as Silver Arrows)

Peter.

Hi Peter,
I think you misunderstood. I meant that the lift and drag numbers before 1974 were from wind tunnels that were built to study airfoils or aircraft. The only 1:1 scale automotive tunnel before the oil embargo was the GM Harrison tunnel used to test cooling system flow. Since that time really wonderful study centers have sprung up all over.
But in particular, the Saint Cyr "giant" tunnel of 1920 was not an automotive type tunnel. The test object was suspended by 5 wires and the forces on the wires gave you the lift and drag. I think the nozzle exit area was about 4 or 5 sq meters. Which would be about 1:5 scale for an automobile.

I see aerohead posted this.

The EPA uses coast down tests for drag measurements. Advertising can, of course, use any numbers they like.
-mort

[MetroMPG]

More quantified info about the Malibu's aero tweaks, and how many counts of drag (0.001) each contributed:

10 counts: Underbody panels - two in the mid-body area under the floor pan on either side of the center tunnel, and two in the rear area covering the fuel tank and rear area on either side of the exhaust

10 counts: Rounded front corners - from the bottom of the fascia up through the headlamps - help air flow smoothly along the Malibu's body sides

10 counts: Tire deflectors positioned forward of the front tires act as "mini-air dams" to minimize wind disruptions

7 counts: The closed upper grille on select models pushes wind to the sides of the Malibu

7 counts: Outside rearview mirrors are specifically designed to deflect wind without "upsetting" the airflow

7 counts: Shutters in the lower grill opening on select models open and close automatically to maximize aerodynamic efficiency. This increases cooling airflow to the engine under certain conditions, such as under high-engine loads at low speeds, and reduces aerodynamic drag when extra cooling is not needed

5 counts: The front air dam redirects airflow to minimize aerodynamic disruptions

5 counts: The notch angle of the vehicle - the angle from the top of the rear glass to the trailing edge of the decklid - was optimized to reduce wind drag

2 counts: An integrated decklid spoiler incorporates a crisp, trailing edge that helps separate air from the rear of the Malibu.

Also noteworthy about those grille shutters, something I'd been wondering about up here in the Great White North: seems we automatically lose the aero benefit during the winter...

When ambient temperatures fall below freezing, the active shutters operate in "ice mode." By working with a thermometer that monitors outside air temperature, the ice mode will prevent movement of the aero shutters until ambient temperatures rise above the freezing mark. Sensors work with onboard computers to calculate when the ice mode is appropriate.

Source: 2013 Chevrolet Malibu is No Drag in Aerodynamics - MarketWatch

[lunarhighway]

very interesting numbers, i'm surprised at the effect of tire deflectors, because if the numbers are right than that would mean small plastic rectangles in front of the tires have as big an effect as smoothing out the entire underside of the car? no wonder just about every new car has them.

how well would these numbers transelate to other cars i wonder..., because assuming these mods would have a similar effect on my car i might have gone from a stock 0.29 to 0.263 and i might go to 0.256 when my actuated grill block is done... i very much want to believe this is true, and the way the car coasts certainly makes it possible to imagine.