Ford Fusion aero mods: Cd from 0.34 to 0.21

[Cd]

Perhaps one of us could visit a Ford dealership and post some images of the underside of a stock Fusion.
It must be pretty messy to create that much drag !

[cfg83]

MetroMPG -

Originally Posted by MetroMPG

Quantified:

0.34 - original Cd

-.08 - lowering (that's massive! and it's the only time I've seen it quantified)
-.025 - full grille block
-.015 - mirrors deletion (doesn't mention wipers though)
-.01 - full belly pan

I suspect they couldn't mod the door handles or add skirts in order to keep within the "stock" definition for bodywork. Probably a class thing.

EDIT: the slide isn't exactly comprehensive. It doesn't address the decklid extension or the smooth wheel covers...

Hrmmmmmm, I want to say "now I am glad I never did a belly pan". But, I think the Belly Pan benefit is being effected by the lowering. Would the belly-pan benefit have been more if they had never lowered it? Do you know what I mean? Did they test/simulate each mod independently?

CarloSW2

[Daox]

You have to keep in mind that this is a different application than we are aiming for. They are aiming for low drag, but also with a high emphasis on controlling lift. Therefore, some things are not going to apply to us. Number one is that super low front. We simply can't do this if we want to drive on the road. This, along with the lowering is definitely going to lower the effectiveness of the belly pan. The other thing is that rear spoiler.

[MetroMPG]

Are you sure that lowering wouldn't make a smooth belly pan even more important? As the gap under the car diminishes, doesn't airspeed increase?

[MetroMPG]

Originally Posted by aerohead

This is the first ever for me time that the effect of lowering had been assigned a numerical value.Its new grist for the mill.

I have also seen it in reference to the Lexus sedan, but not 0.08!

One of the most aerodynamic cars on the road, the LS 430 earns a 0.26 coefficient of drag, 0.25 with the optional air suspension.

(The air suspension drops the car 1 inch at highway speeds.)

Source: http://www.automallusa.net/2006/lexu...0/reviews.html

[Cd]

When they say that the LS430 was tested at .25, do you think that they cheated a little ?
What about those big pimpin' open spoke wheels , huge side mirrors , and overall boxy shape ?

Do you think it actually has a .25 out the showroom door ?

They could say it had a .10 drag coefficient and no one would know the difference.

[roflwaffle]

I think it does. If my Camry, built in 92, has a .34 drag coefficient, I don't see why, with the inward curving c-pillars, taller rear end, dual exhaust, lower ride height, underbody covers and spoilers, etc... All supposedly optimized in a wind tunnel, the Lexus couldn't see .26.

While they were at it, engineers further reduced wind noise and body NVH (noise, vibration and harshness) by testing the new car in the same wind tunnel used by Japan Railway for their bullet trains. Airflow around bumpers, fenders and mirrors was fine-tuned. Gains were made from the tiniest of things, such as adjusting the angle of the front grille bars, and adding small spoilers on suspension components beneath the body's sealed floorpan

[cfg83]

MetroMPG -

Originally Posted by MetroMPG

Are you sure that lowering wouldn't make a smooth belly pan even more important? As the gap under the car diminishes, doesn't airspeed increase?

But if you are lower to the ground, isn't the "smaller frontal opening" to the undertray of the car allowing for less air to travel to get all turbulent and messy?!?!? I have no idea. The more I learn about aerodynamics the less I know. There are general principles like removing side view mirrors, wheel skirts, and keeping the window closed, but it seems like without a wind tunnel,YMMV (Your Mileage May Vary).

CarloSW2

[MetroMPG]

I went looking for a source to quote, but didn't find one.

But I thought the rule for flow rate through an orifice (gap under the front of the vehicle) is that it's effectively proportional to orifice size for a given pressure.

And when you consider that dropping car closer and closer to the road may actually be increasing pressure at the air dam as the gap shrinks, the effect may be even more pronounced.

[james]

I would guess that although the pressure may be greater just below the airdam on a lowered vehicle, and the airspeed may be higher, there would be a lower volume of air flowing under the vehicle, so the effect of the tray would be less. (just a guess)