Hatchback Aerodynamics, Downdraft Spoiler

[DocS]

The Sonic, compared to all the other hatches I've owned, gets disgustingly dirty on the back end. I've been noodling about trying to figure out an aesthetically pleasing solution to this. Some have suggested brush skirts (like you see on big rigs), vortex generators, or just washing the car a lot.

I saw a minivan, I didn't get the make or model but it looked early 2000's, with rear spoiler that looked like it would redirect air down the back of the vehicle. At first I thought this would create a huge drag by basically acting like an air damn but then I thought it might create a net reduction in drag by disrupting the low pressure zone off the back of the vehicle.

I don't know enough about this stuff to properly verbalize my thoughts. I might do some quick sketches to show what I'm thinking but if anything seems dramatically wrong with my thinking can some who truly knows about this stuff respond. And please provide data, links, pics, or other evidence. I'm a very source oriented individual.

 

[JesusTheAgnostic]

I know that the Nissan Juke gets even worse than the Sonic. I feel your pain though sometimes I go off road and take the dirt path and the hatch gets absolutely filthy.

 

[SonicFlow]

I've noticed the same. Design seems to attract the dirt..

 

[Natesriv]

stubby back creates a pressure "vacuum"... which just swirls dirt to the glass and hatch. Also lessens MPG's...
Would be odd, but it's possible to temporarily put some cardboard extensions (just like the big rig setup you mention) and drive for a week with that... see if MPG's increase...dirt I don't think would be affected.

 

[DocS]

stubby back creates a pressure "vacuum"... which just swirls dirt to the glass and hatch. Also lessens MPG's...
Would be odd, but it's possible to temporarily put some cardboard extensions (just like the big rig setup you mention) and drive for a week with that... see if MPG's increase...dirt I don't think would be affected.

Are talking extending the back end horizontally? The skirt I was talking about is something like THIS.

From the research I've done the low pressure zone that forms on the back of the stubby end causes the dirt, dust, and grim kicked off the rear tires to flow to the rear end where it stays. I would presume, this is just a presumption by the way as I've never actually watched one of these brush skirts in action, that it would at least reduce the amount of crap entering that low pressure zone. But it strikes me that it would reduce mpg.

 

[DocS]

I saw one of these on a Subaru Forester in my parking lot. It's a dust deflector. This is what I was talking about when I said "down draft" spoiler.

The Foresters normal spoiler has a downdraft vent in it. I think this would help more than the standard Sonic spoiler without creating to much extra drag.

 

[Natesriv]

No, I've seen some big ribs that have ... like vertical spoilers on the back of the trailer... helps airflow... The "grass skirt" look I think is for gravel and rocks .... I think.....

 

[The Champ]

Virtually all hatchbacks, SUV's and minivans suffer from this problem.

That's why they come with rear window washer/wipers - to clean the back glass.

I had my first hatchback in 1984, and have had everything but the minivan (didn't want to lose my man card... )

 

[DocS]

I know this is a problem that all flat backed vehicles share. It seems much more severe on the Sonic than on other cars, like my wife's Yaris. That's why I'm kicking around potential solutions to mitigate or eliminate the issue.

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