Civic hatchback aerodynamics

[basjoos]

On Sunday I discovered another advantage of having complete underbody panelling. I was driving through Asheville, NC just after a Thunderstorm had dumped a bunch of rain on the road. I didn't see the deep pool of water on the road ahead and hit it at 55MPH. Got through it after about 3 seconds of zero visibility through the windshield due to flying water, but with only a 4" by 4" opening in the grill and the underbody panels, very little of that water was able to get into my engine compartment and try to flood the engine.

[basjoos]

I added an extension to my rear wheel skirt to extend the skirt down to the bottom of the car. The extension is a piece of coroplast that fits on over the existing rear sheep skirt. It is held on with velcro on top, magnetic strips along the parts that overlap the metal body of the car and with two screws at the bottom. There is a piece of aluminum bar incorporated into the bottom that is bent to provide tire clearance at the bottom. Also added a coroplast side skirt between the wheels on both sides and wheel spoilers on all 4 wheels. The spoilers were made from a piece of aluminum angle with a coroplast extension added to it. I initially made the side skirts and spoilers on the long side, noted where they dragged as I negotiated my usual roads, and then trimmed them down to where they now rarely drag on the road. Its too early to tell what effect these mods are having on my mileage other than the car coasts a bit better than it did before. The main effect I have noticed is that there is a lot less dust on my rear window after driving on gravel roads than before.


Front wheel spoiler

[krousdb]

Radical! Doesn't look too dorky either. I will be doing the wheel spoilers. Yours look just like what is on my Prius. Such a simple mod to do. I dont know why I havent done that yet.

Well actuallty I do. I need to pass inspection first. Then I will worry about mods. BTW, my 72 MPG trip to work today had no belly pan. MIght be able to squeeze out a few more mpgs once I get the aero mods back on.

[Mighty Mira]

Cool deflectors! Your car is an inspiration.

[The Toecutter]

You're doing what the auto industry claims to be impossible. I salute you.

I can't wait for you to experiment with this car as much as you can. Then when you ever get a newer car, you can do these same mods, only make them look professional and not like a rolling science project. Imagine shoehorning a diesel in there, and getting the same or better performance, but 80-100 mpg without codfishing and without gentle driving.

[zpiloto]

Nice job. Something to think about, when I did my side skirts I flaired the back end out about 3" with a spacer which negates the need for the rear deflector. Course your's look better than mine. Like the black paint I'll put that on my list.

[krousdb]

Can someone explain the benefits of the skirt that runs between the wheelwells?

[Mighty Mira]

Originally Posted by krousdb

Can someone explain the benefits of the skirt that runs between the wheelwells?

If the wind is nearly parallel to the path of the car (or dead calm), then the air only gets moved out of the way once, out of the way of the first wheel. Now that I understand the effects of crosswinds, I am reluctant to try side skirts, because they will slow you down with a crosswind.

[ZugyNA]

xx

[ZugyNA]

Originally Posted by basjoos

That is the one nice thing about southern summers. Although they may not be the most comfortable for the driver, those hot and humid conditions give the best FE. When I was getting that 62mpg@75mph, the ambient temp was around 85F with high RH, since a stalled warm front was sitting over the area.

If you are interested in the effects of ambient temp, altitude, and humidity on HP:

http://wahiduddin.net/calc/calc_hp_dp.htm