Aerocivic - how to drop your Cd from 0.34 to 0.17

[basjoos]

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I started this project after the Katrina-insired gas price runup since I have a long commute. I first learned to drive during the 1970's oil embargo and have been perfecting my hypermiling tenchniques ever since. My car is a 92 Civic CX, which I bought new, and was giving me low 60's to low 50's before I started aero modding it.
Side view

Side view with open hatch

Rear view of boattail

Cargo area inside boatail, extending the interior of the car into the boattail added 20cu ft to the interior space. Also there is a hidden compartment under the new load floor in the boattail.

Radiator inlet slot (coroplast has since been replaced with aluminum sheet)




The end result is a car with such low drag that the results of coastdown testing is linear out to 90mph (it coasts almost as well at 80mph as it does at 50mph). I have to get it over 90mph before I start to feel the wind load from high-speed driving. OEM max speed was 95mph. I have had it up to 100mph with plenty of power remaining at that speed (estimated top speed of about 140mph). Wind noise is much reduced from stock. Approximate mileage on a flat road at 85F, 95mpg at 30 to 65mph, 85mpg at 70mph, 65mpg at 80mph, 50mpg at 90mph.

Additional mods planned, include replacing the current one-size-fits-all radiator inlet slot with a driver-adjustible radiator door. Eventually I plan to automate the door by using a Basic Stamp or similar process controller to monitor the coolant temps and adjust the opening to the actual cooling needs.

Most of my driving is at night, especially in the winter, and night driving is costing me 2 to 3 mpg in additional electrical load from the lights. About half of this loss is from the parking lights, the remainder is from the headlights. I want to replace the parking and dome lights with LED's. Since retrofit LED headlight kits are still several years off, I want to investigate installing a switch to kill one of my headlights and/or a dimmer control to reduce the headlight's intensity and power drain for situations where I don't need the full intensity of the headlights for visibility.

NOTE: if you arrived here from another site, you may be viewing this topic as a single post.

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[basjoos]

More pics:
Side view of nose, front wheel spoiler, and front wheel well skirt (nose and skirt are now aluminum sheet, spoiler is still coroplast)

Front view of front wheel spoiler

Side skirts made of coroplast (there are 2 side skirts on each side, one even with the inner edge of the tires, the other even with the outer edge of the tires).

Rear wheel spoiler (coroplast)

Underbody panelling (coroplast and aluminum flashing, I plan to replace it with alumunum sheet whenever I next need to remove the panelling for service).

[basjoos]

More pics:
Conveyer roller inside of front skirt

Front skirt slightly open with wheels cuts all of the way to the left.

Windshield wiper windscreen

Fairing behind muffler

Interior side rear view mirror (replaces deleted exterior side rear view mirrors)

Low-tech hand throttle

SuperMID

Another view of the car

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[Lazarus]

Very Nice.
Basjoos how many hours do you think you have in it to get it to this point?

[basjoos]

Probably about 250 hours and a materials cost of about $400 spread out over the past 2 years. It has paid for itself in fuel savings several times over.

[igo]

Basjoos. I haven't seen pictures of your car for a while. I see the boat tail has been improved in looks and function.

What did you use for the rear window?

I have to give credit to you. Areo moding a civic to the max is not an easy undertaking.

[basjoos]

The rear glazing is Lexan. Once I conclusively proved the FE benefits of the boattail on my car, I rebuilt it with more durable materials (aluminum sheet and Lexan) than the original prototype was built of (coroplast and clear vinyl) as well as utilizing the additional space enclosed by the boattail..

[newtonsfirstlaw]

Originally Posted by basjoos

The rear glazing is Lexan. Once I conclusively proved the FE benefits of the boattail on my car, I rebuilt it with more durable materials (aluminum sheet and Lexan) than the original prototype was built of (coroplast and clear vinyl) as well as utilizing the additional space enclosed by the boattail..

Is there anything to note when working with Lexan? I have clear vinyl on mine, but maybe I'd replace it.

[MetroMPG]

Hey basjoos -

LOTS of visitors coming in from other sites right now - check the hitcount on this thread relative to some others.

If your car draws anywhere near this much attention in real traffic, you must have to be VERY careful around the rubberneckers!

[basjoos]

I used 1/8" Lexan, which can be drilled, sawed, and bent into a curve as needed.

I sometimes have a problem with rubberneckers piling up and backing up traffic alongside my car. But the worst are the few who can't drive in a straight line while they are staring at something alongside them and start curving into my lane.

[Coyote X]

After you swap out to LED park lights if you want to reduce the headlight load you can wire up some relays to switch them to series load instead of parallel. That will make them dimmer but not really dark. It will cut the load in half though

The other thing would be using some relays to switch them out you can add several silicon diodes in line. You get a .7V drop across a diode so add 5 of them in series will drop you 3.5V. Just make sure to pick big enough diodes to handle the load.

[MetroMPG]

I've heard of an instance where a university team solar car was forced off the road due to rubbernecking. Ended up catching a culvert and flipping the solar car. Fortunately nobody was hurt.

EDIT: the comparison of your Civic to a solar car (in terms of aero optimization) isn't that much of a stretch either either.

[Peakster]

Whatever happened to your additional 'wind screen' :

aero20.jpg

[SVOboy]

Rain?

[Peakster]

Originally Posted by SVOboy

Rain?

Mmm. I don't think so. Not according to this previous post by basjoos:

The second windshield added about 4mph to my terminal velocity on the "calibrated" downhills on my drive. I drove through some light rain and didn't even notice it on the vinyl other than the occasional drop running back along the vinyl. Most of th rain (and bugs) follows the smooth airflow over the vehicle. And best of all, no evidence of the "A" pillar vortex based on the behavior of the water droplets on the front side windows.

[basjoos]

Coyote X, good idea about using series connecting the headlights and also using doides to customize the voltage drop.

The aero benefits of the "second windshield" (by eliminating the "A" pillar vortex and smoothing the airflow over the front of the car) were undeniable, but I had some operational problems with it when operating in cold rainy weather. I'm in the process of replacing the clear vinyl on the "windscreen" with Lexan. The vinyl was clear enough when looked at straight through (90 degrees), but was hazy when viewed through at an angle (30 degrees) as it is near the bottom of the windscreen. It also had a tendancy to overwealm the Fog-X and fog up on the inner surface when driving in cold, wet conditions. The Lexan should take care of the low angle visibility problem and I need to get a good watertight seal along the front and sides of the "windshield" so water can't find its way onto the hot hood and end up condensing on the cold inner surfaces of the "windshield". Also considering adding a windshield wiper to the "windshield" to placate any cops that might freak out at a car driving in the rain without wipers, even if I don't really need them.

[newtonsfirstlaw]

Basjoos, you might want to stick a sock full of crystalline kitty litter (it's silica gel, the cheapest source you can find) somewhere in that space to get rid of any lingering moisture that finds its way in there.

[free-electron]

I read this and was so impressed I had to write about it on my blog.

You can read my thoughts at http://www.energyrefuge.com/blog/caf...-be-that-hard/

[Darxus]

Nice.

I was recently thinking about wheel spoilers and I thought of something I think is relevant.

Your front wheel spoiler mostly pushes air down, where it will end up hitting the tire (or ground) still anyway. I believe that won't help you any, and that it would be more efficient to just push the air directly to both sides of the wheel. Possibly more to the outside of the car than under the car due to the rest of your aerodynamics. So you would have a wedge where the leading edge is a vertical line.

And I would expect you to benefit from putting another set of spoilers behind the rear wheels (working well with your dual layer side skirts).

Of course I have no idea if these would give you enough benefit to be worth you doing.

[MetroMPG]

Originally Posted by Darxus

And I would expect you to benefit from putting another set of spoilers behind the rear wheels (working well with your dual layer side skirts).

That's a good observation for behind the rear tires. But do you mean to add a "boat tail" rather than "spoiler"?

You'll see wheels/tires effectively boat tailed on this car:
http://www.design-classic-cars.de/auto-union/stuck1.jpg