2006 Civic Coupe Aero Mods

[aerohead]

The term is from Goro Tamai, and describes what happens when an otherwise smooth, 'flat', underbody is 'cambered' downwards, creating a crude venturi, in which the flow velocity is accelerated, and static pressure reduced, in opposition to the upper body's suction peak attempting to produce lift.
If properly 'tuned', it can cancel the upper body lift.
On a road vehicle, SAE 'breakover' clearances between the two axles would have to be respected, or the car could 'high-center' on driveway ramps and railroad crossings.

[freebeard]

At Permalink #!& I left out the Colani C-Form.

[JacobLeSann]

Thank you aerohead, I enjoy when you type in words I can actually comprehend! That’s very relevant and helpful information. I’m still trying very hard to make the rear work better.

freebeard, you’re very proficient at linking old threads. Have you seen anything on grille shutters? I’d like to see where/how I can run a push/pull cable through the firewall. A pull-cable shutter system is doable and could work great on this car.

[freebeard]

Were I as good as you say, you'd be looking at a picture of the B2 Passat (VW Dasher) radiator shutter. As it is, here's a link to various types that show up in a search: duckduckgo.com/?q=B2+Passat+radiator+ducting+shutter&iar=images&i af=type%3Aline&iax=images&ia=images

Lots to choose from. But of course, the choke cable needs a hole in the firewall. I never could bring myself to cut one.

[JacobLeSann]

Well, quick update. I spent all of today tuft testing various trunk spoiler lengths, angles, heights, etc. This time I did them all within a set time frame as well as the same route. I found out that the flow down the rear glass didn’t really vary much at all. I will get some photos and update this.

Perhaps Honda has indeed done the best in this area of the car.

1 step forward, 2 steps back! :smiley

[JacobLeSann]

Today’s candidates:



Flat deck spoiler with 45 degree rear up-kick.



Flat deck spoiler with 20 degree rear up-kick.



20 degree deck spoiler, rising a total of 3” at the rear edge.

—The Shootout———

First off, my bad for the camera quality. It was hand-numbingly cold today and for the most part I just recorded inside the car. All I have at hand is my phone and a homemade stand that sits in the passenger footwell. Crappy roads all over.



The flat deck spoiler with the 45 degree up-kick produced similar airflow to everything else I’ve tried. It really sent that long red tuft into the air!



The 20 degree up-kick had about the same flow, although the red tuft had dropped a bit.



The fully-angled 20 degree deck spoiler seemed to hold the longer tuft at a similar height. Airflow down the rear glass didn’t look any different.



For contrast, I tested my deck spoiler on its own. The red tuft had come in closer, but is still hovering 2-3” over the rear. The rear glass airflow looked…The same.



For the sake of “why not?”, I ripped everything off and tested the stock trunk lid. The red tuft would alternate between touching the rear edge of the trunk lid and floating 1” above. Once again, the rear window had similar flow.



As a last note, here’s a side shot I got of the car with the 45 degree up-kick in place. If you look closely you will see the red tuft flying with the birds. Wow! That’s not even close the trunk. Interesting.


————Conclusion?——-

Hmm…Not sure. Nothing seemed to have really affected the airflow on the rear windshield. That red tuft is the only real deviation, though I’m not wholly sure what it means. From what I’ve seen/read, that tuft should be much closer to the trunk lid. If that’s correct, then the stock trunk performed best.

However, I am not measuring or testing pressures. It’s very possible that these shapes and extensions can make varying differences in pressure on this vehicle. I really should build a magnehelic testing setup. I could try and use some water/dust testing as well.

So…More to learn.

[JacobLeSann]

I found a blueprint of the car, and printed it out. I have poor computer skills so it’s tiny. The EBLA from the trunk’s rear edge to where it contacts the end of the roof is 17 degrees. It’s very weird to measure given the roof curvature.

So it looks like that’s another piece of the puzzle.

——————————————-

From what I understand, these are the three problems with the top rear of the car:

-EBLA is a bit too steep. Should be 6 degrees lower as a rule of thumb.

-Separation bubble ahead of trunk lid, Center of rear glass. This disrupts flow and could easily be causing lift.

-Boundary layer seems thick. When using a long tuft to estimate EBLA, it likes to float 1-3” above the rear of the car. This seems to be reflected in the rain.

——————————————

As I plan to keep this car another 1-2 years, I want to build a proper fiberglass bodykit designed to lower drag. For this section of the car, I don’t want to modify anything but the trunk lid (I have an OEM spare). I want to make it aesthetically pleasing, at least to my eyes. Most importantly, I want to have functional rear glass visibility.

Given those parameters, I think I’ve done pretty much everything so far. Maybe the next step is seeing what happens if I energize the boundary layer…? Hmm..

[freebeard]

That red tuft is the only real deviation, though I’m not wholly sure what it means.

Theoretically, Coefficient of Lift is affected.

For this section of the car, I don’t want to modify anything but the trunk lid (I have an OEM spare)

Bullnose on the fences isn't helping. [Run a straight fin from the corner of the lid to whatever trailing edge you choose. Then box in a cavity around the license plate]?

[JacobLeSann]

Not a bad idea. With the roundness of the stock rear end, and the angles/locations at which it tapers, making a box cavity around the trunk makes sense. And yes, the bullnose doesn’t help. Unintentional detail that came about from the trunk shape.

I don’t have a drawing (at work rn), but I’ve considered having a panel across the top of the trunk lid, which wraps around the sides of the rear end. I can use my spare bumper to build the lower portion, creating one big hollow truncation. Sort of like a box cavity.

Much like the rear end of the Porsche 935, VW XL1, and so on. Extending the rear body lines out into 4 distinct fences, with a recessed centre. The main complications in doing this are taillight visibility, license plate visibility, and shuddering/rubbing causing wear on surfaces.

Think of a box cavity/tail extension, but built into a clamshell that allows trunk opening.

————————————

P.S. after my trip, I’ve still seen no toll road camera charges come in the mail. I think my spoiler blocks the rear plate from overhead cameras. One way to save money!

[aerohead]

Originally Posted by JacobLeSann

I found a blueprint of the car, and printed it out. I have poor computer skills so it’s tiny. The EBLA from the trunk’s rear edge to where it contacts the end of the roof is 17 degrees. It’s very weird to measure given the roof curvature.

So it looks like that’s another piece of the puzzle.

——————————————-

From what I understand, these are the three problems with the top rear of the car:

-EBLA is a bit too steep. Should be 6 degrees lower as a rule of thumb.

-Separation bubble ahead of trunk lid, Center of rear glass. This disrupts flow and could easily be causing lift.

-Boundary layer seems thick. When using a long tuft to estimate EBLA, it likes to float 1-3” above the rear of the car. This seems to be reflected in the rain.

——————————————

As I plan to keep this car another 1-2 years, I want to build a proper fiberglass bodykit designed to lower drag. For this section of the car, I don’t want to modify anything but the trunk lid (I have an OEM spare). I want to make it aesthetically pleasing, at least to my eyes. Most importantly, I want to have functional rear glass visibility.

Given those parameters, I think I’ve done pretty much everything so far. Maybe the next step is seeing what happens if I energize the boundary layer…? Hmm..

That's likely a good call.
The three cars I have , with Bonneville spoilers, which set land speed records, happened to place the spoiler's tearing edge right at the AST-III contour interface.
* The Ford Fusion 999 ended up with an EBLA of 13.0-degrees
* The GM Chevy Cobalt ECOTEC had EBLA = 10.0-degrees.
* I do not have the HOTROD Magazine, 'Project Red Hat', Chevy Camaro with me.
* Just for giggles, if you can figure out how to place the HONDA under the AST-III, as directed, the scale measurement it depicts could be compared to what you've fabricated so far.
As always, we're discussing 'shape drag', so, proper aero solutions 'ARE' going to have a particular 'look' to them, when seen in 'true length' as with your blueprint.
One out of one atmospheres agrees!