5th generation civic hatchback - improving aerodynamics

[AndrewJ]

[MetroMPG]

That is so funny. I laughed. Thanks.

PS - don't try to cook the pizza on the plastic wheel cover. It only works the other way around.

[SVOboy]

Oooh! I get it now.

[AndrewJ]

So I started on this bit last week, but never got around to posting about it.
I figured that some skirts with integrated wheel spoiler-type-things would be a good next step.

Lucky for me, Honda already put some lovely side-skirts on my car about 13 years ago!





Now, unfortunately they're not exactly doing me any aerodynamic favors in their current configuration. Nothing a heat gun can't fix though.
Simply remove the fasteners from the bottom, heat and bend.

[SVOboy]

Haha, I would never have expected that,

Did you prop up the back at all in order to hold stuff in position?

[AndrewJ]

No, not yet, and I only have one side done. I don't know what kind of plastic that it's made out of but it takes a LOT of heat to soften it up sufficiently, and it smells bad when it's heated up.

But anyway, I need to maybe put a piece of 1" x 1/8" aluminum behind it to hold it straight. That, and I'll be making little wheel spoilers/boattail things to go on either end. I figure the combination of the two will support it quite nicely.

[SVOboy]

I'm pretty sure it's some kind of PCV. Prolly getting cancer from the fumes,

I wonder if any old generic honda body kit skirts would work for this purpose...

[basjoos]

I heated up and bent a 90 degree into a piece of coroplast and screwed it onto the underside of that black plastic piece. The coroplast is flexible enough to bend out of the way when contacting the road surface (easy enough to do when carrying a heavy load in the back) and can easily be replaced if/when its gets eroded down too far by occasional scrubbing with the road's surface. The back portion of the side skirt especially tends to scrub the road when going over high curbs, etc. When I installed my underpan, I slipped it between that black plastic piece and the car's body to hold it in place before drilling and tapping screw holes through to the metal body.

[AndrewJ]

So, first off, cut the middle out of the ultra-classy plastic wheel covers.
It cuts pretty easily with a utility knife, but for the thicker bits a Dremel works better. (and it's harder to slice off a finger with a Dremel )




Now trim it up so that any protrusions on the top side are minimized.





And then attach your pizza pan to the what's left of your wheel cover. I used some liquid nails-type construction adhesive. It looks like it'll hold up well, but just in case it doesn't I have some stainless steel wire I can thread it together with.





And here they are installed.
If you look closely in my photo from yesterday you can see that I greased up the wheel where these hubcaps press-fit in. When I tried it yesterday they really took some effort to go on, and they didn't come off well. Now they're much easier (but not so easy that they'll come off all on their own)





I'm going to give these a week or so of driving before I do the rear wheels, just in case there are any changes I want to make.
The neighborhood cat approves.

[SVOboy]

Looks great! What's next?

[AndrewJ]

I have no idea.


One of these three: (whichever I'm in the mood to tackle)
1) finish side skirts
2) mock up rear wheel boattail/diffuser type-thingie
3) testing

[diesel_john]

That looks great

[Stan]

Well done, Andrew...can't wait to see the results of new a-b-a testing on your favorite hill!

(This is turning into one of my favorite threads!)

[MetroMPG]

Agreed on the favourite thread status. Nice work.

[bennelson]

Love the pizza pan hubcaps! Kinda a cool futuristic armoured car look.

There are so many things on this forum that are very inspiring!

[AndrewJ]

Thanks guys!

No pressure, right?

[AndrewJ]

So, I went and did a bit more coastdown testing this morning. I started with a much higher top speed, 80mph, so that any aerodynamic drag would be much more pronounced. Hopefully the Excel spreadsheet would be able to produce a much more accurate drag coefficient for my car that way.

I tested at a different site today, there was a slight incline, so I made sure that there were equal data points on opposing runs to average each-other out.

So once again, the raw numbers:

Vehicle Weight (with occupant) 2300lbs/1043.26kg

Frontal Area 1.768 m^2

Crr 0.0169

Test run-----V1-----V2----V3----V4-----V5----V6
0 sec---------80-----80----80----80-----80----80 mph
10 sec-------69-----68-----70----68----70----68 mph
20 sec-------61-----59-----62----59----62----58 mph
30 sec-------54-----50-----55----51----55----51 mph
40 sec-------46-----43-----49----42----49----42 mph
50 sec----------------------42----37----43----38 mph
60 sec----------------------34----35----31----36 mph
70 sec----------------------30----31------------- mph

Solve for the Cd and it spits out a very reasonable 0.254

Looks like I've already beat my goal of besting an Insight's 0.26

[SVOboy]

You mean the insight's .25?

Very nice work though. I should have you test out my new pulsing spark plugs,

[AndrewJ]

Dammit!!

So close!!!

Well, back to the old drawing board...

[Daox]

I did read through this entire thread at one point, but have since forgotten. Did you do any pre-modification coast down tests with the spreadsheet to validate its accuracy? I'm not trying to question your results, but rather the accuracy of the spreadsheet's calculation. This is just one thing that I plan to do before I start doing any aero mods on my own vehicles. This would ensure that even if the spreadsheet is wrong I would have a baseline to work from and can more accurately evaluate the test data.

BTW, I too was under the impression that the Insight's cd was .26? I've never read differently anywhere else.