5th generation civic hatchback - improving aerodynamics

[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.