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Old 12-31-2009, 10:48 PM   #21 (permalink)
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Thanks to everyone for all the encouragement! It was fun to build and I think it will serve its purpose well. If I can find some time on a day without wind (we get one or two each year), I'll try to take some video of tufts and see what the air is doing.

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Old 01-01-2010, 11:36 AM   #22 (permalink)
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Fubeca, that turned out really well. I'm impressed with the finished look. Wish my handiwork was that polished.

About your test results: what speed were you driving? I didn't see that mentioned.

You likely realize the percentage difference between A & B runs increases with increasing speed.

Brett (bondo) reports a ~20% change with his cap on the highway (here and here), but with all due respect (and I mean that), he hasn't yet done a "controlled as possible" A-B-A test. Also worth noting: he drives at 70 mph, which would show a greater percentage increase than I would see, for example, because I tend to test around 90 km/h / 56 mph.
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Old 01-01-2010, 11:47 AM   #23 (permalink)
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Very nice work!

December 31, 2009 at 3:37 p.m. Fubeca wrote:

"So I don't think the test is really all that valuable. I'll be interested to see how my mileage looks over time."


The A-B-A tests are best in warmer weather with calm wind. Wind tunnel tests are the best do to controlled conditions and refined calibration. Mileage records over time do create a real world average for that specific driver and that specific vehicle.

That said, you did one fine job of fabricating you aerocap. Very nice lines! I wish I had a full scale wind tunnel we could park your truck in with your aerocap on it and do some testing of it's performance toward cd reduction.


Keep up the good work.

Bondo
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Old 01-01-2010, 11:47 AM   #24 (permalink)
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Even if it's a 4% gain at your typical speeds, it's still a significant gain that'll pay for itself in no time.

If you drive 10,000 miles a year at speeds that will net that 4% improvement, that's 19 gallons not burned: 513 gallons vs. 532 gallons. (19.5 mpg vs. 18.8 mpg)

@ $2.75 a gallon, you save $52.25.

So your mod starts giving a healthy return on your investment early in year 2.

And that's a conservative estimate of fuel prices. I'd be willing to bet it's going to be much more than $2.75/gal in the US in 8 or 10 months.
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Old 01-01-2010, 11:49 AM   #25 (permalink)
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Quote:
Originally Posted by bondo View Post
Mileage records over time do create a real world average for that specific driver and that specific vehicle.
This is true of course. And in that case, the more data the more convincing it is.
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Old 01-01-2010, 11:49 AM   #26 (permalink)
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Sorry - I forgot to mention speed. It was at 55mph. I do expect to see better improvements at higher speeds.

I'd love to see what it looks like in a wind tunnel too!
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Old 01-01-2010, 11:55 AM   #27 (permalink)
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This is a pretty awesome looking cap! I can't believe you got it done so quickly.
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Old 01-01-2010, 02:59 PM   #28 (permalink)
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Thanks again for all the compliments. I am satisfied with the result for the time that I put into it. I only spent about 12 hours total on the project (I already had all of the materials).

It is a great proof-of-concept for me that will allow testing. If I really like it I may work on doing something more permanent along the lines of Bondo's very nice creations. Who knows, he may be producing them soon and I'll just be able to buy one.

It does look really good in pictures - but it has more than its fair share of imperfections up close. It really was a quick and dirty build.
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Old 01-02-2010, 10:58 AM   #29 (permalink)
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MPGiata - '90 Mazda Miata
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Winter beater Metro - '00 Chevrolet Metro
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Quote:
Originally Posted by Fubeca View Post
Sorry - I forgot to mention speed. It was at 55mph. I do expect to see better improvements at higher speeds.
If you plug your truck's numbers into the aero & rolling resistance tool, you could project what the 4% improvement you saw at 55 would translate into at different speeds.

Quote:
I'd love to see what it looks like in a wind tunnel too!
There's always the poor man's wind tunnel! On-road tuft testing, eg. http://ecomodder.com/forum/showthrea...per-11522.html

Thanks again for sharing the project & for the time put into testing (I appreciate the effort it takes).
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Old 01-02-2010, 11:09 PM   #30 (permalink)
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I will probably try tuft testing if I get a reasonable day and some time. Today we had no wind but the high was -4F. I decided not to try any testing

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