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Old 11-28-2007, 08:46 AM   #2 (permalink)
MetroMPG
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,513

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 60.16 mpg (US)
Thanks: 4,058
Thanked 6,957 Times in 3,602 Posts
My thoughts while making this:

- compound curves are hard to get right (I got the "roof" of the tail eventually, but not the sides right).

- I need to round the transition from roof to sides; right now it's a sharp angle (unlike the car's shape ahead of it).

- The side-of-hatch to side-of-tail transition is messy. I really need to start the boat-tail sides at the forward edge of the hatch sides. Also, you can't tell in the photos, but the right side is tapered further than the left side (at first I was focussed entirely on roof taper, and didn't taper the right side as much as it looks like I could have).

- I tried to project the existing tapering lines of the bodywork into the tail without any big changes, but I could possibly be a little more aggressive. Only tuft-testing would say for sure (looking for clean flow, right to the back of the tail)

- Ryland: I had the same thought about getting a junk hatch. I know where there's a '95 sitting in a farmer's field about 20 minutes away.

- Materials? If this is worth making a "good" copy, I was thinking: fibreglass over high density foam (messy, complicated, time consuming, little experience with the materials); junk hatch with attached sheet metal, faired & painted (also time-consuming, but I'm more familiar with the materials & methods); lightweight plastic or aluminum frame covered with sheet plastic/sheet metal... Plexiglass? Might be hard to form into compound curves (the stuff I've used in the past was fairly brittle. Also, how to join the top & sides in a rounded transition?)

- Not sure about dimples or VGs though. Since I'm an amateur, I'm just trying to stick to the basics: reducing the size of the trailing wake by tapering the shape as much as possible without causing flow separation. Also, I recall reading that dimples don't work for automotive scale/shapes.

- a finished version which I leave permanently on the car could serve as an attachment point for an extended version for highway use.
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Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown



EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
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