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Old 03-12-2013, 06:59 PM   This thread is in the EcoModder Project Library | #1 (permalink)
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
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MetroMPG's Honda Insight boat tail extension (cardboard) tuft video; ABA test +9.7%

(Aww, how cute - my second cardboard boat tail.)

I haven't even finished the cosmetic details of the car's new removable/adjustable upper & lower grille blocks. But since I only ever drive this car on the open road, it drives me nuts to be wasting all those extra millilitres of fuel because it doesn't have a boat tail.

I literally think about it ... Every. Time. I. Drive.

Ultimately... eventually... I have in mind a hitch-mounted, "cargo carrier"-based type of tail (along the general lines of this one and this one). But that's quite a big project, and a ways off.

So, until that happens, this quick 'n' dirty prototype will have to tide me over:
  • CAD construction (Cardboard Aided Design)
  • very small, light internal wood frame (may contain some aluminum tubing also, because aluminum makes it more high tech)
  • it'll hang from a bracket through the rear bumper (through factory holes over the licence plate)
  • it'll attach via straps to factory tie-down hooks inside the hatchback's cargo area
  • 2 more don't-fall-off! straps will run up the rear glass to the top of the hatchback
  • the factory hatch will remain openable/accessible with the tail on the car (with the top straps disconnected, obviously)
  • a skin of heavy plastic film plus lots & lots & lots of duct & hurricane tape will make it weather proof. And sexy.
  • protective film will guard the paint where the tail is in contact with the bumper
  • tail lights will be left where they are, exposed in cut-outs, like this coroplast Prius tail -- so only the lic. plate, light, and reflectors will be mounted on the end of the tail (maybe also side marker lights)
I'm basically just winging it (ha), eyeballing the curves & angles.

Ultimately this could also be reproduced in coroplast if it turns out to work OK.

Expectation management: don't expect rapid progress or significant updates to this thread for another week or three. TMP! (Too Many Projects). I just wanted to get it started to get the creative juices flowing. (Fluid dynamics of creative juices?)

And it goes without saying, it won't be nearly as pretty (or as long, or as effective) as Jim's tail:

================================================== ========

Project summary...
updated April 23, 2013

Length 79 cm / 31 inches

That makes the car+tail = 4735 mm (186 in.) overall. That's 3 inches shorter than the most popular/best selling car in the U.S. (2012 Toyota Camry).
14 kg / 31 lbs

Top: from ~13 through ~16 degrees
Bottom: from ~6 through ~13 degrees
Sides: ~16 through ~24 degrees

Bottom clearance departure angle: ~18 degrees
Duh. It's cardboard, glue, tape & leftover wood, half dozen ratchet straps and heavy duty garbage bag plastic. Maybe 20 bucks in materials.
Test results:
1) Tuft testing video posted on April 22 (post #66) shows smooth, attached flow on top, and attached but turbulent flow toward the rear on the sides.

2) A-B-A testing on April 23 (post #77) showed a 9.7% improvement in fuel economy at 80 km/h (50 mph).

Real world results:
109 mpg (US) / 2.2 L/100 km round trip fuel economy on a ~300 km round trip where my previous average fuel economy was ~95 mpg (US). See post #168 for details.

Tuft testing video:

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