Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 03-12-2013, 05:59 PM   This thread is in the EcoModder Project Library | #1 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
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
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





Dimensions:
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).
Weight:
14 kg / 31 lbs
Curves/Angles:
(Approximate)

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

Bottom clearance departure angle: ~18 degrees
Cost:
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:


Attached Thumbnails
Click image for larger version

Name:	tail-box-started-640.jpg
Views:	707
Size:	35.4 KB
ID:	12678  
__________________
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
  Reply With Quote
The Following 24 Users Say Thank You to MetroMPG For This Useful Post:
101Volts (09-27-2013), 2000neon (03-14-2013), aerohead (03-12-2013), BamZipPow (04-02-2013), blownb310 (05-09-2013), California98Civic (04-24-2013), Cd (01-28-2015), echo-francis (05-06-2013), ECONORAM (05-02-2013), HyperMileQC (03-14-2013), jime57 (04-27-2013), jkv357 (06-05-2014), Joggernot (07-28-2013), Jyden (03-13-2013), myrefugeisintheLord (03-12-2013), Nevyn (05-03-2013), planetaire (02-02-2014), pRoy (04-24-2013), SpeedyCorky (04-30-2013), turbothrush (03-14-2013), UltArc (10-02-2013), wmjinman (04-22-2013), wyatt (04-25-2013), YeahPete (04-16-2013)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 03-12-2013, 06:33 PM   #2 (permalink)
Learning Aeromodding
 
myrefugeisintheLord's Avatar
 
Join Date: Feb 2011
Location: Spokane, WA.
Posts: 199

Metro - '93 Geo Metro 4 door hatchback
90 day: 35.26 mpg (US)
Thanks: 59
Thanked 45 Times in 32 Posts
VERY COOL! I'll be keeping a close eye on your thread!
  Reply With Quote
Old 03-14-2013, 02:21 PM   #3 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,562
Thanks: 7,738
Thanked 8,554 Times in 7,041 Posts
Here's a material that is essentially coroplast with an aluminum skin on both sides: AlumaCorr. I haven't found a local supplier.

I've started a removable, redwood framed and shrinkwrapped, test boattail. I'm hoping my camera shows up before I get too far along. I intend to do the final version in Polymetal. It's $148 for a 4x8' piece, $104 if I have a shop order it for me.

It sounds like you have six attachment points. I would think with the reduced base pressure there wouldn't be too much suction trying to pull it off. Vibration and tail-wagging must be the bigger problems. I plan on two roof rack style clamps on the driprail and pegs into sockets already in the bumper brackets. With some straps to hold it down.
  Reply With Quote
The Following User Says Thank You to freebeard For This Useful Post:
JacobLeSann (11-20-2023)
Old 03-14-2013, 05:54 PM   #4 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
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
Ooh, that sounds good. Do you have a thread going that I missed? Feel free to post the link.
__________________
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
  Reply With Quote
The Following User Says Thank You to MetroMPG For This Useful Post:
tyrone (04-14-2013)
Old 03-14-2013, 09:51 PM   #5 (permalink)
EcoModding Apprentice
 
Blue Angel's Avatar
 
Join Date: Feb 2013
Location: Ottawa, ON, Canada
Posts: 190

Previous Car - '12 Chevrolet Cruze Eco MT
Team Chevy
90 day: 44.29 mpg (US)

535d XDrive - '16 BMW 535d M-Sport
Thanks: 17
Thanked 59 Times in 38 Posts
Quote:
Originally Posted by MetroMPG View Post
  • CAD construction (Cardboard Aided Design)
  • very small, light internal wood frame (may contain some aluminum tubing also, because aluminum makes it more high tech)
- CAD = Kewl
- Aluminum? Get some titanium fasteners, just because

I'll be watching this thread, not because I actually intend to boat-tail something, but more for the watching the build process.
__________________
2016 BMW 535d
4100lb XDrive Eco-Yacht
  Reply With Quote
Old 03-15-2013, 12:17 PM   #6 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,562
Thanks: 7,738
Thanked 8,554 Times in 7,041 Posts
No thread yet. I'll probably bump an old thread (Project: the Third) but like I said, my camera is probably around here somewhere, I just can't lay my hands on it.

"Pix or it didn't happen."
  Reply With Quote
Old 03-17-2013, 01:24 AM   #7 (permalink)
It's all about Diesel
 
cRiPpLe_rOoStEr's Avatar
 
Join Date: Oct 2012
Location: Porto Alegre, Rio Grande do Sul, Brazil
Posts: 12,548
Thanks: 0
Thanked 1,622 Times in 1,447 Posts
I've already seen some folks attempting to fix dents with cardboard, using plastic adhesive tape to weatherproof it. Others just used epoxi resin over the cardboard, as a cheaper alternative to fiberglass
  Reply With Quote
Old 03-17-2013, 01:36 AM   #8 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,562
Thanks: 7,738
Thanked 8,554 Times in 7,041 Posts
One could run the corrugated cardboard through a paper shredder, then a blender, add in a water soluble glue (or lime) and have paper maché.
  Reply With Quote
Old 03-19-2013, 12:21 PM   #9 (permalink)
Aero Wannabe
 
COcyclist's Avatar
 
Join Date: Dec 2007
Location: NW Colo
Posts: 738

TDi - '04 VW Golf
TEAM VW AUDI Group
90 day: 53.2 mpg (US)
Thanks: 705
Thanked 218 Times in 169 Posts
I am looking forward to some test results from this mod as I know you will be documenting any changes you see in mpg. I have been planning something similar for my hatchback but I want to keep the taillights functional so the sides would be recessed like yours. I may leave a gap at the top to see out of and have wondered if the air would re-attach.
__________________
60 mpg hwy highest, 50+mpg lifetime
TDi=fast frugal fun
https://ecomodder.com/forum/showthre...tml#post621801


Quote:
Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.
  Reply With Quote
Old 03-19-2013, 02:23 PM   #10 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
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
The ghetto wasn't built in a day...

The flow will re-attach if you respect the proper shape (ie. not too "fast" or steep a curve/angle from where you've made the "step").

---

I've been playing with this a bit more:

- Making it up as I go along, I've pieced together a very ghetto wooden 1x2 frame to which both the outer skin and 6 securing straps will attach, and which provides the "contact patches" with the car: carpeted pads that press against non-painted surfaces (or normally hidden, painted surfaces):



(... actual frame is much more ghetto looking than diagram ... but includes more triangulation for strength, not shown)

- Also revising on the fly, I'm no longer going to use external straps over top of the hatchback. Instead, I'm routing the straps from the frame, to the beefy hatchback gas strut mounts inside the car on the "C" pillars.

I'll snap some pics this evening to show how that will work.

Quick 'n' dirty? So much for this being a "quick" project!

I originally envisioned slapping this together in a couple of hours so it could save me a few drops of fuel on a pair of recent highway trips. Instead I've probably got about 5 or 6 hours in it, and the skin isn't even on yet!

It's still "dirty" though.

Attached Thumbnails
Click image for larger version

Name:	frame-pads-tiedown-plan.jpg
Views:	8240
Size:	65.2 KB
ID:	12717  
__________________
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
  Reply With Quote
The Following 6 Users Say Thank You to MetroMPG For This Useful Post:
a8ksh4 (05-22-2013), aerohead (03-19-2013), BamZipPow (04-02-2013), COcyclist (03-19-2013), ECONORAM (05-02-2013), radioranger (04-25-2013)
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com