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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 10-22-2009, 10:12 AM   #21 (permalink)
Master EcoModder
 
Join Date: Nov 2008
Location: 18603, USA
Posts: 758

The Crimson Crawler - '04 Hyundai Elantra GLS
90 day: 36.71 mpg (US)
Thanks: 219
Thanked 60 Times in 45 Posts
Could you make it so that you open the hatch to be the "top" of the boattail, and the rest of it extends/unfurls from inside the car?

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 10-22-2009, 01:32 PM   #22 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 19,236

Blackfly - '98 Geo Metro
Team Metro
90 day: 67.58 mpg (US)

ForkenSwift - '92 Geo Metro EV
Last 3: 95.68 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 38.25 mpg (US)
Thanks: 1,937
Thanked 4,651 Times in 2,323 Posts
Unfortunately not. The top of the hatch is actually about 6 inches of the end of the roof. Opening it even part way increases frontal area and hammers Cd.



Semi-related: Video: Illustrating the Vast Importance of Aerodynamics (open hatchback experiment) - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
__________________
Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed
Ecodriving test:
Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L



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
Old 10-22-2009, 02:09 PM   #23 (permalink)
PSmodder lurker
 
Join Date: Jan 2009
Location: Chino
Posts: 1,444
Thanks: 22
Thanked 728 Times in 429 Posts
Bubble butt



Here's another view of the removeable tail. The clear/body color PVC panels welded into a rear-body conforming airfoil. The inflatable would have multiple high pressure tube spars either longitudinally or transverse (interestingly the transverse 'bumps' offer some aero benefits, Mythbuster testing?)
The temporary structure could be held down with straps & there is a rigid spar coming from the trailer hitch, holding the signal harness, plate & rear light assemblies. It also tucks in & tidy up the inflatable tube ends.
At the end of the day, it could also serve as the children's slide on the front lawn.
  Reply With Quote
Old 10-24-2009, 04:22 PM   #24 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 8,230
Thanks: 9,874
Thanked 4,268 Times in 2,364 Posts
bowling for fuel

Quote:
Originally Posted by botsapper View Post


Here's another view of the removeable tail. The clear/body color PVC panels welded into a rear-body conforming airfoil. The inflatable would have multiple high pressure tube spars either longitudinally or transverse (interestingly the transverse 'bumps' offer some aero benefits, Mythbuster testing?)
The temporary structure could be held down with straps & there is a rigid spar coming from the trailer hitch, holding the signal harness, plate & rear light assemblies. It also tucks in & tidy up the inflatable tube ends.
At the end of the day, it could also serve as the children's slide on the front lawn.
I'd set up bowling pins on the curb and then see how many can be knocked over with a left turn!
Wow,the imagery is just too good!
I do think maybe Kamm has a point with "practical" length issues.Something this long might want to be half car/half trailer.I'm to squeemish to attempt something that radical in pure cantilever.Not sure what a strong momentary sidewind gust might do.
We do need an EcoModder wind tunnel!
  Reply With Quote
Old 10-24-2009, 06:02 PM   #25 (permalink)
EcoModding Apprentice
 
Bicycle Bob's Avatar
 
Join Date: May 2008
Location: N. Saskatchewan, CA
Posts: 1,319

Appliance White - '93 Geo Metro 4-Dr. Auto
Last 3: 42.35 mpg (US)

Stealth RV - '91 Chevy Sprint Base
Thanks: 47
Thanked 189 Times in 138 Posts
The area swept by a turning car is symmetrical fore and aft of the rear axle, so overhang, especially if tapered, will not hit stuff.
Most cars can use more tail area for crosswind stability. The center of "lift" is usually about 25% of the way back, since the front is redirecting the air, while the center of mass falls naturally around 50% back. The tail does generate more side force, but it is on the back axle, which has traction that otherwise makes the front end wander. Even with long tails, several streamliners have added a tail fin for stability. More side force, within the ability of the chassis to support it, may even give a boost by working as a wing-sail.
  Reply With Quote
The Following 2 Users Say Thank You to Bicycle Bob For This Useful Post:
aerohead (10-28-2009), Sven7 (03-27-2012)
Old 10-24-2009, 06:04 PM   #26 (permalink)
...beats walking...
 
Old Tele man's Avatar
 
Join Date: Jul 2009
Location: Tucson, AZ
Posts: 5,795
Thanks: 146
Thanked 1,297 Times in 967 Posts
...pardon my simplistic analogy, but it sure "looks" like a really bad case of the "...tail waggging the dog..." situation to me.
__________________
2014 Toyota Prius 1.8L eCVT
2009 Pontiac Vibe 1.8L/SFI 4A
2004 Pontiac Vibe 1.8L/MFI 4A

2011 Chevrolet LTZ Cruze 1.4LT 6A
1971 Dodge Charger 318 3A
1970 Plymouth AAR 'Cuda 340/6BBL 4M
1968 Dodge Charger 383 3A
1967 Plymouth Barracuda Formula S 383 4M
1965 Plymouth Barracuda Formula S 273 4M
  Reply With Quote
Old 10-24-2009, 06:10 PM   #27 (permalink)
Master EcoModder
 
Join Date: Nov 2008
Location: Madison AL
Posts: 1,123

The Geo - '93 Geo Metro
Team Metro
90 day: 45.16 mpg (US)
Thanks: 30
Thanked 40 Times in 37 Posts
Quote:
Originally Posted by Old Tele man View Post
...pardon my simplistic analogy, but it sure "looks" like a really bad case of the "...tail waggging the dog..." situation to me.
Not if you ran some strings to opposing sides of the car, that hooked on the inside of the balloon.

i.e. top left hooks to bottom right
  Reply With Quote
Old 10-24-2009, 09:58 PM   #28 (permalink)
Left Lane Ecodriver
 
RobertSmalls's Avatar
 
Join Date: Aug 2008
Location: Buffalo, NY, USA
Posts: 2,258

Prius C - '12 Toyota Prius C
Thanks: 79
Thanked 280 Times in 193 Posts
With something as useful and beautiful as this, why would you want it removable?

Okay, I suppose it would interfere with your ability to load akward cargo and parallel park. But if you drop the requirement that it be able to be stored inside the Metro, it becomes easier to design and build, since you can use a single rigid frame. Storable in the garage is almost as good. You'd use the boattail on road trips, and leave it at home for commuting.

@Botsapper: That's a very nice render. But if you taper the sides, bottom, and top at the same angle, you preserve attached flow with shorter overall length. Actually, with the Metro taillamps being almost half as wide as the rear of the car (based on counting driveway tiles), you probably want a square rear truncation, with the license plate mounted above or below the taillamps.

MetroMPG: How long do you think you're going to make the boattail?
  Reply With Quote
Old 10-24-2009, 10:23 PM   #29 (permalink)
EcoModding Apprentice
 
Bicycle Bob's Avatar
 
Join Date: May 2008
Location: N. Saskatchewan, CA
Posts: 1,319

Appliance White - '93 Geo Metro 4-Dr. Auto
Last 3: 42.35 mpg (US)

Stealth RV - '91 Chevy Sprint Base
Thanks: 47
Thanked 189 Times in 138 Posts
The bottom is not so well supplied with air, even with a great belly pan and rounded. 4 degrees on the belly pan is usually as conservative as 15 deg on the top and sides. If the tapers were continued to a point at the back, it should be only slightly higher than the stagnation point at the front. A bit of rake will help cancel the lift and induced drag if the air goes over the top faster than underneath.
  Reply With Quote
Old 10-24-2009, 10:39 PM   #30 (permalink)
Master EcoModder
 
Join Date: Dec 2008
Location: Southern WI
Posts: 809

AlienMobile - '00 Honda Insight
Team Honda
90 day: 80.05 mpg (US)
Thanks: 92
Thanked 529 Times in 183 Posts
Quote:
Originally Posted by Bicycle Bob View Post
The bottom is not so well supplied with air, even with a great belly pan and rounded. 4 degrees on the belly pan is usually as conservative as 15 deg on the top and sides.
Nice to hear from you again!

If I am reading what you have said about the relative lack of air on underside of the vehicle compared to the sides and top, it would seem that you could conclude that the taper on the underside of the aerocivic is too steep.

I remember reading in that thread somewhere, that you asked Mike if he had performed tuft testing in that location. How much higher can the 4 go before air detachment would be a concern in this location?

Jim.

  Reply With Quote
Reply  Post New Thread


Tags
boat tail, testing

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Project: Rebuilding an '01 Honda Insight as a nonhybrid Fabio Hybrids 158 01-12-2013 11:59 AM
How to get instant fuel consumption from Megasquirt TELVM Instrumentation 11 08-29-2011 02:47 PM



Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com