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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 05-21-2013, 05:59 PM   #91 (permalink)
Master EcoModder
 
christofoo's Avatar
 
Join Date: Mar 2012
Location: Salt Lake City
Posts: 292

00C - '00 Toyota Corolla
90 day: 43.54 mpg (US)
Thanks: 147
Thanked 188 Times in 72 Posts
Quote:
Originally Posted by MetroMPG View Post
Woohoo!

After seeing the latest pictures, I'm a little concerned about this transition:

Hopefully it's not too abrupt, going from horizontal on top to the "template" angle. (If it is, do you have the ability to make a bigger radius/smoother transition there?)
Me too.

If the horizontal surface was just a deck lid it would have an abrupt lip, but if it were an aero-fish-scale (from the roof-line to the template) it should be rounded. I wasn't sure which to do in planning, now I'm thinking I guessed wrong in both cases.

It might work fine the way it is if I do a rear-window treatment (full or half? ...) to get separation right along the template and keep the air flow away from the trunk.

When I tuft test, I'm expecting to see the roof-to-rear-windshield radius pull the airflow down, a little turbulence at the base of the windshield followed by a lot of horizontal air-flow along the trunk line to the lid transition, where it will fall apart at the sudden ~19 drop.

The alternate solution, if I wanted just an Aero Box with no rear windshield treatment, should have been a very gradual curve from the horizontal trunk line back to the template - with a radius similar to the roof-to-rear-windshield. (This is what I think now.)

EDIT: what I think I'm trying to say - case 1 no detachment before trunk: need a large radius to move horizontal airstream back to the template - also I should arguably head to 12 instead of the template. Case 2 detachment somewhere on the template: need a small radius (~4") to keep reattachment stable. (I'm not really sure what I've got here, a 4" radius from 0 to 19 doesn't look like much visually.)

If I have to make a big change to that transition, the lid will get reborn in aluminum with snipped-out-fiberglassed-forward-corners, just like the rest of the box. (Hands down my favorite method between the two, so much so that I don't want to bother editing my somewhat bungled glass-over-foam version.) The lid would need compound edges but they would be well within the limits of tuck shrinking. That would set me back to the tail end of phase 2, basically, most likely needing to edit the upper lip of the box, but both items ought to go pretty fast. Cross that bridge when I get there though...

EDIT: Between the two methods, I'd expect the rear-window-treatment to work the best aerodynamically, because it is the closest to ideal profile in the final product, whereas relying on a large curve to bend the flow off the trunk results in not one but two regions of non-ideal flow. The big question of course is how big the split is and thus which is favored in cost-benefit. (If only I had CFD...) My guess is that the split is significant, considering the prevalence of Kammbacks in the eco (hybrid) market, also the more extreme Kammback-like sedans (Elantra, Cruze) ever since Congress 2007 wrote the CAFE hike.



Last edited by christofoo; 05-21-2013 at 06:45 PM..
  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 05-21-2013, 10:11 PM   #92 (permalink)
Not Doug
 
Xist's Avatar
 
Join Date: Jun 2012
Location: Show Low, AZ
Posts: 10,755

Chorizo - '00 Honda Civic HX, baby! :D
90 day: 35.35 mpg (US)

Mid-Life Crisis Fighter - '99 Honda Accord LX
90 day: 33.43 mpg (US)

Gramps - '04 Toyota Camry LE
90 day: 33.15 mpg (US)
Thanks: 7,021
Thanked 2,007 Times in 1,531 Posts
How would you attach the Kammback? I do not know of any good solutions for that.
  Reply With Quote
Old 05-22-2013, 03:01 AM   #93 (permalink)
Master EcoModder
 
christofoo's Avatar
 
Join Date: Mar 2012
Location: Salt Lake City
Posts: 292

00C - '00 Toyota Corolla
90 day: 43.54 mpg (US)
Thanks: 147
Thanked 188 Times in 72 Posts
Quote:
Originally Posted by Xist View Post
How would you attach the Kammback? I do not know of any good solutions for that.
My thought was a sandwich of aluminum lip, weatherstrip foam tape, exterior caulk, glass (or auto body for the lower section of the full Kamm, in my head the half-Kamm might all attach to the glass). I'd double check, but I'm assuming exterior caulk is as reversible against polished surfaces as its indoor counterpart. Accidental forces will be distributed, but deliberate focused forces can debond either the tape or the caulk, made possible by the flexibility of the tape and the aluminum sheet Kamm.
  Reply With Quote
Old 05-22-2013, 10:10 AM   #94 (permalink)
Hypermiler
 
PaleMelanesian's Avatar
 
Join Date: Dec 2007
Location: Texas
Posts: 2,320

PaleCivic (retired) - '96 Honda Civic DX Sedan
90 day: 69.2 mpg (US)

PaleFit - '09 Honda Fit Sport
Team Honda
Wagons
90 day: 44.06 mpg (US)
Thanks: 611
Thanked 428 Times in 280 Posts
Quote:
Originally Posted by christofoo View Post
When I tuft test, I'm expecting to see the roof-to-rear-windshield radius pull the airflow down, a little turbulence at the base of the windshield followed by a lot of horizontal air-flow along the trunk line to the lid transition, where it will fall apart at the sudden ~19 drop.
I can confirm that there is some slight separation at the middle bottom of the rear window, but it reattaches before the end of the trunk.
__________________



11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles
  Reply With Quote
Old 05-22-2013, 10:43 AM   #95 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,272

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

MPGiata - '90 Mazda Miata
90 day: 52.07 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)
Thanks: 3,808
Thanked 6,686 Times in 3,466 Posts
I wish I'd paid more attention to your initial planning diagram or I would have mentioned that transition sooner. I'll admit until it became "real" I didn't really look closely at it.

If you're willing to build a Kammback structure on the back of the car, I think that'll net your best drag reduction.

If not, I think adding a radius to the transition on the box lid would work.

But before fretting too much about all this, see what the tufts say! Maybe we'll be pleasantly surprised to find it's working as-is.
__________________
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: Oops, I did it again! Bought another cheap, 3-cylinder Mirage. Mods in progress...
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
Old 05-22-2013, 06:46 PM   #96 (permalink)
Burn lean and prosper\\//
 
Join Date: Jul 2012
Location: scranton pa
Posts: 576

VLX - '93 Honda Civic VLX
Team Honda
90 day: 51.1 mpg (US)
Thanks: 55
Thanked 65 Times in 54 Posts
doesnt brucepick have a kammback on his hx? ask him for some advise on how strong his is. its the same generation honda just a 2 door instead of a sedan. maybe he would have good tips on how to make a strong one.
__________________
Burn lean and prosper \\ //
  Reply With Quote
Old 05-22-2013, 11:38 PM   #97 (permalink)
Not Doug
 
Xist's Avatar
 
Join Date: Jun 2012
Location: Show Low, AZ
Posts: 10,755

Chorizo - '00 Honda Civic HX, baby! :D
90 day: 35.35 mpg (US)

Mid-Life Crisis Fighter - '99 Honda Accord LX
90 day: 33.43 mpg (US)

Gramps - '04 Toyota Camry LE
90 day: 33.15 mpg (US)
Thanks: 7,021
Thanked 2,007 Times in 1,531 Posts
Quote:
Originally Posted by slownugly View Post
doesnt brucepick have a kammback on his hx? ask him for some advise on how strong his is. its the same generation honda just a 2 door instead of a sedan. maybe he would have good tips on how to make a strong one.
He built a short one and tuft-tested it and tried a long one and removed it. I do not know what improvement he saw on the short one.
  Reply With Quote
Old 05-28-2013, 12:11 AM   #98 (permalink)
Cyborg ECU
 
California98Civic's Avatar
 
Join Date: Mar 2011
Location: Coastal Southern California
Posts: 6,297

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
Thanks: 2,373
Thanked 2,155 Times in 1,463 Posts
Quote:
Originally Posted by christofoo View Post
When I tuft test, I'm expecting to see the roof-to-rear-windshield radius pull the airflow down, a little turbulence at the base of the windshield followed by a lot of horizontal air-flow along the trunk line to the lid transition, where it will fall apart at the sudden ~19 drop.
Agree with this prediction and Palemelanesian's affirmative. Here is my pic of tufts pasted to the body of my civic on a damp morning after a ride reaching sustained 45-50 mph speeds: http://ecomodder.com/forum/member-ca...sting-tail.jpg

__________________
See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.



  Reply With Quote
The Following User Says Thank You to California98Civic For This Useful Post:
PaleMelanesian (05-28-2013)
Old 05-28-2013, 10:35 AM   #99 (permalink)
Hypermiler
 
PaleMelanesian's Avatar
 
Join Date: Dec 2007
Location: Texas
Posts: 2,320

PaleCivic (retired) - '96 Honda Civic DX Sedan
90 day: 69.2 mpg (US)

PaleFit - '09 Honda Fit Sport
Team Honda
Wagons
90 day: 44.06 mpg (US)
Thanks: 611
Thanked 428 Times in 280 Posts
2nd opinions are always welcome!
__________________



11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles
  Reply With Quote
Old 05-31-2013, 02:45 PM   #100 (permalink)
EcoModding Apprentice
 
Join Date: Oct 2012
Location: United States
Posts: 110
Thanks: 0
Thanked 5 Times in 5 Posts
So more cargo room in the back, won't that raise the front a little ( or a lot )? If that happens have you looked into ways to keep the car leveled as if there was no extra cargo in the back?

  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com