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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 12-16-2008, 02:11 AM   #1 (permalink)
EcoModding Apprentice
 
Join Date: Sep 2008
Location: Australia
Posts: 109
Thanks: 1
Thanked 5 Times in 5 Posts
Kamm back speed at which it starts to work?

Kamm back speed at which it starts to work?
I used to have a book that gave a guide to the speed at which the airflow held its shape, but I have misplaced it.
Any references online etc.

Cheers

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 12-16-2008, 01:31 PM   #2 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 12,634
Thanks: 20,298
Thanked 6,282 Times in 3,888 Posts
speed

Quote:
Originally Posted by Geebee View Post
Kamm back speed at which it starts to work?
I used to have a book that gave a guide to the speed at which the airflow held its shape, but I have misplaced it.
Any references online etc.

Cheers
The coefficient of aerodynamic drag for your car is fixed,and remains constant,once up to about 20-mph ( 33 km/h ),and the experts now say that aero drag is significant by 35-mph ( 56 km/h ).
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 12-16-2008, 02:56 PM   #3 (permalink)
Pokémoderator
 
cfg83's Avatar
 
Join Date: Dec 2007
Location: Southern California
Posts: 5,864

1999 Saturn SW2 - '99 Saturn SW2 Wagon
Team Saturn
90 day: 40.49 mpg (US)
Thanks: 439
Thanked 528 Times in 355 Posts
aerohead -

Quote:
Originally Posted by aerohead View Post
The coefficient of aerodynamic drag for your car is fixed,and remains constant,once up to about 20-mph ( 33 km/h ),and the experts now say that aero drag is significant by 35-mph ( 56 km/h ).
Since I think most cars spend the majority of their time above 30 MPH, would it be safe to say that aero-mods "always help", but that the return, the "bang for the buck", is better above 35 MPH? I keep thinking there's an "economy curve" that would slope up and apex around 55 MPH, and then start to slope down with diminishing returns. Orrrrrrrrr, would the apex of the curve change as a function of the Cd (aka basjoos)? Kind of a BSFC for each Cd.

CarloSW2
__________________

What's your EPA MPG? Go Here and find out!
American Solar Energy Society
  Reply With Quote
Old 12-16-2008, 04:04 PM   #4 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 12,634
Thanks: 20,298
Thanked 6,282 Times in 3,888 Posts
apex

Quote:
Originally Posted by cfg83 View Post
aerohead -



Since I think most cars spend the majority of their time above 30 MPH, would it be safe to say that aero-mods "always help", but that the return, the "bang for the buck", is better above 35 MPH? I keep thinking there's an "economy curve" that would slope up and apex around 55 MPH, and then start to slope down with diminishing returns. Orrrrrrrrr, would the apex of the curve change as a function of the Cd (aka basjoos)? Kind of a BSFC for each Cd.

CarloSW2
I think the low speeds are a"wash" for aero,and emphasize to people that I meet, that my mods are virtually useless around town.So yeah,I think they really begin to shine at the higher velocities.------------------ The thing about the "apex" is that as one continued to streamline towards the ultimate,say Cd0.11-12.that you could push that curve up,forestalling the effects of the air.---------- The whole premise of CAR and DRIVER's "Crisis-Fighter-Pinto" was,leave the 70-mph speed-limit alone,and streamline the cars so the achieve the same mpg at 70,they then achieved at 55.----------------------- With the T-100,I've got data from 45-mph(72km/h),to 80 mph(129km/h),and the speed/mpg plot is pretty linear.The best mpg is at 72 km/h (39-mpg),it falls to (36.5 mph) at 88 km/h,and by 120 km/h she's down to 32-mpg.The jump to 129km/h costs a whole mpg.It's not legal to test at higher speeds so I'm stuck.Best mpg should occur in the 35-40 mph range (56-64 km/h) but it's not safe for me to attempt steady-speed driving at those kinds of velocities to check mpg ( no scan-gauge!).These lower speeds will always remain the domain for best mpg but I can't imagine the highway motorist surrendering to such speeds.So in the meantime,the mods will help.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 12-16-2008, 04:04 PM   #5 (permalink)
TacoModder
 
mobilerik's Avatar
 
Join Date: Nov 2008
Location: San Diego, CA
Posts: 108

rik's prerunner - '03 Toyota Tacoma Prerunner Double Cab TRD 4A
90 day: 29.68 mpg (US)
Thanks: 0
Thanked 2 Times in 1 Post
Speaking of... In which direction does the BSFC curve shift/stretch as a result of a decrease in Cd?
  Reply With Quote
Old 12-16-2008, 04:07 PM   #6 (permalink)
EcoModding Apprentice
 
CobraBall's Avatar
 
Join Date: May 2008
Location: North Texas
Posts: 112
Thanks: 0
Thanked 2 Times in 2 Posts
Quote:
Originally Posted by cfg83 View Post
aerohead -
...aero-mods "always help"...
CarloSW2
Kammback creates drag. It doesn't reduce drag.

To make an object stable while in motion, the center of gravity must be forward of the center of pressure. This is true for high speed automobiles, airplanes, rockets or javelins.

Kammbacks are used in Top Fuel Funny Cars for two reasons. 1. to keep downforce or pressure on the rear tires. 2. To increase drag aft of the CG.

In the movie World's Fastest Indian Burt Munro did a stability demo with a pencil, the pencil became stable when the CG was moved forward of the CP. Burt wanted to add weight to the front end of his Indian MC to shift the CG forward of the center of pressure, thus make it more stable.

IMHO, dams, wings, spoilers, kammbacks are "thangs" that are used to overcome bad aero design. Anything and everything that has mass and moves in a fluid creates drag.
  Reply With Quote
Old 12-16-2008, 04:30 PM   #7 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 12,634
Thanks: 20,298
Thanked 6,282 Times in 3,888 Posts
Bsfc

Quote:
Originally Posted by akashic View Post
Speaking of... In which direction does the BSFC curve shift/stretch as a result of a decrease in Cd?
I think at the eco-modding forum there are some BSFC maps which have been posted in the sticky.Hucho gets into this very well,shows the shifts,and how the gearing should be optimized to get the full-monty.Without the graphics we shouldn't even touch this,and we probably should take it over to the general eco-modding page.I don't have my text.From G.W.Carr,"The Development of a Low-Drag Body Shape for a Small Saloon Car",MIRA Report #2,1965, he shows that you can lose up to 45% of the streamlining benefit without gear-matching.------------ That's all I have with me.------------ The engine see's a lower load with streamlining,and will over-rev without the taller gearing,shortening it's life if not self-destructing.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 12-16-2008, 04:39 PM   #8 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 12,634
Thanks: 20,298
Thanked 6,282 Times in 3,888 Posts
kammback

Quote:
Originally Posted by CobraBall View Post
Kammback creates drag. It doesn't reduce drag.

To make an object stable while in motion, the center of gravity must be forward of the center of pressure. This is true for high speed automobiles, airplanes, rockets or javelins.

Kammbacks are used in Top Fuel Funny Cars for two reasons. 1. to keep downforce or pressure on the rear tires. 2. To increase drag aft of the CG.

In the movie World's Fastest Indian Burt Munro did a stability demo with a pencil, the pencil became stable when the CG was moved forward of the CP. Burt wanted to add weight to the front end of his Indian MC to shift the CG forward of the center of pressure, thus make it more stable.

IMHO, dams, wings, spoilers, kammbacks are "thangs" that are used to overcome bad aero design. Anything and everything that has mass and moves in a fluid creates drag.
The Kammback citing may have been used in the context of separation-free flow up to the point where the car body was chopped off.And with Cd0.37,the K-cars were remarkably "cleaner" than their contemporaries.And yes,the K-cars did have cross-wind stability problems.The up-shot is that Dr.Morrelli solved that one back in the 1980s,so we're better protected from those challenges.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 12-16-2008, 04:51 PM   #9 (permalink)
Master EcoModder
 
Join Date: Jul 2008
Location: Silly-Con Valley
Posts: 1,437
Thanks: 182
Thanked 234 Times in 180 Posts
Quote:
Originally Posted by akashic View Post
Speaking of... In which direction does the BSFC curve shift/stretch as a result of a decrease in Cd?
BSFC only has to do with the engine. Aerodynamics does not effect it whatsoever. It affects how much power it takes to cruise at a given speed, so it affects where on the BSFC map you fall at a given time, but it does not change the map in the slightest.

-soD
  Reply With Quote
Old 12-16-2008, 05:06 PM   #10 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 12,634
Thanks: 20,298
Thanked 6,282 Times in 3,888 Posts
aero/BSFC

Quote:
Originally Posted by some_other_dave View Post
BSFC only has to do with the engine. Aerodynamics does not effect it whatsoever. It affects how much power it takes to cruise at a given speed, so it affects where on the BSFC map you fall at a given time, but it does not change the map in the slightest.

-soD
Hucho claims in his text that should a person streamline their car,that the road load can shift so far,as to knock the engine out of it's island of highest BSFC.The car will also overspeed,and if the gearing is not changed such that the engine "see's" the same load as before the streamlining,then MPG potential from the drag reduction can suffer up to 60%.

__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Optimum piston speed? Frank Lee EcoModding Central 75 02-22-2016 04:50 PM
How to get instant fuel consumption from Megasquirt TELVM Instrumentation 11 08-29-2011 02:47 PM
[aero-mods(aft-body streamlining/boat-tails)Part-3 History/Timeline cont'd aerohead Aerodynamics 10 08-13-2010 12:50 AM
will bicycle speedo work as speed sensor for MPGuino? modmonster OpenGauge / MPGuino FE computer 2 08-28-2008 05:55 PM
Basic EcoDriving Techniques and Instrumentation SVOboy Instrumentation 2 11-17-2007 11:38 AM



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