Aero improvements....what's really practical? - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Go Back   Fuelly Forums > Fuel Talk > Aerodynamics
Search Today's Posts Mark Forums Read Click Here to Login
Reply
 
Thread Tools Display Modes
 
Old 06-12-2007, 09:03 AM   #1
Registered Member
 
SL8Brick's Avatar
 
Join Date: Jun 2007
Posts: 180
Country: United States
Aero improvements....what's really practical?

Hi everyone....I'm kind of new here and still trying to get a grip on things, so please bear with me. I'd also like to clarify that automotive background is in the performance field, so my approach regarding aerodynamics has always been "performance 1st"....but I'm willing to change.
I've been sifting through the mountain of info here and I continue to come up with the same question: What's really practical when it comes to aero mods? And where should we draw the line between the potential sacrifice of safety for overall efficiency?
For example: Boat-tailing....I'm beginning to understand the design benefits. Please correct me if I'm wrong here, but doesn't the shape of the boattail induce neutral flow characteristics to achieve efficiency? As opposed to a drag inducing, mildly spoiled rear end which has the potential to create usable downforce.
I'd like to cite an example from auto racing history. During the 1950's some auto mfgrs designed race cars with neutral aero efficiency(ie:Jaguar C-type, Alfa Romeo Discovolante(sp?)). Both vehicles were rather competitive in thier respective classes, but were almost completely void of downforce and lacked the outright handling necessary to be dominant. And later designs from these mfgrs often swayed away from the neutral lines in exchange for more aggressive surfaces with downforce/lateral stability benefits.
I've always been under the assumption that you don't have to drive a racecar to benefit from aero mods. If I were driving @ 75mph(legally) on an open highway in 40mph crosswinds or 55mph through twisting roads on a mountain pass, I'd much rather have a small rear spoiler than a large boattail.
There are more obvious mods that could widely be considered less practical(ie:wiper/ext.mirror delete).
What are some genuine opinions regarding this subject?

Thanx, SL8Brick
__________________

__________________
1993 Volvo 240 Wagon - 323k miles (awaiting recommissioning)
1999 Audi A6 Avant Quattro - 149k miles(the NEW daily driver)
SL8Brick is offline   Reply With Quote
Old 06-12-2007, 09:20 AM   #2
Registered Member
 
brucepick's Avatar
 
Join Date: Feb 2007
Posts: 722
Country: United States
Location: Connecticut
I think its a matter of what you're trying to achieve with your aero project.

My mechanic buddy drives a car nearly identical to mine however with an intercooled turbo, and larger turbo + i/c to be installed soon. When he saw my front air dam extension he immediately wanted to mold a copy in fiberglass HOWEVER he wanted me to give it a forward-sloping front surface to create downforce.

However creating downforce from aero flow will tax some of your forward motion energy. It's not free. So my version of the air dam has a near-vertical front, and his version will have a slanted front. He does need the downforce since he takes 75+ mph curves fast enough to lift the inside front wheel.

I don't drive my car hard enough to need the extra downforce. I have heavy duty sway bars and 205 tires vs. the oem 185's so that's enough for the handling and traction I need.

Volvo 240s reportedly have a c/d of about .40 which is very high. My 240 really didn't "glide" (coast) until I got the air dam + forward belly pan done. It would just start slowing down seriously, even on downgrades on 65 mph limited access state roads. With the dam + pan done it glides much better, and on a steep enough hill will maintain or gain speed. It's all a matter of what your priorities are.
__________________

__________________
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
brucepick is offline   Reply With Quote
Old 06-12-2007, 11:31 AM   #3
Registered Member
 
Join Date: May 2007
Posts: 163
Country: United States
Quote:
Originally Posted by brucepick View Post
I think its a matter of what you're trying to achieve with your aero project.

However creating downforce from aero flow will tax some of your forward motion energy. It's not free. So my version of the air dam has a near-vertical front, and his version will have a slanted front. He does need the downforce since he takes 75+ mph curves fast enough to lift the inside front wheel.
Same here with the air dam. My purpose was to direct air from under the vehicle, which it does rather nicely as well as around the front tires.

One note for you to file away. With the side skirts, I lose almost no efficiency in heavy cross winds.
__________________


Proud owner of Stinkerbutt!
[SIGPIC][/SIGPIC]
-Air Raid cone filter, direct to TB
-Homebrew front air dam
-Homebrew side skirt
-Torza top bed cover
-Now featuring front wheel canards!
kitcar is offline   Reply With Quote
Old 06-12-2007, 04:53 PM   #4
Registered Member
 
Join Date: Mar 2007
Posts: 1,138
Country: United States
A boattail will have lower drag. If lift becomes a problem, then you might have to think about priorities.

Since the boattail extends from the rear, it will tend to point a car into a crosswind, which might actually help self-correct.

That's about all I have to say about that. :-)
__________________
Bill in Houston is offline   Reply With Quote
Old 06-12-2007, 06:21 PM   #5
Tuggin at the surly bonds
 
Silveredwings's Avatar
 
Join Date: Apr 2006
Posts: 839
Country: United States
Thanks Forrest. 'course I'm an excellent driver.
__________________
Reality is merely an illusion, albeit a very persistent one. - Albert Einstein
Silveredwings is offline   Reply With Quote
Old 06-13-2007, 11:07 AM   #6
Registered Member
 
SL8Brick's Avatar
 
Join Date: Jun 2007
Posts: 180
Country: United States
Quote:
Originally Posted by Bill in Houston View Post
A boattail will have lower drag.
I agree wholeheartedly, Bill.


Quote:
Originally Posted by Bill in Houston View Post
If lift becomes a problem, then you might have to think about priorities.
And that's kind of my point.....lift can almost always be a problem. Even in everyday driving situations.

Take for example the Audi TT(2000-2006): When the 2000my TTs first hit the US streets in 1999, the rear spoiler was optional and Audi even offered a OE roofrack set-up for the coupes. When the drivers of the spoilerless TTs began complaining in mass about eratic handling charachteristics(especially during high speed cornering), Audi issued a recall which offered a free spoiler to any spoilerless TT owner(Audi also had a waiver to sign for any owner that rejected the spoiler). Simultaniously, the spoiler became standard equipment on all later production models. Realizing the sensative aerodynamics of the car, Audi also discontinued all OE roofrack components for the TT coupes(much to the shegrin of many customers).
__________________
1993 Volvo 240 Wagon - 323k miles (awaiting recommissioning)
1999 Audi A6 Avant Quattro - 149k miles(the NEW daily driver)
SL8Brick is offline   Reply With Quote
Old 06-13-2007, 11:18 AM   #7
Registered Member
 
MetroMPG's Avatar
 
Join Date: Dec 2005
Posts: 4,223
Country: United States
I wonder how much of an issue this is for people who are driving for fuel economy (ie. who tend not to drive fast).

TT drivers losing it at autobahn speeds (whether or not they're actually on an autobahn) don't really ring alarm bells on the issue of aero mods for economy, personally.
MetroMPG is offline   Reply With Quote
Old 06-13-2007, 01:14 PM   #8
Registered Member
 
SL8Brick's Avatar
 
Join Date: Jun 2007
Posts: 180
Country: United States
Quote:
Originally Posted by MetroMPG View Post
I wonder how much of an issue this is for people who are driving for fuel economy (ie. who tend not to drive fast).

TT drivers losing it at autobahn speeds (whether or not they're actually on an autobahn) don't really ring alarm bells on the issue of aero mods for economy, personally.
Point taken.....thanx for the reply!
__________________
1993 Volvo 240 Wagon - 323k miles (awaiting recommissioning)
1999 Audi A6 Avant Quattro - 149k miles(the NEW daily driver)
SL8Brick is offline   Reply With Quote
Old 06-15-2007, 11:31 AM   #9
Registered Member
 
Join Date: Feb 2007
Posts: 104
Country: United States
Most production cars produce lift at speed, not downforce. Cars like Ferrari, the TT, Corvette, etc are the exception.

Regarding the boattail, I think you could design a boattail with neutral lift characteristics or with positive or negative if desired. The primary way the tail works is by reducing the cars turbulent wake.

Downforce does not have to come from a F1 type wing though. F1 racers take the extra drag because they also have lots of power and the higher cornering speeds are to their benefit while they do not care as much about FE. Diffusers, splitters, and similar devices are used in many other race cars to generate downforce. Spoilers like on the back of NASCARs can also be used to tuned to reduce drag while also adding downforce.

FWIW, my butt-o-meter says that my LeBaron feels more solid on the highway with a gille block and filling the gap between the body and the bottom of the bumper cover. My FE is also better than ever.
__________________

__________________


GasSavers_BluEyes is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Trying to add a car bw61374 Fuelly Web Support and Community News 1 08-17-2013 08:14 AM
SMS banner. DTMAce Fuelly Web Support and Community News 3 03-08-2010 10:56 PM
Some hypermiling techniques illegal in my state! theclencher Hypermiling 57 08-06-2007 02:17 PM
If you're jealous of Matt, (or have 56k) don't look here. bagpipe goatee General Discussion (Off-Topic) 8 11-15-2005 07:24 PM
Search feature added Matt Timion Fuelly Web Support and Community News 1 09-26-2005 03:02 PM

Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 05:45 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.