MEGA metro airdam - Fuelly Forums

Click here to see important news regarding the aCar App

Reply
 
Thread Tools Display Modes
 
Old 07-30-2007, 04:41 AM   #1
Registered Member
 
jwxr7's Avatar
 
Join Date: Jan 2007
Posts: 291
Country: United States
MEGA metro airdam

Check out some pics in my garage of the airdam I put on sunday. http://www.gassavers.org/garage/view/272
What do you think?
I have seen alote of talk on airdams lately, so i decided to give it a try. I was going to use lawn edging at first but decided to go with coroplast for a more rigid installation (plus I have plenty of coroplast lying around), and I could pick any height. I cut the 7" tall strip with my tablesaw, sure beats a razor cutter . It is about 3.25" off the ground. It rubbed once on the way to work this morning when i crossed railroad tracks too fast. I need to point it like a cow pusher only for roadkill .
I just hope it helps my aero instead of hurting it. I will attempt some coast down testing someday soon hopefully.
__________________

__________________
Best tank= 81.23 mpg on july 1st 2008
SAVE SOME GAS, SAVE THE WORLD!

jwxr7 is offline   Reply With Quote
Old 07-30-2007, 05:01 AM   #2
Member
 
Join Date: Jun 2011
Posts: 49
Country: United States
Location: FL
I'll be interested to see the results. An air dam is a compromise, it's not going to help unless the increase in frontal area produces less drag than the underside of your car did. I don't know what the underside of your metro looks like, but I suspect that it's pretty draggy under there, being that you don't have a full undertray. I was looking into an air dam similar to yours for my civic, but I'm planning on a full undertray now because it's not going to be as prone to damage.
__________________

varg is offline   Reply With Quote
Old 07-30-2007, 05:10 AM   #3
Registered Member
 
Join Date: Mar 2007
Posts: 1,138
Country: United States
Sweet.

Flat black paint is your friend...
__________________
Bill in Houston is offline   Reply With Quote
Old 07-30-2007, 05:11 AM   #4
Registered Member
 
jwxr7's Avatar
 
Join Date: Jan 2007
Posts: 291
Country: United States
Yeah, a compromise it is . I think I would prefer an undertray but that would be harder for me to do. All the coroplast i have is in precut strips 17" x 74" so no large sheets. They are longer than the car is wide at least, so i could piece something together in strips.
__________________
Best tank= 81.23 mpg on july 1st 2008
SAVE SOME GAS, SAVE THE WORLD!

jwxr7 is offline   Reply With Quote
Old 07-30-2007, 05:24 AM   #5
Registered Member
 
Join Date: Jun 2007
Posts: 61
Country: United States
Send a message via Yahoo to GasSavers_BMac
Nice, I used that house trim at HD. It was 5/16" thick and very rigid but it will snap before it bends too far. Requires a big radius bend.

Where abouts are you in Michigan?
__________________
1998 Dodge Dakota Sport 5.2 auto,
Aero Cap,
Cam advanced 4 degrees,
MSD 6TN,
MSD Blaster2 Coil,
MSD 8.5mm SuperConductor wires,
Borg-Warner cap & button
Halo plugs,
PCV jar
and more to come...
GasSavers_BMac is offline   Reply With Quote
Old 07-30-2007, 05:30 AM   #6
Registered Member
 
jwxr7's Avatar
 
Join Date: Jan 2007
Posts: 291
Country: United States
Quote:
Originally Posted by Bill in Houston View Post
Sweet.

Flat black paint is your friend...
Thanks, i actually ran out of my normal black gloss paint part way thru so i finished over it with my hi temp stove paint. It matches the bumper plastic much better.

Quote:
Where abouts are you in Michigan?
I'm near Leslie (1/2 way between jackson and lansing).
__________________
Best tank= 81.23 mpg on july 1st 2008
SAVE SOME GAS, SAVE THE WORLD!

jwxr7 is offline   Reply With Quote
Old 08-01-2007, 11:56 AM   #7
Registered Member
 
jwxr7's Avatar
 
Join Date: Jan 2007
Posts: 291
Country: United States
tested airdam

Well I did some coast down testing last night. I did them on a mile stretch of road near home. It is pretty flat in the middle where I was coasting, unfortunatly there were stop signs at each end so i had to accelerate pretty hard then end up braking at the other end. So the test was a bit wasteful on gas . I did bi-directional north/south runs so I could use the data for drag coefficient calculations and stuff. It wasn't A-B-A, just A-B unfortunately. I taped the speedo with a vid cam and watched it back w/ stopwatch. I timed speed between 55 and 45 mph (55 and 50 for Cd calcs). Conditions were 93 F (33.89 C), 30.03" hg pressure, 3 mph E NE winds, test mass estimated 1991 lbs (903.1 kg).

To find Cd I needed to remove the rolling resistance from the road load forces to single out the aero part. I didn't do a low speed coast down like I was suposed to because I wasn't sure I could rely on my speedo at those speeds. So instead I measured the force needed to roll the car at a fixed low speed on level concrete. I did bidirectional pulls that averaged out to 10.62 lbs. The comes out to .00586 rolling resistance (10.62lbs/1812lbs car weight without me in it). That seemed aweful low to me, but I did the test on smooth concrete not the road surface I did the other test on. I decided to double that # for the road surface to .0117 which seems more on par for LRR tires. I had to estimate frontal area too, the book I was using gave a formula to estimate it (.9 x height x width of the vehicle). Of course I wanted to try my own estimate by Analyzing a scaled down front view picture of the car and finding frontal area that way. With my frontal area estimate Cd came out to .327 without the airdam and .315 with it. Using the books area formula Cd came out to .260 for no air dam and .251 with it. Remember the rolling resistance is an estimate too so the relative results are all I'd go by not the actual values. Too many estimates = who cares.

Cut to results... Coast down time averaged 16.0 seconds with airdam and 16.3 seconds from 55- 45 mph without. In the 55-50 coast down range the airdam average acceleration was -.2846 m/s^2 and .2800 m/s^2 with out. So the airdam didn't help by a small margin. I probably made it too big. All else being equal, the drag coefficient did improve with the airdam by .01 ish but it did not make up for the added frontal area as seen with the acceleration rates.
I will probably shave off at least 2-3 inches and put it back on. It rubbed too much anyway, it plowed gravel pretty bad coming into my driveway .

Disclaimer... These are results from a newbe tester using Cd formulas out of a book called "propulsion systems for a hybrid vehicle", I probably did it the hard way
__________________
Best tank= 81.23 mpg on july 1st 2008
SAVE SOME GAS, SAVE THE WORLD!

jwxr7 is offline   Reply With Quote
Old 08-01-2007, 12:05 PM   #8
Registered Member
 
brucepick's Avatar
 
Join Date: Feb 2007
Posts: 722
Country: United States
Location: Connecticut
(shameless self-promotion here)

See my recent thread on coroplast construction - especially re. attaching a belly pan to the coroplast air dam. Mine is really holding up nicely now.
__________________
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 08-01-2007, 12:20 PM   #9
Registered Member
 
jwxr7's Avatar
 
Join Date: Jan 2007
Posts: 291
Country: United States
Yes, nice idea with the corner bead .

A much smaller better shaped air dam or just good undercarriage smoothing is probably in my future.
__________________
Best tank= 81.23 mpg on july 1st 2008
SAVE SOME GAS, SAVE THE WORLD!

jwxr7 is offline   Reply With Quote
Old 08-01-2007, 12:46 PM   #10
Registered Member
 
Join Date: Mar 2007
Posts: 1,138
Country: United States
Quote:
Originally Posted by jwxr7 View Post
I taped the speedo with a vid cam and watched it back w/ stopwatch.
Nice work. On digital video if you put it into your computer you can use the time stamp for each frame as a way to calculate the time elapsed. If yours was digital... Just a thought.

I am hoping that the next generation of ScanGuage will have a way to store data. Then the coast-down data could be logged on that, and it would take the time measurement error out of the equation.

Anyway, good job, and thanks for posting.
__________________

__________________
Bill in Houston 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
Stupid Idea landspeed General Fuel Topics 5 02-28-2007 08:40 PM
Love this place! brelandt Introduce Yourself - New member Welcome 7 01-01-2007 09:02 AM
Cardboard box + duct tape = LxMike Aerodynamics 18 11-18-2006 10:53 AM
best milage WITH bike on back :) argylesocks General Fuel Topics 7 09-25-2006 07:08 PM
p07 ECU $15 Matt Timion For Sale 4 08-27-2006 11:25 AM

» Fuelly iOS Apps
Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 11:59 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.