Metro aerodynamics [ Archive] - GasSavers.org - Helping You Save at the Pump

'95 Metro LSI ...

I was under mine last weekend looking at that. Thought it would be easy until I crawled under...EEEEEoWQWWWWW! Not an easy one. That exhaust sure throws a curve ball at ya.
Still pondering how I am going to do it, so maybe I can learn from your trial/error/success.

Looking at the back, wonder how much drag the rear bumper cover is causing by hanging down so low. Do you thing a rear bumper modification, with a more upswept under pan would help?

Do you thing a rear bumper modification, with a more upswept under pan would help?absolutel

At the junkyard I saw a Metro with a body kit... do you want me to get it for you?

It's primer grey... my favorite color :)

Matt, what year(s)? 89-94 2dr? would be seriously interested in some pics...been thinking about some side skirts too.

Matt, what year(s)? 89-94 2dr? would be seriously interested in some pics...been thinking about some side skirts too.

I'll snap some pictures today and find out.

i suspect it's an 89-94 swift GT. you can sell those body add-ons on the teamswift site also. they had different bumpers, rocker panel skirts and sometimes a rear hatch spoiler.

suspect it's an 89-94 swift GT. you can sell those body add-ons on the teamswift site also.

Any idea how much they go for? Is it worth my while? Will I make a handsome profit?

hatch midwing - 125 ish (not same as roof level wing)
rocker skirts - 125-175 ish? saw one set on ebay for 225+

http://www.teamswift.net/viewforum.php?f=15

browse to your heart's content...

hatch midwing - 125 ish (not same as roof level wing)
rocker skirts - 125-175 ish? saw one set on ebay for 225+

http://www.teamswift.net/viewforum.php?f=15

browse to your heart's content...

Nice... I will hit the junkyard today with the camera.

Found a guy who will sell used F & R bumper covers, side skirts and rear spoiler for 175 CDN. Don't know if he will ship to me or not yet, waiting to hear back from him.

Color matches my car to boot! :)

The body kit was gone... how sad.

I wonder if you could find a junked Honda Insight and get some underbody panels from it that you could modify to fit under the Metro.

I wonder if you could find a junked Honda Insight and get some underbody panels from it that you could modify to fit under the Metro.

I would cry with joy if I found a junked honda insight :)

I don't know if they'd fit other cars though.

Thanks for checking anyway. Hope this guy will ship.

Hey matt...found a wrecked insight last weekend when I was 'junking'. Can PM you the name and number of the yard if you want...deal specifically in late models...sure they know what they have.

It's pointless in getting under panels from an Insight. The best solution is to do your own.

I wonder if you could find a junked Honda Insight and get some underbody panels from it that you could modify to fit under the Metro.

Provided the body is in good shape, it's best possible application would be a conversion to electric. Battery room out the ***...

A 336V pack of Optima Yellowtops and a 107 horsepower Siemens motor/inverter setup would yield ~120 miles range at 65-70 mph(Or about 180 miles range at 55 mph), 0-60 mph in ~8 seconds, and top speed around 150 mph. Would cost roughly $20,000 to do.


But why go through all that effort and part with all that cash trying to get an Insight undertray, when for much cheaper you could make your own?

aero mod updates:

some photography of interest:

Awesome Metro! Cant wait for the results. :)

cardboard rear undertray

well, screwed up the

in hindsight, i should have just re-attached the rear tray and done another run before pulling them all off.

to be honest, it didn't occur to me that it might have been hanging down the whole time affecting all the undertray runs until after i had removed them all.

big, self-administered dope-slap

Don't worry yourself too much, you have proven to use that coroplast is the stuff to use, :)

i did 2 bi-dir "naked" runs for comparison, which produced very similar numbers:.

Isn't "streaking" illegal up yonder? Even if it isn't, it's a bit cold outside to run naked, isn't it?

I'm hoping that your tray was hanging the whole time. I had a 57 MPG bi-directional run at 55 ave speed, and that was with my spare 4th cylinder along for the ride. :)

It was 25F warmer outside though and I was using constant throttle, bleeding off speed uphill and gaining speed downhill. Hmmm. Maybe not a fair comparison to holding 55.

Just got back from picking up my Coroplast!!! I'm excited 'cause I only paid $9.25 for each 4x8 sheet. The real kicker is that the vinyl supply company I purchased it from has multiple colors available. White, Off-White, Green, Yellow, etc. I got it in black so I wouldn't have to deal with painting it. Yeah, no overspray...not that it would matter, the paint on my car is pretty much 'dead' anyway. Going to check the weather for tommorow (day off), maybe get it done.

***What kind of hardware/screws did everyone use for installation? Just self tappers or did you drill holes?***

Self tappiung screws with predrilled holes when screwing into plastic or steel. Use washers to keep the head from pulling through. For coroplast to coroplast I used coarse thread drywall screws. They hold the coroplast well. After a week my coroplast is secure. Nothing has losened up.

Just completed cutting and fitting my rear tray. Thought I would start in back where the panel is smaller so I get used to working with the coroplast. Am planning on tucking the panel up above my rear bumper lip (nice and clean), but I need to get some different hardware 1st.

My question for anyone/everyone is...would it benefit the aerodynamics of the vehicle if I attached it under the rear bumper cover and let some stick out the back? I'm not worried about the looks of the vehicle, so if it had a 3" lip of coroplast sticking out the back would this direct the airflow more efficiently? Lower the drag? Thoughts?...

not that I know much but that seems very streamlined. I think thats a beneficial aero way to do it. Deleting that lower bumper lip like you describe with the overlap, I think thats a great idea.

i would do it, xfi. when i did my car, there was a slight upslope to the rear tray just from the way things were laid out. so it would make sense to keep that upslope going right on past the bumper if you're ok with how it looks.

i may do something similar when i do my permanent version.

but i haven't played with my undertray since last week's aborted test. i've been preoccupied with the forkenswift lately. i'll try again in the next week or so for another comparison run.

i've been preoccupied with the forkenswift lately.

Forkenugen!

hoo ha. that's funny.

we toyed with the idea of doing a vw rabbit pickup conversion (there's one sitting in someone's back yard not too far away). we could have called it a forkenugen!

Don't ruin a perfectly good Rabbit like that!

You know what I'd do with a Rabbit pickup? Aeromod that thing to hell like Phil Knox's truck, install LRR tires, synthetic transmission oil, adjust to a 0/0/0 alignment, correct all brake drag, load the *** end up with 2,500 pounds of flooded lead acid batteries, install an 11" Kostov motor and Zilla 1k. Basically, for $8-10k, you could make a 150-200 mile range electric truck that tops 110 mph and does 0-60 mph in 16 seconds(slow, but able to hold its own against a Diesel VW Rabbit), 0-30 mph like a Ferrari(fun for around town in this regard, blow off Corvettes. Just hope you scare them off so they don't blow your doors off when you run out of go after 2-3 seconds of tire smoking. Add more expensive sealed batteries and Zilla 2k if you really do want it to keep on pulling, which adds $5,000+ to the cost). And you wouldn't have even touched advanced batteries or weird voodoo AC motors and **** like that.

To make a 20 mile range 30 mph commuter out of it would be a waste of a perfectly good truck. So much potential. Similar trucks have been made without aeromods, and have gotten 100 miles range at 60 mph, 80 mph top speed, for roughly $8-10k. So the next logical extension for maximizing range and top speed is to make the design more efficient, and I don't know anyone that's tried a severe body makeover for drag reduction. Reducing drag coefficient from .45 to .25 would theoretically double the range! In practice, it might be more around 50% more. Who knows.

If I had the cash and wasn't tied to my current project, I'd try it!

Finished the rear tray. It sticks out the back about 5". The way I installed it (so it wouldn't 'scoop' air) is flat. No angle up at all.

Thinking about finding a rear bumper cover from a swift gt (still trying to get some reasonable shipping from the one I found) and relocating my license plate upward inbetween the lights. Then cutting the rear bumper cover and angle the coroplast upward. Don't want to hack up this one, the license plate would be in the way anyway.

On another note-purchased a rear hatch from a 'U PULL IT' yard. Happens to be white (and off an XFi) to match my car. Removed the rear glass from it then stopped by a custom marine upholstery shop. I explained to him I would like a 'canvas' rear cover and zip out window in the back. Scheduled an appt for the week of May 8th. I figure this will lighten my vehicle and provide excellent flow through ventilation in the summer.(NO A/C). He even has white material to match the car...Nice guy...didn't laugh to much at the request. :)

Seriously impressive. Ask them how many hours it took to fab and then paint them panels?

I'd like to know more about working with sheetmetal for this purpose, if the builder is willing to share.

Those side skirts are hot! very professional looking. I will have to try to make some in the summer.

the guy posted a description

some pics of this weekend's project

wow! that looks great. Almost factory.

I agree... that looks awesome. Makes me drool a little.

OK so where is the DIY? Id like to order a set for the Del Sol. Do you take Paypal?

Yes, very nice indeed.:) How many hours you put into that? I noticed in the pics that you still have your mud flaps on. If you took them off wouldn't that help with the drag also?

OK so where is the DIY? Id like to order a set for the Del Sol. Do you take Paypal?

I'm with this guy. How'd you match the paint? DIY it, brotha!

i'll do the DIY when i'm completely finished.

That grill block is ghetto.

The side skirts look nice. How are they held on? Velcro?

yup, velcro. i decided against drilling thru the sheet metal for fasteners because of rust concerns. i prob could have sealed it properly, but i have a bad habit of doing things the hard way. :(

Yes, very nice indeed.:) How many hours you put into that?

enough that several times i stopped and thought... man, i'm putting way too many hours into this...

including making the prototype/mockup, i'd say probably 3 or 4 hrs. and i have another hr -ish to go to finish the driver's side.

I noticed in the pics that you still have your mud flaps on. If you took them off wouldn't that help with the drag also?

yup. absolutely right. but...

1) the rears serve as a handy attachment point for the skirts, saving having to form a more complex shape at the trailing edge to meet the bumper. so there's that functional reason. plus,

2) it's a black car and gets dirty fast. i decided to make this concession to vanity over aero in order to keep crud off the doors, rockers & rear bumper.

3) they're narrow - barely wider than the tires (155's). though i was sorely tempted to get the big ones with the chrome naked lady silhouette...

I like how you did them wheel skirts. I don't like the velcro, BUT it still does look very slick.

I bet when you finally finish all possible aeromods, you'll be getting 75 mpg... in AMERICAN gallons.

He's already getting low 80s on his test track. Mehbe he'll just never leave it, :p

Yeah, low 80s in imperial mpg.

He still needs a front air dam, lowered ride height, side skirts, shaved door handles, rear diffuser, tapered roof spiler, the list goes on...

The impact of all aero mods on highway mpg would be about 40-50% for most cars, but about 5-10% for city mpg.

After that, it's time for weight reduction, and a fuel efficient but powerful diesel. Say, a 112 hp Opel 1.3 CDTI common-rail turbo-diesel. You'd get 90+ mpg with that and aero mods, and 0-60 mph in 7 seconds... Wouldn't that be a real sleeper? And you'd be able to run it on B100...

No, low 80s in us mpg. He was at like 99.x in IMP because he said, oh so close to the goal.

Wow!

He should be shooting for 100s then...


But on his site, his record run is just over 60 U.S. mpg, unless he needs to update.

I'm going by what he's done in his 7.3 mile test loops in the daily report thread. Today he got 81.x us I believe.

the list goes on...

.... and on... no kidding.

the test loop avg speed is 20 mph, so aero mods have a limited impact there, and the route is pretty optimized (couple of great hills). my main goal is to raise my hwy avg, and aero is the way to go for that.

That boat tail should turn a few heads.

80mpg is crazy. What if you had a tank that was that high. I would of thought it was impossible before i started reading up on fuel economy. Now 40mpg in a hummer wouldn't surprise me.

i cleaned off the old duct tape & cardboard grille block. i have an idea how to do it nicely (have one more krazy karpet left to cut up).

also, i traced the outline of my front wheel well onto newspaper... i see removable highway-only front wheel skirts in my future.

also, i traced the outline of my front wheel well onto newspaper... i see removable highway-only front wheel skirts in my future.

I was actually thinking about fromt covers that were held in place with rubberbands that would allow the wheels to push them out when needed. On the inside of the covers would be a small roller on each side for the tire to push against. But that would be way too funky looking. I think I will stick to things that people won't notice. Heck, I average about 30 MPH so aero mods really won't buy me much.

Can you do A-B-A teesting with and without the wheel covers again? I would like to see that repeated with all four wheels covered.

rubber bands, or a sheet of teflon plastic on the back of the skirt where the tire would contact.

i'll add "wheel skirts: all or nothing" to the things-to-test list. (i'm going to have to quit my work and go into testing full-time.)

i was wondering if there would be some complimentary dynamic in covering all 4 wheels vs. just the rears or just the fronts. e.g. the rears improved FE approx 2.8% at 95 km/h. maybe the fronts will be similar on their own. but maybe the net effect of front + rear skirts will be greater (or less) than simply summing their individual effects.

rubber bands, or a sheet of teflon plastic on the back of the skirt where the tire would contact.

i'll add "wheel skirts: all or nothing" to the things-to-test list. (i'm going to have to quit my work and go into testing full-time.)

i was wondering if there would be some complimentary dynamic in covering all 4 wheels vs. just the rears or just the fronts. e.g. the rears improved FE approx 2.8% at 95 km/h. maybe the fronts will be similar on their own. but maybe the net effect of front + rear skirts will be greater (or less) than simply summing their individual effects.

I think the back skirts are effective because they are more likely to disturb an otherwise smooth flow past the wheels than the front ones where air is rushing around the front corner around the front wheels (I certainly will defer to your imperical measurements). My gut intuition tells me that you are much closer to a point of diminishing returns for front wheel skirts as opposed to the bigger drag you're prpbably getting from turbulent air underneath the car. Prefered remedies seem to include lowering the car, a front air dam, and a belly pan (probably in that order). Just a thought.

I think the back skirts are effective because they are more likely to disturb an otherwise smooth flow past the wheels than the front ones where air is rushing around the front corner around the front wheels

your reasoning sounds good

this is why tuft testing would be useful.

Yes, that would be interesting. I assume you're using the poorman's wind tunnel: someone else drive the test car down a multi-lane road while you observe from a chase car. You could video tape it at different driving speeds in real-time and review the tape in playback. You could also more easily compare test runs. If only one side of the car has your mods, you could compare the difference in a single run. What fun. Too bad we have to work. :)

Of course if you have two drivers and a closed course, I've also seen the observer use a smoke generator connected to a long pipe extended by hand from the chase car or pickup truck bed. Maybe too many safety issues to manage though (don't try this out on the road or at high speeds).

I know this thread has been 'asleep' for a month, but I thought that this would be best here.

Check out this 75mpg Metro :) http://www.1989geometro.com/index.html

http://www.1989geometro.com/images/car1.jpg
(Edit: added image)

I know this thread has been 'asleep' for a month, but I thought that this would be best here.

Check out this 75mpg Metro :) http://www.1989geometro.com/index.html

That thing is so freaking cool!

They actually have working front wheen skirts too! Sweet.

all that for 75mpg????

AHAHAHAHAHAHAHAHAHAHAAHA

I'm sorry to **** on the party but 75mpg can be achieved without hacking a car.

Awesome find, XFi - thanks!

XFI - just out of curiosity, how did you come across that page?

all that for 75mpg????

AHAHAHAHAHAHAHAHAHAHAAHA

I'm sorry to **** on the party but 75mpg can be achieved without hacking a car.

Go ahead and show us how then.

XFI - just out of curiosity, how did you come across that page?

Did a search using 'geo metro fuel mileage'. On the first page.

Your site comes up under 'geo metro mpg' :)

Metrompg, and you said it was diffucult to hypermile the metro/swift/fireflea ;)

Go ahead and show us how then.

Darin is already getting 62mpg, but a xfi should get 70mpg with the same mods. I think with some engine tuning and maybe the whole underbody covered it's possible.

What "engine tuning" do you refer to?

Metrompg, and you said it was diffucult to hypermile the metro/swift/fireflea ;)
I know, I know....

I still wonder how you charge the battery with no alternator.

Charging: the last 2 weeks: solar (15W 12V panel). If I drove more often, I'd have to get more solar capacity, or use a charger like XFi is.

...I could see how those 3 things would easily get 75 mpg combined - without using hypermiling techniques.

Just imagine what you could squeeze out of it with technique on top of the mods...

Exactly. :cool:

What "engine tuning" do you refer to?

As in safc2, or e-manage.

Eh, we need some controlled testing on that, for the time being, metro pwns us.

Eh, we need some controlled testing on that, for the time being, metro pwns us.

with better tuning of the timing, some cams, and a/f I could totally see 5mpg on any car.

The newspaper article on his site - it's the Syracuse Herald. Syracuse NY is only about 200 km from here...

That car just rocks. :D

XFi, you get my vote for coolest link of the month.

He could prolly affect FE 20mpg with cams, but mainly bad. The one guy has had success, but I doubt those results are typical.

That is such a neat car! I generally need all four seats in my Metro, but if I was doing long commutes to work I can certainly see the benefit of doing something like this.

I was thinking about those extra seats...

Maybe, for the times you do need them, the right side seats could be accessed by flip-up panels. A return to the old days of rumble seats. Add a removable bubble canopy, and Bob's your uncle.

The builder suggests the best way to do this kind of car is to center the passenger pod. But I think having it off to one side is more practical: he's got a lot of storage space under the right side.

They could offer pickup trucks like this. Tandem narrow box.

Hey Darin...up for a road trip to check it out? Meet you in NY :)

Maybe, for the times you do need them, the right side seats could be accessed by flip-up panels. A return to the old days of rumble seats. Add a removable bubble canopy, and Bob's your uncle.

They could offer pickup trucks like this. Tandem narrow box.

Can you imagine fabricating something like that? What's crazy is that I actually like the idea...:D

As for the pickup trucks I've noticed a construction company in my city that has a number of flatbed delivery trucks with a narrowed cab so longer equipment can be carried on the bed alongside the cab.

Hey Darin...up for a road trip to check it out? Meet you in NY :)

Maybe?

I contacted the e-mail address on the site and got a reply: the site was put up by the guy's son, and I asked him if his dad would be interested in answering questions about the car. He said, yes, he would.

I've already e-mailed him a bunch of questions, but if you've got something you want to know, post it and I'll try to get the answer.

I'm not certain, but I got the impression that the father may not be into computers, so I offered to just phone him if it's easier than playing e-mail relay through his son.

Funny :) I had emailed him too. Got a reply from his son also...keep me updated on any contact. I would SERIOUSLY be interested in seeing this vehicle! If you talk to him 1st, see if he would be up for a visit. A short documentary/link on this vehicle would make a nice addition to your site...

I just noticed that 1989GeoMetro.com is our newest member...hopefully they've found this thread. :cool:

Indeed, i had noticed that as well.

I just saw this thread.

http://www.1989geometro.com/images/18.jpg

I have thought about doing someing like this. Key word "thought".

Talk about hevaly modified. WOW!

Just want to say thanks for all the nice things you guys have been saying about my father’s Aero Car (http://www.1989geometro.com). And no he didn’t turn the car off while driving to get the 75mpg lol. And please don’t forget why we made the website, contact your Senators and tell them to turn up the heat on the automotive makers. We need more cars like this or we will all be riding the bus to work.

We need more cars like this or we will all be riding the bus to work.

Ugh...it would take me an hour to get to work by bus.

Already PM'd you, but let me say again, WELCOME! :)

Just want to say thanks for all the nice things you guys have been saying about my father’s Aero Car (http://www.1989geometro.com). And no he didn’t turn the car off while driving to get the 75mpg lol. And please don’t forget why we made the website, contact your Senators and tell them to turn up the heat on the automotive makers. We need more cars like this or we will all be riding the bus to work.
Yes. I think it's only a matter of time before they start being made. I don't see gas prices going any lower any time soon, which will have all sorts of inflationary effects and serve to increase the real price of fuel even higher.

Congratulations on the awesome car. It would be good if there was some more on how you went about fabricating the different parts of the car so that we might go down the same path, particularly the front wheel skirt.

Cheers!

It would be good if there was some more on how you went about fabricating the different parts of the car so that we might go down the same path, particularly the front wheel skirt.

I agree. I was actually thinking that after all of my projects I might want to get a little car and make it really narrow. That would be an awesome project.

I agree. I was actually thinking that after all of my projects I might want to get a little car and make it really narrow. That would be an awesome project.

Another option for the front wheel skirt might be to make it just like the back skirt, only add a hinge with a spring up near the top. You would then have to attach some sort of apparatus (probably metal rods) to whatever changes the direction of the wheel to steer it, such that it pushed the skirt out of the way before the wheel got there.

Otherwise, a front wheel skirt that goes out as far as it does would have to have a fastback portion on the rear side.

Hawkgt67 (unsure on spelling), tried the hinged model and it flew off!

Hawkgt67 (unsure on spelling), tried the hinged model and it flew off!

yeah I read that too. If it doesn't work on the first try then try it some more.

I just think that the design is too prone to catching wind under it, and I have a feeling that even if it would stay flat I'd hit the off ramp or a curve in the highway and it'd go out and not stop. At 55mph it might take a piece of my fender with it.

I just think that the design is too prone to catching wind under it, and I have a feeling that even if it would stay flat I'd hit the off ramp or a curve in the highway and it'd go out and not stop. At 55mph it might take a piece of my fender with it.

I'm thinking of a design in my head that should work and it will open up thank to the tires but it won't do anything to it. Too bad I suck at drawing.

It involves some magnets and ball bearings.

Well draw it up then, or just do it.

Well draw it up then, or just do it.

I'm too broke to do something of that nature. I think the materials alone will be $100 for both sides.

I'll draw it up later.

here is the design.

http://i32.photobucket.com/albums/d25/Compaq888/wheelskirt.jpg

Compaq888, now THAT is a cool idea, FAR better than mine. Kudos! That's what's so great about forums, you can approach the best ideas so well because everyone can critique and improve upon each other's designs.

With some rare earth magnets (Neodymium Iron Boron (or NdFeb)), it would work perfectly. Any idea for what to use to attach the rod to the skirt? It would be best if it hooked on to the underside of the skirt, that way it wouldn't be visible. Perhaps just welding some sort of disc on top. I have drawn a diagram.

http://i6.tinypic.com/14altsx.jpg
One thing you'd want to do is maximize the distance between the brackets to minimize the play in any other dimensions other than the desired axis of rotation.

Also, I was thinking that some simple rollers would work just as well as ball bearings.

The other thing is, you will want silent rollers, and you also want there to be some sort of force that either acts to return the swivelling skirt to the original position, or at least retards the motion somehow. The last thing you want is it oscillating and banging away in the wind. The magnets would work great - once the tray was remotely near them. But the effective range of magnets is very limited. So either the rod needs to be attached to the skirt with brackets that are tight enough to have a bit of friction, or there should be some sort of spring (or just a length of thin spring steel) attached to the rod to get it to want to recenter after the wheels have gone back to their original position. (Of course, this would all need to be worked out to see if these concerns are valid.)

Of course, the closer the swivelling skirt is to the wheel, the less this would be an issue.

Advantages of the swivelling skirt being close to the wheel:
1. Lower frontal area, the whole purpose of having a skirt in the first place.
2. Less room to oscillate.
3. Skirt is closer to the magnets, so that when it is near the original position, it would bite without any other force necessary.

Advantages of the swivelling skirt being further out:
1. Less use of rollers, and hence less chance of the skirt being anywhere other than aligned where it is supposed to be at speed.

I think the magnets should grabbing at around 20mm.

Unfortunately, you can still see the wheel with full skirts, so it's difficult to get away with the dubious asthetics of pizza trays. Although if you lowered the car, they would be less visible. Spray paint them a matte grey or match the color of the car, it could work better. The trouble with lowering the car is that you might damage your skirts inadvertently. The other thing is, if you already have a full undertray that minimizes drag under the car, why would you even need to bother adding in an air dam to route air somewhere else? It doesn't make sense to me. The only reason after a full undertray that you'd want to lower it would be aesthetics.

Anyway, great thinking and great work.

You could attach a rod to the steering linkage and your green disk so that as you turn the wheel the disk follows. So now no rollers or magnets. This also eliminates road grim, snow, mud, etc. from causing problems with your rollers. What are you going to fill the gap in front of the tire with? This is going to be a big air scoop. However you don't turn the wheels that far at higher speeds so it might not mater.

You could attach a rod to the steering linkage and your green disk so that as you turn the wheel the disk follows. So now no rollers or magnets. This also eliminates road grim, snow, mud, etc. from causing problems with your rollers. What are you going to fill the gap in front of the tire with? This is going to be a big air scoop. However you don't turn the wheels that far at higher speeds so it might not mater.
I think it would be best to allow a little play such that there was no scoop effect unless it was a largish turn, at which point it can be assumed that the car is not going fast enough for the drag hit to matter. Two rods to the steering linkage would work best IMO. Note that these rods are pictured either side. They could be closer together and above the tire, in fact, that would probably work better. The magnets would still be desireable, IMO.

http://i5.tinypic.com/14b2b6t.jpg

That tandem Metro is pretty damn slick.

Ever consider electrifying it? With two seats removed, there is a LOT of battery room and freed up weight to keep you from going over GVWR.

A 1,500 pound pack of lead acid batteries might take that car 150-180 miles per charge at 65 mph. About 2/3 the range of most gas cars.

Okay guys, how about this for some serious aero-mods?

http://www3.telus.net/metro/log/pics/aero1.jpg

I've been drawing this up over the past while to see what the Metro would look like. I think it actually looks pretty cool like this.

The wing would be difficult and would take a lot of testing, but the idea comes from http://www.max-mpg.com/html/tech/main.htm

I'd cruise Sonic in it!

I rather like it.

I figure a Metro's Cd can be brought down to the .25 level. Imagine being able to get 90 mpg highway.

That's pretty cool!

I had a try with my own car. (Apparently the picture I am modifying is of an electric vehicle already! (google image search daihatsu mira should come up with it on the first page)

http://i4.tinypic.com/1622r9y.jpg

Note the skirts, the rear tail (should be tapered on all 3 sides at the same angle, and have a perspex top to retain some visibility), the deflectors. Not visible is the undertray, grille blocking and mirror replacement with camera/screens.

I suppose there is no real reason why you couldn't go all out in extending the boat tail backwards, you'd just have to make some sort of fibreglass canopy for it along with extending some more brake/indicator lights back there. And technically, you could of course extend the tail I have designed to maybe double the original length. It would then become just like a regular car to park, instead of the current park-anywhere capability.

I suppose if a person was really motivated, they could make the sides of the boattail springloaded so that they would spring back against the car if they had the opportunity, and hook up the boattail part to some sort of servo that would extend the middle part out when cruising, retracting it for parking.

It might be possible to get a Cd of 0.25 or less with such a car. You'd have to experiment with instantaneous FE and adjust the angle until you got it right.

Edit: Damn... I think it looks cool! Just had to say that.

For the ultra obsessed, here is the logical endpoint (it's not obvious, but both sides are tapered as well, leading to a tiny rectangle of area behind which there is turbulent flow, approximately 1/4 of the original rear area. I'd estimate that the Cd on this would be below 2.0. There would have to be a note to not store heavy stuff near the end of the boattail.):

http://i3.tinypic.com/16241av.jpg

The wing would be difficult and would take a lot of testing, but the idea comes from http://www.max-mpg.com/html/tech/main.htm

I think you'd need to start the wing at the top of the vehicle for it to work properly, with a gradual slope back. I think the beetle could also have a wing better designed for aerodynamics, but it would hinder rear visibility. I'm surprised they got this good a result to be honest.

It would certainly require lots of testing. You'd probably require a plywood mockup that you could drill holes into, test, then adjust again until it was fine tuned. Then get rid of the plywood and make the real thing.

I'd cruise Sonic in it!

You know, with the aero mods, a 1.6L turbo, and a gutted interior it would probably be a really zippy little race car. Hmm, maybe when I retire it from daily driving one of these days.

I figure a Metro's Cd can be brought down to the .25 level.

That's what it should been designed at. I can't believe it's .34 stock. Even my Aerostar is only .38 (though with 30 sq ft of frontal area).

I think you'd need to start the wing at the top of the vehicle for it to work properly, with a gradual slope back... ...but it would hinder rear visibility... ...You'd probably require a plywood mockup that you could drill holes into, test, then adjust again until it was fine tuned. Then get rid of the plywood and make the real thing.

Yes, I think you're absolutely right on all counts. I think I may do a redesign on the wing and actually turn it into a mini-boattail. It may not be as effective as a full boattail, but I really don't like how the full tails look. I'll sacrifice some aero loss for the sake of aesthetics. The underbelly, skirts, and grill block will probably make enough difference that the losses will be minimal.

Yeah, and I probably will have to do the plywood trick before I find something that really makes a difference.

That Mira of yours is pretty interesting looking. Looks very much like a Ford Festiva.

http://www3.telus.net/metro/metroTail.jpg
Well, there's a mockup of the adjusted spoiler/boattail. It only extends back the same distance as the rear bumper (but it could go maybe 6" over) and it shouldn't (knock on wood) impair vision through the mirror.

Will you be building one then? Someone in the early days of the site posted a link to a guy who had added a foot to the back of my car and was getting 80+ mpg (he was doing other stuff, too, of course, :p)

I'm hoping to. I'm biting off more than I can chew with all the projects that I would like to do. I don't think I would get one of these built until next year, but maybe a cardboard model after I get a MID towards the end of August...???

I'm just fascinated with aero-mods right now since I know they work and I can't do all the engine/transmission magic that you Honda guys are doing...even though there is the 1.3L trans swap, light-pressure turbo, and maybe the Hemi-head to consider...:D

Tranny swap isn't really that bad when you get down to it, it's just plug and play, but turbo and such where compatibility modification/issues come into play are the trickier things. One day I'll try the LPT, jared is in charge of finding me one, need to bug him, :p

Oh, I can do the mechanical work. By "magic" I was mostly referring to all the options the Hondas seem to have compared to the Swift-clones...your response sounded like you mistook my meaning. :p

Well then, get on that stuff, :p

Someone in the early days of the site posted a link to a guy who had added a foot to the back of my car and was getting 80+ mpg (he was doing other stuff, too, of course, :p)
You're probably thinking of Phil Knox. He heavily modified his Honda CRX for fuel economy. Boattail, rear wheel skirts, bellypan, side skirts, front air dam, and lots of other modifications. He only used aeromods, and never touched synthetic transmission oil, LRR tires, and other significant modifications in order to get that fuel economy. Got 90 mpg highway, just by aeromods, no engine change or anything.

http://img.villagephotos.com/p/2006-3/1161345/PhilsCRX1.jpg

http://img.villagephotos.com/p/2006-3/1161345/PhilsCRX2.jpg

I'm glad you found that. I had seen it once and couldn't find it again. That Rex looks good from the front - nose piece is reminiscent of an IROC Camaro - but I think the back is a little odd looking.

However, for 90 mpg highway...wow!

Still no front skirts though. It almost makes me wonder if people have tried them and had stability issues or they just can get a decent working model. :confused:

Front skirts are very difficult to implement. So much so that even experts in aerodynamics don't find them worth the effort to properly implement.

If you use rounded skirts like that chopped/tandem Geo Metro that got near 80 mpg, you increase frontal area enough to cancel out the reduction in drag coefficient. It is difficult to make front skirts that allow you to turn, without wheels or tires rubbing them.

I think the only practical way to get front skirts is to make them turn along with your wheels. That would be difficult and/or expensive to properly implement. But I'm no expert, so I am likely wrong.

Well, there's a mockup of the adjusted spoiler/boattail. It only extends back the same distance as the rear bumper (but it could go maybe 6" over) and it shouldn't (knock on wood) impair vision through the mirror. Damn, that's nice!

You sure are a much more talented photoshopper than I am with MS Paint, heh. :D Looks like it would work well.

But of course, testing will triumph over all.

It reminds me of the time that we were streamlining balloons back in grade school. We had these balloons attached to strings and we had to modify them with paper to see which would go the fastest, as a science experiment.

My idea was to make the front end to be a cone, with the rear just being the back of the balloon. I recall that someone tried it the other way, and knowing what we know now, of course it won, but at the time I thought it must have been some sort of mistake.

Hopefully I have learned from that experience. Trust the scientific method, it works.

Front skirts are very difficult to implement. So much so that even experts in aerodynamics don't find them worth the effort to properly implement.
Only those as hardcore as the team that made the Prove V tried the front skirts. And got rewarded with a 0.13 something Cd for it.

I think that it's not the difficulty so much as that it's a fairly out-of-the-box kind of idea that stops it getting implemented.

You're probably thinking of Phil Knox.
Hey, thanks for those pictures, I've wanted to see them for a long while now!

The only anomaly to my eyes is that spoiler at the back... unless it is somehow covered with perspex on both the top and sides, and was done for visibility reasons. Other than that, beautiful.

If you want to get in touch with Phil Knox, you can find him at the following yahoo group:

http://autos.groups.yahoo.com/group/maxmpg/

He goes by the name aero1898head.

Only those as hardcore as the team that made the Prove V tried the front skirts. And got rewarded with a 0.13 something Cd for it.
.137 to be exact. Damn that's smooth.

.137 to be exact. Damn that's smooth. Thanks for the info!

A bit OT, but you can kind of get a feel where car aerodynamics is going by looking at aircraft. That pulse autocycle was designed by Jim Bede, who has designed some of the most efficient aircraft in the world. He employed a guy by the name of Burt Rutan, who designed the long-ez. The velocity looks almost identical to it, seats 4, and gets something like 8l/100km, which is like a car!

http://www.aerofiles.com/velocity-SEFG.jpg

Strip off the wings and canards, and you can see which direction cars will go for minimizing drag and weight. Since it already has to fit 4 people, two side by side, it already has some of the compromises necessary to seat them comfortably.

In fact, if you bought the top and bottom part of the kit, you might be able to graft it onto a car like mine.

http://www.bpdespins.ab.ca/velocity/images/S_hrxl-rg.jpg

Damn, that's nice!

You sure are a much more talented photoshopper than I am with MS Paint, heh. :D Looks like it would work well.

Thanks. Photoshop (I prefer Corel Photo-Paint) is part of my everyday job. It comes in handy for these type of things. And I kind of cheated since I have the tools. I drew the side-profile in CorelDraw, then opened up 3D Studio and made a 3D version from there.

I only know the basics of 3D Studio, but it does have some physics capabilities. If I could develop a 3D wind tunnel...:cool:

Thanks. Photoshop (I prefer Corel Photo-Paint) is part of my everyday job. It comes in handy for these type of things. And I kind of cheated since I have the tools. I drew the side-profile in CorelDraw, then opened up 3D Studio and made a 3D version from there.

I only know the basics of 3D Studio, but it does have some physics capabilities. If I could develop a 3D wind tunnel...:cool:
*cough* emule *cough* fluent...

Of course, you'd have to figure out how to use it...

Meanwhile, I found this (http://www.fluent.com/about/news/newsletters/04v13i2/a27.htm) while googling:
The Supermileage® competition provides engineering and technology students with a challenging design project that involves the development and construction of a single-person, fuel-efficient vehicle. Vehicles are powered by a small four-cycle engine. Students have the opportunity to set a world fuel economy record and increase public awareness of fuel economy. The engines are donated by Briggs & Stratton.
In 2003 and 2004, the University of British Columbia Supermileage Team (UBCST) won the Supermileage competition with mileages of 927 and 1747 miles per gallon (US), respectively. Their current goal is to continue to improve their designs and manufacturing methods through innovative and effective ideas.
Besides the engine, an efficient drive train, a well-designed yet light frame, and an aerodynamic car body are vital components for low mileage consumption. Because the cars at the Supermileage competition run at low speeds (with a minimum average of 15 mph), the aerodynamic shapes are extremely important. For this reason, the UBCST spent a great deal of time on the design and development of the 2004 body using wind tunnel testing (with 1/4 and 1/2 scale models) and CFD analysis using FLUENT.

What a retarded competition... how about a competition to make an actual car that can accelerate to highway speeds and do everything that normal cars do? If I wanted to travel at 15mph, I'd get a recumbent bicycle.

Hmm, that does give me an idea for another topic, but such a competition outlined here would never get any substantial backing anyway.

Hmm, that does give me an idea for another topic, but such a competition outlined here would never get any substantial backing anyway. Yes, the more I look at it the more I understand the problem.

Look at the "futurecar" competition:

Best Use of Alternative Fuels Open to alternative fueled vehicle (E85, CNG, LPG, H2, and DME) -- it is based on the sum of the scores for Emissions, Energy Economy, and Vehicle Design Inspection Event
Where the hell is electricity as provided by power stations? It ain't there!

Who is it funded (http://www.engin.umich.edu/futurecar/) by?

The FutureCar Challenge is part of the larger Partnership for a New Generation of Vehicles (PNGV), the national public-private research program begun in late 1993 to develop super fuel-efficient vehicles. This ambitious collaborative effort is making progress in many technical areas including advanced materials, manufacturing processes, and energy conversion and storage devices. PNGV also recognized the need and importance of a competitive educational component like the FutureCar Challenge. There is much at stake in this competition. As part of the PNGV effort, the FutureCar Challenge is connected to the larger, nationwide effort that is already leading to energy, environmental and economic benefits to the nation. The U.S. Department of Energy and the American auto industry, through the United States Council for Automotive Research (USCAR), are principal sponsors of this program. USCAR is an umbrella organization created by Chrysler, Ford and General Motors to do pre-competitive research in variety of advanced automotive technologies.

Hmm, that does give me an idea for another topic, but such a competition outlined here would never get any substantial backing anyway.
Why don't you outline it anyway?

What is really desired?

Minimize total cost of ownership over, say 10 years, while maintaining:
-minimum number of highway and city miles per year.
-minimum acceleration
-minimum range per trip
-minimum range per day with maximum stopping period
-minimum number of passengers
-minimum visibility considerations
-minimum luggage considerations

Off the top of my head.

Pretty much. It would be a performance and luxury oriented hyper-efficient car with one of its key design criteria being affordability, under $10k.

say,

*0-60 mph under 7 seconds
*120+ mph top speed
*must be designed to accomodate multiple fuels, specifically E100/gasoline, B100/diesel, or electricity, not necessarily in the same car. For instance, it could be one platform that will come in a model that runs on ethanol, another might run on diesel, another might run on electricity
*40+ mpg city, 70+ mpg highway if powered by gasoline, ethanol, or diesel, < 150 Wh/mile at 65 mph if powered by electricity
*capability to seat 4 adults 6'5", 200 pounds each
*professional finish, must *look* expensive
*200 miles range or more
*under $10k pricetag for IC/diesel versions, under $20k pricetag for EV
*for IC versions, minimum of 300,000 mile engine life with no powertrain repairs at 95% confidence interval, for EV minimum of 1 million mile motor life and 250,000 mile battery life at 95% confidence interval
*capability to sustain 120+ mph collision with no severe damage to occupants(ie. roll cage, safety harnesses, ect.)
*500W+ premium sound system
*leather interior
*exterior body must be built with replacable modules. Get into a fender bender, pop one off, snap on another, for cheap. The roll cage should be rigid enough to make the car difficult to total, even at racing speeds, but crumple zones adequate enough to keep occupants safe during impact.


We certainly have the technology to do it. Might be difficult to do the EV because that would require NiMH batteries, which Chevron Texaco has the patent of.

It would essentially be a people's car of the 21st century. It would blow away everythnig else on the market.

I imagine such a car would look like a very aerodynamic version of the 60s VW Beetle, longer and much more powerful. Or perhaps an updated Tarta T77a. It would be cheap to make, it would be designed to look as much like a luxury car as possible, it would be designed to be as low maintenance as possible and as cheap to operate as possible, and it would have to be fuel efficient and able to use alternatives where available.

Such a car would be light, weighing ~1,600-1,800 pounds unloaded. The roll cage and properly designed crumple zones would keep it sufficiently safe to allow such a low weight without use of composite materials to keep cost down.

The gas IC version would have to be able to use any combination of gasoline or ethanol including 100% of either, the diesel would need to be able to use any combination of petrol diesel and biodiesel including 100% of either.


How willing do you think the auto industry would be to see something like this made? Don't answer... lol...

Pretty much. It would be a performance and luxury oriented hyper-efficient car with one of its key design criteria being affordability, under $10k.
Interesting.

Why do you keep coming back to NiMH batteries? Are they better than Li-Ion or Li-Poly?

1,750 cycles to 100% depth of discharge for the Ovonics according to UC Davis, and a shelf life that's like NiCds. They basically don't wear out.

Even Chevron Texaco puts them at a conservative 1200 cycles to 80% DoD. With 200 miles range, do the math on battery life... Since not everyone drives 200 miles per trip, and since batteries last much longer with shallower discharge, you can see the advantage.

In contrast, lithium batteries degrade ~4% per year, sometimes faster.

Also, mass production of Ovonic NiMH batteries was estimated at $150/kWh according to ECD chairman Robert Stemple in the 90s. Today, the more conservative estimates provided by UC Davis' Team Fate range from $200/kWh to $300/kWh. For 200 miles range, we need at least a 30 kWh pack for an efficient car that uses 150 Wh/mile.

Too bad the oil industry has the patent.

Take the projected cycle life of these batteries and prokected cost in mass production, and you get a battery cost on the order of $.02-.04/mile. This is extremely cheap given an electric motor needs no maintenance and given electricity for such a car is around $.015-.02/mile. So cheap, that even if the gasoline for most gas cars were given away for free, the electric car would still cost less to operate.

As for real world figures, Southern California Edison put like 3 million miles on their EV fleet with NiMH batteries. They only had 6 battery module failures. Each Toyota RAV4 has like 24 battery modules. The RAV4s that have been in use the longest have approached 150,000 miles on the same pack, no degredation in range or power yet, the others with less miles show no degredation either. Toyota conservatively rated the packs at 100,000 miles, but no one really knows how long they will last in real world use. In theory, these batteries will last at least 170,000 miles before they only deliver 80% of their range in the RAV4 EVs(although these RAV4s aren't being discharged to 100% all the time, so actually longer than that, in theory). These RAV4s only have 100 miles range. Imagine an EV with 200 miles range.

The amount of car battery packs that can be made from the world's nickel reserves far outnumbers the amount that can be done from the world's lithium reserves as well.

5,000,000,000 kg of nickel is produced each year.

The Toyota Prius hybrid has 1.3 kWh battery pack from that 10 kg of nickel. So basically, for every kWh of battery, you'd need 7.69 kg of nickel.

A midsize EV with attention paid to aerodynamics(~22 square foot frontal area, .18 Cd) and about 2,800 pounds curb weight would need 180 Wh/mile at 70 mph. So, for 200 miles real highway range, that's a 36 kWh battery pack with 277 kg of nickel in it. This battery pack would also allow for roughly 180 horsepower to be delivered to the motor for a 0-60 mph time of roughly 7 seconds and top speed in excess of 160 mph.


But nickel production could be ramped up. The known commercial reserves are 62,000,000,000 kg(USGS), so that is enough for 224 million electric cars. Or, if we can miraculously access that 160 million tonnes estimated to be all through the Earth, enough for 578 million EVs!

So, that is enough nickel for 18 million new EVs each year. And this is only one battery chemistry.

We didn't include lithium, we didn't include lead acid(ie. Firefly batteries). The world's readily accessable lithium reserves are enough for about 100 million EVs of the type outlined above with 200 mile range packs.

We do have to be cafeful though. What's good about battery material is that it's recyclable. But getting that material can be an environmental disaster. We must be careful not to turn this planet into a giant strip mine.

But again, the oil industry has the battery patent, and is sitting on it. It is viable, it is plentiful.

Long informative post snipped
Thanks for the excellent post!!!

I'm glad that someone who isn't a vested interest has done the research on this for me. Kudos.

So, basically it comes down to life cycle... they don't wear out.

I don't suppose these batteries can be manufactured in your backyard...

I suppose that relegates us to using lead acid in the meantime, correct? Stick one in Phil Knox's CRX, I wonder what sort of highway range it would have?

I suppose that relegates us to using lead acid in the meantime, correct?

Indeed.

Stick one in Phil Knox's CRX, I wonder what sort of highway range it would have?

This is pure guess, but I'd say a 1,125 pound pack of Optima Yellowtops for 300V nominal would give 130 miles range at 65 mph.

If you want to get 200+ miles range with lead acid, you're going to need a lightweight tubeframe chassis and a lightweight/aerodynamic body to place on it, that can contain both the weight and volume needed for that range. You're looking 200 miles range with a 2,000 pound battery pack if the car can be kept aerodynamic enough and has LRR tires and such. This car would need to attain ~150 Wh/mile efficiency at 65 mph or so, and this is a car that would weigh around 3,200-3,500 pounds loaded with 2,000 pounds of batteries. An electric musclecar could perhaps be designed around such a concept. It would not be easy. A vehicle with a 23 square foot frontal area would need a drag coefficient of ~.16-.18 to do this.

To actually do this with a conversion instead of a custom built vehicle, your only option is a small pickup truck, loaded with about 2,400 pounds of batteries, and with extensive aeromods.(See Phil Knox's gas powered Toyota T100 pickup. Aeromods got it over a 30% improvement in highway mileage. Roughly the same will apply to eelctric car range.)

There are electric pickups that got 120 miles highway range using a large amount of lead acid batteries. They had no LRR tires and no aeromods.

With aeromods, I have no doubt they'd get at minimum 150 miles highway range, perhaps 200 miles. I don't know anyone who has been crazy enough to try this yet. If I had the cash, I'd be glad to.

See the following:

http://www.austinev.org/evalbum/37

http://www.austinev.org/evalbum/185

Note: "Red Beastie" was unfortunately destroyed about a week ago. The owner was gone from home and a dumptruck parked uphill blocks away began rolling after its parking brake had failed. It crashed into the owner's home and caught fire, destroying the home, his Indian motorcycle collection, and both his electric vehicles, including "Red Beastie", one of the 100+ mile range electric trucks linked above.

If you want to get 200+ miles range with lead acid, you're going to need a lightweight tubeframe chassis and a lightweight/aerodynamic body to place on it, that can contain both the weight and volume needed for that range. You're looking 200 miles range with a 2,000 pound battery pack if the car can be kept aerodynamic enough and has LRR tires and such. This car would need to attain ~150 Wh/mile efficiency at 65 mph or so, and this is a car that would weigh around 3,200-3,500 pounds loaded with 2,000 pounds of batteries. An electric musclecar could perhaps be designed around such a concept. It would not be easy. A vehicle with a 23 square foot frontal area would need a drag coefficient of ~.16-.18 to do this.

As I said in PM, I think that the ideal shape for this sort of thing is long and thin. Thin to minimize frontal area/Cd, and long both to fit in more batteries and to increase Cd. It can afford to be thin because all the weight is hardly higher than the tyres. Kind of like a longer, aerodynamic and wider version of the Tango.

http://www.commutercars.com/images/gallery/studio/index/indexfiles/Quarter.tift.jpg

For those who are interested, I have updated my site with a page about the XFi Aero Car that was posted in this thread in June.

http://metrompg.com/posts/photos/1989xfiaerocar-trimmed.jpg


I sent the builder/owner some additional questions, and he wrote back with more detail about himself and the car. I posted the Q & A at MetroMPG.com, and his son also put up a new page on his site with my questions. So, if you'd like to know a bit more about this project, you can find out at either:

http://metrompg.com/posts/xfi-aero-car.htm

and/or

http://www.1989geometro.com/ - in "questions asked"

There was a lot of activity in this thread while I was away. Just got caught up on it all.

I love the Photoshop stuff. (Or Corel, Mark?)

The rear Metro wing and the boat-tails are great stuff. I was out staring at the back of my car last night, wheels turning (in my head) ... :confused:

For those who are interested, I have updated my site with a page about the XFi Aero Car that was posted in this thread in June.

Nicely done!
Great info...wish I could get some of those custom machined taller 5th gears! :) Would have normal gearing for 'power' and 'long legs' like yours! :)

Those custom gears would be the best of both worlds, wouldn't they.

Did you also send other questions to the Aero Car builder? If you heard back and have anything to add, please share!

Never heard anything back...emailed his son more than once, but didn't want to bug him anymore.

Good Follow up on your part!

The Questair Venture provides a good example of an aircraft boat tail shape that could be easily adapted to fit a car. This very fast homebuilt has been called "the flying egg" and has a very short tail, but presumably has attached airflow to manage the speeds that it reaches. It has a 48" wide cockpit, comparable in width to that of a subcompact car.

http://www.aircraftpaintschemes.com/linedraw_details_guest.asp?AircraftID=367

http://www.airbum.com/pireps/QuestairVentureNose-on.jpg

http://home.triad.rr.com/mcintyre5/Questair.gif

http://www.wallacecompany.com/venture/

Here are some line drawings of the Venture. Its tailcone seems to exceed the 10 to one ratio that people have quoted are being the sharpest taper that can retain an attached airflow. This aircraft is one of the fastest prop-driven homebuilts and holds a number of speed records in its class.

http://img.photobucket.com/albums/v417/MikeMariettaSC/80MPG%20Honda%20Civic/Venture_t_th.jpg

http://img.photobucket.com/albums/v417/MikeMariettaSC/80MPG%20Honda%20Civic/Venture_s_th.jpg

Here are some line drawings of the Venture. Its tailcone seems to exceed the 10 to one ratio that people have quoted

My understanding is the "10" refers to max "degrees" (from vehicle direction of travel/air flow direction) that a plane can change inward. And one of the Chalmers reports shows that it's actually more of a range, from 10-20, with a sweet spot in there somewhere.

I also read a Phil Knox quote recently that says an elliptical curve (beginning from parallel to wind flow) to up to 20 degrees inward can still maintain attached flow - you just can't go to 20 degrees instantly. That's my understanding, anyway. Would explain the appearance of this airplane.

http://autos.groups.yahoo.com/group/maxmpg/message/809

Coroplast to the rescue! Cut my front undertray this evening. Just some minor tweaking to get it done.

It will be relatively easy to install/remove, so I can probably do a test run with it as well. Eventually.

Tomorrow! I'll take over for you at work.

Celica wing seen:

http://xs205.xs.to/xs205/06352/celicawingsmall.jpg (http://xs.to)

Guess I could have gotten a little closer...but there are 2 small vertical wings that are angled inward at each end.

Fixed it!

Hmm. Vertical winglets or not, that Celica wing would be about as helpful for aerodynamics as a ram implosion device or a set of roof racks!

Hmm. Vertical winglets or not, that Celica wing would be about as helpful for aerodynamics as a ram implosion device or a set of roof racks!
That was funny.

Well, I should have said "as useful for fuel economy...", but you got what I meant.

Well, I should have said "as useful for fuel economy...", but you got what I meant.

I disagree...as per usual. Remember the "science fair project" or whatever where the guy claimed an mpg gain from vertical wings....angled inwards?

The VW wing with verticals angled outwards?

It's my contention that SOME of these wings increase mpg, acting like LARGE vgs.

The Mitsubishi vg research also worked WITH a wing? With all the attention they paid to CD values...do you think the wing caused overall drag?

How do they work? My guess is that wings and vgs create a strong focused flow that breaks up large/inefficient vortexes that form at the back of vehicles.

On a trip last summer I was trailing a big rig pulling one of those container boxes on a trailer...I could move up close and then back out some...I could feel the big rolling vortexes coming off this truck...each one sucking it backwards...and about blowing my car off the road.

BIG BAD UNCONTROLLED ROLLING VORTEXES are evil.

Small controlled vortexes and larger directed flows are GOOD!

Of course...a properly formed boat tail is HEAVEN ON EARTH.......

I disagree...as per usual. Remember the "science fair project" or whatever where the guy claimed an mpg gain from vertical wings....angled inwards?

Winglets on planes are used to reduce lift-induced drag caused by wingtip vortices by increasing a wing's aspect ratio without increasing its span. Though most of the 2 winglets' horizontal lift vectors cancel each other out, the net is a small amount of forward lift or 'thrust' thereby reducing drag a little more. Here's the problem: where there is lift, there is induced drag (and parasitic drag) that opposes thrust. The drag likely exceeds the thrust gain but so its just a small side benefit to the planes.

I don't imagine winglets are giong to be very effective in decreasing a car's Cd.

It's my contention that SOME of these wings increase mpg, acting like LARGE vgs.

The Mitsubishi vg research also worked WITH a wing?

As I understand VGs, they are used along a curve of a surface with the intent of extending the area of laminar flow along that surface. They had a small effect on a sedan shape when placed on the back part of the roof near but not on the knee of the curve. This made air flow a little more smoothly over the back window. I don't think the 2 big winglets on the back (with no surface behind them) will work the same way as the VGs are used.

It's still possible they could reduce the turbulence behind the car but at what cost in terms of drag? In that respect, I agree with you about designing for the "boattail effect." :)

I disagree...as per usual. Remember the "science fair project" or whatever where the guy claimed an mpg gain from vertical wings....angled inwards?

But they were minus the giant horizontal trunk wing.

The Mitsubishi vg research also worked WITH a wing? ... do you think the wing caused overall drag?

Unquestionably. You just have to have a look at the CFD images in the PDF to see it. In both the "with" and "without VG" examples, the wing extends into clean (unseparated) airflow, which increases drag. Don't forget: this car is a turbo high-performance AWD racing machine, not a fuel-sipper, and its wing is there to generate downforce.

In fact, I think it's likely that they put the VGs there in the first place to get more downforce from the wing, rather than cleaning up the overall Cd, and the tiny reduction in Cd was a happy accident:

CFD results in Fig. 10 also show
that the velocity of the airflow along the bottom surface
of the rear spoiler increases by addition of VGs, which
reveals that a decrease in lift (an increase in down-force)
did occur.

...

With all the attention they paid to CD values...

I think that's an overstatement. The Mitsu is a brick, and their interest in Cd is more about road-holding than efficiency. If they just wanted more FE, there wouldn't be a wing on the back.

I think that's an overstatement. The Mitsu is a brick, and their interest in Cd is more about road-holding than efficiency. If they just wanted more FE, there wouldn't be a wing on the back.

And yet...there is the page you found showing the advantages from a small lip at the back of a vehicle...I see them on most newer cars...there is the VW wing with angled surfaces...there is the 2 angled vertical fins science fair project...ALL made for increased FE.

So it looks like...DESPITE...the drag caused by these angled surfaces...they reduce overall drag.

Yes...many wings are designed to produce downforce or for decoration...but I'm saying that if they are designed for FE...they work for FE. :cool:

And...I'm always right. :D

Yes...many wings are designed to produce downforce or for decoration...but I'm saying that if they are designed for FE...they work for FE.

On that point, we are in violent agreement.

I was only answering the issue you raised of the Mitsu wing being a FE instrument, which it definitely isn't.

Ok...you win. :thumbup:

Airplanes do? :D

Airplanes do? :D

Airplanes have them only for the purpose of reducing wingtip vortices, which are side effects of producing lift. The heavier the wing loading, the higher the WTVs.

Some racing cars have winglets (short ones) because the wings have a small aspect ratio and produce heavy downforce, and so probably benefit from reducing WTVs.

If a wing was used for a modest amount of flow redirection, it should produce only a small amount of induced drag (proportional to the amount of lift produced and therefore WTVs).

Finished cutting the front

Why I'm procrastinating on this, I don't exactly know.



Probably because you just KNOW that you SHOULD be testing vortex generators? :) :cool:

Have to give you points for persistence! Tell you what: before I make a fiberglass boat tail, I'll test VGs first.

Have to give you points for persistence! Tell you what: before I make a fiberglass boat tail, I'll test VGs first.

I wish you lived closer to me. I don't have time to do anything to my car. I haven't done any of the aero mods on my car.

Have to give you points for persistence! Tell you what: before I make a fiberglass boat tail, I'll test VGs first.

You'll have to test the boat tail with VG's:p

I'll have to test VG's on my VG's.

---

Front portion of the undertray is in place & fastened. I got most of the center section done this evening too.

I - gasp - drilled holes in the underbody to fasten the coroplast. I think that's the real reason I've been procrastinating. I just feels so wrong to drill underneath - thinking of rust.

Once all the panels are in place, I'm going to do a B-A test, where I do some runs with the full tray, then remove it on the roadside and repeat the runs. I'm not doing A-B-A. Too complicated.

After the test, I'm going to have the car professionally undercoated and then put the panels back on.

The trickiest area left to do is the rear control arms. They hang down LOW into the flow - they're located about at the halfway point between the road and the bottom of the rear bumper. I'm thinking I may try to use the coroplast to extend them backwards in a teardrop shape. Complicated, but they're definitely a drag problem the way they are now, all blunt and exposed to the flow.

optimistic that the tray could be significant - I'm smoothing out some serious "excrescences".

Anyone want to make any guesses on what the tray is worth @ 55 mph? After seeing the effect of the unloaded roof racks on the top of the car, I'm cautiously optimistic that the tray could be significant - I'm smoothing out some serious "excrescences".

You mean the whole undertray itself vs. not having one?

4-7%.

That's what I meant, yes.

So you're suggesting a 4-7% FE increase, or a 4-7% change in Cd?

Spent a couple more hours on the tray this evening.

Anyway, the rear portion is in place. The hard part was coming up with a way to extend & taper the control arm surfaces upward toward the bumper and still allow flex in the tray to move with the suspension.


Nice. Don't forget to put the VG's under there:p

So you're suggesting a 4-7% FE increase, or a 4-7% change in Cd?

Change in FE.

I'm going for 5% increase in FE. It will really help the P&G. I'm optimistic when do you think you'll be able to test.

Finished tapering one of the control arms today (15 mins). I'll put in the time to finish it up tomorrow, and since I'm going away mid-end of the week, I'll try to get in some runs before I leave.

I'd be tickled to get +5%. Seems a reasonable estimate.

Here's some info to use for an edumacated guess:

That increase would be at a steady state speed. I would think that there would be a better increase in your city driving even though the speeds are realitively slow because of the increase in coasting ability. Althought I think it would be impossible to quantify. Looking foward to your results.:D

Recorded a couple of runs this evening with the undertray on.

I'll try to do temperature compensation calcs later, and see what that says, but the other thing I need to consider is that (a) I possibly made things worse by adding the tray, or (b) it didn't help any!

WOW 57 degrees nice:thumbup: I would really be suprised if it did not help there is too much data that say otherwise. Could you tell if the coast down were better? That's one thing that really jumped out at me was how much longer the speed took to bleed off and how much longer the coast was on my usual routes. Like you said need to test the same day. Just run the fireflea through the paces when you get back from your sea adventure. Got any pic's?

Can't really comment on the coasting.

No pics yet. I'll get some though.

Can't really comment on the coasting. I'd like to say it coasts longer, but that may be the placebo talking :) I don't have a regular route with "benchmarks" I can compare it to.

I may get a chance to do the A-B before I go. I don't think I'm leaving until the end of the week. I figure it will take me around 10 minutes to remove the 30 or so screws and take the tray apart/off at the side of the road.

The only thing I'm wondering is whether I should do (1) one A&B bi-dir run for a range of different speeds, (2) or stay at one speed, and do a number of A's and B's.

I'd prefer to know the difference at several speeds, but (2) generates more reliable results.

It takes a long time to do these runs.

Just test 2 speeds and interpolate say 30 and 60 MPH and then maybe a coast down for your drag reduction but than again "you should be working":)

Excellent weather today (little wind), so took a couple of hours off and did 6 bi-directional runs @ 90 km/h (56 mph).

Yup, you certainly win the for the closest estimate. What's your source, BTW? I'd like to know how they calculated the figure and what's taking into account.

Just noticed something:

Excellent weather today (little wind), so took a couple of hours off and did 6 bi-directional runs @ 90 km/h (56 mph).

3 with, 3 without the undertray .

57.78 mpg (US) - with undertray
56.55 mpg (US) - without undertray

1.23 mpg difference, or 2.2% increase with tray

Not really happy with the results. It was a lot of work for such a small gain. But them's the numbers.

A question for the aero enthusiasts: my car rides quite high off the ground - 6 inches or maybe slightly more. Would an undertray help more on a lower vehicle (like the A4, which probably has 3 or 4 inches of clearance)?

Well that's better than nothin.:p I thought it would be higher to. I think your onto something with the ride hight. You may already have seen this.

http://www.wisil.recumbents.com/wisil/demma/aero_review.htm
"With increasing ground clearance, the airflow in the nozzle-type space between the vehicle underbody and the ground produces low pressures causing overall lift to be lowered to negative values and then to rise again as ground clearance continues to increase. The increase in overall lift is due to the fact that the flow velocity under the car decreases as ground clearance increases, thus reducing the low pressure level. Air drag increases as a function of ground clearance though this increase is smaller by one order of magnitude than that of the lift forces. ...lift variations occur mainly in the nose of the car."

I think there's something wonky in that math. I don't believe 10% Cd reduction = 2% FE increase. Maybe someone can work it out with better numbers before I get to it.

To add insult to injury, doing these runs dragged my tank average from 81.x to 79.x . AAARG! :mad: I would really like one 80+ tank this year!

I had to pulse and glide all the way home to try to reverse some of the damage - it was lower than that when I left the test road after the last run.

Thanks for that link, zpiloto. I haven't put much effort into understanding effects of ride height on drag yet, aside from knowing the basics: that lower is better than higher, and 3 inches is about optimum.

1.23 mpg difference, or 2.2% increase with tray

Not really happy with the results. It was a lot of work for such a small gain. But them's the numbers.

A question for the aero enthusiasts: my car rides quite high off the ground - 6 inches or maybe slightly more. Would an undertray help more on a lower vehicle (like the A4, which probably has 3 or 4 inches of clearance)?

That's the pattern I see more and more...you should EXPECT 2-3% increases with most mods? Those 10 percenters are few and far between?

Also...you could lower your car by using smaller wheels/tires and not pay a penalty due to your trans change? I'm guessing that you went past the sweet spot as far as your final drive ratio. Just a guess though.

Your decrease in CdA wrt to your increase in mpg depends on your average speed. at a ~35mph average, I figure you've dropped CdA to ~.27-.3 to see a ~12% increase in FE. If your average speed is lower, then you've managed to drop the CdA even more.

The speeds all the tests were done at were between 88-95 km/h.

According to the aero & rolling resistance tool I made from Dan's spreadsheet formulas:

http://metrompg.com/tool-aero-rr.htm

I've would have reduced my Cd from .34 to .294 to see a 12% FE gain @ 55 mph @ 15C ambient.

That sounds about right! Of course, you can't just sum up FE increases, they are cumulative. ;) If that calculator is right, I should see +15mpg@50mph average from LRR tires/proper pressure (of course that's my dumbass fautl for not mindin' my units), and +24mpg@50mph if I can magically cut my CdA in half. I like that calculator. :D

+15 mpg? Do you mean +1.5?

Nope, +15 if I can drop on overinflated LRR tires with a 0,0,0 alignment because I'm hoping it cuts my Crr in half. At least by my reasoning, because on the beater I currently have, all the tires are mismatched and from the junkyard, I never checked pressure because I severely underestimated the impact of rolling friction, and the alignment is so bad I've had two blow out because of wear/nasty camber (wore to the metal on one side, tons of tread on the other), so god knows what toe and caster is. In any event, given my current ~55-50mpg@45-50mph average, new LRR tires, overinflation, and proper alignment should make a world of difference.

edit- by never I mean I've inflated to the sidewall pressure on each tire three or four times over the 8 months I consistently drove it. Each time, especially the last long trip. I noticed a significant increase via my butt dyno in how I was able to accelerate, especially at lower speeds uphill, so I'm guessing I've been really negligent and can hopefully see a big improvement.

You should fill out your garage/car info. Sometimes hard to recall exactly what everybody's driving if it only gets covered in their original intro thread.

Wow, I never even bothered with an intrductory post! In any event, now that I've been pretty much stationary I haven't driven it for the last month or so. My pickup gets half the mileage, but at less than 200 miles per month, I'm paying an extra $12 so I don't go deaf due to my ghettotastic glasspack exhaust. Of course that's what I get for a few hundred dollar car, but I'll hopefully swap out the engine, put it into my $75 clean version, get nice LRR tires, and start driving it again.

I realized today that if I put front wheel skirts on the car it'll look like a shoe.

That's probably what made me think of it. But more of a sneaker look, not a high-top. :rolleyes:

I had the car rust-treated today, so I removed the rear wheel skirts.

Hey I just read a post in ScionLife that the drag coefficient of my xB is 0.35

It's been really gross and mucky outside, so washing my Metro would be dumb since it would just get dirty 10 minutes later. Now that my Metro is caked with road grime this is what she looks like:

82

I would think that the clean parts of the car are where the air is going smoothly over the vehicle, but look at all that turbulent air coming from the front wheel arch! Also note how much dirt accumulation occurs on the rear of the car:

83

Winter should be a perfect time to test out some Aero mods!

I read somewhere that some aerodynamicists sometimes use dust in the wind tunnel for exactly the same reason - where it accumulates on the car shows areas of low pressure better.

Also, don't kick off the "snuds" (snow & mud) that accumulate behind your tires. Once they're built up, they effectively "boat tail" the air flowing past the wheels and help streamline it.

Also, don't kick off the "snuds" (snow & mud) that accumulate behind your tires. Once they're built up, they effectively "boat tail" the air flowing past the wheels and help streamline it.
Oh, I thought those were boogers.

Hey I just read a post in ScionLife that the drag coefficient of my xB is 0.35

If I would have known that you were unaware of this number, I'd have told you!

I found that figure after seeing the AC Propulsion Ebox, wanting to see whether their claims for range and efficiency appeared reasonable, and then doing a search and plugging the numbers into the drag equations we all know about.

Thinking of doing some aero modifications at some point with my Geo. (even if it's just a one-time thing). Just a few images to bounce around on this site:
112
What the air is probably currently doing:
113
109
111
And of course if I was really ambitious:
116
Should the rear end taper be the same height as the front point to leave the air least-disturbed when leaving the car?

Find a 93 flat bumper. I tested them and they are better. I don't have any real mileage numbers but from doing a pretty thorough coasting test I can say they are better for the front end than the curved bumper.

http://www.teamswift.net/album_pic.php?pic_id=10323

Find a 93 flat bumper. I tested them and they are better. I don't have any real mileage numbers but from doing a pretty thorough coasting test I can say they are better for the front end than the curved bumper.
I would've thought that a flatter front bumper would be better. The downward angle of my current bumper seems like it rams a lot of air under the car. This is also why my '85 Fiero had a Cd of 0.37 compared to the SE version having a Cd of 0.35:

Non aero nose (my '85 SC Fiero) Cd: 0.37:
114
Aero nose ('86 SE Fiero) Cd: 0.35:
115

It seems as a rule of thumb that air should flow around the sides or top of the car, not under it. The only problem is that I'm sure the '93 bumpers are not interchangeable with my '97. I would have to fabricate the flat bumper myself.

My dad has gone to Las Vegas on vacation so that means I can finally use the garage for aerodynamic modifications without freezing outside.

I finally replaced my barely-working driver side windshield wiper with a "Reflex" blade which doesn't have hinges. Not only should it be good for aero, but it keeps the window streak free:

141

Next was the removal of the mirrors. Man, If I knew that the mirrors were this easy to remove I would've done it long ago! Just 3 screws for each door and they're off. I stuffed the holes with paper towel and covered the void with plastic:

142

143

To compensate for the loss of the side mirrors, I clipped on a large panoramic mirror to the existing interior mirror:

144

Up next is the wheels skirts and Kammback.

Good stuff. :thumbup: There's about a 2.3% increase in FE at 90 km/h in mild temps (more in winter).

Don't crash into anyone without the mirrors - takes a while to adjust your driving to compensate. (You WILL find yourself automatically looking to where they used to be, for a while.)

Don't crash into anyone without the mirrors - takes a while to adjust your driving to compensate. (You WILL find yourself automatically looking to where they used to be, for a while.)

Yeah, I know what you mean. I drove to Wal-mart just before they closed tonight so I could get a panoramic mirror (after removing the side mirrors), and I never knew just how much I used the mirrors until they were gone. Kept looking at the void space :o . The panoramic mirror covers everything except behind my head. I'm planning to mount a convex mirror on the inside of the driver's door like basjoos did.

A 2.3% inclease in FE is quite substantial for little cars like ours!

That's a good point.

You won't see a definitive difference in tank to tank comparisons from removing 1 outside mirror. The change is too small (which isn't to say it's not effective, just that it's effect will be lost in normal FE variability).

Ah! OK. All that should show up, I'd wager, comparing highway tanks.

not sure if these images will show up in this forum
http://www.teamswift.net/album_page.php?pic_id=7939
these pics does anybody sell them????

Nope. Think you've got to roll your own.

Undertray

My dear mother gave me her old kitchen table and chairs (can you tell that my parents are just itching for me to leave the house? :D) and when I stuffed them into the Geo, only the table's legs could only fit in the hatch. The table top was sticking out with the hatch wide open, creating tons of drag.

It was late at night so I took the Trans Canada Highway back to my dad's house doing 35 mph. I couldn't believe it. I needed 0.7 GPH to keep the Geo in the 33-35mph range all the way home (around 50mpg at that speed) 0.7GPH got me into the high 45-48 mph range just hours before (around 65mpg).

Clearly aerodynamics play a big role even at low speeds since the table and chairs only weigh 100 pounds at most.

Wind- how strong and what direction?

At 8:30pm is when I drove home and the temperature (http://theweathernetwork.com/weather/24h/pages/YQR.htm?CASK0261) then was -11*C (12.2*F) with winds coming from the south-east @ 20km/h (12.4mph).

Earlier that day, (let's take 1:00pm for instance) 0.7 GPH got me into the 45-48mph range and the weather at that time was around -9*C (15.8*F) with north-west winds @ 7km/h (4.3mph).

Clearly aerodynamics play a big role even at low speeds since the table and chairs only weigh 100 pounds at most.

I get the feeling that many people mistakenly assume that

Even at just 20 mph, 1/3 of the total power (about 1.2 hp) required to move a Metro goes to overcoming aero losses. 1/5 of the power at 15 mph.
Is that from a source of empirical data on the metro? I'd really like to see more of that curve.

I'm going to do a little test run today. I'll drive west to Moose Jaw, Saskatchewan on the Trans Canada Highway (very straight an flat road). First run with hatch up:

214

I'll record MPG at different speeds (let's go with 35, 45, 55, and 65mph) and the second run with hatch closed:

215

(again recording MPG at those same speeds).

I'm interested to learn what percentage MPG loss/increase there is to each speed. (this has made me wonder for a while since MetroMPG got a 2.3% MPG increase when removing mirrors @ 55mph in mild temperatures, while I got a 2.23% increase when driving 70mph in really cold temperatures, without mirrors).

Wow. Ambitious, Peakster. I'm guessing it's not -25C today. :D

I'm also guessing you're going to see a dramatic drop in FE. My WAG = -20%. (Better put a stick under the hatch to hold it open!)

SW: it's

Wow. Ambitious, Peakster. I'm guessing it's not -25C today. :D

I'm also guessing you're going to see a dramatic drop in FE. My WAG = -20%. (Better put a stick under the hatch to hold it open!)

SW: it's theoretical data: http://www.metrompg.com/tool-aero-rr.htm

EDIT: Did you put the mirror back on? Or is that an older pic?

20% was a good guess... for 40mph ;) . Take a look at the video (http://www.youtube.com/watch?v=nn7IJo06h5E) and see the difference for yourself.

BTW, I've had the mirrors back on the Geo for weeks now. The