Steve's Intro
 

Hi,

I'm in the SF Bay Area and looking to do an EV conversion in the (perhaps not so) near future and because of my range requirements (30 miles at 70 mph) I am considering aero mods (along with rolling resistance mods) to help achieve it. Yes, I'll need Lithiums to come down a bit in price, too, but that's happening. In the meantime I'm trying to learn everything I can about car aerodynamics--fortunately I have a bit of a head start since I know a little about aerodynamics from rocketry.

For now, I've just finished reading Road Vehicle Aerodynamics by A. J. Scibor-Rylski, the only book on vehicle aerodynamics my local college library has--it's quite good and worth a read. I'm looking for Hucho and the other "classics" and am reading various SAE papers to see what can be gleaned from them. Answer: plenty!

Haven't decided on a donor car yet--and won't until I have a better handle on the aerodynamics. I also plan to go visit an EV1 and hopefully take some measurements--there's a lot we can learn from that car. I've also written a simulator (along the lines of the EV calculators on the net) that helps figure out contributions to drag from rolling resistance and aerodynamics at different speeds, etc. Learned a lot from that, too.

In the meantime, I'll add comments to other threads where I think I've found something that may be helpful....

--Steve

Welcome to the site! Do you have any idea what kind of car you want to use for the EV?

Welcome to the site. I look forward to seeing some work get done. :)

Thanks guys...

SVOboy: Re vehicle: Light and aerodynamic. An EV1 would do just fine :-)

I've scoured vehicle specs for months. I know what the lighter gliders will be (Swift clones, Tercel, etc.) and have chased down all the CdA numbers I can find (not that they're necessarily accurate). What I'm now wrestling with is what style (sedan, fastback, hatch, etc.) I can most easily mod to get a CdA that will work for me (5 sq ft would be nice--EV1 was 4 sq ft). The problem with modding a sedan (or coupe) is that boattailing the "upper" part (the rear glass) would potentially screw up the trunk. The problem with the hatch is that you have to really extend the whole rear end. I haven't looked at the older fastbacks yet to see what's available and what might work. I would really like something without a trunk since I often haul stuff that fits with a hatch that doesn't fit in a trunk.

Darin mentioned the Honda Insight, but the problem is they're darned expensive around here--more than my total budget, unless I get really really lucky like Red did (I've looked and am not holding my breath).

Also, I'm mindful of the fact that it may just be a lot easier and cheaper (if this process takes long enough) to spring for a couple more battery cells to extend the range than it will be to do the aero mods to accomplish the same thing.

The newer cars are really coming down in Cd, but the A's are getting bigger and the weights are increasing to ridiculous proportions as well (they'd be out of my price range as well, of course). It is very frustrating.....

--Steve

If I were going to convert an EV, I'd really take a good look at a CRX. Great aero, lightweight, and just a nice little car.

Daox:

I found a CdA of 5.71 sq ft for the 1990 Si--true, that's not a *horrible* CdA, but I'd want to get it down to 5. It's on my short list, though. Unfortunately, they stopped making them in '91 so you don't get airbags and some other features you'd get with something from around '95. You can get them for not much money (2k or less) and older cars around here are less rusty than they are in some areas of the country, so that helps. Also, I'd prefer a decent interior and the older cars (of any make/model) tend to have pretty trashed interiors. Several have been converted to EVs, so I wouldn't be breaking any new ground there (always a plus).

--Steve

Craigslist had an EV Aztek kit car last week, a small Bombadier the week before or a boxy Mountain View utility, and many Gems, Xebras, or electric cop car Mustang the other day........constant reading enjoyment for me! Unfortunetly; no EV velomobiles yet.

Oh; by the way- welcome!

countersTrike

Steve, what cars have you found that have a CdA of under 5?

Doax: Under 5? Nothing (of course). That's why I'm studying the heck out of aerodynamics. The only way I'm getting 5 or below is to get (an affordable) Insight or something that's over 5 and mod the heck out of it. So what I'm trying to do is figure out what mods are most likely to succeed (for a given car), how much effort they are, etc etc. and weigh them against other options. It's just a small matter of homework :)

--Steve

Would you mind posting a list of the CdA values you have collected?

There are two major sources of CdA numbers that I've been using. Neither is ideal from the point of view of authentication. They are:

http://www.mayfco.com/tbls.htm
http://en.wikipedia.org/wiki/Automob...g_coefficients

The problem is that I believe a lot of the wiki info came from the mayfield (mayfco) numbers, so they're not an independent confirmation. Second, many of the mayfco numbers are estimates, but they don't say which ones, nor do they say which part (Cd, A) is estimated.

In addition to the above, I have occasionally found, for newer cars, CdA numbers from Car and Driver (their full reviews often have them), manufacturer websites occasionally have Cd numbers and you have to estimate the area (I am finding that .85 of WxH seems to give a decent number). I haven't been looking at newer cars much because for my application they weigh too darn much. Seems like for every year after 1995, the same exact car model puts on about 200 lbs.

Do you know of other sources for this info?

--Steve

welcame Steve :)

I don't really have any other sources. There was a real recent post about carfolio.com to get some info from. It seems alright. I was hoping you had compiled a spreadsheet with a bunch of small compacts and could just paste them into the post. :) I'd have to double check, but I believe in Hucho's book he recommends height times width times .81.

Yeah, I looked at carfolio.com -- lots of the data was missing (random check), so I haven't bothered looking there any more. I also don't know where they got their data from, so I don't know whether to rely on it or not.

Re the .85 factor, I've heard of .8 and .81; I picked .85 since it seemed to match the EV1 and Insight numbers. I think it would depend on how rounded (side to side) the body is and cars vary quite a bit in that (the Prius is darn near rectangular!). For my uses, the .85 is likely "worst case" which is what I'm designing to. If whatever vehicle I end up with turns out to be a little better, that's a welcome "plus".

As far as my "spreadsheet"--it's just numbers on of paper--I've mostly started from lightweight vehicles and tried to add CdAs as I could find them. Maybe this will help:

Since weight is important to me, and weight (at least curb weight) is fairly easy to find, I looked at a *vast* array of vehicles and discovered that American mfrs don't make light cars. So I ruled all those out--basically I was looking for 2,000 lbs (900 kg) curb weight or less. The other set of cars I ruled out were sports cars--no room for batteries and, usually, their CdAs are horrible because despite the low "A", they have crappy Cds (usually). There are exceptions--'93 Mazda RX-7 is listed at 5.61 but its curb weight is 2600 lbs. The '95 Mitsubishi eclipse GSX and GS-T are listed at 5.92. I also wanted a car that was popular so I'd be able to get parts, etc. so that ruled out a lot of foreign cars -- even the Insight didn't sell that well, so that, too, might be iffy (from my point of view).

What's left (for me) is a set of light cars with horrible CdAs: Tercel only weighs about 1800 lbs but the CdA is listed in the low 7s. Geos are light, too, but are about 6.8 or so (for those that I could find)--the problem there is the payload capacity (in lbs) isn't that great. Some Subarus aren't too bad; something called the SVX has a CdA of about 6.0 for the '92, but I haven't (yet) found the weight--also don't know what it looks like. Honda Civics are pretty bad: '94 DX is 7.22 for example (don't know what body type) and they seem weigh up in the 2200 lb region.

The problem with compiling a list is that there are so many considerations, I wouldn't know how to sort it for someone else--that and the fact that the CdAs really aren't available for most cars. I mean, do you cut it off at a CdA of 7? 6.5? How about year: go back as far as 1990? 1980? (I know, you were hoping for whatever I *did* have, but I kinda got going there :) )

My best advice is 1) decide what mfrs you're willing to consider, 2) consider what CdAs you're willing to live with. Then go to mayfco and click on the boxes for those mfrs. There are so few cars listed you can see at at a glance what, if anything, matches your criteria. After that, it's just slogging, model by model looking at various car sites for whatever scraps of info you can find. What I've found so far is darn few cars are under 6; most are in the mid-6s to mid-7s.

If you have specific criteria in mind, I could look through my notes (about 20 pages worth) and see if I notice anything (assuming I have the relevant info) that would be of use to you.


--Steve

Hey Steve, welcome to EM. If you are still hunting for an Insight, your best bet would be to just physically go to the local Honda wrecking yards and check it out for yourself. The yard I got mine from didn't even know it was an Insight, they had it listed in their stock as a Civic coupe so you can't really rely on them to know what they have got.

The Suby SVX isn't a bad looking car, it is a V6 though
http://kenbattleservices.com/db3/002...mages/SVX1.jpg
And it weighs 3600lbx

Thanks Red,

I read your build thread with great interest. I'll have a go at a local junk yard, as you suggest--probably this weekend. Thanks for the photo of the SVX. It is heavy, as you say; what counts, of course, is how heavy it is after I get rid of the ICE-related stuff and the V6 sounds like it would reduce the weight by quite a bit (though I'm not enough of a car guy to guess at how much). Still, starting with 3600 lbs, I'd have to remove 1600 lbs of stuff to get down to a glider of 2000. That sounds like more than the ICE stuff is likely to weigh, and even at 2000, I'm still way over what a Tercel glider would weigh (not that I'm in love with Tercels, but they *are* light).

--Steve

P.S. Somehow I missed it, but now I see from your profile you're in my neck of the woods. I'm mid-Peninsula and the yards I know about are mostly in San Jose. Where did you find your Insight, if you don't mind sharing?

Thanks, its been a fun experience. Cool cool, I'm over on the other side of the bridge in the Easy Bay.

It would take some major gutting to get the SVX down to 2000lbs. Its a kind of luxo-sport so most of the weight could just be tied up in sound deadening and creature comforts. But it a 3.3 V6 with a 4spd Auto tied into an AWD system, so if you were to gut the drive train entirely you might get close. I can only use Heeps drive line as a comparison but the engine, transmission and transfer case alone weigh in at ~700-800lbs, so the Suby could be possible.

I found my Insight at Action Auto Wreckers in San Jose. SJ seems to be the best place for Hondas from what I've seen. There are a couple of yards up in Hayward that are ok, and there is a ton up in Sacramento. Never looked for any Japanese parts up north, but if you are looking for anything domestic, Sac has some of the biggest yards.

Very useful info, thanks! It's funny about Action Auto Wreckers--their ad in the Yellow Pages says "All American Cars and Trucks" so I had crossed them off my list when thinking about Japanese parts! Glad you set me straight on that one.

--Steve

Nah they have 3 yards, a Honda Mazda, GM, Chrysler all within walking distance of each other.

Thanks H4MM3R....

Red: visited the auto wrecker--you got a *great* deal on your Insight...all the stuff I saw there looked like a train had hit it (head on). Nothing I'd consider for a project car. Back to Craigslist...or maybe Sacramento for a look-see....sigh.....

--Steve