JoeS
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Re: Aerodynamic Mods to Reduce Drag

Fri Sep 05, 2014 10:50 am

There are many schemes for captive nuts; however, they presume the skirt is screwed on from the outside leaving an exposed screwhead. I was thinking something more along the lines of an inside clamp onto an inserted lip that would be invisible from the outside for those who worry about looks. I agree that using rivnuts or something similar is much easier, and I also personally prefer simply screwing in from the outside (use SS) as function trumps aesthetics in my book. :geek:
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

NeilBlanchard
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Location: Maynard, MA Eaarth
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Re: Aerodynamic Mods to Reduce Drag

Sat Sep 27, 2014 6:26 pm

Today was a perfect day, and I took as much advantage of it as I could - I got most of the fiberglassing done on the wheel skirts and strakes, including on the inside to try an keep water out.

Image
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I will hopefully will get the Kamm panels done (on the outside, at least) tomorrow, and I may decide to fasten it to the car.

I noticed the improved coasting and the improved mileage, too. It is good to have this close to done.
Sincerely, Neil

http://neilblanchard.blogspot.com/

JoeS
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Re: Aerodynamic Mods to Reduce Drag

Sat Sep 27, 2014 7:32 pm

Neil, thank you for posting. Looking forward to your finishing this and then publishing the before/after test results.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

JoeS
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Re: Aerodynamic Mods to Reduce Drag

Fri Apr 17, 2015 12:20 pm

A little over a year ago I tried an experiment using some foam-cored sheets and simply taped them on.

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Now, with "my" i-MiEV (wife has her 'own'), I'd like to continue the experimentation. The material I'll use is a simple foam sandwich which I can epoxy sheathe with either fibreglass deckcloth or some very thin carbon cloth. Not a problem to produce a thin yet stiff fender skirt.

The issue is how to attach it -

After considering various cantilevered clamping techniques (which would only work in a couple of spots) I've come to the conclusion that a simple rivnut should work in both the sheet metal as well as the plastic bumper, with six rivnuts per side. The disadvantage is that I will now have six permanant holes in the wheelwell periphery. I could probably camouflage the fasteners (either with or without the fender skirt) with a dab of white paint.

Since both the sheet metal and bumper are very thin I think I need to use soft aluminum rivnuts, after appropriately coating the drilled hole to prevent galvanic corrosion. I was unable to find any plastic rivnuts which would do the same thing.

Questions:

1. I am open to suggestions for fender skirt attaching schemes
2. Anyone know of any plastic rivnuts?
3. Should I be concerned about corrosion between the aluminum rivnut and the car's sheet metal, recognizing that the rivnut is less noble?
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

Phximiev
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Location: Phoenix

Re: Aerodynamic Mods to Reduce Drag

Fri Apr 17, 2015 2:09 pm

What was the result of the experiment and how did you measure the difference in performance?
2012 iMIEV ES
2014 Chevy Volt

JoeS
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Re: Aerodynamic Mods to Reduce Drag

Fri Apr 17, 2015 6:28 pm

Phximiev wrote:What was the result of the experiment and how did you measure the difference in performance?
I think I mentioned here that the one-day test was inconclusive. Quite frankly, I don't think we would notice a difference while driving because many other variables have a greater influence. The way I look at it is that every little thing helps… besides, if it's good enough for my Gen1 Insight it's good enough for the i-MiEV. :geek:

I agree with NeilBlanchard that a full-length full-width smooth floorpan under the i-MiEV would be a significant help. Now, about that squared-off aft end...
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

Don
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Re: Aerodynamic Mods to Reduce Drag

Sun Apr 19, 2015 8:48 am

Since the initial tests were inconclusive, I think I'd stick with the tape idea until you determine they work well enough to justify drilling holes in the car. Since your car and the panel are both white, it should be easy enough to find some white tape which will closely match both. You might have to re-do the tape every six months or so, but hopefully by then you'll have an idea of whether they do anything for you - They don't do anything for the look of the car, so unless they prove really useful to extend range/efficiency, I don't think you'd want to drill holes . . . .

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2017 Chevy Volt Premier
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1979 Honda CBX six into six

pbui19
Posts: 143
Joined: Tue Jan 07, 2014 12:17 pm

Re: Aerodynamic Mods to Reduce Drag

Mon Apr 20, 2015 8:41 am

I am definitely going to do some aero mod, though I think the gain depends very much on your driving application. I believe highway speed would benefit most with aero mods, and not so much for around town.

A recent experiment with my '99 3-cyl Chevy Metro gave surprising & encouraging result. A cheap garden edging tie-wrapped for an air damp and partial grill block increased highway mpg from high 40s into low 50s. Further mods pushed mpg into the high 50s, flirting 60 mpg, with wheel covers, removal of passenger side mirror and windshield wipers. I also had similar improvement, though not as dramatic on the '95 Corolla, from 35 to 45 mpg.

It's more challenging on an EV to quantify the change though, as we "refill" daily and at fewer miles per refill.

I was planning to remove the iMiev windshield wiper since it usually doesn't rain in Calif after April, but this year weather is all funky

jray3
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Location: Tacoma area, WA
Contact: Website

Re: Aerodynamic Mods to Reduce Drag

Mon Apr 20, 2015 9:57 am

pbui19 wrote:I am definitely going to do some aero mod...
It's more challenging on an EV to quantify the change though, as we "refill" daily and at fewer miles per refill.

But with CanIon we have much more precise consumption data that can be de-linked from the 'refill' intervals.
Go for it pbui- we need more i-modders. Turns out I've got too many projects, and have promised the wife to mess around with our newest, most reliable, most efficient car the least of all. Go Figure! :roll:
2012 i-SE "MR BEAN" 94,000 miles
2000 Mazda Miata EV, 78 kW, 17 kWh
1983 Grumman Kurbwatt EV,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

Phximiev
Posts: 1187
Joined: Thu Jan 15, 2015 7:25 pm
Location: Phoenix

Re: Aerodynamic Mods to Reduce Drag

Mon Apr 20, 2015 1:12 pm

Aerodynamic improvements would seem to be worthwhile. Someone mentioned the Insight, so I found this:

http://www.insightcentral.net/forums/mp ... leage.html

All leads to the question of how you measure it?

I saw an older Insight the other day in the parking lot of the Changing Hands bookstore in Phoenix. It looked as if all of the drag areas had been eliminated and it had wheel 'skirts/covers'. I couldn't tell if it had a belly pan though. All red and looked great.

Definitly debatable, but wouldn't one need a wind tunnel to property measure it? Anyone here an engineer with that kind of experience?
2012 iMIEV ES
2014 Chevy Volt

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