iMiEV CdA?

[jray3]

Thanks Neil, and here I was wondering whether to resurrect an old thread!

 

[BillThompsonMIEV]

I guess my ignorance will now appear. It seems early on in this topic, the co-efficient of drag is .35. After this new information, what is the co-efficient of drag? My old 2006 Honda Civic Hybrid had a drag of .29 (I think). What is the i-MiEV?

 

[evcar]

just to point out that european (narrower) version of iMiEV (and also C-Zero/iOn) have Cd = 0.33
as compared to 0.35 US MIEV. Also new 2013 Leaf has Cd=0.28 (worth pointing out, older Leaf Cd=0.29)

 

[alohart]

It is easier to achieve a lower Cd with a longer vehicle. So the Leaf's better Cd when compared with the i-MiEV is partially due to the Leaf's greater length. The i-MiEV is derived from a Japanese kei car which is really a city car where a low Cd is not so important as with a car designed for more high-speed highway driving.

But that said, the i-MiEV's Cd could certainly have been lower had Mitsubishi tried harder. Non-North American i-MiEV's have a spoiler above the rear window that probably lowers its Cd. The front and rear fenders that protrude out from the sides probably add drag. The underside could have been more enclosed and smoother. But redesigning the existing kei car would have added cost to an already expensive car.

 

[Llecentaur]

I wonder if a spoiler or deflector in front of the window wiper can improve airflow. There seems to be quite a bit of turbulence noise at 60 mile/h coming from that area.

 

[NeilBlanchard]

A deflector on the wiper on most cars is almost useless; though conceivably on the i MiEV it might have a small benefit? I think putting on a 'all season' wiper blade would be as good as a deflector:

The back of any car is where most of the drag is generated. and the i MiEV could also benefit a fair bit from a smoother underside, as well - it has a very rough underside.

 

[jray3]

Using Neil's calculated area of 25.447, (cause I normally drive with mirrors and tires exposed to the wind) and the following calculator, http://gtechprosupport.com/support/AeroDragCalc.htm yields the following horsepower (and kW) cost at various mph.
82-32.7 (24.4)
80-30.4 (22.7)
75-25.0 (18.6)
70-20.4 (15.2)
65-16.3 (12.2)
60-12.8 (9.5)
55-9.9 (7.4)
50-7.4 (5.5)
45-5.4 (4.0)
40-3.8 (2.8)
35-2.5 (1.9)
30-1.6 (1.2)
25-0.9 (0.67)

So given that a gentle push will overcome rolling resistance, a gentle push plus a hairdryer will propel an i to 35 mph! (and demonstrates once again, more than 3x the power required at 55 mph is needed to hit 80.

For more scientific data, I just found this great German study with a wealth of tech data and a true coastdown test on slide 16.
http://www.aachen-colloquium-china.com/pdf/Vortr_Nachger/2011/27_Eckstein.pdf

 

[Don]

That looks about right

Note that the HP required *doubles* between 55 and 70 mph! You can really see why we can go so much farther at 30 or 35 mph. 35 is one quarter of what's needed for 55 and then it doubles again for 70 . . . . guess what? I'm in no hurry :mrgreen:

Fuel used in boats with displacement hulls is a similar proposition - There is a really efficient speed and then only slightly faster, there is a really expensive speed

Don

 

[jumpjack]

So have we got a final value for iMiev CdA? :?:

 

[NeilBlanchard]

24.052 sq ft of frontal area X 0.35 = CdA = 8.4182 sq ft.

 

[jumpjack]

24.052 sq ft of frontal area X 0.35 = CdA = 8.4182 sq ft.

thanks

 

[barrylevine]

oahumiev, now that you've had these for almost a half-year, I was wondering what your opinion of the AirTabs is now?

I'm the weekend Miev driver while my wife is the daily commuter, she had driven the car for a few months before putting the AirTabs on and she noticed a big difference in the handling, prior to the AirTabs she complained the Miev would be "nudged" during windy days at freeway speeds which would freak her out. Since putting the Airtabs, haven't heard that complaint once so yes, the Airtabs have helped with stability during windy days at high speeds. As for any FE gains, it takes us 12 bars to get to Honolulu and back home which is the same prior to installation. I've got to imagine that if one drives at higher speeds more frequently than lower speeds, these Airtabs might make a larger impact, we're relegated to 55mph speed limits here, no complaints however as the Miev is perfectly happy not having to get up to 75mph as they do on mainland interstates.

I'm a little late to this discussion, but interested in trying these, at least for the stability benefit. Another possible benefit I'm curious about is whether Airtabs can reduce the annoying low frequency rumble one gets with open rear windows. This is especially bad even at 30 mph. I assume it indicates some kind of turbulence, and I wonder if the Airtabs abrogate this noise.

Also, I wonder why you installed these just in front of the hatchback. Are they too large to fit on the top of the hatchback itself?

Thanks all.
Bought a 2016 iMiev this July. "Little car that could" in a nutshell.

 

[PV1]

I doubt the Airtabs would help with that, but the window vents certainly help. Bear has them and doesn't have the issue at all, but Koorz lacks them and can sometimes suffer from the buffer.

Although, the i-MiEV doesn't have that problem anywhere near as bad as on the C-Max. Even just cracking open a front window will cause it.

I might have to invest in tabs. With our climate changing, winter keeps getting warmer and windier (it was 78 degrees yesterday and is 60 right now. Absolute madness considering the average of 20). I keep thinking my wheels are loose when it turns out to just be the wind :x . Regardless of that, I'd just be happy if they keep the back window clean.