NeilBlanchard
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Aerodynamic Improvements for Longer Range

Sat Nov 08, 2014 7:49 am

A typical car with a Cd of ~0.34 has a bit over 50% of the load on the drivetrain - at 30MPH.

The drag from aerodynamic flow increases by the square of the speed. So, at 55MPH the aero drag is ~78%.

Here is an online calculator for this: http://ecomodder.com/forum/tool-aero-rolling-resistance.php

Aerodynamic drag is a total loss. Which is why aero drag is more important than vehicle weight. Because we have two ways to reclaim some of the kinetic energy of the moving car: the best way is to use the kinetic energy to do what it is already doing - moving the car forward. The second way is to use regenerative braking - when you need to slow the car down. Regen is always going to be less efficient than coasting because regen can only reclaim some of the kinetic energy as electricity, because the motor and charger and the battery each have losses.

I know it is possible to greatly increase the efficiency of a car. I have been averaging ~50% above the EPA rating on my ICE car (2005 Scion xA) for over 5 years. I have lowered the Cd of my car from ~0.31 to ~0.26 - I did a coastdown test, and I have made several improvements since then. One of which I added side view video mirrors in place of the "paddle" optical mirrors. They are backup video cameras with ~140° view angles and I have two 7" LED backlit monitors side by side right in front of me. I have virtually no blind spots on the sides of the car. And this reduces both the frontal area (by about 1 sq ft) and it reduces the Cd, as well.

I have a 4/5ths grill block. I have smooth wheel covers. I have front wheel skirts to close the gap between the wheel and thee wheel opening. I have rear wheel skirts, and strakes. I have Kamm panels on the sides and the top of the hatch. I need to add a partial belly pan in the back, and complete the Kamm back with a panel under the rear bumper.

I don't think we can get that much of an improvement on the Leaf, because the Leaf is already so much more efficient than any ICE. My spouse and I together are already averaging 2.5X better energy efficiency than I am on my aero modded Scion xA.

So, has anybody here done any aerodynamic mods to your Leaf?

edatoakrun
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Re: Aerodynamic Improvements for Longer Range

Sat Nov 08, 2014 10:03 am

NeilBlanchard wrote:...I don't think we can get that much of an improvement on the Leaf...


Reducing the distance from belly pan to road surface would likely give the greatest benefit.

A few have lowered ride height of their LEAFs by altering the suspension, but I can't recall any efficiency reports, before and after.

This could be easily tested by swapping the stock wheels/tires with those with smaller radius, though very high-speed/high-motor rpm efficiency would suffer, and you would, of course, change the speedometer/odometer errors from stock.

I'm surprised no one with frequent freeway speed driving needs, who does not require high (I do a lot of off-pavement driving, and need the stock ride height) road clearance, hasn't reported trying this.

MY 2013-15 LEAFs improved efficiency over 11-12's by partially blocking the front air intake.

You might get some more improvement by blocking further, though you have to take the LEAF's cooling needs into account.
no condition is permanent

NeilBlanchard
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Re: Aerodynamic Improvements for Longer Range

Sat Nov 08, 2014 9:03 pm

Actually, going too low hurts the drag. Race cars have to avoid lift, but downforce adds drag. Low drag needs to be neutral.

As the car moves forward, the air has to move back into place behind it - and the turbulence at the back is where most of the drag is created. By having less air flow under the car, this sucks the air in from the top and sides, creating a lot of turbulence behind the car. Ideally the pressure on all sides of the back of the car are as close to equal as possible; which would let the air settle back into place with as little motion as possible.

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drees
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Re: Aerodynamic Improvements for Longer Range

Sat Nov 08, 2014 10:59 pm

Yep, lowering on the LEAF only really helps because it will pull the wheels/tires deeper into the wheel wells, so they are exposed less to the wind. That said, I do have Tein lowering springs on my LEAF and can't tell any significant difference in efficiency on highway trips, but then again, I didn't attempt to collect any detailed data, either.

Sounds like you already have a good handle on where you can improve the LEAF based on your experience with the Scion. BTW - post pics, would love to see the work. All the same concepts there will work on the LEAF. [Edit: Found your thread on Ecomodder for those who want to see Neil's work - looks great]

As with all vehicles, generally the biggest gains will be in reducing the size of the hole the car leaves in the air by tapering the rear of the car using a kammback shape. The biggest problem there is building anything that looks even half-way acceptable, but it'd still be interesting to mock something up using some coroplast (maybe with all the left over political signs) to see what's possible.

Aside from that, the usual suspects would be interesting:

1. Smooth wheel covers - steel wheels with smooth wheel covers - since the LEAF S comes with steel wheels, it shouldn't be hard to test this.
2. Grill block - The biggest need for cooling probably comes from the cooling system. Anywhere besides Arizona could probably block half of it easily.
3. Mirror delete is interesting. Since you already have a camera setup, it would be interesting to compare.
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woodgeek
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Re: Aerodynamic Improvements for Longer Range

Sun Nov 09, 2014 4:10 am

Interesting thread....I know video cameras for the side mirrors are coming...but are they street legal now?

People like to bash the poor Cd's on the Leaf, but I think that's unfair. For a given volume, the best way to lower the Cd is to go long and thin (Cds on trains are amazing). There an implicit penalty on short, stubby, wide cars.

IOW, we know that the Leaf is tall (headroom is nice), seats three across the back (seats 5 is nice) and has plenty of cargo. Lots of volume in a stubby package = limits to how low Cd can go. Take the same volume, make it low slung, less headroom, narrower (seat 4) and longer cargo bay and hood, and you would have a car with great Cd that lacks the features we love, and that would look like an EV1 or a Volt or a Prius C.

Loving the LEAF's form factor and hating the Cd makes about as much sense as folks that say 'Keep the goverment's hands off my Social Security!'. :lol:

NeilBlanchard
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Re: Aerodynamic Improvements for Longer Range

Sun Nov 09, 2014 4:59 am

Hopefully Tesla gets video mirrors approved for the Model X; and if they are, I am sure the model S will get them, too. So, on new cars they are not allowed - yet. I have to put my stock optical mirrors back on for safety inspections. But I have had them for about 5 years now, and they are fine the rest of the time.

Here are my video mirrors:

Image

Notice I have a small optical mirror - this is for when I am getting out of the car when parked on the street, and because habits are hard to break. Having both monitors in one place means I see over 180° in one glance. At dusk and in the rain, video mirrors are great. At night you see lights, but the resolution is lower. In bright sun, they are less useful, because of limitation in the cameras and the monitors. A shround would be a good thing.

I do not get blinded by high beams behind me. I see the rear bumpers of vehicles that are even with my shoulders - so virtually no blind spots. I see large vehicles behind me in both monitors; though a rear view optical mirror is still better for this.

The downside to the super wide angle view is that cars look much farther away that they are. You can learn how to just this by turning your head to see the car once you know it is there from the video mirrors.

As far as testing things, we are leasing our Leaf S, so I don't think my spouse will let me test stuff more complicated than the smooth wheel covers. Since we have use of regen, it is very unlikely to be an issue for cooling brakes. And I have no issues with the brakes on my Scion - cool brakes are the pride of a practiced ecodriver!

Another point that needs to be made is when the aero drag is lower, the coasting is better. When the coasting is better, you accelerate less. The energy consumption is lowered, and you accelerate less.

Coasting is taking full advantage of road candy!

Cd is the key thing - the shape of the car is what matters most. The bluff back of the Leaf is the biggest challenge to lower drag. Tapering the top - and sides down and inward is how to gain the most improvements. So, having the back longer would help, and the practicality of the inside volume could remain as it is.

Once the Cd comes down, reductions in frontal area have less and less affect. In Car&Driver's recent wind tunnel testing of five cars, including the Leaf, they showed that Cd trumps frontal area: the Model S ties the Prius for CdA.

The Model S' Cd of 0.24 equalizes it's much larger frontal area, making it the same aerodynamic drag as the Prius.

NeilBlanchard
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Re: Aerodynamic Improvements for Longer Range

Sun Nov 09, 2014 5:54 am

Another case in point on aero drag and longer ranges - a modified gen 2 Prius with a 20kWh battery pack going 129 miles in EV mode:

http://ecomodder.com/forum/showthread.php/208-km-129-mi-ev-mode-2007-prius-30107.html

Image

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EVDRIVER
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Re: Aerodynamic Improvements for Longer Range

Sun Nov 09, 2014 9:57 am

I created a mount inside my grill that catches the air from the front of the car and hits three generator fans and then feeds the power to one smaller and faster fan under the back of the car that pushes the car faster with a net gain for efficiency. One of my Unity-Plus TM products I will soon be offering for the LEAF.

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drees
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Re: Aerodynamic Improvements for Longer Range

Mon Nov 10, 2014 12:05 am

Hahah, nice job making fun of everyone in this thread, EVDRIVER. :roll:

Back on topic - are there any good ways to install aero wheel covers on the stock alloy wheels?

The only way I've found is to use threaded zip-ties as this guy did on TMC - see these two posts:

http://www.teslamotorsclub.com/showthre ... post241921
http://www.teslamotorsclub.com/showthre ... post242524

He said he got about 5% improvement in efficiency at highway speeds - not bad. Of course, you can always get the same effect by driving a few MPH slower, too.
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cwerdna
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Re: Aerodynamic Improvements for Longer Range

Mon Nov 10, 2014 12:19 am

I personally don't pay attention to ecomodder, but the Gen 2 Prius posted earlier brought to mind this modded one: http://priuschat.com/threads/1000-mile- ... ost-869017. Supposedly that guy has access to a wind tunnel.

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