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IssacZachary
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Re: Aeromod nissan leaf improved aerodynamics increased range

Tue Mar 14, 2017 3:59 pm

LeftieBiker wrote:That Kammback would sell well as an aftermarket Leaf accessory.

Along with wheel skirts. :mrgreen:
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kidjan
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Re: Aeromod nissan leaf improved aerodynamics increased range

Tue Mar 21, 2017 12:22 pm

NeilBlanchard wrote:
kidjan wrote:It's also worth noting that aero mods on an electric vehicle with regenerative braking should result in a bigger efficiency increase than on an ICE vehicle, because any air resistance slowing the vehicle down could have been converted into electricity. In essence, poor aerodynamics are a penalty paid twice by cars with regenerative braking.


Lower drag also means better coasting, and coasting is the best use of the kinetic energy of the moving car. Regen is great for when you need to slow down, but coasting means you accelerate less in the first place, then use it better. Regen is icing on the cake.


Understood, but when traveling over hilly terrain, or going down a mountain pass, all of that potential energy is either A) converted into kinetic energy, which is then wasted heating brakes or B) reclaimed through regen. I live in Utah; I can add 12% or more driving down little cottonwood because the road is pretty slow and steep (30 to 40 mph). But I do far less well on Parleys (I-80), because the flow of traffic is so much faster. At 60 mph or so, wind eats a lot of the regeneration I could be getting.

I could drive slower, but I'd likely be rear-ended.

kidjan
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Re: Aeromod nissan leaf improved aerodynamics increased range

Tue Mar 21, 2017 12:23 pm

lorenfb wrote:While traveling on freeways (50% of driving) at 60 - 65 MPH in the past, my overall average was about 4.5 miles/kWh.
Presently, my freeway speeds are 50 - 52 MPH. My overall average is now 5.1 miles/kWh. That's about a 13% improvement
without any aero mods, and how simple was that!


These things aren't mutually exclusive. You can do both.

VitaminJ
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Re: Aeromod nissan leaf improved aerodynamics increased range

Tue Mar 21, 2017 12:32 pm

kidjan wrote:Understood, but when traveling over hilly terrain, or going down a mountain pass, all of that potential energy is either A) converted into kinetic energy, which is then wasted heating brakes or B) reclaimed through regen. I live in Utah; I can add 12% or more driving down little cottonwood because the road is pretty slow and steep (30 to 40 mph). But I do far less well on Parleys (I-80), because the flow of traffic is so much faster. At 60 mph or so, wind eats a lot of the regeneration I could be getting.

I could drive slower, but I'd likely be rear-ended.

Two things:

Under A: you don't need to use the brakes and waste the kinetic energy. Let's say your target speed is 60mph. When coasting downhill you can accelerate to 65-70-75mph without braking, then point the nose of the car up the next hill and wait until the car decelerates back down to 60mph before adding throttle. If you have aero mods you will both gain more speed downhill and bleed less speed off as you coast uphill.

And B: regen is less efficient than just coasting, which was the original point. Regen should only be used when it's absolutely necessary to slow down, like in traffic or going into a corner, red light, etc. and even then it's best to just coast all the way to a stop (but like you said there are rear-ending risks and risks of being a jackass on the road to worry about). But to your example of I-80 downhill, with aero mods you can maintain that faster 60mph speed AND the increased regen of lower speeds because you have effectively lowered the braking force of the drag so for the same speed you can increase the braking force of regen.

Maybe that's exactly your same point haha oh well I already typed it.
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NeilBlanchard
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Re: Aeromod nissan leaf improved aerodynamics increased range

Fri Mar 24, 2017 11:36 am

VitaminJ wrote:
kidjan wrote:Understood, but when traveling over hilly terrain, or going down a mountain pass, all of that potential energy is either A) converted into kinetic energy, which is then wasted heating brakes or B) reclaimed through regen. I live in Utah; I can add 12% or more driving down little cottonwood because the road is pretty slow and steep (30 to 40 mph). But I do far less well on Parleys (I-80), because the flow of traffic is so much faster. At 60 mph or so, wind eats a lot of the regeneration I could be getting.

I could drive slower, but I'd likely be rear-ended.

Two things:

Under A: you don't need to use the brakes and waste the kinetic energy. Let's say your target speed is 60mph. When coasting downhill you can accelerate to 65-70-75mph without braking, then point the nose of the car up the next hill and wait until the car decelerates back down to 60mph before adding throttle. If you have aero mods you will both gain more speed downhill and bleed less speed off as you coast uphill.

And B: regen is less efficient than just coasting, which was the original point. Regen should only be used when it's absolutely necessary to slow down, like in traffic or going into a corner, red light, etc. and even then it's best to just coast all the way to a stop (but like you said there are rear-ending risks and risks of being a jackass on the road to worry about). But to your example of I-80 downhill, with aero mods you can maintain that faster 60mph speed AND the increased regen of lower speeds because you have effectively lowered the braking force of the drag so for the same speed you can increase the braking force of regen.

Maybe that's exactly your same point haha oh well I already typed it.


Exactly - well said.

I call the technique swooping. As you get used to driving on a route, you learn to start coasting at / before the crest, so you don't go so fast on the way down to be unsafe or get a ticket; and you learn where you can carry speed to get part way up the next hill by coasting down the previous one. Another method is to use a bit of acceleration near the bottom of the hill to extend the benefit of the car's kinetic energy.

Making sure your tires are well inflated is also key. The stock Leaf Ecopia tires are very low rolling resistance, and having them inflated to 42PSI or 45 (up to the sidewall max of 51PSI) will help lower rolling drag, and this lowers the consumption, and raises the range.

kidjan
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Re: Aeromod nissan leaf improved aerodynamics increased range

Fri Mar 24, 2017 12:25 pm

Understood, but for mountain passes, "swooping" doesn't apply. That's my point--you grind battery on the way up, regen on the way down. The only thing that helps is less wind resistance on the way up, and less on the way down to increase the amount of regen that can happen.

I'm really not talking about "coasting" at all. Agreed regen isn't beneficial there.

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IssacZachary
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Re: Aeromod nissan leaf improved aerodynamics increased range

Fri Mar 24, 2017 2:22 pm

The regen vs. coasting isn't as easy as this is better than that.

If you were to go down a long straight slope with no speed limit simply coasting wouldn't be the most efficient choice. Basically the car would speed up until the force of gravity on the car is equal to the force of aerodynamic drag and rolling resistance. At that point you wouldn't be using any electric energy, but you wouldn't be gaining any either. Once at the bottom the car would have a lot of kinetic energy that you could still use to coast on for a while more. But that would be about it.

On the other hand, let's say you regen and keep you speed down low most of the hill. You would have a lot less air drag, so a lot more energy would be being converted back into electrical energy. Now regen isn't the greatest. But at least you'd be getting something back. As you near the bottom, however, it wouldn't make much sense to regen right down to the bottom and then switch right back to electric propulsion. Instead, at a certain point closet to the bottom the car could be "shifted" into neutral and you could build up momentum. Air drag would increase, but it would only be momentarily, not the whole mountain. You could build up quite a bit of momentum then and have enough to keep coasting after the long down hill slope.

Monarch pass is a perfect example of where this would work. Clear from the top down the whole pass has a speed limit of 45mph with corners as slow as 25mph. Most trucks don't do over 35mph. You could put it in B mode and use the cruise to maintain 25 to 35mph down nearly most of the whole mountain. Near the bottom the speed limit changes to 65mph. At that point you can easily "shift" into neutral and coast up to 65mph or more. I bet in that small section you could hit over 80mph if you tried by just coasting. But if it were possible to coast clear from the top (which it isn't because of the curves) I doubt you'd get much more than 80mph because by that point you'd nearly have more air drag than gravity.
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kidjan
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Re: Aeromod nissan leaf improved aerodynamics increased range

Sat Mar 25, 2017 12:11 pm

I'm really unclear what point you're trying to make. The bottom line is wind resistance is wasted energy that could have been put into regen in many instances--for example going down a long mountain pass--hence the thread on improving aerodynamics.

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IssacZachary
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Re: Aeromod nissan leaf improved aerodynamics increased range

Sat Mar 25, 2017 8:13 pm

kidjan wrote:I'm really unclear what point you're trying to make. The bottom line is wind resistance is wasted energy that could have been put into regen in many instances--for example going down a long mountain pass--hence the thread on improving aerodynamics.

That there are times when it's better to regen brake and go slow down a hill, and times when it is better to shift into neutral and let the vehicle speed up. It's not a "this is always better than that" situation. On a long slope it's best to regen brake from the top down most of the way. But if you're close to the bottom, the amount of energy you would get from regen braking would be less than the kinetic momentum you could build up by coasting.
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kidjan
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Re: Aeromod nissan leaf improved aerodynamics increased range

Mon Mar 27, 2017 9:53 am

I understand your point now.

Still, we're talking about aerodynamic efficiency. If I'm going down parleys canyon (roughly twelve miles of travel, ~2500 feet drop) the optimization you're describing isn't noteworthy. 11.5 miles of regen is going to dwarf what you're talking about. And aerodynamic improvements will help both the coasting and regen scenarios, for that matter.

If we're talking about hilly midwestern terrain with 100 ft climbs here and there, sure. But in a state like Utah, where 500 ft of elevation gain is normal (I do something close to that just dropping my kid off at school), optimizing aero to improve regen is a lot more interesting.
Last edited by kidjan on Mon Mar 27, 2017 10:07 am, edited 1 time in total.

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