Aerodynamics of electric vehicles ...
- Thread starter odie
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It’s kind of a strange argument. All vehicle would use less fuel if they were more aerodynamic.
There are some benefits though with pure electric. They don’t need grills and wheels don’t need to be designed around as much cooling with regenerative braking. Even so, many customers want the look of grills and open wheels.
It also depends on the application. It’s not that critical at slower speeds as the effects of aerodynamic friction go up exponentially with speed. So a grocery getter may not need extreme shapes.
There are some benefits though with pure electric. They don’t need grills and wheels don’t need to be designed around as much cooling with regenerative braking. Even so, many customers want the look of grills and open wheels.
It also depends on the application. It’s not that critical at slower speeds as the effects of aerodynamic friction go up exponentially with speed. So a grocery getter may not need extreme shapes.
The List is not really useful, we only have half the data there, also need Frontal Area.
https://www.caranddriver.com/features/a15108689/drag-queens-aerodynamics-compared-comparison-test/
Take a look at the list at the bottom shows how frontal area and Coefficient of Drag play a role.
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This is a pretty good piece on Cd if you can stomach Cammisa.
I think the VW XL1 hybrid prototype had a Cd of just 0.159. I am unaware of anything lower in the automotive world. The drag coefficient of the limited production version has increased slightly from 0.186 to 0.189.
Sort of a silly comparison, but a Cessna 172 (going by memory) has a total zero lift aircraft Cd of less than 0.03. And about 6 square feet of "drag" area.
Sort of a silly comparison, but a Cessna 172 (going by memory) has a total zero lift aircraft Cd of less than 0.03. And about 6 square feet of "drag" area.
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My first Alfa had a Cd of 0.29, in 1992 and it was a road car. It had a very nice effect on top speed, and fuel consumption wasn't horrible either but I didn't do enough freeway to get the benefit of either.
I think the VW XL1 hybrid prototype had a Cd of just 0.159. I am unaware of anything lower in the automotive world. The drag coefficient of the limited production version has increased slightly from 0.186 to 0.189.
Sort of a silly comparison, but a Cessna 172 (going by memory) has a total zero lift aircraft Cd of less than 0.03. And about 6 square feet of "drag" area.
The Pontiac Banshee IV was pretty extreme. They didn’t publish any drag coefficient though.
I remember seeing images of the results of an aerodynamics contest from maybe the 1930s. Many were round designs, but one entrant seemed to believe that a flat, vertical windshield was aerodynamic.
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it's pretty useful. Frontal aero doesn't very that much among categories of cars. I mean, you're correct,you can't measure CdA without "A", but the reality is that if you're comparing similar cars, the one with the lowest Cd is almost always going to have the lowest CdA.
CFD has completely changed the game when it comes to this stuff. The fact that a Tesla Model S has aerodynamics similar to the EV1 shows just how things have changed from the days of mock-ups, wind tunnel, repeat...
No discussion of car aerodynamics is complete without a nod to the king of all home-brew projects: The Aerocivic
I understand that aerodynamics are an important part of an EV's range but don't know that I would go so far as to call them "key".
Otherwise we would see a lot more extreme designs. But what we really see in many cases is a manufacturer's existing model like an SUV or pickup truck with a battery added. Not exactly vehicles known for a low CD.
Regarding the EV's lack of requirement for a large opening for a radiator and intake grills for brake cooling, we know that manufacturers already have a lot of "fake" cosmetic features on cars. Like dual or quad exhaust tips that when you look under the car prove to be for style rather than function and huge scoops and intake ports or in the case of Hondas, fake grills on the rear of the vehicle. What a joke.
Anyway, Tesla has done a good job styling the Model S front end to look more traditional, they need to do something with their pug nosed Model 3 and Model Y too. A "fake" piece of chrome or something imitating a conventional grill would go a long way towards improving their appearance.
Otherwise we would see a lot more extreme designs. But what we really see in many cases is a manufacturer's existing model like an SUV or pickup truck with a battery added. Not exactly vehicles known for a low CD.
Regarding the EV's lack of requirement for a large opening for a radiator and intake grills for brake cooling, we know that manufacturers already have a lot of "fake" cosmetic features on cars. Like dual or quad exhaust tips that when you look under the car prove to be for style rather than function and huge scoops and intake ports or in the case of Hondas, fake grills on the rear of the vehicle. What a joke.
Anyway, Tesla has done a good job styling the Model S front end to look more traditional, they need to do something with their pug nosed Model 3 and Model Y too. A "fake" piece of chrome or something imitating a conventional grill would go a long way towards improving their appearance.
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I think it's pretty key. A 10% reduction in drag= a 5% increase in range. Take something like Volvo's XC40, which is basically a legacy product that's been electrified, and a Cd of .34, and compare it to a ground-up EV in the same category, a VW ID4. The Drag is Cd is .28, and front area is roughly the same--so drag is likely about 20% less. That equates to at last 20 extra miles per charge. That's pretty significant (and at higher speeds, when you're likely to need the range more, such as long trips, that number is going to increase since power requirements increase at roughly the cube of speed).
I think the reason you don't see more crazy designs is because of CFD, which allows you to model changes in design in a way that is orders of magnitude more efficient. This allows manufacturers to produce cars that don't look ridiculous but have incredibly low drag. The Tesla Model S (impossibly low CdA and still looks amazing) and the new Rivan Truck (almost HALF the drag of a similar-sized Dodge Ram) are just a couple more examples.
I mean, drag matters for ICE-powered cars as well, but I think with the whole range anxiety thing (and the reality that charging on the road isn't as efficient) it's just become a much more significant focus for designers.
If you need any proof of the benefits of CFD in design, it's worth noting that the Honda Insight and the VW ID4 have almost identical drag coefficients. They were designed at very different times, using very different tools.
There were a lot of those. The most egregious was the 90s Mustang that looked like a hood scoop but had some hex patterned plastic piece.
But tradition is weird. I’ve heard some EVs even pump in a fake exhaust note.
My friend's drop dead gorgeous BMW i8 plays engine noise through the radio. Debbie thinks it's stupid. She loves the car; who wouldn't?
I believe the Porsche Taycan somehow amplifies the electric motor noise. I hear it is amazing...
They need the noise outside. In certain situations a EV can creep up behind a pedestrian. Those can be dangerous and deadly for the person if they don’t know the car is behind them.
A lot of the ICE car aero drag comes from air going into the hood and under the car (say the bumper cover scooping air like a spoon in a bowl of soup).
There is much less cooling need for an EV, the engine requires a lot of air around to cool it in addition to the radiator, and the air flow around exhaust manifold and pipe all the way also requires a certain amount of air flow to keep things cool. Removing that need means EV can be much more aerodynamic, blocking air going under the hood and under the car. Without exhaust pipe also means the whole area can be covered up as long as the suspension movement is not impacted.
Wheel wise, hybrid should be about the same as EV, but you still need enough worst case cooling going downhill on an already full battery. You don't want an overheated brake so you still need to size the airflow for the weight of the vehicle in an EV, or find a way to dump that heat from regen downhill traffic into the radiator.
There is much less cooling need for an EV, the engine requires a lot of air around to cool it in addition to the radiator, and the air flow around exhaust manifold and pipe all the way also requires a certain amount of air flow to keep things cool. Removing that need means EV can be much more aerodynamic, blocking air going under the hood and under the car. Without exhaust pipe also means the whole area can be covered up as long as the suspension movement is not impacted.
Wheel wise, hybrid should be about the same as EV, but you still need enough worst case cooling going downhill on an already full battery. You don't want an overheated brake so you still need to size the airflow for the weight of the vehicle in an EV, or find a way to dump that heat from regen downhill traffic into the radiator.
There are a bunch of EVs regularly on my neighborhood, and I can hear a whoosh style sound. But tuning an exhaust style noise seems more like it’s for the driver than anything else. I heard the programming is tied to the acceleration and speed in some cases. Not sure how this is done as an add on for a Tesla, but I heard many of these are factory setups.
I sat in (but didn’t ride in) a GM EV1 when visiting my cousin for her wedding. But a friend’s mom worked for Southern California Edison, and apparently they paid for the entire lease to encourage employees to try it. It didn’t make any odd noises going forward, but it had a backup beep like a delivery truck.
Yep ... aerodynamic drag is a function of Cd x A. The other factor in the HP needed to maintain a constant speed is the rolling resistance of the tires, which is a function of the tires and the weight of the vehicle.
I ran all the numbers on my C5 Z06 (the Cd is 0.32), and at 60 MPH it takes 21.2 HP total to maintain that speed which broke down as 11.0 HP of aerodynamic drag and 10.2 HP of rolling resistance. So at 60 MPH, the aerodynamic drag is 52% and rolling resistance 48%.
At 80 MPH it becomes a total of 39.7 HP, with 26.0 HP (65%) for aerodrag and 13.7 HP (35%) for rolling resistance.
At 120 MPH it becomes a total of 108.3 HP, with 87.9 HP (81%) for aerodrag and 20.5 HP (19%) for rolling resistance.
At 175 MPH it becomes a total of 302.3 HP, with 272.5 HP (90%) for aerodrag and 29.9 HP (10%) for rolling resistance.
Aerodrag force is a squared function of velocity and the aerodrag HP is a cubic function of velocity, so aerodrag HP becomes huge (and a huge percentage of the total HP required) as the speed increase of course. Rolling resistance HP is linear.
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Yes and no. Yes, there are challenges when you cut holes into the front of the car, but if you manage the air flow coming in (keep it as laminar as possible and provide a place for it to go), it's certainly possible to mitigate the big hole in the front. The A Class and some other vehicles have managed it well. Additionally, the underside of the car and controlling air separation at the back are really where the magic happens.
