An Electric Very Light Car?
Saturday, August 7, 2010 at 10:59AMEdison2’s Very Light Car Scoffs at Electric Avenue said AutoBlog Green in January, highlighting the irony of our internal combustion engine powered car sitting in the midst of all the electrics at the Detroit Auto Show.
But electric vehicles are here to stay and an electric VLC makes sense. Our breakthroughs in platform efficiency make all vehicles way more efficient, regardless of power source, and in an electric help solve issues of cost and range.
Billions are being invested in electric vehicle technology for a number of reasons. EV’s provide a path to energy independence and with American jobs, whether in the creation of green energy sources or in the mining and processing of coal. As a new industry, electric cars have the potential to revitalize important sectors of our economy. Electric vehicles are particularly efficient in short-cycle applications, such as Postal Service vans or some predictable commuters, and the relocation of emissions to a distance can be an advantage. Night-time charging will utilize excess generating capacity, and as the electric grid becomes green so can the future of transportation.
Currently, however, electrics cars have real issues. Batteries are heavy, big and costly. With electric drives cars get heavier, performance suffers and costs go up. Range is especially an issue, as witnessed by the numerous EVs in the 100-mile range X Prize alternative classes that made it to the knockout stage, versus only one EV in the 200-mile range mainstream class.
The hope and plan for electric cars is that the tremendous investment in battery technology will cause the weight and expense of batteries to go down, increasing range and decreasing costs of electric cars. But another way to increase the range of electric vehicles is with VLC innovations: a car that simply takes less energy to move can go farther and faster with a smaller, lighter and less expensive battery pack.
Coming soon, perhaps: an electric Very Light Car.
Reader Comments (95)
Back to the discussion of the relative importance of rolling resistance and aerodynamics.
Firstly, let me thank Kevin for fixing up my spreadsheet related to the Aptera performance. More on that in a moment.
My original argument was that rolling resistance is about equally important to aerodynamics even at highway speeds for vehicles with low aerodynamic drag. Reviewing my spreadsheets, I find great support for this argument with the EV1. At 55 MPH, a full 50% of the power is going into rolling resistance and this drops to 42% at 65 MPH. This suggests the importance of rolling resistance even on highways.
One nice thing about the EV1 is there is great data from the INL (Idaho National Labs). This includes energy consumption at 45 MPH and 60 MPH. This data gives me great confidence in my analysis assuming a 78% efficiency in the drive train.
So back to Aptera. Well it looks like I messed up the drag coefficient and frontal area numbers. Of course I had a little help from Aptera. Aptera started with a claim of Cd = 0.11 in 2007. This changed to a claim of 0.15 in 2009. Now Kevin claims the number to be 0.21. If that is the case, it is worse than the EV1 and close to the Prius at 0.25.
I also messed up the frontal area. So in the end my CdA was only 25% of what it should have been. Pretty bad.
Still, using Kevin's improved numbers, I find the rolling resistance accounts for 37% at 55 MPH and 30% at 65 MPH. This is still a significant percentage of the overall force needed to push the vehicle down the road.
One thing seems painfully clear; weights, Cd, and frontal area all seem to increase as cars near production readiness. The same fate may befall the Edison2 team.
Later
John C. Briggs
Thanks, John - you're welcome.
I agree both weight / rolling resistance and aero drag are important, of course. The EV1 is a pretty heavy car with really good aero - so you'd expect it to have a higher "crossover" speed between rolling / aero drag dominating. The Edison2 is ~30MPH, Aptera ~42MPH. You make a good point that both forces remain important even when one is larger.
I'd be interested in hearing Barnaby's opinion, but here's my view on Aptera's aero design just based on visuals. They did OK on the body, but the front wheel struts and pods could be much better. Note that there are at least 3 bars in each strut, and they are closely spaced and not necessarily optimized cross section. The wheel pods are kind-of blocky too and could be thinner and streamlined better. Lastly, the wheel pods are quite close to the body, which can contribute to "interference" drag (see: http://jeb.biologists.org/cgi/reprint/154/1/439.pdf ). Note that in comparison, the Edison2 cars have single struts with a very elongated teardrop cross-section, thin and streamlined pods and the pods are pushed outboard quite a bit (which improves handling too).
Regarding the trend of weight and Cd when the Edison2 moves to a production design - I agree 100% with you that it will get less optimum. That's OK, as it still should be able to perform better than anything else out there. For example, even though I understand why Barnaby designed the wheel struts and pods as they are (optimized to compete in the XP) for a production car it needs improved aesthetics. I think that the wheel treatments of the GM “Autonomy” concept car would be one approach to consider. See: http://hdhalla.tripod.com/GeneralMotorsAUTOnomy.jpg and http://www.ridelust.com/wp-content/uploads/2002_autonomy.jpg The wheel “pods” are connected via 2 struts (upper and lower) with an open area in-between. This would certainly increase drag a bit vs. today’s version, but would look a lot nicer !
Kevin
The Aptera is front wheel drive, and the middle piece is the drive shaft, so they would have to either enclose it (which would be hard because of the CV boot), or they could possibly have a trailing piece behind the rotating shaft that helped have a cleaner flow?
This is the biggest thing about the Edison2 VLC -- the struts are fixed, so they can be fully streamlined.
I very much doubt the Aptera is a Cd as poor as 0.21, though I could be wrong. I think they have serious weight issues (the rumors on the Aptera Forum are 2,300-2,700 pounds!) when the target was 1,500-1,800 pounds. The other major challenge for Aptera, IMO is they have some electrical losses -- they had heating problems, apparently.
But enough about Aptera, I want to discuss the VLC EV, and the Li-ion and TW4XP; since they are consulting with Edison2. I hope we hear about how a low mass, low drag, VLC EV can get down around (or below) 100wH/mile -- that would be at or around what the early Aptera prototypes were getting.
I've no doubt that an VLC EV could do very well, and my only concern is with the rear wheel drive limiting the regenerative braking. The Li-ion is front wheel drive, and this may be part of how it achieved the best efficiency; save the E-Tracers.
Sincerely, Neil
It is interesting that Edison2 is consulting with Li-ion and TW4XP. Li-ion carefully manages each cell on their batteries, and TW4XP uses a high voltage system.
The Raceabout with its four wheel hub motors delivered very good mpge for a heavier car with a fairly conventional body design.
Some hub motors on Solar Racers are 98% efficient, and use just 1200 to 1500 watts at 60mph. That would be only 20 to 25 Wh per mile at a highway cruising speed.
Hello,
The Raceabout has direct drive motors, but they are not hub motors. I asked one of the team members, and with the very open wheels, you can see the large brake disks that occupy the space where the hub motors would have to be. I'm fairly certain the Raceabout is similar to the FVT eVaro in this regard: they use drive shafts without any reduction gears, and custom made motors.
Sincerely, Neil
Neil,
Insightful comments about rear wheel drive vs. regeneration in the eVLC.
Just to clarify my position on the Aptera Cd - I reconciled the published XPrize MPGe data with the supposed weight (820Kg/1800lbs) and used the 1.85M^2 frontal area from your guesstimate (thanks) - and then massaged the Cd and net electrical efficiency in a spreadsheet to try to get it all to net-out correctly. The end result suggested a Cd of about 0.21 and a (rather poor) 60% net electrical efficiency. When I compare the 0.21 Cd to other "known" Cd's, I'll say that it is probably within +/-10%, but it is still a guesstimate.
You mentioned that the center "bar" in the Aptera front struts is the driveshaft. If that shaft is 1 inch diameter, then the drag of the driveshaft alone (not counting the rest of the strut) is about the same as a 10 inch wide teardrop shaped single strut. In other words - Aptera would have been better off to have a SINGLE streamlined structural strut of, say, 6 inches wide, and hide the driveshaft in it (similar to what Edison2 did).
I'm interested in seeing what the Cd x A value for the LI-Ion car is, as I think it will also be very good.
regards,
Kevin
Greetings,
The challenge with covering the *whole* suspension package on the Aptera is highlighted by comparing it to the way the Edison2 VLC is set up:
On the VLC, all the suspension is located inside the hub of the rim -- the airfoil strut is *fixed*. The aerodynamic wheel fairing/pod does not move up and down with the suspension motion. The steering motion is the only requirement that their design has to finalize. I think it is not possible (or it would require a major redesign) to add front wheel drive to the VLC. Or, maybe I'm wrong, and they had planned for this possibility?
On the Aptera 2e, it is a double wishbone, and the front wheel drive requires a drive shaft and the CV joint are required -- and all of these elements must move up and down, and so I think their best (only?) improvement would be to have a trailing "wedge" close behind the rotating drive shaft the is fixed in position to fill in the turbulent zone, and that moved up and down with the suspension motion. The resulting shape would be *very* close to an airfoil, and the drag penalty of the drive shaft would be virtually nil.
I think the drive shafts are the majority of the increase in Cd from 0.11 to 0.15 (these are CFD generated numbers, and are probably a little idealized?). The side mirrors are the other major contributor (the "Zen" model had video cameras in dimples). I think the new Aptera wheel fairings/pods are actually significantly better aero drag than the previous units. The air flow between the wheels and the main chassis makes things asymmetrical, and the new shape works better in it's actual situation.
The measured Cd of the VLC (by the same "old" method as used by Aptera?) is 0.145. The new SAE method gives a Cd of 0.161. This includes the cooling air flow through the engine bay, and the spinning tires up inside the wheel pods, etc.
I'm curious to hear if the VLC got tested in any "yaw" situations while in the GM wind tunnel, to mimic crosswinds? Since the engine cooling comes from a NACA intake on either side of the VLC, it is likely that at least the cooling is affected in cross winds. My guesstimate solution to improve this is to locate the cooling intake on the underside of the VLC -- this would make it more forgiving to crosswinds, and it could help by reducing rear lift a little, possibly?
BTW, I think that the outboard wheel fairings/pods on the VLC and the Aptera 2e *may* *not* be the ultimate low drag scheme. The body itself may be the best, but when you have to add the wheels, the drag may then go higher than other schemes. For example; here is a Mercedes development model of their Bionic/Boxfish car that has a Cd of just 0.095:
http://img.photobucket.com/albums/v724/NeilBlanchard/CarBEN%20EV%20Concept/Bionic-Car-Body-lg.jpg
The computer model of the boxfish itself had a Cd of a staggeringly low 0.06:
http://2.bp.blogspot.com/_nDFb67ks_mU/SSCNKR9ipvI/AAAAAAAAAA0/espJJtz-1ww/s1600-h/mercedes-benz_bionic_concept_car2.jpg
So, it is possible that a very practically shaped car, with an EV drive train (that doesn't require very much cooling air flow) could be as low Cd as 0.1. Here's my attempt at such a design; which has seating for 5 humans:
http://neilblanchard.vox.com/library/post/carben-concept-ev-an-open-source-project.html
The *key* to such a design is to have articulated front wheel covers, that move at sharp steering angles, to allow space for the tires; but that remain in place at highway speeds -- because the wheels only move a *little* bit when steering at higher speeds. Since this kind of design is one cohesive shape, there is much less chance for "interaction" between the outboard wheels and the chassis.
Sincerely, Neil
Someone correct me if I am wrong, but I believe Aptera started life without mirrors and with rear wheel drive. It was only after testing and examining the laws that they had to switch to FWD and mirrors. Wonder if other vehicle manufacturers will be forced to do the same.
You are correct John. The rear wheel drive was dropped because front wheel drive provides better traction (especially on a three wheeled vehicle) and because it allows much more regenerative braking.
I think the optical mirrors only law needs to be changed. I've been driving with video mirrors for almost 2 years now:
http://neilblanchard.vox.com/library/post/eyes-forward-video-mirrors-on-my-xa.html
They are not perfect, but with better screens, and maybe with optically corrected video lenses, they would be better overall.
Sincerely, Neil
Neil Blanchard,
Our thinking is parallel in many respects, particularly with the objective of avoiding the weakening effect of side doors. Look at US 7,758,094 granted last month. You might also look at US published Patent Application 11/893,497 for various related possibilities.
But more interesting now is that you brought up the boxfish work by Daimler Benz of a few years ago. If you recall, they discussed that they gave up about 50% for lowering the body from free flow height where they got about .06 for Cd. Wheels added some as well.
Perhaps you will not feel "beat over the head" like Kevin on the next post when I continue to emphasize the benefits of elevating the car so that the ground plane does not degrade Cd by that huge amount. And of course, the airship body shape is close to .04 for Cd which is about the most thoroughly measured shape in existence, but only in free flow conditions.
Why would we not make serious effort to benefit from these well known facts? Open thinking folks like you could accomplish a lot in that direction. Of course you would risk offending Kevin for talking about something that looks funny.
Neil Blanchard,
Thanks for pointing out that Aptera had gone to front wheel drive. That does indeed improve traction, but would only relate to regenerative braking efficiency in extreme situations, that might include driving on ice, but the overall effect would be nil.
Hi Jim,
The Schlörwagen (that I mention in my blog several times) also demonstrated the effect of ride height (which is somewhat different from the effect of the outboard wheels I am referring to). If the ride height is too high, then more of the wheels/tires are exposed to the air flow, and if it is too low, then the air is "squished" and the air flow is restricted and slowed; also causing drag. They settled on a "happy medium" of about 6", if I am not mistaken. The underside of the CarBŒN design has a minimum of 6" near the front wheels, and it rises to about 12" at the rear bumper.
All braking works the same, no matter how the stopping power is generated: about 70% of the braking power is generated by the front wheel(s) because of the weight shift that happens when a vehicle slows down. Front brakes always have to be larger/stronger for this reason. If the rear brakes are too strong, they will lock up, even in normal stopping events. So, if the front wheels only have friction brakes, then they must balance the braking power generated by the rear wheels. The regen from the rear only would not be able to stop the vehicle on it's own -- and a lot of regen would be wasted because if you apply too much braking to them, they will lock up; even in normal/good conditions. So, you either get very long stopping distances, and/or you heat up the front brakes; instead of regain some of that energy through regen.
So, to get the most regenerative braking possible, the front wheels must be used. The FVT eVaro gets virtually *all* of it's braking power from the regen on the front wheels, and it uses the friction brakes only below 5 mph. And the eVaro can do the 60-0 stop in 130 feet.
Sincerely, Neil
Hi Neil,
I couldn't find the Schlorwagen info, but from your discussion it seems clear that this was a study of a standard car, with wheel wells and all that goes with it.
Edison2 shows the benefit of eliminating that issue by putting the wheels in separate pods, far enough out to minimize interference. This arrangement surely has merit, and it makes possible a simple body form that works fairly well.
But if the body is elevated, and it can be a boxfish or an airship, the ground effect can be minimized, and as the discussions here have shown, the aero drag is significantly more important than weight. Thus, the penalty of the road effect on vehicle efficiency is very strong. Why not work to eliminate it?
Yup, you have to really grit your teeth to focus on something really unusual looking.
Kevin thinks the strange looking Miastrada will not sell, and many agree, but if it did, it could do more for the reduction of CO2 than all the currently popular stuff put together. Yes, I expect a 12 hp engine could push it along at 80 mph, so people could get along with their lives as they now seem to like.
Hi Jim,
Here's all the Schlörwagen pictures I have found:
http://smg.photobucket.com/albums/v724/NeilBlanchard/Schlor%20Pillbug/
Pretty amazing for 1938, or any time, for that matter. It is anything *but* a standard car, I think?
Sincerely, Neil
Thanks Neil for the link to Schlorwagen pictures. The Dymaxion is not too different from this, and that also performed very well, except that it did not survive the banker's cut.
The Schlorwagen looks even more like a half airship, with the ground plane representing something like a split plane, such as is used in computational fluid dynamics to reduce computer time for modeling. It might not have been ever made low enough to function like this. Since they settled on 6 inches, that would have resulted in high velocity air flow under the vehicle and thus low pressure under the vehicle, which would be the basis for forming vortices as air flow mixed rearward. Morelli used 'camber' which really means that there is there is a curve to the underbody that causes slower air flow toward the rear and thus the air flows meeting at the rear are matched in velocity. It sounds like you might be using this effect.
But neither the Schlorwagen nor the Dymaxion would have been conceivable in elevated forms, which would have allowed airship like performance. This is because they were constrained by the fundamental requirement for double wide seating. If we could imagine these as much thinner bodies that are bodies of revolution, roughly four feet in diameter, then they could have been raised so that ground clearance would be sufficient such that free flow conditions were approximated. With single wide seating, the resulting overall vehicle height can be about six feet. But if you start with a car body that is seven feet wide and five feet vertically, and add three feet of clearance underneath, the result would be unmanageable. (As a rule of thumb, I say the clearance needs to be about half the square root of the projected frontal area. Morelli's (1982) wind tunnel work seems to be consistent with this rule.)
If we are proceding on the assumption that wheel pods are separate aerodynamic entities, as with the Edison2 designs, the Schlorwagen study of elevation where wheels protrude more with higher elevations, is not relevant.
.
Hi Jim,
The air around the car doesn't have a velocity relative to the ground -- except when the vehicle pushes it up/down/sideways as it moves relative to the ground. The front of the car moves the air up/down/sideways, and the back of the car needs to fill in the part of that "hole" where the air can't get back into in time. It's the atmospheric pressure that pushes the air back in to fill the "hole" that the vehicle has created.
The underside of the vehicle cannot have as steep of an angle of closure as the top and sides, because the ground limits the quantity of air that can move back into the "hole". Raising the vehicle up makes it possible for more air to return that way, but the increased frontal area of the tires/wheels increases the drag.
So, both the Aptera and the Edison2 designs have their wheels outboard of the main chassis, so, each wheel is acting like the main chassis; the front pushes the air up/down/sideways, and the back part needs to fill in the space that the air cannot get back into in time. AND, each of the outboard wheels interacts with the air that the main chassis is pushing up/down/sideways, so by definition, the spaces in between the wheels and the main chassis is different than the chassis in free space.
The ride height matters for both monolithic designs like the Schlörwagen/Bionic/CarBŒN and Edison2/Aptera designs. The original Morelli car (the banana car: http://ecomodder.com/forum/showthread.php/interesting-aerodynamic-cars-mike-vetters-etv-also-avion-11732-7.html#post186034 ) interestingly is more or less a monolithic design.
Sincerely, Neil
Neil Blanchard,
Thanks for the ecomodder link. Now I understand that we are talking about two different things. The paper I am referring to defines what I call the Morelli shape. It is a theoretical shape that differs from the vehicle of the Popular Mechanics article that you show.
See: See the book, Impact of Aerodynamics on Vehicle Design from an International Conference held at the Café’ Royale, London , 16-18 June, 1982. The book is the proceedings of that conference and was published by Inderscience Enterprises Ltd., La Motte Chambers, St. Helier, Jersey, Channel Islands, UK , in 1983. It is a special publication (SP3) published “in parallel” with the Int’l. J. of Vehicle Design. The ISBN is 0 907776 01 9. The sponsoring technical society was the International Association for Vehicle Design. The Inderscience site is http://www.inderscience.com/conf/index.php.
Also you might look at the book on solar cars by Eric Thacher where the basic Morelli shape is discussed with reference to these projects.
After you see this paper, then tell me where you think the Aptera shape came from.
Curiously the automotive world mostly ignored this work, and even Morelli discusses real world issues in the conclusion of that paper that seem to lead him to ignore much of his own work.
Neil Blanchard,
Your perception of air velocity is incorrect. There is significant air velocity relative to the vehicle and this exceeds the velocity of the vehicle such that the air has this velocity relative to the ground, under the vehicle especially. This is the fundamental premise that Morelli shows to be the cause of vortices.
Over population and over crowding is becoming a major factor in appropriate vehicle design.
In China, wind resistance is a non issue when the roads are so overcrowded that traffic hardly moves -- One solution is a giant elevated vehicle; a 1400 passenger elevated bus that cars can travel under as it straddles multiple lanes.
A recent university of Oregon study found that a person's decision to have one more child has twenty times more impact on global warming than any other choice a person can make.
The following stories are courtesy of Car Tech:
62-mile traffic jam snarls up Beijing
by Staff Writers
Beijing (UPI) Aug 24, 2010
The world's largest traffic jam, stretching up to 62 miles, is now in it's 10th day in Beijing.
The massive tie-up has been blamed on road construction aimed at alleviating congestion caused by thousands of trucks transporting coal and perishable goods into Beijing.
At the back of the line in Inner Mongolia, trucks were reported to be inching along at 2 miles per day.
Stranded motorists -- many who were passing the time playing cards -- have complained about vendors capitalizing on the mega-traffic jam by selling bottled water, instant noodles and other foodstuffs at four times the regular price.
Congestion is expected to last for nearly another month, until the roadwork is completed.
While Beijing has taken measures to ease traffic, including introducing odd-even number traffic controls and staggered working hours, usual tie-ups on the roads are further compounded by a continual onslaught of newly purchased vehicles.
Beijing Mayor Guo Jinlong said the city aims to increase the rate of commuters using public transport to 40 percent this year from 38 percent last year.
China, the world's top emitter of greenhouse gases, overtook the United States as the world's largest auto market in terms of vehicles sold in 2009.
Beijing had a total of 4.4 million vehicles on the roads during the first half of this year, figures from the municipal commission of transport show. During the same period, the number of vehicles increased by 1,900 per day on average.
At that growth rate, the total number of vehicles in the Chinese capital would hit 7 million by 2015, said Guo Jifu, head of the Beijing Transportation Research Center, the state-owned news agency Xinhua reports.
Guo Jifu warned Monday that Beijing's road network could only accommodate 6.7 million vehicles.
Average driving speeds in Beijing would likely drop to less than 9.3 miles per hour in five years if the number of vehicles continues increasing.
Beijing scored the highest on the "commuter pain" index in an IBM Global Commuter survey, which ranks the emotional and economic toll of commuting.
A stunning 95 percent of those surveyed in Beijing said that roadway traffic had negatively affected their health, compared with 29 percent of overall respondents around the globe.
"Our government should pick up the pace of urban infrastructure construction and spend some of its budget," said Niu Fengrui, director of the Institute for Urban and Environmental Studies at the Chinese Academy of Social Sciences, reports the Global Times.
earlier related report
Solution to Beijing's traffic woes? The elevated 'super bus'
Beijing (AFP) Aug 24, 2010 - China's capital Beijing, recently named along with Mexico City as having the worst traffic jams in the world, is looking for solutions. One could be the elevated "super bus".
The bus, due to be tested in the coming months in the western part of the city, travels on rails and straddles two lanes of traffic, allowing cars to drive under its passenger compartment, which holds up to 1,400 people.
"We're going to start laying down test tracks along a six-kilometre (four-mile) stretch towards the end of the year," Song Youzhou, the chief executive of design firm Shenzhen Hashi Future Parking Equipment, told AFP on Tuesday.
"From the second half of 2011, we're planning to test the bus with passengers on board," he said, noting that after a full year of trial runs, authorities would make a decision on whether to use the bus on a wide scale.
Song said Hashi was in talks with three Chinese carmakers to produce the eco-friendly bus, which runs on both electricity and solar power.
Authorities hope eventually to install 180 kilometres of "straddle bus" lines including a route to the capital's international airport, Song told the official Global Times.
Song said the "super bus" could ease traffic congestion by up to 30 percent, as it does not take up actual road space, but special tracks would have to be put down, elevated bus stops built and new traffic signals developed.
Only small and medium-sized vehicles will be able to pass under the bus, meaning drivers will have to be extra-vigilant. An alarm would sound if an oversized vehicle attempted to pass, the report said.
Song said the bus had to be tested with car drivers in real-time situations to detect any possible problems.
According to government data, Beijing is on track to have five million cars on its roads by year's end. The four million mark was passed in December.
The head of the Beijing Transportation Research Centre, Guo Jifu, warned this week that traffic in the capital could slow to under 15 kilometres an hour on average if further measures were not taken to limit the number of cars.
Private cars are currently kept off Beijing's roads for one day per week depending on licence plate numbers.
Beijing's air is among the most polluted in the world, and the problem is getting worse amid high demand for private vehicles from its increasingly affluent residents.
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Solution to Beijing's traffic woes? The elevated 'super bus'
Beijing (AFP) Aug 24, 2010
China's capital Beijing, recently named along with Mexico City as having the worst traffic jams in the world, is looking for solutions. One could be the elevated "super bus". The bus, due to be tested in the coming months in the western part of the city, travels on rails and straddles two lanes of traffic, allowing cars to drive under its passenger compartment, which holds up to 1,400 people ... read more
Greetings,
I am responsible for this as anyone else -- I think we need to try to stay on topic; i.e. the EV VLC.
Sincerely, Neil