Annoy As Little Air As Possible
Friday, August 20, 2010 at 06:00PMTo say that the Very Light Car displays great aerodynamic efficiency is an understatement. This summer we spent a shift in the GM wind tunnel in Warren, Michigan, and we just flat-out nailed it. We recorded a 0.16 coefficient of drag: the best results ever seen in their wind tunnel, we were told.
No wonder. Our Chief of Aerodynamics is Barnaby Wainfan, the aerodynamics fellow at Northrup Grumman. The goal of aerodynamic efficiency is to punch as small a hole in the air as possible and try to close it seamlessly behind you, or as Barnaby says “annoy as little air as possible.”
Air separates as it flows around a car and inevitably creates a “dead zone” of low pressure behind, an inefficiency known as “base drag”. A way to help close the air is with a tail: either a horizontal “beaver tail”, seen on our X Prize competitor Aptera, or with the vertical “fish tail” we employ.
A big part of not annoying air is keeping it from entering the car except as necessary, such as for cooling. Contemporary cars often have oversize grills and usually exposed wheel wells: both allow air to enter and bang around inside the car. The car grabs this air and accelerates it to the speed the car is traveling and the energy for this comes from the engine.
With the Very Light Car we enclose the wheels outside the body in pods. This design allows a smaller frontal area, with each wheel pod also poking its own small hole in the air. We are deliberate about exactly where and how much air enters the car. We then put the air back outside where it will do the most good, reintroducing it into the “dead zone”. We also avoid exposing anything to the air that we do not have to, using cameras instead of mirrors and flush-mounting the door latches.
Drag coefficient (Cd) might be the headline number but to know actual drag you need to factor in this frontal area. When Cd and frontal area are multiplied together, the product, CdA, allows you to directly compare different cars. It turns out a Hummer H2 (which not only is huge but also has a terrible aerodynamic shape) has about 9 times the drag of the Very Light Car. Even a 2010 Prius, a car with a very good Cd (.25), has almost twice our drag.
At Edison2 we take great care and pride in making only definite and supportable claims about our car. Our drag numbers were obtained by the dedicated and competent engineers running one of the world’s top wind tunnels. We have since backed those numbers up with the best-ever coast down results measured by an equally impressive and credentialed facility.
The overall goal in aerodynamic efficiency is a car that moves through the air with minimal effort. The ultimate would be if the only drag was the friction of air against the car’s body. That perfection may be unattainable, but the Very Light Car comes close.
Reader Comments (39)
Cd of .16 is quite good for a car, but you are still throwing away a lot.
Simple things first; you 'poke' four small holes in the air instead of two, which could be easilly remedied by the wheel train arrangement. A little work needs to go into the fairing that allows wheels to turn or have spring action. There is a minor penalty for length, but this is a lot less than having a back wheel which has to start all over again, and it is in dirty air as well. Dirty air makes laminar flow a little messier than otherwise might be happening.
Then you insist on dragging along near the road, which causes higher velocity under the vehicle, which is the basic beginning of vortices, as discussed by Morelli, 1982. Of course your aerodynamicist has read this article. But oops, maybe not an aero aerodynamicist from Northrop. They do not usually worry much about the ground plane at Northrop. In the space business at Lockheed we did not worry about that either, but in Marine Systems the ocean surface interface was a major consideration with surface ship configurations.
Dragging along near the road was remedied by Morelli with his fore-runner of the Aptera like shape where he managed to get Cd of about .04 in the wind tunnel. That was with a simple body without wheels or anything else except a width that would accommodate two people. Unfortunately that shape sort of made rear seats difficult, and thus, we have the Aptera. I point out that by the time they put wheels etc. on Morelli's shape, Cd went up to about .20 and the automotive industry mostly ignored the whole effort.
I suspect that the whole problem of vortices was considered in your design ( I was just kidding about your Northrop guy), but the requirement for a rear seat and low configuration limits what can be done.
Still, Edison2 did well, and of course there is only so much tradition bashing that can be done at one time. Maybe when things get really difficult with energy, as soon I think they will, it will be time for some more serious tradition bashing.
The automotive tradition accepts that a car is a 'bluff body' which is an absurdity if anybody cares at all about efficiency. The Morelli shape with a 'beaver tail' was involved in closing the flow at the rear in a way that minimized vortices. The focus in that concept was camber which arranged for air flow from all directions as it converged at the rear to be at velocities that were equal. Thus as the air streams came together there was no rotational effect introduced.
0.143 CD for the SunRaycer tested in the GM wind tunnel
http://www.prnewswire.com/news-releases/gm-commemorates-30-years-of-aerodynamic-progress-99933789.html
Interestingly, GM used to claim this number to be 0.125 but now use the 0.143 number. I think GM recently found some errors in the calibration of their wind tunnel.
The production car with the lowest CD was GMs own EV1 with a drag of 0.195. However one has to wonder if they tested it today it might be 0.22 due to recalibration.
Also the joy of being the new comer, Edison2 has no rearview mirrors. Great that is where Aptera started out too. However they found that California law requires rearview mirrors and they had to put them on to get homologated. Of course, you could fight the law instead.
Edison2's accomplishments with low drag are truly amazing. But history has shown these numbers tend to worsen as the vehicle nears production.
Later
John C. Briggs
I ran some "what if" numbers using a modified version of JCBriggs spreadsheet to see what the sensitivity of MPG would be when Edison2 adds the weight of batteries. Of course, these are guesstimates. It looks like for each 500 lbs added, the highway mileage will fall by only about 7% (at 65MPH) and about twice that much at a constant 40MPH. If the 800 lb VLC gets ~120MPG at 65MPH, then it would get 111MPG with +500lbs and 104MPG with +1000lbs. Using XPrize methods for electric powered cars (and assuming a net elect. efficiency of 70% plug-to-wheel), this equates to about 260 and 243 MPGe (for +500 and +1000lb). At a constant 40MPH, the MPGe numbers would be a phenomenal 530 and 467 MPGe respectively!!!!!! Lastly - the range with using, say, the ~500 lbs / $8000 / 16 KWh battery from the Chevy Volt would be ~100 miles at 65MPH and ~200 miles at a constant 40MPH ! Add the benefits of regenerative braking and FUTURE green potential of eCars (see - I get it...but it's sadly going to take 30 years to get the grid off of fossil fuels) - and things start looking really good.
So...I've become a believer that an electric Edison2 car makes sense in that it will be more practical and affordable than other eCars. It would be reliable, clean and simple.
I would still like to see a turbo-diesel version of the Edsion2 car as well, which could get over150MPG on the highway, and could run on biodiesel (made from Algae?). This car could easily have a 1000 mile range, and be refilled in minutes, and actually generate LESS greenhouse gasses than the electric version (with today's grid). I still see this as a more optimum solution for at least the next 20+ years...but admit that the electric version is OK too, and gets better over time.
Kevin
Kevin,
My thinking evolves much along the same lines as yours, but there are some things you do not seem to include adequately.
You show effectively that some weight could be added without much overall impact, and I would tend to use that to work in a hybrid system, along the lines of the dual drive arrangement of the Prius. This 'synergy' drive means that much of the energy gets directly coupled from engine to wheels without being subjected to electrical losses, and the electrical part is used for regenerative braking but it also allows a smaller engine because the load peaks are carried by the electrical system. The smaller engine means weight is reduced, and the whole thing might come out not a lot heavier.
It is also important to note that the Prius engine has been developed, partly due to the load leveling assistance of the electrical equipment, to attain a thermal efficiency of 36% to 38%. So our prior assumptions about internal combustion engines are not entirely right. I also point out that a 16 hp Kubota engine that offers 35% efficiency is surprisingly light weight, that being about 190 lb. That Kubota engine would probably do fine on your biofuels if that becomes a reality. But we also must note that the Kubota engine does not make the cut for NOx when it comes to automotive engines of the near future and so catalytic converters are needed, and these are also a hoped for and possibly near term development.
So it seems there is a lot to sort out before we really know the best configuration.
We also have a possibility that hybrid vehicles with small engines running on natural gas could be parked next to households and used to make electricity. This would greatly surpass central power plants in system efficiency if the heat discharged from the engines could be used to provide heat to the same households. This heat would heat houses in winter and run diffusion chiller air cooling systems in the summer. This would displace otherwise necessary burning of natural gas. I refer to this as a 'best and highest use' for natural gas. Natural gas will last a long time if we use it this way, instead of using it wastefully in central power plants where most of the heat is simply thrown away.
Though this is all a bit more complicated than hoped for wind and solar, it has the advantage of being a nearly zero cost change and offers the possibility of rapid scale-up to make a meaningful difference.
Kevin, that was a Kubota diesel engine.
Jim,
Well...everyone is is entitled to their opinion, but I don't think a hybrid makes any sense for Edison2, not to mention the much higher risk and development effort. I say - stick with simplicity: either a straight BEV, or a straight turbo-diesel (I say DO BOTH!). Hybrids exist to try to get fuel-burning range and convenience plus regenerative braking to help with urban driving cycle MPG. With Edison2's low weight and drag - EV range would be pretty good (great if you go for a 1000 lb battery), and you get regen. The benefit of allowing the engine to run at a more constant opterating point exists in series hybrids, but is small and is even smaller for a diesel.
Kubota diesels are fine, but more aimed at stationary industrial applications. The are a bit heavy for their power (sorry, the 16HP model is not enough). Efficiency is OK, as is the Prius atkinson-cycle engine, but world-class turbo diesels from VW and Audi, etc. are even better - some with net thermal efficiency over 40% (and they meet emissions too). Since 40-50HP would be adequate - someone could chop one of these engines in half ! Realistically, there are some 3-cyl engines such as the new small Mercedes that probably fit the bill nicely. I'm sure Ron Mathis can school all of us on the details of cutting-edge turbodiesels.
My research into Stirling Engines and all things energy related has clarified the benefits of "Combined Heat and Power" where waste heat can be used for secondary purposes such as heating a home. I think your <thinking> is OK on this. However, using an automobile as the basis for CHP seems bizzare to say the least. I see that you patented that concept - good luck with commercializing it.
Speaking of commercialization - I understand the aero principle behind your "miastrada" idea that you keep beating us over the head with. Sure...the Cd of the body structure can be lower if you raise it way up off the ground. However, by the time you add all that outrageous undercarriage - you're going to negate most or probably all of the aero benefits, and it will handle like a shopping cart. And...sorry, but "extremely bizarre" aesthetics doesn't sell except if you want to drive it next to the "star trek enterprise car" in the next parade.
I've developed commercial products of various types my whole career, and have learned some keys to success (always willing to learn more, by the way). Being innovative and leveraging laws of physics in new and beneficial ways are important, and we agree on that. However, the product must be SIMPLE, RELIABLE, ATTRACTIVE (enough) and COST EFFECTIVE to be a sales success.
Sorry to be a little "snippy" here, but you keep trying to be "Mr. know it all" yet your comments are often idiotic. I can tell that you know some technical factiods - maybe you have a physics degree ? The balanced merging of physics with practicality is what engineering is all about...and I think you need to take a few of those classes before you arrogantly criticise people such as Barnaby Wainfan, who is clearly a world-class expert, as proven by what Edison2 has just done.
Anyway - as much as I know about technology (which is significant), I remain in awe of the acheivement the Edison2 has just done. This is truly a dream team. They didn't just talk about how to make cars better - they did it.
Personally, I really like the in-home CHP (combined heat and power) idea and think that it combines well with EVs and solar.
So in-home CHP is basically a natural gas driven engine. The idea is a little bizarre so hang in there. When I first heard of it I thought it was ridiculous.
If you need heat for your home, you turn on this generator and have it make electricity. The electricity is a premium product that is sold on the grid if you don't need it at that moment. What you will use immediately is the "waste" heat from the generator to heat your home. This system is highly efficient because all the energy is put to valuable use. In contrast, if natural gas is burned in a power plant, the waste heat is generally dumped into the environment. So 50% to 60% of the energy content of the nat. gas is wasted.
I think this system matches well to solar PV systems which are weak in the winter.
John C. Briggs
OK, I'm feeling bad for dissing Jim Bullis. Although I meant what I said, and felt that he was offensive with his comments about Barnaby's skills - I should have held my "tongue"...sorry Jim.
Upon reflection - the world needs more people thinking about ways to help humanity dig out of the energy problems in which we find ourselves...and sometimes people that may seem like crackpots actually have breakthrough ideas. Keep it up...but try to be more balanced and respectful to those that deserve it.
Combined Heat and Power is one of those concepts that makes good intuitive sense, and at first seems like the "perfect" solution. However, it actually only works well in very isolated cases - usually where the waste heat can be used beneficially directly at a low temperature (like heating a home or pool). If one learns thermodynamic principles of entropy, exergy, carnot efficiency, etc. - many of the cases that look appealing fall apart.
For example - many people suggest putting a small steam engine or peltier device to run on the exhaust heat of cars. Sounds good...but the temperature is low so the efficiency will be very low, and the total amount of useful work that can be extracted is extremely small (not cost effective). Similarly, the waste heat of a natural gas burning hybrid car + generator is too low to efficiently run a condensation-cycle air conditioner with enough BTU output to be useful. You're probably much better off just using a heat-pump and run it off of electricity. If you live in a cold climate, then CHP can work in the winter pretty well because the waste heat can be used directly without further conversion.
Kevin
Kevin,
Your understanding of CHP and mine are totally different. I was not talking about turning waste heat into work again. I agree that is inefficient. I was talking about using the waste heat to heat a home. Even very low quality heat is suitable for that purpose.
John C. Briggs
Kevin,
The bizarre CHP system was preceded in the patent literature by Toyota among others. All that is not completely resolved, but it turns on fine distinctions whether there is a patent or not.
When you label something constructive as 'bizarre' I wonder where this comes from.
Why is it offensive to point out things that Barnaby seems to have failed to adequately consider? Is he a hero figure that is immune. Even Isaac Newton missed a few things, so Barnaby should not be upset.
And you say 16 hp is not enough, but it does seem quite adequate if full aerodynamic features are implemented. Yes, the undercarriage I show on the web site is a little complex, and maybe there are some simplifications coming along. Look at the patents some more to get a hint.
OK - John, you're right that CHP as a term is technically just for using the waste heat directly, which is actually where waste heat usage works best. I expanded in my description to other uses of waste heat which really should be called something else, but often are discussed in the same conversations as CHP. I'll stand corrected...but please read my comments and you'll see that I actually did partition the two distinctions without clarifying it very well. For what it's worth - Jim Bullis had mentioned using the waste heat to run an evaporation-cycle air conditioner with waste heat, so that is why I included this in my comments.
Jim - well...OK. I should not have been so judgemental - sorry. Of course Barnaby, myself, or anyone else is never above questioning...but with respect. I over-reacted when I perceived a lack thereof. I really don't have much to say about your car patents, which I did actually skim. I'm sure you know that getting a patent does not guarantee it works, is practical or is even unique. Maybe bizarre was too strong a word...I'll leave it at that.
On a more positive note, I saw in another chat area that you've run across professor David MacKay in the UK. I've read his book and actually had a couple email conversations with him. I 100% agree with your assessment that something is very wrong there. I think he is smart enough and educated enough to know that his analyses about the efficiency of electric cars are bunk, but most of his book is nicely transparent. He basically admitted (though not directly) that his agenda was to get electric cars into the wold ASAP, and it didn't seem to matter to him that this is a big waste of money and does not help save energy or CO2 emissions until the power plants get off of fossil fuels. He is no longer a professor, but is a political appointee in the UK government - and believe me, he is a "bought man" on this issue. The X-Prize rules and the way that they have dealt with any questioning about their similarly distorted analysis shows that there is clearly the same agenda behind-the-scenes in this country. I think the underlying hope is that it creates local jobs and helps get the transition to greener power going, even if it is the cart before the horse.
Kevin
Kevin,
I think it is gasoline where we have put the cart before the horse. We consume way more gasoline in this country than we can get from local resources.
With renewable energy at a few of percent right now and EVs being at basically 0%, I would say we have the horse before the cart on the EV front. USA produced RE electrons are already here and waiting for EVs.
Later
John C. Briggs
Kevin and John C. Briggs,
Thanks for the lively and knowledgeable discussions. I realize the chances of selling out of the box ideas are less than slim, and I also can often find myself annoying people with my efforts to provoke reactions. Sorry for when that happens.
Since we are talking about carts and horses, I will concur with Kevin about getting the cart before the horse, but I add that the horse has a broken leg. Hence, the well intended efforts by such as Dr. MacKay and our own EPA could be sending us (the whole developed world and the rest as well) into serious problems.
Some years ago I was coasting along on with happy assumptions about electric vehicles in the future of the world, and hoped to be lining up my thoughts accordingly. My wife pays little attention to these things but somehow she picked up on the question about coal as the source of electricity, and I realized I had not seriously examined the system. Then we reeled here in California with $13 natural gas, as Enron and other traders were cashing in on efforts by such as Calpine to modernize electricity production using that gas, much of this being driven by the imaginary wonders of free enterprise and de-regulation. Both Calpine and PGandE hit bankruptcy. And we emerged with California building peaking natural gas plants on its own cash, and then the ban of coal fired generation came on us. I am aware of corporations moving in to buy the Calpine facilities with an eye to profit on California foolishness in this regard. One company that is happy to sell natural gas generated power to California is NRG which states in their annual report (2008) how profitable this is in peaking situations, even though most of their output in the country is still from coal fired plants.
I am indeed quite alarmed by the economic condition of California. We can not afford this kind of action. But there is much more of a problem shaping up with the Electric Vehicles on a national, and indeed, the whole developed world basis.
Up until a few months ago I was mostly dismayed by the fact that the move to electric vehicles was the wrong course of action since it steered us away from the environmentally good hybrid of the Prius sort. The real motivation here seemed to be to reduce need for foreign oil, but there seemed to be a scheme to trick environmentalists into thinking it would help with CO2.
However, we recently had an EPA study report that said that 'carbon' capture and sequestrian was technically possible, and a course of action was set to achieve that goal. The cost of that 'technically possible' solution was stated without much discussion, but when analyzed with the added knowledge that CO2 was 44/12 as heavy as carbon (of course they know this, but in the zeal of promotional fervor, this is glossed over). Anyway, this portends badly for the effective cost of using coal as a fuel. It is not hard to figure out, using the fact that Powder River Basin coal costing about $12 a ton at the mine with about $8 for transportation and that this coal is about 50% carbon (yes, real carbon), that this will hugely increase the cost of electricity. So what is wrong with this? It is just an adjustment that is needed? Ok. But if the economy continues to not recover, perhaps some of the reason for business negativity is in this threat of a non-competitive production environment.
So that is why I say the horse has a broken leg. And we can point out our own EPA and the UK government advisor Dr. David MacKay as being a cause of the break. After the economy as the problem, we still need to think about how we will get public enthusiasm for real CO2 reduction measures when they realize that the EV was just a trick having no real benefit in that regard.
Of course we can fall back on the hope that renewables will make it. I suspect that this hope will evaporate soon, and the disasters will unfold as I described.
Jim,
Honestly have trouble understanding what you are complaining about. California has shown excellent leadership here.
1) Coal is bad for CO2, California bans it. Problem solved.
2) With the California grid using no coal, EVs powered from the California grid produce less CO2 per mile than gasoline powered cars, today.
3) In the future, California is requiring 33% renewables by 2020. So you don't have to hope for a renewable energy future, you will have it.
4) Cost, are you kidding me, If you are talking about the cost of powering a vehicle, gasoline is about 5X the cost of even your expensive California electricity. If you can afford to pay for gasoline, you can afford to power your EV with electricity.
California has also gone further than any other state to reduce consumption. As a result, California's use half the electricity of most Americans.
Later
John C. Briggs
I should have added another thing in my comments about David MacKay's promotion of EV's. One of his motivations to justify his distortion of energy facts is that he feels that if we can get a huge amount of BEV's on the road, these batteries plugged into the grid will provide the "energy storage" needed, without the Wind and Solar power plants needed to add storage of their own. Underlying this scheme is the assumption that people won't mind their battery life being reduced by the charge / discharge cycles to provide load-levelling (for free) of the grid on a grand scale. I agree with the need for energy storage, but not this scheme.
This is another one of those ideas that seem <technically> feasilble, but I believe to be totally unworkable in practice. Not only would people not like their expensive batteries dying earlier, but it assume that there are always enough cars plugged-in to support the required (somewhat unpredictable) peaks. Also, it REQUIRES a "smart grid" and smart battery controllers that don't really exist today. I believe this all to be based on mainly wishful thinking and would be much more expensive than other options that maximally leverage the energy infastructure we already have, as I've described previously here.
Kevin
Kevin,
No one in the "smart grid" (I had that term) assumes they will have free use of people's batteries. This has always been envisioned a service that people would be paid for. Also, deep cycling the batteries would indeed shorten their life. However, it has already been shown that shallow discharges (below 20%) have no measurable impact on the battery life.
Additionally, although you are skeptical of the "smart grid", you must realized that "demand response" has already been widely implemented in California. It is not some future technology exercise. It exists today and is used today to balance the grid. The "smart grid" advocates are just trying to expand that function. Personally, I don't have a problem with the power company adjusting the timing of my water heater if that helps something. Particularly if I can save some money.
Anyway, such controllers have been used for years in off-grid and battery backed up on-grid renewable energy systems.
Later
John C. Briggs
John C. Briggs,
Your points need to be discussed carefully, and I hope to get to it soon.
Kevin,
That MacKay charging scheme might not look so bad if there were bizarre cogenerating guys parked all over the place, just firing up their engines when needed and of course, when they could use the heat for some real purpose. (Even freezing water with chillers could qualify as useful, if this was a form of cold storage.) For the most part, I would use the cogeneration to enable charging of the vehicles without use of the wasteful central power plants.
But in general, our assessments of MacKay and his EV promotions are in close agreement. I also add that in the UK the problem seems nearly upon them, since they have mostly blown their North Sea gas reserves in making their economy seem good over the past 25 years or so. Shifting to electricity is going to lead them into crisis mode ahead of us in the USA.
John C. Briggs,
Yes, electricity has a big cost advantage over gasoline for driving cars. That is at today's prices for coal and natural gas. But these prices are subject to demand, and the cost of electric is also subject to additional costs of doing things like 'carbon' capture and storage.
The test of California's leadership is the effect of our actions when the rest of the country goes along with that example and over time. I perceive that banning coal is a badly conceived plan, though it might seem that the effects are tolerable as long as the rest of the country relies a lot more on coal than natural gas. We are also starting to get some indications California voters have been mislead about the impact of this policy on costs of electricity.
One other point about natural gas is that as its price goes up, the industrial users of this fuel will be further placed in a bad competitive position relative to world business environment.
Jim,
OK, firstly, not coal, California doesn't use coal. So that is solved. Secondly, if natural gas prices go up, the cost of electricity may go up a little, perhaps 3 cents/KWH as we saw a couple of years back. Oh but gasoline prices went up at the same time, so electricity was still cheaper.
Then again, California is requiring 33% renewables by 2020, so you will be less subject to the cost of fossil fuels no matter what.
It is too bad that gasoline is starting at a 5X disadvantage to electricity. This makes all your arguments seem well, let's say, "challenging."
As far as California leadership goes, do you know that there two two different pollution standards that states can choose from, either the California standard or the EPA standard. Something like a dozen states have adopted the California standard.
So if you see California headed in the wrong direction, other states see it headed in the right direction.
Honestly, I am amazed that you continue with this line of argument. It is clear that EVs have advantages in cost of fueling and pollution. Why you don't argue about the real problems of EVs, I have no idea. 1) range, 2) battery cost. Fueling is such a huge advantage for EVs, I cannot believe people try to make a go of this argument.
If you look at the X-Prize, EVs rule the alternative class and fossil fuels rule the main stream class. That seems to be clearly tied to the requirement of 100 miles in the alternative class and 200 miles in the main stream class. The EVs are tough to do at 200 miles.
Later
John C. Briggs