More About Coastdown Testing
Tuesday, August 31, 2010 at 11:34AMThe engineering department at Edison2 greatly appreciates the informed comments and gentle prodding we get on the Blog page. We have and will continue to do our best to put actual information up here. We hope everyone will realize that we also have our jobs to do so sometimes it might be a while to answer even really good questions.
We didn’t have stopwatch on it but it seemed to take only about 5 minutes before Kevin pointed out that the C term in our last blog post didn’t make a lot of sense. He’s absolutely right, it doesn’t, and the reason for that is also the reason that the car industry needs coastdown testing and does not just rely on wind tunnel numbers.
The SAE standard that defines coastdown testing is J2263. It’s available for download from multiple places online but because it’s copyright material you have to have to pay for it. It’s an interesting read if you’re into this kind of thing (and a great cure for insomnia if you’re not) and it delves into some of the complexities that surround this. For example, how do you account for rotating weight? A wheel not only has linear inertia because it’s travelling but it also has rotating inertia because it rotates. J2263 discusses this at length and in detail.
Whether or not stuff like rotating inertia is significant depends on the numbers you’re trying to find. If all you really want to know is how much drag there is at any given speed, the coastdown method is great. Plot speed against acceleration (and, since mass is constant, acceleration gives you force) from the coastdown and you have the drag profile. It happens that car drag profiles very reliably fit the A + Bx + Cx^2 three term general form.
Here’s a parallel: if you want to know downforce, do you take a bunch of pressure taps and attempt to integrate the pressure contours you generate over the car’s planform area? You could but it’s kind of messy. Far better to measure the downforce directly because that intrinsically integrates the air pressure over the whole body.
So what happens is, the coastdown people do a curve fit on the speed/drag plot and that gives the A, B and C numbers and all the complexities are handled right there. While the C number, being squared, sort of corresponds to aero, it doesn’t necessarily do so exactly. It’s just like saying we don’t care very much what our pressure distributions are because we know accurately how much downforce we have.
That said, we at Edison2 like to be sure of our ground as much as the next person so we asked the coastdown engineers to dive into the sea of numbers and calculate our Cd given our 1.702 m^2 (18.3 ft^2) frontal area. These guys are good at this and proved it when the number they delivered, 0.157, agrees within 2% the number we saw in the wind tunnel.
It’s an interesting factoid that the Very Light Car rolled about 8100ft (over 1½ miles) while coasting down from about 71 to 10 mph (the standard is actually from 115 to 15 km/h). If we were to assume linear speed decay, the force to decelerate would be about 20.4lb. This matches the ABC coastdown numbers at a little over 40mph, right in the middle of the speed range. Overall, we’re happy that we’re dealing with facts.
And if you really want to see how good the VLC is, take your own road car up to a bit over 70 on a level road, knock it into neutral and see how far it goes. Even though it weighs some multiple of the VLC, bet it’s less than 1.5 miles. Please use common sense and do this only where it’s safe and legal.
Edison2’s engineering department goes to a lot of trouble to model performance, which is why we were able to make some very good primary decisions about our cars’ layout and characteristics. But we’ve also learned a hard lesson over the years: there comes a point where you just have to go out and try it. When what you observe in reality doesn’t line up with the model, the reasons why are worth study.
Reader Comments (58)
8100ft coast down for a four passenger car! A battery electric VLC with a 12 kWh battery might exceed the range of the Nissan Leaf with its 24 kWh battery.
This study on planetary boundaries underscores the need to conserve resources with everything we build and consume. http://www.nature.com/news/specials/planetaryboundaries/index.html
Several of the Earth's life support systems have already been pushed far beyond capacity.
Building a better preforming car with one third the resources is really important. Powering the car with clean energy is equally important. Nanotech solar technology uses just one percent of the raw material to achieve equal or better solar energy conversion for much lower total cost per kWh.
Thanks again for more info! I rolled-up my (educated guess) at how to arrive at an "effective" Cd using the EPA coastdown parameters. It assumes that the "B" term (viscous drag) is all aerodynamic and that the mechanical viscous drag (say, from bearings) is insignificant. I think this is a pretty good assumption, esp. at higher speed. It also assumes a specific speed, and is only valid at that speed.
So....using the A,B,C coastdown parameters (which are in units of lbs force and mph), X=speed in mph, and A=frontal area in square meters (I know...mixed units) - try the following:
Cd = (37.13/A) x (C + B/X)
If you use 1.702 sq m and 65 mph, and the A,B,C parameters Edison2 provided, you'll get Cd = 0.157 (at 65 mph).
Note that the Cd value will change with speed, but 65mph seems like a good choice because it is a normal highway speed.
I'd be interested in someone else using this to calculate the Cd's of other cars from the EPA database (or from XPrize coastdown data), and see how the calculated effective Cd compares to published values. I'm 95% sure that this is what the EPA is doing when they told Edison2 their Cd based on the coastdown data.
All comments are welcome!
Kevin
I just realized - the "A" in my equation is confusing. It is the front area (in sq meters) - NOT the "A" parameter from coastdown, which is not relevant to aero drag.
Sorry about that.
Kevin
I'm sure the academic discussion is interesting to many, but I'm a practical person by nature-- so when do I find out if I will I be able to buy it?
Yes Edison 2, tell us your desires and wishes after winning the x-prize. Temporary small scale production like Panoz?, which as far as I understand, is an official car manufacturer of the U.S., or are you wanting to sell the design to a major auto manufacturer? Keep in mind that major car manufacturers typically mess up great concepts. The Mercedes M-class original concept design is much better than what the production version came out as.
The production version: http://www.theautochannel.com/media/photos/mercedes/1998/98_mercedes_m_class.jpg
The concept version: http://www.autospies.com/images/7-28-05/2010-mercedes/1.JPG
Now out of those two, which one looks like the better product?
It just seems like too many major companies are taking the shortest road to profit lane before considering the quality of the end product to consumers, and I for one would hate to see something like Edison 2's awesome, un-tamed like a wild lion V.L.C., become plagued with "features" and so it ends up just another C., or worse that the big car company will just purchase the design to throw it away, or stash it away for "later." That happening, would be a real shame. One of my closest relatives owned Lampi, which was a fluorescent lighting company here in the United States. Now this company made the best fluorescent lights for Home Depot, and Lowes, but it's now out of business because of the big time corporation G.E., decided we were competition, and so we were extinguished from an employee who was afterward found to be embezzling the company (Lampi), and it turns out all along he was working for GE! All of this I write to let Edison 2 know now before it's too late. BE CAREFUL gentlemen! There are a lot of people out there who's greed knows no bounds, and I speak from second hand experience on this, and it's a horrible thing to watch an honest company with well paid employees all losing their jobs all because of one big corporation wanting every last bit of the market for themselves. Hidden agendas can be found in the most un-expected places. I have a very good perception of people, and what it is that they are really after, which is why I know Edison 2 has good intentions. So that's my advice on possible production, be careful who you guys do business with. If it helps for your information, I would rather have to pay extra money (up to a point anyway) for the purest efficiency car, than to have a watered down version that is more C than VLC.
The Empa study posted below did not include the large amounts of embedded energy used to produce a gallon of gasoline, nor did they consider the environmental costs and geopolitical risks and costs of dependence on petroleum for transportation. A recent report from the German military said that peak oil could destroy western democracies; a large price indeed for not kicking our petroleum addiction.
In the Empa study, battery electric cars compare favorably to petrol cars. Factor the environmental, geopolitical, and embedded energy costs of petroleum addiction, and the good case for electric cars increases exponentially. And unlike petrol cars, battery electric cars can be powered by any clean energy source.
The following report is from Car Tech --
Car Tech -- Electric Cars Greener Than Expected
Battery powered electric cars are often promoted as the ideal solution to the challenges of future mobility, since they produce no exhaust gases in operation. Li-ion batteries have established themselves over competing lead-acid and nickel metal-hydride (NiMH) types because they are lighter and can store more energy.
by Staff Writers
Dubendorf, Switizerland (SPX) Sep 02, 2010
It is not an easy task to compare the environmental effects of battery powered cars to those caused by conventionally fuelled automobiles. The degree to which manufacture, usage and disposal of the batteries used to store the necessary electrical energy are detrimental to the environment is not exactly known.
Now, for the first time, a team of Empa scientists have made a detailed life cycle assessment (LCA) or ecobalance of lithium-ion (Li-ion) batteries, in particular the chemically improved (i.e. more environmentally friendly) version of the ones most frequently used in electric vehicles.
The investigation shows that if the power used to charge the battery is not derived from purely hydroelectric sources, then it is primarily the operation of the electric car, which has an environmental impact, exactly as is the case with conventionally fuelled automobiles.
The size of the environmental footprint depends on which sources of power are used to "fuel" the e-mobile. The Li-ion battery itself has, in contrast, a limited effect on the LCA of the electric vehicle. This is contrary to initial expectations that the manufacture of the batteries could negate the advantages of the electric drive.
The environmental impact of batteries for electric vehicles
Battery powered electric cars are often promoted as the ideal solution to the challenges of future mobility, since they produce no exhaust gases in operation. Li-ion batteries have established themselves over competing lead-acid and nickel metal-hydride (NiMH) types because they are lighter and can store more energy.
Li-ion batteries are also basically maintenance-free, display no memory effect (loss of capacity when repeatedly charged after partial discharge), have a low self-discharge rate and are regarded as safe and long-lived. For these reasons they find use in many products such as laptop computers. But are they also environmentally friendly?
Researchers at Empa's "Technology and Society Laboratory" decided to find out for sure. They calculated the ecological footprints of electric cars fitted with Li-ion batteries, taking into account all possible relevant factors, from those associated with the production of individual parts all the way through to the scrapping of the vehicle and the disposal of the remains, including the operation of the vehicle during its lifetime.
Data with which to evaluate the rechargeable batteries was not available and had to be obtained specifically for this purpose. In doing so the researchers made intentionally unfavorable assumptions. One such was to ignore the fact that after use in a car, a battery might well be used in a stationary setting for other purposes.
Other relevant LCA information was obtained from the "ecoinvent" database (www.ecoinvent.org), managed by Empa. The electric vehicles evaluated were equivalent in size and performance to a VW Golf, and the power used to charge the batteries was assumed to be derived from sources representing an average European electricity mix.
A new petrol-engined car, meeting the Euro 5 emission regulations, was used for comparison. It consumes on average 5.2 liter per 100 kilometers when put through the New European Driving Cycle (NEDC), a value significantly lower than the European average. In this respect, therefore, the conventional vehicle belongs to the best of its class on the market.
More a question of the power source rather than the battery
The study shows that the electric car's Li-ion battery drive is in fact only a moderate environmental burden. At most only 15 per cent of the total burden can be ascribed to the battery (including its manufacture, maintenance and disposal).
Half of this figure, that is about 7.5 per cent of the total environmental burden, occurs during the refining and manufacture of the battery's raw materials, copper and aluminium. The production of the lithium, in the other hand, is responsible for only 2.3 per cent of the total.
"Lithium-ion rechargeable batteries are not as bad as previously assumed," according to Dominic Notter, coauthor of the study which has just been published in the scientific journal "Environmental Science and Technology".
The outlook is not as rosy when one looks at the operation of an electric vehicle over an expected lifetime of 150'000 kilometers. The greatest ecological impact is caused by the regular recharging of the battery, that is, the "fuel" of the e-car. "Refueling" with electricity sourced from a mixture of atomic, coal-fired and hydroelectric power stations, as is usual in Europe, results in three times as much pollution as from the Li-ion battery alone.
It is therefore worth considering alternative power sources: If the electricity is generated exclusively by coal-fired power stations, the ecobalance worsens by another 13 per cent. If, on the other hand, the power is purely hydroelectric, then this figure improves by no less than 40 per cent.
The conclusion drawn by the Empa team: a petrol-engined car must consume between three and four liters per 100 kilometers (or about 70 mpg) in order to be as environmentally friendly as the e-car studied, powered with Li-ion batteries and charged with a typical European electricity mix.
john,
Any study that talks about the 'mixture' or 'mix' of sources of electricity immediately demonstrates dishonesty, whether intended or not. The issue is how the generating system would respond to new loads. Not what it is doing to handle an existing set of power requirements.
First, all the hydro, nuclear, wind, solar in existence are fully tapped out and if it is possible to build more, then the existing demand will immediately take up the new outputs.
Even if someone owns their own solar panel and chooses to run the output directly into a car the economic reality is the same. The choice to run the power to the car removes the other option, which would be to run the solar panel power to the grid. And in this option, coal power would be reduced. But if the power goes to a car, coal power is increased to cover the lost solar panel source. Thus there is always an economic connection that defeats any attempt to pretend that the load of electric vehicles will not be carried by burning coal.
It will only be when there is reserve capacity from 'renewables' that this will be different. And that reserve capacity will exist after renewables have first displaced the need for coal fired power. That is going to take a long time, especially since renewables are generally not affordable in comparison with coal systems.
Jim -- Actually I agree with you on solar power. If a house has solar PV panels connected to the grid, then it is a good idea to feed excess solar power directly into the grid. Peak solar power production coincides with peak demand for power on the grid. Solar power helps the grid when it needs it most, and it provides distributed energy that reduces stress on the grid. At night between 11pm and 7 am is the period of lowest demand on the grid, and this is also the time most people will choose to recharge their electric cars. Grid connected solar panels help the grid during peak hours when it needs it most, and then the grid can return the favor, recharging electric cars at night when there is excess grid power.
If the house is off the grid, then different synergies would exist between the solar powered house and the electric car. The car's big battery could store excess solar power during the day, and then feed some back to the house at night as needed. If an off grid house occasionally needs extra power, then the off-grider might drive by the local "filling station" to pick up a few quick charge kWhs, along with a gallon of milk and a loaf of bread.
Obviously the total number of electric cars will be small at first, just as the total number of houses with solar PV panels is relatively small even now. For maximum benefit, electric cars really should be sold with alternative energy power systems, The VLC, with its lower energy demands, makes the whole idea of solar powered BEVs much more affordable. Electric cars and clean energy will likely improve and evolve together as matched systems.
Two relevant reports are posted below . The first report addresses the dangers of relying on peak oil to power our transportation system. The second report outlines an abundant power source that could make fossil fuels obsolete within just a few years. (If electric vehicles are available to make use of power produced with this abundant source of energy)
First:
German military report: Peak oil could lead to collapse of democracy
By Daniel Tencer
Wednesday, September 1st, 2010 -- 7:48 pm
Peak oil has happened or will happen some time around this year, and its consequences could threaten the continued survival of democratic governments, says a secret Germany military report that was leaked online.
According to Der Spiegel, the report from a think-tank inside the German military warns that shrinking global oil supplies will threaten the world's economic foundations and possibly lead to mass-scale upheaval within the next 15 to 30 years.
International trade would suffer as the cost of transporting goods across oceans would soar, resulting in "shortages in the supply of vital goods," the report states, as translated by Der Spiegel.
The result would be the collapse of the industrial supply chain. "In the medium term the global economic system and every market-oriented national economy would collapse," the report states.
That collapse could, in turn, cause many countries to abandon free markets principles, the report states. Deals would be struck between oil-exporting and oil-importing countries that would fix prices and remove large amounts of oil from the global market place.
"The proportion of oil traded on the global, freely accessible oil market will diminish as more oil is traded through bi-national contracts," the report states.
That would prompt some governments to abandon free market economics altogether, the report suggests. With peak oil causing "partial or complete failure of markets ... [a] conceivable alternative would be government rationing and the allocation of important goods or the setting of production schedules and other short-term coercive measures to replace market-based mechanisms in times of crisis."
But the report also warns that the economic crisis caused by shrinking oil supplies and skyrocketing prices could be seen by the general public as a failure of market economics as a whole -- and with it, the political institutions that created those economic systems.
Public anger at the existing system would create "room for ideological and extremist alternatives to existing forms of government." Populations would fragment along political lines and "in extreme cases" this could "lead to open conflict."
Peak oil -- which refers to the moment when the world's production of oil begins to shrink -- is a controversial concept, but few doubt the basic logic underlying it: That eventually the world's finite supply of oil will run out, and nations will have to turn to other sources of energy, or face economic disaster.
With the report, Germany joins the growing ranks of Western governments apparently alarmed by the prospect of peak oil.
Last Sunday, the UK Observer reported that Britain's Department of Energy and Climate Change is refusing to release documents related to peak oil, even though, as the Observernoted, previously released documents argue the veil of secrecy around the issue is probably "not good."
The UK government is reportedly canvassing leading scientists and industrialists for their advice on how to build a contingency plan for peak oil.
And earlier this year, a report from the US Joint Forces Command stated that "by 2012, surplus oil production capacity could entirely disappear, and as early as 2015, the shortfall in output could reach nearly 10 million barrels per day."
The report continued, "While it is difficult to predict precisely what economic, political, and strategic effects such a shortfall might produce, it surely would reduce the prospects for growth in both the developing and developed worlds. Such an economic slowdown would exacerbate other unresolved tensions, push fragile and failing states further down the path toward collapse, and perhaps have serious economic impact on both China and India."
Not everyone agrees that peak oil is a reality -- at least not yet. Detractors point out that predictions of peak oil have been made since the 1950s, and the date for it was originally pegged at around 1995. But the discovery of new oil fields and the development of new technologies for oil extraction mean that oil production has continued unabated in new oil fields even as traditional oil supplies run dry.
Peak oil skeptics argue that rising oil prices are responsible for the continuing supply of oil -- as oil gets more expensive, extracting it from difficult places becomes more profitable. Some argue this process could continue for decades.
But environmentalists point out that these new alternative methods of extracting oil are more environmentally harmful than traditional methods. Producers in the Alberta oil sands, for example, use large amounts of water to push oil out of sand, and the thick oil produced by this process is significantly higher in carbon content than the light, sweet crude imported from the Middle East.
Second report:
Obama could kill fossil fuels overnight with a nuclear dash for thorium
If Barack Obama were to marshal America’s vast scientific and strategic resources behind a new Manhattan Project, he might reasonably hope to reinvent the global energy landscape and sketch an end to our dependence on fossil fuels within three to five years.
By Ambrose Evans-Pritchard, International Business Editor
Published: 6:55PM BST 29 Aug 2010
252 Comments
Dr Rubbia says a tonne of the silvery metal produces as much energy as 200 tonnes of uranium, or 3,500,000 tonnes of coal
We could then stop arguing about wind mills, deepwater drilling, IPCC hockey sticks, or strategic reliance on the Kremlin. History will move on fast.
Muddling on with the status quo is not a grown-up policy. The International Energy Agency says the world must invest $26 trillion (£16.7 trillion) over the next 20 years to avert an energy shock. The scramble for scarce fuel is already leading to friction between China, India, and the West.
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There is no certain bet in nuclear physics but work by Nobel laureate Carlo Rubbia at CERN (European Organization for Nuclear Research) on the use of thorium as a cheap, clean and safe alternative to uranium in reactors may be the magic bullet we have all been hoping for, though we have barely begun to crack the potential of solar power.
Dr Rubbia says a tonne of the silvery metal – named after the Norse god of thunder, who also gave us Thor’s day or Thursday - produces as much energy as 200 tonnes of uranium, or 3,500,000 tonnes of coal. A mere fistful would light London for a week.
Thorium eats its own hazardous waste. It can even scavenge the plutonium left by uranium reactors, acting as an eco-cleaner. "It’s the Big One," said Kirk Sorensen, a former NASA rocket engineer and now chief nuclear technologist at Teledyne Brown Engineering.
"Once you start looking more closely, it blows your mind away. You can run civilisation on thorium for hundreds of thousands of years, and it’s essentially free. You don’t have to deal with uranium cartels," he said.
Thorium is so common that miners treat it as a nuisance, a radioactive by-product if they try to dig up rare earth metals. The US and Australia are full of the stuff. So are the granite rocks of Cornwall. You do not need much: all is potentially usable as fuel, compared to just 0.7pc for uranium.
After the Manhattan Project, US physicists in the late 1940s were tempted by thorium for use in civil reactors. It has a higher neutron yield per neutron absorbed. It does not require isotope separation, a big cost saving. But by then America needed the plutonium residue from uranium to build bombs.
"They were really going after the weapons," said Professor Egil Lillestol, a world authority on the thorium fuel-cycle at CERN. "It is almost impossible make nuclear weapons out of thoriumbecause it is too difficult to handle. It wouldn’t be worth trying." It emits too many high gamma rays.
You might have thought that thorium reactors were the answer to every dream but when CERN went to the European Commission for development funds in 1999-2000, they were rebuffed.
Brussels turned to its technical experts, who happened to be French because the French dominate the EU’s nuclear industry. "They didn’t want competition because they had made a huge investment in the old technology," he said.
Another decade was lost. It was a sad triumph of vested interests over scientific progress. "We have very little time to waste because the world is running out of fossil fuels. Renewables can’t replace them. Nuclear fusion is not going work for a century, if ever," he said.
The Norwegian group Aker Solutions has bought Dr Rubbia’s patent for the thorium fuel-cycle, and is working on his design for a proton accelerator at its UK operation.
Victoria Ashley, the project manager, said it could lead to a network of pint-sized 600MW reactors that are lodged underground, can supply small grids, and do not require a safety citadel. It will take £2bn to build the first one, and Aker needs £100mn for the next test phase.
The UK has shown little appetite for what it regards as a "huge paradigm shift to a new technology". Too much work and sunk cost has already gone into the next generation of reactors, which have another 60 years of life.
So Aker is looking for tie-ups with the US, Russia, or China. The Indians have their own projects - none yet built - dating from days when they switched to thorium because their weapons programme prompted a uranium ban.
America should have fewer inhibitions than Europe in creating a leapfrog technology. The US allowed its nuclear industry to stagnate after Three Mile Island in 1979.
Anti-nuclear neorosis is at last ebbing. The White House has approved $8bn in loan guarantees for new reactors, yet America has been strangely passive. Where is the superb confidence that put a man on the moon?
A few US pioneers are exploring a truly radical shift to a liquid fuel based on molten-fluoride salts, an idea once pursued by US physicist Alvin Weinberg at Oak Ridge National Lab in Tennessee in the 1960s. The original documents were retrieved by Mr Sorensen.
Moving away from solid fuel may overcome some of thorium’s "idiosyncracies". "You have to use the right machine. You don’t use diesel in a petrol car: you build a diesel engine," said Mr Sorensen.
Thorium-fluoride reactors can operate at atmospheric temperature. "The plants would be much smaller and less expensive. You wouldn’t need those huge containment domes because there’s no pressurized water in the reactor. It’s close-fitting," he said.
Nuclear power could become routine and unthreatening. But first there is the barrier of establishment prejudice.
When Hungarian scientists led by Leo Szilard tried to alert Washington in late 1939 that the Nazis were working on an atomic bomb, they were brushed off with disbelief. Albert Einstein interceded through the Belgian queen mother, eventually getting a personal envoy into the Oval Office.
Roosevelt initially fobbed him off. He listened more closely at a second meeting over breakfast the next day, then made up his mind within minutes. "This needs action," he told his military aide. It was the birth of the Manhattan Project. As a result, the US had an atomic weapon early enough to deter Stalin from going too far in Europe.
The global energy crunch needs equal "action". If it works, Manhattan II could restore American optimism and strategic leadership at a stroke: if not, it is a boost for US science and surely a more fruitful way to pull the US out of perma-slump than scattershot stimulus.
Even better, team up with China and do it together, for all our sakes.
I suggested a Manhattan sized project to distribute water throughout North America to enable creation of massive standing forests throughout our desert regions. It has yet to gather a whimper of interest, even though it appears that this is much like what Pres. Hu of China was talking about when he spoke of forest development.
Where can I find the Belgian Queen Mother ? We don't even need to scare the heck out of her with fear of nuclear power, which I understand is very strong in much of Europe.
Well, blog activity is down, except for spam! For me, I know one reason is that my kids are back in school – and taking more time with homework help, etc. I’d still like to hear if someone can take my equation and see how it correlates with published Cd data. You’ll need to know frontal area, and the EPA coastdown parameters.
Based on some of the other people’s inputs on the blog, I’ve read up a bit on San Diego’s power grid details. The facts are better off than I expected vs. going greener. Here’s some summary info:
www.chulavistaca.gov/clean/conservation/Climate/documents/
SDGEEnergySupplyandDistributionOverview.pdf
See page 10. “Market” and “DWR” are power bought from the grid outside California. Look at the projection by 2015 – almost no coal, 26% renewables. It’s a good start, but still more than half fossil fuels. Also, cogeneration is more prevalent than I had expected – see:
www.industcards.com/cc-usa-ca-s.htm
I was thinking about Neil’s comments about Aptera switching to front wheel drive to enable more effective traction for regenerative braking. Of course, Edison2 could do the same – but it may be difficult to incorporate CV joints into the unique front suspension (inside the front wheels). I thought of a different possible solution that is probably easier to implement on the VLC. The batteries could be rear-biased to give a significant rear weight bias, like my old Porsche 911. This is proof enough that good handling can be achieved with high rear weight bias, although power-off oversteer needs to be controlled (as improved in later 911 years). Although one might argue that 50-50 or even front weight bias has advantages, the rear bias gives fantastic acceleration traction, decent rear decel traction and great braking performance. It keeps the steering very nimble (probably not an issue with such a very light car anyway) – but is not the best for driving in snow or very slippery conditions.
Lastly, I’m curious to see the efficiency results of the VLC engine. My attempts at modeling in a spreadsheet seem to indicate that the BSFC (brake specific fuel consumption, which is the engine efficiency) was good but not great. If true – that lends even more credence to the success of the Edison2 aerodynamics and low weight – and gives hope that even more improvement is possible.
Regards, Kevin
Hi Kevin,
With natural gas under $4 we get along ok in California, though I always check that little trick where we buy power on the spot market, which is of course, mostly coal based. If natural gas is cheap enough, there is not much need for this since we have plenty of natural gas generation capacity.
You probably saw the plan by SDGE to get people to sign up for 14 days a year on no power, in return for lower rates. Yup, when it gets hot 14 days a year you would turn off your air conditioner. Now that is an electric power system to admire!!
Oh, that was a projection for 2015? Do you suppose they think that the natural gas abundance calculated at a $7.50 price point will materialize if the price remains at $4? The fact is from EIA that half the rigs have been taken off natural gas development that were in use two years ago, -- but new projections seem to be a little slow in coming.
Then imagine when the EPA drags the coal users of the country out for a flogging with the requirement for 'carbon' capture that will increase effective costs for using fuel by a factor of ten or so. Yup, that might triple the use of natural gas, and imagine how long the reserves will last when that rate of consumption sets in.
How do you suppose this set of circumstances looks to industrial planners who are thinking about economic expansion in California?
Kevin,
You mention oversteer with your Porsche. Does this oversteer effect ever lead to overturning tendency?
My sense of steering dynamics leads me to think that having the weight rearward will make the car almost immune to the overturning torques that can come from fast lateral acceleration that can be caused by rapid pivot of front wheels.
Interestingly, the Xprize folks required both the accident avoidance maneuver which would show what I am talking about here, and also required a radial acceleration test where constant radial acceleration was caused by turning in a circle of specified diameter.
I wonder if this is why the old VW bus with its rear engine did so well, even though it always appeared top heavy.
I continue to revise the wheel system of my elevated airship vehicle, which I still intend to build, and as I refine weight distribution it seems that the above could be an important consideration.
I think Neil reported that the front drive FTV used regenerative braking for most of its stopping power, and produced very good stopping distances in the tests. Hub wheel motors might do the same for the VLC if the hub motors can be made compact and light weight enough. In addition to the advantages of four wheel drive and four wheel regenerative braking, hub motors on each wheel would offer interesting low speed maneuvering capabilities. With the car's 70 inch wide track on a 100 inch wheelbase, left side motors could be powered in the opposite direction of right side motors to give the VLC a zero turning radius.
That wide 70 inch track evidently keeps the low slung VLC very stable in turns. I did not see any body roll in videos of the VLC; not even in high speed turns where the VW chase car was showing substantial roll. Batteries in the floor or under seats would further lower the VLC center of gravity.
The following report from Car Tech would seem to indicate that China could be a very good market for the VLC. Chinese authorities have the power to mandate very light cars to reduce exploding energy use and pollution, just as their government mandated a one-child policy to diffuse China's population explosion:
Car Tech
China to have 200 million vehicles by 2020: state media
by Staff Writers
Shanghai (AFP) Sept 6, 2010
The number of vehicles on China's roads will more than double to at least 200 million by 2020, a top official was quoted Monday as saying, further straining the nation's environment and energy supply.
China must make it a top priority to develop fuel-efficient and alternative energy cars, the China Securities Journal said, citing Wang Fuchang, vice minister of the Ministry of Industry and Information Technology.
China's auto sales hit 13.64 million units last year, overtaking the United States as the world's top car market, while sales this year are forecast to hit 15 million units.
As of the end of 2009, there were 76.2 million vehicles in the country, according to government figures.
China's auto sales have slowed in recent months, partially due to seasonal factors, but August saw a surprising 55.7 percent year on year jump, boosted by Beijing's new subsidies for energy-saving vehicles.
The surging car use has brought mounting concerns over pollution, soaring energy demand, and traffic gridlock.
A top official with the country's environment minister, Liu Ziquan, was quoted Monday as saying vehicle exhausts had overtaken other major sources as the top cause of air pollution in cities.
Road congestion has also worsened, highlighted by a recurring traffic jam dozens of kilometres (miles) long on a major highway leading into Beijing from the northwest.
It can be said that the same electrical engineering can be applied to cars on their lighting from interior lighting to exterior lighting consisting of <A HREF="http://www.car-stuff.com/headlightlens.htm">Headlight Lens</A> to Fog Lights. I believe electric cars will have more efficient lighting in terms of eco friendliness and less electrical generation.
Jim,
It makes me smile to visualize you riding your miastrada model down the driveay, sitting on it kiddie-car style ! I wonder what the neighbors think ?
Seriously, the best and most concise book I've ever seen on car handling is "How To Make Your Car Handle" by HP Books. This covers all the correct terminology and how the interactions are all tuned to give good handling. Mainly science with a little art thrown in. I highly recommend it.
The issue with older Porsche 911's is different from "roll over" tendency you mention. These have power-off oversteer which means that if an inexperienced driver suddenly lifts off the gas halfway through a hard turn - the car's back end tends to come around and before you know it - you're offroading hind-end-first through the bushes. You'll see a lot of 911's in junkyards with smashed back ends....from single-car crashes. Newer 911's tamed this handling weakness. Otherwise, the handling is fantastic, esp. by the standards of the day.
Rollover tendency is actually more simple - related to center of gravity vs. track width. Shopping carts vs. F1 cars, or miastradas vs. normal cars. Go around a tight corner with too high a CG and you'll be doin' some 2-wheel stunt driving.
Kevin
Can anyone tell where this spamming is coming from? I can't see any pattern in the content, but anything that offers something for sale is probably spam. I usually get zero spam on my gmail account.
Jim,
Honestly your argument than any EV will be powered by coal is just ridiculous given that you live in an area that has proven that using less than 1% of electricity from coal is possible. Oh but in the future, blah blah blah...
Dude how often do we run into a problem that is difficult to solve and we don't know how to fix it? We don't know if it is possible to fix it. Thank God that California has shown that it is possible to fix the electric grid. Now all we need to worry about is keeping it fixed. This is a much easier task.
But in the future if natural gas blah, blah, blah, Dude it is already fixed, and getting better every day more renewables are added. Chill my friend, the argument is extremely weak.
Other Humans,
So that CoastDown data has this A, B, C format which is great but does not match the simplified model of a car that has no B term. So I resampled the data to and refit it to F = A1 + C1 v^2 type of curve fit. The fit is not as good, but it allows calculations of a few key items.
Crr = 0.012
CdA = 0.244 m^2
CD = 0.143 (assuming 1.702 m^2 area)
The numbers seem pretty reasonable and most impressive.
John C. Briggs
Yes, Kevin, the neighbors always laugh. I call it a soap bucket derby vehicle since I sit on a soap bucket from Costco bolted to an articulated, six wheel system to show how a narrow and tall vehicle can be stable. It breaks the mold when it comes to standard concepts about how vehicles must be low to the ground. But most neighbors that stop and talk go away with some new ideas in their heads.
I think you, along with many others, might be overlooking a roll-over issue if you think it is all about radial acceleration and CG and wheel base. There is actually a severe lateral accelertion that comes from a rapid pivot of a front wheel when initiating a turn, and this is a strong source of roll over torque if that acceleration is applied to significant mass, such as is the case with a front mounted engine. VW and Porsche (same grandpa, I think) might have been well aware of this.
So John,
Future projections are blah blah? I think the future is entirely the issue here. I get around just fine, and since I live close to the coast the cost of electricity for cooling is not a big thing. In fact, I mostly pay the poor house rates for electricity and expect to easily keep it that way. So whatever happens will not matter much to me directly, but how it will be for the next few generations does concern me. And without better thinking, things look to be heading in for serious trouble. Blah blah.
Maybe you respond to arguments about the economy. That is a here and now issue. And if I were planning expansion of an industrial operation, I would be quite concerned about the cost of power in the next few years. But that is in the future blah blah blah. And maybe that has something to do with the fact that jobs, and especially real manufacturing jobs, are not being added. That is now blah blah.
Well, Jim you are living in the future. A future free of coal powered electricity. So you have already proven a future without coal is possible.
There is no doubt that higher energy costs (electricity and petrol) will have an impact on our economy. The exact impact is less clear. Europe already pays more for electricity than Californians and much more for gasoline than Americans. So perhaps the impact of higher energy costs is not so bad.
Generally we adapt and change as energy costs change. Also, part of energy costs include the desire to reduce pollution. The days of consuming energy without regard to the pollution it creates must come to an end. The exact mix of energy is not yet clear, but electric powered vehicles look to have at least as good a chance as any of the alternatives.
So we will be entering a world with some number of EVs and their impact will become more clear in a few years. With renewable energy and EVs, it is a future we will probably like. But we shall see.
Later
John C. Briggs