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)
I agree with you Sar315. Some companies get by with selling a "kit car" by shipping the engine and car separate since most people choose the engine type after they have chosen the car anyway. This is one way that the old Nissan Skylines came to the U.S. Factory Five kit cars have also been doing well in small number sales, however, to really approach common mainstream building it has to be an official government legal car, and that means selling them as a whole unit. The biggest problem I see with building a car in such a way is the framing. It's hard to get machines to build a steel tube frame cheaply. If it were cheap, every car on the road would have a built in roll cage since it greatly enhances driver crash survivability. Using the principles of tube strength is great for the car once it's built, it just isn't cheap to produce in mass quantity. Good luck Edison 2, I know it will be really tough to actually produce such a pure car. One thing to think about Edison 2 is to temporarily sell the car as a niche product, maybe as a kit car, to gradually acclimate people to such a different way of thinking how a car should be built. Most people are "see it to believe it" kind of people, so most people will have a hard time comfortably wrapping their mind around a 700 pound car being safe. Any current auto manufacturer looking at your design(s) will tell you that, so Edison 2 will for a while anyway, will be stuck in small number production, just because of the risk involved if it doesn't sell because too many people haven't seen it's success and will be scared to be the first ones to jump in potentially shark infested waters. Once a few brave people however, show that the water is fine, everyone will jump right in to. Whether there are or aren't actual sharks in the water, they won't care until it's too late. So the brave are rather admitting the possibility, and taking on the risk, because every crash, and every time you drive a car, it's a gamble. You just hope the dice won't have your name on it, so people buy heavy cars to try to help win the odds in their favor. Even though in the case of the Jaws movie, the first ones in the water were not the ones to be eaten. No one will jump in water were they couldn't see their arm in front of them. No one will buy a production car until it has seen people surviving a crash. One idea is to try posting a video (youtube or some other public access video library) of an Edison 2 production version, VLC crashing into an SUV, versus a small Toyota crashing into an SUV, and show the condition of the dummies, or monkeys afterward. That would at least be some proof that a 700 pound car can survive a crash. Me personally, I know that most things I can avoid with active safety, however, being rear ended by some idiot who's texting while driving their SUV is what worries me most, because that's one place where I don't have a lot of options to avoid an impact if things get bad very quickly. That's many obstacles to overcome Edison 2, I wish you the best of luck, and I'll be the first to jump in if I get the chance.
As a member of the EAA (Experimental Aircraft Association) I would like to see a "kit" of the two seat side-by-side model. Let's stop debating and go into production! I could live with even 70MPG.
Yes Mark Albert, I'll second that, and that would be so awesome if they did!
Now that the Edison2 has won the X-prize, when can I buy a "roller" kit to fit my own Yamaha 250 or 300cc Kubota Diesel into?
A kit would be fun. Follow the example of Ultralight aircraft makers and do the mfg that's unlikely in a double-garage, and leave the easy bolt-together part to the "experimental" end-user. Could it be licensed as a light motorcycle "body accessory" given a previously-licensed DOT-compliant motorcycle-donor (VIN, plate/tag, serial number from major mfg product)? Could you make money on a run of 1000 kits?
Thanks for advancing the State of the Art.
Cheers.
I would like to see a VLC kit made available. However, early on, Edison2 made it clear that they are aiming for the mass market; and plan to license their technologies instead of trying to manufacture the VLC themselves. DOE grants and loans for advanced vehicle development should be available to Edison2. This should give Edison2 ample funding to perfect mass market consumer friendly versions of VLC technology.
In the meantime, battery and electric motor advances are making a battery electric VLC more attractive every day.
Radial wound electric motor technology has better torque and efficiency characteristics for automobile applications, and does not require China's horded rare earths to build.
Amprius nano silicon cathodes have doubled Li-ion power density to 450 Wh per kg. A 12 kWh Amprius battery would weigh only 60 pounds. 12 kWh would give an electric VLC ample range for most daily driving. A 24 kWh battery would weigh about 120 pounds and would probably provide more than 300 km range in a VLC at moderate speeds
These are USA technologies, for a 100% made in the USA electric VLC.
Well congratulations Edison 2! You have done extremely well! You have won a great race, and overcome many challenges that others thought was impossible. Surely, it's the most important, and historical race I have ever witnessed, and being a science/biologist nerd, it's also been the most exciting. I hope you get a huge, and expensive bottle of Champagne to celebrate with, in addition to the well deserved $5million.
The world needs to switch to zero carbon energy and electric cars powered with that clean energy.
The bottom line is that we simply must stop burning anything for energy. 392ppm CO2 is way past the safety zone. Climate models do not factor massive CO2 and methane emissions from melting permafrost in the Arctic. This feed forward mechanism will greatly accelerate global warming, and it has already started. We are in far worse shape than we think. Continued use of fossil fuels will push Earth past a tipping point where feed the forward mechanisms take over and accelerate global warming uncontrollably. Hundreds of Giga tons of CO2 and methane could be released from the Arctic permafrost, and deep ocean methane hydrates. Methane is a 23 times more powerful global warming gas than CO2.
Planet wide conversion to clean zero carbon energy is essential.
In transportation, electric cars are the future because:
1) Electric cars can use clean zero carbon clean energy sources
2) Electric cars make extremely efficient use of clean energy.
VLC technology makes electric cars that much more affordable. In yesterday's NYTimes, Oliver indicated that VLC in-wheel suspension technology alone could reduce the weight of any car by 180 kg. That would save a great deal of energy over the 150,000 km life of any car (and even more energy would be saved over the 450,000 km lifespan of EVs)
As a part of the switch to zero carbon energy, every electric car should be sold with a clean energy power supply. This could be in the form of a matching solar carport, or might even include building centralized zero carbon clean energy sources to feed the grid all the power used by electric cars.
We could revitalize our economy by building tens of millions of light weight electric cars powered by carbon free clean energy. All 100% made in the USA.
I agree with you John on some things. First, yes, we should stop combustion for energy. It's just the tiny little problem of all people knowing that we still have a lot of oil left to burn! And that it is still a lot cheaper than solar, or any other power source options makes it still the most valuable to our economy.
Biologist -- Any discussion of the cost of electric vs gasoline powered cars must consider the true cost of oil. CBS published the following examination of the cost of oil, Aug 12, 2010 http://www.cbsnews.com/stories/2010/08/12/opinion/main6767046_page2.shtml?tag=contentMain;contentBody
By several accounts the actual price we pay for gasoline in the US is well over 10 dollars a gallon. A 1998 study put the actual cost at over 15 dollars per gallon, and that was before the three trillion dollar Iraq war and the Gulf oil disaster.
If we paid the true price of 10 to 15 dollars per gallon right at the pump, everyone would be driving solar powered battery electric cars right now. Few would be willing to pay the actual cost of $200 to fill their tank, especially when the total cost of solar powered electric cars would be a tiny fraction of that amount. But we actually do pay that 10 to 15 dollar price per gallon through taxes and other externalized costs.
Oil powered IC engines are inefficient, noisy, balky, high maintenance, CO2 spewing anachronisms. The Prius is an IC car, even though it has electric drive to help the gas motor operate more efficiently.
A VLC electric car would weigh less than half as much and be twice as affordable, compared to a heavier electric like a Volt or a Leaf. With the savings you could buy a bunch of solar panels that will give your electric VLC 25 years of pollution free fill ups directly from the sun. And the electric VLC might last 25 years too, with the only major maintenance being battery replacement every 8 years.
Of course batteries are advancing very quickly now, so in eight years new batteries will probably give the car a 500 mile range, and last longer than the electric car.
What a massive waste of time.
All this wonderful science wasted on a car that will never be put into mass production.
Could you please do the right thing and give the Xprize money to someone that intends to build an efficient car that people can buy?
The Progressive sponsored fiasco has left several companies in the red, companies that would have otherwise have devoted their cash to prepping their cars for the real world instead of a contrived and pointless competition.
All your fabulous numbers are for a car with no airbags, ABS, aircon, boot space, mirrors or even wind down windows. In short, a show car.
Neil,
Ouch. But I feel your pain brother.
I guess the difficult part with cars is that it probably takes $100M to $500M to get into production. So nothing at the Xprize is anything close to that.
Perhaps Aptera is the closest thing to what you are talking about. But it is unclear if it will ever ship.
Another "waste of time" was the Partnership for the Next Generation Vehicles (NGV). In this exercise the 3 major car companies all produced vehicles that were 80 MPG. Nothing came of it.
Interesting to note that no major car company participate in the X-Prize. GM was very vocal saying that they were not interested in a "science experiment" and that they build real cars. Sigh, I guess they are correct.
Later
John C. Briggs
Neil, John -- You might be interested in the report below from Scientific American -- Li-ion plans a 39,000 unit production run starting in December, and Edison2 also plans to perfect and market its technology, some of which is patented. The etracer has modest production goals, in keeping with the 100k price they plan to ask for their 1300 pound electric motorcycle. Its not easy to steer, according to the story. I would much rather have a light weight electric scooter and not have to depend on those pop out training wheels to stay upright. Some designs like the heavy etracer motorcycle with its training wheels and the super heavy ballasted Tango do not make much sense. The VW one liter car is a much better design for a fairly narrow car, and it exceeds its lofty one liter per 100km goal.
Solar racers and 2500 mpg cars have had contests for years without 10 million dollar prizes. These cars cost hundreds of thousands to develop and are unlikely to ever see mass production. Nevertheless, teams keep building new improved cars for the next race. Actually the x prize 100 mpg minimum seemed pretty modest to me. 68 mpg hybrid diesel 4WD SUVs with 200 hp and 350 lb of torque are being mass marketed in Europe right now. The small light weight Edison2 platform should be capable of much more than 100 mpge.
SciAm Report on x prize winners:
Sep 17, 2010 06:27 PM in Technology | 3 comments
Automotive X PRIZE winners take a victory lap through New York City and ponder the future
By Larry Greenemeier
Perhaps the biggest winner of the Progressive Insurance Automotive X PRIZE competition is the X PRIZE Foundation itself. The organization, formed in 1996 with the Ansari X PRIZE competition to stimulate private spaceflight, not only issued a challenge to seen if automakers could build a vehicle that could get 100 miles per gallon (or the electric equivalent, measured as mpge), it found three teams capable of meeting the challenge.
"There's a science to designing a prize: It must be audacious but achievable," X PRIZE Foundation Chairman and CEO Peter Diamandis said Friday as the competition's winners gathered at New York City's Classic Car Club in a sort of a victory lap (they had been announced the day before at a ceremony in Washington, D.C.). The competition offered engineers some portion of a $10 million prize if they could meet a clear goal on a set deadline, with several checkpoints along the way. If that goal hadn't been met, none of the prize would have been awarded.
The size of the prize was chosen to give the competition credentials and provide the initial motivation for contestants, Diamandis said. It now also helps the winners defray some of their costs at exactly the time they most need an infusion of funding, he added.
By defining the goal and not the way to accomplish that goal, the foundation sought to stimulate creativity in a society that has increasingly become risk averse, Diamandis said. Within the confines of the competition, "if you win, you get the glory," he said. "But if you lose, you don't get any blame."
Another objective of the competition is to change the way people think about innovation. For example, the original X PRIZE was designed in part to help the public understand that the government isn't the only entity capable of space flight, according to Diamandis. The next X PRIZE competition, the Google Lunar X PRIZE, is offering $60 million (half chipped in by Google and the other half from NASA) to land a robotic rover on the moon and use it to complete certain objectives.
Mooresville, N.C.'s Li-ion Motors, which won $2.5 million in the "alternative side-by-side" vehicle category, plans to begin production of 39,000 Wave II vehicles in December. The initial cost for a Wave II is expected to be just under $40,000, although Li-ion team leader Ron Cerven on Friday said the company will continue to work on the technology to make it more efficient and eventually drive down the cost. For example, the car is going back into the wind tunnel for additional testing—the company believes it can surpass 200 mpge.
The prototype Wave II that won the X PRIZE has a body that's essentially made up of four fiberglass pieces. Steel bands run throughout the body to protect passengers in the event of a collision, Cerven said. Work will also continue on the materials used to make the car's body. Germany's SAERTEX Group makes a reinforcing fabric that Li-ion plans to use to make future versions of the Wave stronger and lighter.
Swiss firm Peraves AG won the $2.5 million prize for the best alternative vehicle in which passengers sit in tandem, as on a motorcycle. Its battery-powered E-Tracer is essentially an enclosed motorcycle based on the company's MonoTracer body. Peraves designed a new electric powertrain for the X PRIZE competition. Peraves has spent an estimated $10 million over the past 25 years developing its vehicles.
Riding an E-Tracer will require a motorcycle license and a bit of training, particularly in steering the vehicle, said Jim Lorimer, who sells Peraves vehicles in the U.S. through a Glenn Allen, Va. company called 21st Century Motoring. He adds that E-Tracer riders should at the very least be familiar with the concept of countersteering, a technique motorcyclists use to initiate a turn toward a given direction by first steering counter to the desired direction. Peraves is hoping to bring the E-Tracer to market in the fall of 2011. A gas-powered MonoTracer costs about $77,000 today, and an electric-powered E-Tracer is expected to cost about $100,000. The company's goal is to sell at least 100 per year.
The Very Light Car built by Charlottesville, Va.'s Edison2 stands apart for the other vehicles in the X PRIZE winner's circle for two very significant reasons—work on the car started from scratch more than two years ago and the car features a biofuel-powered internal combustion engine. It would have been easier for Edison2 to put an electric motor in its car, but the team's goal was to build a vehicle that would do its thermal conversion onboard and still achieve more than 100 miles per gallon, founder and CEO Oliver Kuttner said. "We didn't want the X PRIZE to be just an electric car competition," he said, adding that many of the other entrants in the mainstream car category were road cars converted into electric vehicles.
Edison2 built the car's suspension system into its wheels, which protrude from the car like a Formula racer. If applied to any car (not just the Very Light Car), this suspension system could make any car 180 kilograms lighter, Kuttner said.
The next phase for Edison2 is making improvements to its Very Light Car. The first area of improvement will be in the car's fuel efficiency, Kuttner says. Once the car is as efficient as it can be, the engineers will address the issues required to make the car more appealing to the general public, for example the addition of front and rear bumpers and a redesigned door that's easier to operate. The time it takes Edison2 to bring its car to market will depend upon how much funding the company can raise. In the meantime, they're looking to earn revenue by licensing out some of the technology designed for the car.
Images courtesy of Larry Greeemeier/Scientific American
Read More About: X Prize Foundation, Biofuel, Battery, Energy
John,
The SciAm article is interesting.
Let's not jump the gun on the 2011 Peugot 3008 Hybrid4. Firstly, it is not shipping yet. Secondly, no MPG numbers have been released only grams C02/km. The 68 MPG number is flat wrong because people don't know how to convert grams CO2/km to MPG. My calculations show this at 63 MPG. Additionally, this is Euro-cycle driving, figure the EPA testing will be 53 MPG, roughly. Thirdly, OK it is technically an SUV, but it is really small by American standards.
I don't want to be too negative about the Peugot 3008 because it still looks like it has higher MPG than the Prius, which is itself far better than anything else on the US market. However, I will be more impressed when the EPA actually tests a vehicle that can be sold in the USA.
Still, really the worlds first diesel hybrid, pretty cool.
Later
John C. Briggs
Alright John, so fuel is super expensive. However, don't you think it might make sense then to either actually charge the real price at the pump, or to give people on their 10-40, or other tax forms an option of getting a deduction from a copy of their car title, if the car obviously had the highest mpg ratings in order to get that deduction? That would at least be making the cost more realistic to all tax-payers, and therefore make the American people more well aware of the multiple costs of buying an SUV over a Prius over the lifetime of the vehicle, not just it's initial cost. People that are totally mis-informed will do business as usual. So in order to get all people interested in getting more efficient, you have to reveal the true cost of what they are doing. Also, it's a shame that the government overall is depending on people's good will to make them more money. In other words people who have a more fuel economic car are the ones paying that extra cost in their taxes since their cars aren't the ones guzzling the oil. The government, in this case is like an over sheltering parent. If you never let the child meet a not so nice person, that child, much later in life, will get taken advantage of, when it will hurt much more.
I feel your pain Neil. In the United States we have....The Toyota Prius, The Honda Insight, and the worst in fuel economy of VW's diesel line, and basically that's it! That's all the choices you get, 4. I'm not counting Tesla because not even 1% of American citizens are rich enough to make the Tesla their commuter vehicle. With better tax breaks reaping rewards every year however, that might make things more possible for the Tesla. Now look at sports cars, SUVs, and pick up trucks, I won't even try to count the options here, but there are a lot of them, all of them in the U.S. anyway gas/diesel guzzling.
I'm ok with not having scrolling windows as long as I'm not totally freezing or baked when I get there.
I'm ok with not having ABS, because if you are good at braking you'll never need it.
No boot space, I can deal with that by using the seats for storage. It's not like when you go grocery shopping that you have to take the whole family.
No mirrors are fine as long as I still have good rear visibility. The VW L1 uses cameras, and puts the display in an easier to see place on the dash than where mirrors would be mounted.
Two front airbags would be nice, or a totally new air bag system like how Nascar has a helmet cradle might work.
We don't need traction control, control, control, because apparently we're incapable of actually driving.
We don't need heavy automatic transmissions.
We don't need $100,000 dollar sports cars to be electric, what all working people in America need is reliable, affordable, and more energy efficient transportation. I am energy source agnostic. Whether it's fuel powered or electric, more calorie efficient is the best answer.
Right now, other countries have so much better options for efficient vehicles, anything would be an improvement.
Wave Disk Generator serial hybrid uses 60% of fuel for vehicle propulsion, and scales as small as motor scooters and as large as delivery trucks, due to its small size, low weight, and low cost.
This Wave Disk Generator would produce amazing mpge and performance when combined with the VLC platform. Production costs would be much lower because it eliminates the conventional hybrid IC engine, transmission, cooling system, emissions, and fluids, resulting in a lighter, more fuel-efficient electric vehicle, without the range limitations.
ARPA-E’s 37 Projects Selected From Funding Opportunity Announcement #1
Project Title: Wave Disc Engine Organization: Michigan State University Funding Amount: $2,540,631 Website: www.msu.edu
Brief Description of Project
The Wave Disk Generator revolutionizes auto efficiency at lower vehicle costs. Currently, 15% of automobile fuel is used for propulsion; the other 85% is wasted. A Wave Disk Generator hybrid uses 60% of fuel for vehicle propulsion.
MSU’s shock wave combustion generator is the size of a cooking pot and generates electricity very efficiently. This revolutionary generator replaces today’s 1,000 pounds of engine, transmission, cooling system, emissions, and fluids resulting in a lighter, more fuel-efficient electric vehicle. This technology provides 500-mile-plus driving range, is 30% lighter, and 30% less expensive than current, new plug-in hybrid vehicles. It overcomes the cost, weight, and driving range challenges of battery-powered electric vehicles.
This development exceeds national CO2 emission reduction goals for transportation. A 90% reduction is calculated in CO2 emissions versus gasoline engine vehicles. Wave Disk Generator application scales as small as motor scooters and as large as delivery trucks, due to its small size, low weight, and low cost. This technology enables us to radically improve the atmosphere and human health of major global cities.
Why ARPA-E Funding and Not Private Capital
•
This is cutting-edge research with a research risk that private capital won’t accept.
•
Mathematically difficult transient combustion technology is well situated for university researchers.
•
Requires developing new low-cost, high rpm generators, which currently do not exist in automotive markets.
•
Breakthrough automotive research is difficult to fund without committed large customers.
Uniqueness/Benefits of Technology
The Wave Disk Generator replaces the automotive internal combustion engine, radiator/water pump, fuel/air control, transmission, and generator found in today’s hybrid vehicles, resulting in a “hyper-efficient” serial hybrid vehicle that provides a 3.5 times improvement in fuel consumption efficiency.
Wave Disk Generator Consumer Benefits:
•
Full-size vehicles with 500-mile driving range
•
Compressed natural gas, hydrogen, gas or renewable fuels
•
Elimination foreign oil dependence
•
30% lower vehicle costs
•
90% less CO2 emissions
Addressable Market & Potential Customers
Wave Disk Generator light-vehicle platforms offer 30% lower prices plus refueling costs that are one-third those of traditional hybrids. Based on an OEM cost of $500 per vehicle, Wave Disk Generator provides cost and efficiency leadership to a $25 billion annual power component market supplying 50 million new automobiles and light trucks annually. Continued oil and gasoline price increases could motivate rapid consumer vehicle replacements over the next 15 years.
Key Team Member Bios
Dr. Norbert Müller, associate professor, mechanical engineering and principal investigator with over 15 years of expertise in the invention, development, design construction, and testing of innovative turbo machinery.
Dr. Tonghun Lee, assistant professor, mechanical engineering, with research expertise in laser spectroscopic imaging of advanced propulsion and energy conversion systems.
Dr. Indrek Wichman, professor, mechanical engineering, has 30 years’ experience in combustion modeling and experimentation including vehicle fire safety.
Dr. Patrick Kwon, associate professor, mechanical engineering, with expertise in advanced materials design and manufacturing; manufacturing processes; mechanical behavior of materials.
Dr. Elias G. Strangas, associate professor, electrical engineering, with hybrid vehicle power train experience; works on the analysis and design of high-efficient electrical machines, drives, and power electronics.
Dr. Fang Peng, professor, electrical engineering, with expertise in hybrid transportation power electronics, controls, and motor drives.
Roger Koenig, adjunct professor, with over 30 years experience in research management, technology start-up creation, fund raising, and M&A, including 10 years as a public tech company CEO & chairman.
Miscellaneous
Wave Disk Generator hybrid platform research needs to be accelerated and collaborated to quickly transition to commercialization. This new platform can uniquely provide hyper-efficient vehicles with superior customer cost, safety, and utility. U.S. automotive technology leadership can be re-established globally. A near-term solution is offered to energy dilemmas of diminishing oil supplies and 80% reductions needed in global CO2 emissions.
It seems like it would be easier to make a VLC amphibious than a Chevy Tahoe or Toyota Camry. Amphibious vehicles seem practical in flood prone areas. It floods a good deal in Houston. A VLC with pontoons and a little Yamaha outboard to get across flooded streets and an EZ Tag to run on the Hardy Toll Road sounds like an excellent commuter car.
Sir,
Can u explain how we are calcualting the A, B & C values with respect to Speed and time using coastdwon method....
A plot of vehicle "speed" (V) versus time (t) can be differentiated (theoretically using a "fitted" curve or numerically from the data itself) to obtain deceleration (a) versus time (t); i.e.: dV/dt = a. The mass (m) seems to be assumed constant and equal to vehicle weight / gravity (an argumentative assumption, but probably reasonable), so the deceleration force (F) is taken as a/m. The plot of force (F) versus time (t) is of the form A+Bt+Ct2 (parabolic), from which the coefficients of hysterisus rolling resistance (tires) and aerodynamic drag (form and surface) can be approximated if "A" and "B" are taken to be due to the static and dynamic roll resistance and "C" is taken to "sort of correspond" to the aero drag. The result is "sort of" rough but reasonable, but wind tunnel testing and dynomometer tire testing can give more accurate results for each, which is why such testing is generally done first; coast-down testing then acts as confirmation.