Quote:
Originally Posted by drmiller100
Or, as you did, we can take some educated guesses, and start laying the car out and get it done.
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Hi Doug,
Actually this is not what I did at all. Although this approach can work, I tend toward the methodical, analytical approach used in designing things like airplanes and cars. I like to avoid unpleasant surprises, especially if I am spending hard-earned money. There was never a time when I thought of this as a hobby.
So I started with spreadsheets, combustion textbooks, electric motor textbooks, the assistance of highly-regarded people in aerodynamics and business, my own experience in building and racing successful motorcycle roadracers and sailboats, some skills in welding and machining,etc. I looked at actual BSFC charts from many engines and engine types, looked at actual dyno curves for various electric motors, actual charging and discharging efficiencies for various batteries and associated charger electronics. I've worked for Ford, and can tell you that this sort of thing goes on all the time in their engineering departments.
As a result, when Ford brings out their new Focus, there is essentially no doubt about what its EPA test results will be. In the same vein, Boeing is rarely off by more than 1% on performance predictions.
Prior to building anything, I ran real world data through my model for performance prediction. If I predicted a 2004 Honda Accord to get 40 mpg in the urban cycle, then I would know that my model was wrong.
Then, even having some data to work with, I first built a two-wheeler powered by a 50cc engine, then a three-wheeler powered by the same 50cc engine. Then the same three-wheeler, powered electrically... and then the plug-in hybrid.
So we think about things in different ways, and your assumption that I am a git-er-done kinda guy is probably not quite on the mark -- if anything, I tend to overthink things.
We look at engines in pretty fundamentally different ways. I think first about combustion efficiency in converting fuel energy into heat, and think of heated air expanding and moving a piston. Not until the exhaust valve opens do I think of that hot air as "exhaust". I don't, for example, think that exhaust pushes the car down the road.
But differences in approach are what makes the world go round. Your approach of low frontal area and good aero will certainly provide pretty good mileage. Traditionalists like me and the Edison people will try to tell you that the engine should be far smaller than you are planning, and be pretty thoroughly tweaked even then -- but if you surprise us all, then it will be more fun for you.
Good luck with the project,
Ken