Building a 100mpg consumer vehicle

[drmiller100]

Originally Posted by Ken Fry

Hi Doug,



Regards, Ken

Ken,
thank you for your thoughts. We certainly think about things differently, but obviously there is one physical model which is the real world.

My idea starts with the idea of looking at where fuel goes towards. Fuel goes towards 3 main topics, then from there gets split down.

First, fuel heats the radiator.
Second, fuel heats the exhaust gasses out the tail pipe.
Third, fuel creates exhaust gasses which push the car.
Fourth, fuel creates energy which gets thrown away by pumping losses and the like.

Of the third topic, there are three main resistances to pushing the car around. There is weight (1/2 mvv). There is aero resistance (vv*Cd*Frontal area). There is rolling resistance.

We can back into real world with the math, eventually.

We can come up with excuses as to why all the investor money is gone, but the car is not designed yet.

Or, as you did, we can take some educated guesses, and start laying the car out and get it done.

[drmiller100]

Ive been reading the blogs from the edison 2 team.

The leaders there have provided some GREAT information in building a car. Highly recommended reading.

[dcb]

Originally Posted by drmiller100

...Tandem REALLY SUCKS according to my lady. She refuses to ride around with her knees 2 feet apart, and I don't want a car which is 12 feet long....

As you say, there is the real world. Airplaines dont fly sideways for a reason, regardless of personal taste. I always have to take the needless opinions down a notch where things like frontal area are concerned.

You can have a tandem that you don't have to straddle however. But you are on a different path which is fine but will impede your 100mpg goal.

[drmiller100]

Originally Posted by dcb

You can have a tandem that you don't have to straddle however.

how??????

[dcb]

use bucket seats and make the structure more like a box than a beam

[drmiller100]

Originally Posted by dcb

use bucket seats and make the structure more like a box than a beam

wheel base ends up pretty long unless you do what I'm doing.

[Ken Fry]

Originally Posted by drmiller100

wheel base ends up pretty long unless you do what I'm doing.

The MonoTracer is 12 feet long and its wheelbase is about 10 feet. Of course, handling changes with a passenger on board. The overlap is pretty slight. Another 6 inches in wheel base would eliminate it for most passengers.

The Piper Cub had tandem seating with only the feet and lower calves of the rear person overlapping the front person.

I think overlapping according to your plan it is a good idea for keeping the wheelbase short. Loads of concept cars support your approach.

The side-to-side change of CG that comes with your arrangement can more easily handled than in something like the Aptera, because you are not offsetting the people so far. They had a much wider track than you are planning and still seemed to have handling problems in the last version. They temporarily fixed that at the X Prize, by stiffening the suspension substantially, if I recall. You will probably have the advantage of lower CG.

[Ken Fry]

Originally Posted by drmiller100

Ive been reading the blogs from the edison 2 team.

The leaders there have provided some GREAT information in building a car. Highly recommended reading.

Yes, I think that their's is a great approach. Also Oliver Kuttner is about 1000% better as a spokesperson than Marques was for Aptera, in my view. Their vehicle, with its 250cc engine and sophisticated combustion control, points the way for success in obtaining 100 mpg: a very small highly-loaded engine being the fundamental key. Great demo for the value of doing the math first.

Jason Hill's work on the visual design of the body has been really impressive, too. Check out his blog: designby11

[drmiller100]

Originally Posted by Ken Fry

The MonoTracer is 12 feet long and its wheelbase is about 10 feet. Of course, handling changes with a passenger on board. The overlap is pretty slight. Another 6 inches in wheel base would eliminate it for most passengers.

The Piper Cub had tandem seating with only the feet and lower calves of the rear person overlapping the front person.

I think overlapping according to your plan it is a good idea for keeping the wheelbase short. Loads of concept cars support your approach.

The side-to-side change of CG that comes with your arrangement can more easily handled than in something like the Aptera, because you are not offsetting the people so far. They had a much wider track than you are planning and still seemed to have handling problems in the last version. They temporarily fixed that at the X Prize, by stiffening the suspension substantially, if I recall. You will probably have the advantage of lower CG.

My CG should be something near 12-18 inches off the ground, and pretty far forward. I'm actually not very worried about tipping.

Where did you CG end up?

As for the mono tracer, that is EXACTLY what I am talking about. I only found one pic of someone in the back seat - a little twig of a lady, and she looked pretty scrunched in there, with the driver pretty squeezed up.

I'm a big dude. My lady is not Petite. For her to get into the car, it had better be a LOT more friendly for the passenger then the Mono tracer or a piper cub.

I equate the Piper and the Mono to being sportscar like. My goal is people compare it to a Prius for getting in and out of.

[Ken Fry]

Originally Posted by drmiller100

Or, as you did, we can take some educated guesses, and start laying the car out and get it done.

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