Designing an FE Car from the ground up.

[Mighty Mira]

Toecutter, I like your way of thinking.

I've always been a performance nut too, long before I started caring about fuel economy. And I think something shaped like the Precept and done the way you are talking about according to the criteria you set out would sell.

But since I started getting in on the FE kick, the engineer in me sees the shape of current cars with the Cd of 0.33 or so, and then a dolphin with Cd of 0.004, and sees an improvement to be made of approximately 80 times! Of course, if that figure is to be believed. This link makes me think otherwise.

Even just the streamlined body is 0.04, which is about 8 times better than what most cars are currently.

And seeing as cars like the following sold once:


It should be possible to have the driver in a more forward position, which gives more room for the boattail, and hence, lower Cd. It also means more usable space, since there is no penalty to starting out with the largest cross sectional area fairly early.

The Mercedes Benz Bionic Car is a step in the right direction, but even that is a little compromised IMO.





Both articles are well worth reading btw.

Of course, if you want to really optimize for low Cd, something like the Sailfish, Tuna or Mackerel are good to observe.

Sailfish (note that the sail is down at top speed, it folds back into a groove):


Yellowfin Tuna:


Mackerel:


Mako shark:


Marlin:


All are essentially streamlined bodies in three dimensions, somewhat elongated I suspect to make changing direction/propulsion easier.

I guess I just like the idea of reducing my vehicle costs to practically zero, especially over long distances at highway speeds. Equipping a car to get FE equivalent to such low drag means of course reducing engine size OR pulse and glide driving. Both have their downsides - P&G means that cruise control is not practical, you need a larger starter motor and a good way to control the engine properly, to turn it on and off safely etc. A reduced engine size lawnmower style motor means that getting up a steep hill will mean slowing down significantly.

A couple last pictures: the Orca or Killer Whale:




Note that the widest point is about a third the way back.

Adding some wheels, removing the sharp edges (I probably should have elongated the back JUST a fraction)...

[Sludgy]

I'm surprised that nobody posted drivetrain designs. Efficiency starts with the engine, transmission and its accessories. Here's my candidate for an ultra-efficient drivetrain:

ENGINE

Two cylinder gas engine, a "boxer" layout for good balance and even firing.
About 1.5 liters
Undersquare bore and stroke
Cast iron block
Aluminum heads
DOHC
4 valves per cylinder
Atkinson cycle cam timing primarily, but high valve overlap at high speed
Direct fuel injection
Lean burn, open loop at idle, closed loop at load.

ACCESSORIES

NO belt drives
Ebullient (boiling water) cooling or thermosiphon
Electric radiator fan
High capacity (NIB?) alternator (mounted on crankshaft, like a Harley Davidson) generating electricity only on decelleration or low battery voltage
Deep cycle battery
Electric power steering (or none)
Water-based based adsorption system A/C using either ammonia, lithium bromide or silica gel. (A/C would be powered by exhaust heat.)

TRANSMISSION

Magnetic eddy current CV automatic transmission. This would not require fluids, clutches, bands or torque converter. These are already commercially available from Magnadrive. http://www.magnadrive.com/

This drivetrain should power a Corolla-sized vehicle from 0-60 mph in 10-12 seconds, and could get upwards of 50 mpg highway WITHOUT weird shapes or aero mods. In a Prius body, it'd get 60 mpg. In a streamliner, it'd get 100 mpg.

The logical company to develop an drivetrain like this would be Subaru, since they already make boxer engines. Subaru doesn't seem to be focussed on economy these days, though.

[JanGeo]

Get real guys - use this shape...

Attachment 10

[Mighty Mira]

Originally Posted by JanGeo

use this shape...

Attachment 10

What's the Cd on that?

Get real guys -

I suppose that I'm not "real" as far as the conventional mindset is concerned, and the US auto market is more conventional than most.

However, I'm asking a few questions that seem to be going unasked...
Why does an FE car have to have the vestigial aerodynamic ugliness of 3 box design?
Why does an economy car have to be shaped like an inefficient box?
Why should an economy car have less room for passengers? Why can't it use the same parking spaces available to full-size cars or even SUVs?
If we are going to have a boattail, why not halve the length by sloping up from the floor as well as down from the roof?

Most of all, I'm asking if there is a market for a car that costs less than $10k and can virtually completely insulate the buyer from fuel price rises? Why can't we have the practicality of an econobox (speed, storage, protection from weather) with the cost to run near that of a bike, if the compromise is looking a little weird at first?

I think a case can be made for starting off with the most efficient shape and then only throwing away components of that shape once every avenue of both retaining that shape and satisfying other constraints has been tried, rather than working the other way and trying to make the three-box design as aerodynamic as possible. With higher fuel prices changing the underlying economic assumptions of the automobile and a whole new array of technology and knowledge at our disposal since the last energy crisis (1970s), it would befit us to spend a little time questioning all our assumptions.

[Mighty Mira]

Originally Posted by Sludgy

I'm surprised that nobody posted drivetrain designs. Efficiency starts with the engine, transmission and its accessories. Here's my candidate for an ultra-efficient drivetrain:

Thanks for that, very interesting!

My point with starting off with the aero stuff is that it once you determine (minimize) the maximum and steady state load conditions, then you are in the best position to select an appropriate engine size and even the basic type of engine (electric, gas, almost rubber bands etc). Although potentially it will do a bit of chugging on acceleration and hill climbs. With all that you'd be able to get away with a smaller engine and thus the load on it would be higher and more efficient. With a 1.5l engine it'd be a sportscar.

Very interesting about all the belt driven accessories.

[The Toecutter]

I think such a car should be designed with the possibility of there being a choice multiple drive systems one could buy for their vehicle.

For instance, the above diesel concept I mentioned. It should also be designed so that it could accomodate an electric drive and lots of batteries. Imagine, for instance, if there was this huge space under the floor to fit 2,000 pounds of lead acid batteries. In a car that aerodynamic, it could have 150-200 miles highway range on cheap lead acid batteries, no NiMH or Li Ion needed. Sure, the car might end up weighing 4,500 pounds in such a case, but with a dual 8" motor setup and Zilla 2k controller with a series/parallel shift in place, it would still do 0-60 mph in 6 seconds. It would probably cost the same as its diesel counterpart, sacrificing some range and incurring a long refeulling time for the benefit of more performance and dramatically lower operating cost. Or for increased performance and range but with higher cost, give the option for advanced batteries, say a Li Ion option to cut the weight down to 2,900 pounds(same as diesel counterpart), extend range to 300 miles, and drop 0-60 time to 4 seconds, but it might cost $20k extra.

The same platform should also be designed around a CNG engine and tanks as well.

Imagine the buyer being able to walk into a dealership and choose which kind of fuel they want the car to run on. With 150 miles range, many would be able to use the pure EV on cheap lead acid batteries for all of their driving needs, while some would rather have the diesel and run it on B100.

The whole idea is to keep costs down though. Going to a plug-in hybrid would mean paying for two drive systems, which would bring the ciost up quite high.

[JanGeo]

Originally Posted by Mighty Mira

What's the Cd on that?

http://www.treehugger.com/files/2005...carbon_car.php
They don't give it but from what I remember it was very low which is why it took so much money to develop its shape. 660cc HOnda motor and 100mpg.

[The Toecutter]

It is a custom called the AeroCarbon built onto a Lotus Elise chassis with a Honda engine.

It has a drag coefficient of .22. Nothing spectacular. I think it's quite ugly, especially for having a Cd as high as .22, when other cars that look much better have attained .16-.18.

Definately needs some work on the overall finish.

http://64.233.167.104/search?q=cache...ient=firefox-a

And if you're going to build the car on such an expensive chassis, at least keep the horsepower high to justify the expense! If the original Lotus Elise engine were maintained, it would still get ~80 mpg, only it would accelerate from 0-60 mph in ~4-5 seconds and top out near 180.

Fuel economy and performance can coexist nicely. If fuel efficiency is to be marketed to the public, it has to be fast. The truth is, a more efficient engine with lower horsepower numbers is not going to affect fuel economy more than ~20-25%. Compare the EPA mileage data on cars of a certain model with their different choices of powerplants. The V8 Mustang, for instance, gets near the same fuel economy as the V6. The V6 Corolla gets about the same fuel economy as the L4.

The real truth is, it's mostly drag that effect's fuel economy. The only way a powerplant swap by itself will give amazingly good fuel economy is if you're keeping it at peak load for normal highway cruising, and that just won't provide adequate acceleration to even keep up with traffic. Even the deplorable Hummer is using only about 30 horsepower to maintain 60 mph. That wouldn't do much to accelerate it! Likewise, a lightweight aerodynamic car will be able to cruise that same speed with only around 6-7 horsepower, and likewise, having an engine that small just isn't practical on anything roadworthy. Anything other than that peak load, and efficiency rapidly drops off.

It upsets me when designers try to tackle increasing fuel economy through mostly engine downsizing, when that is where there are some of the least significant gains to be made. The real gains to be made are the low hanging fruit that is aerodynamics: you expend far less effort, sacrifice far less quality, for much greater fuel economy.

That Ford Probe V? If someone somehow managed to shoehorn a 350+ horsepower V8 into it, I bet it would still get ~45 mpg if driven conservatively!

If you've ever seen the movie "The Wraith", that concept Dodge M4S turbo interceptor that made its appearance in that movie had roughly 440 horsepower. Guess what fuel economy it got? THIRTY-ONE mpg. Why? Its drag coefficient was around .20. Here we are, with our car fleet not even approaching that, still struggling with inline four cylinders and V6s of around 170 horses.

Imagine making an ultra aerodynamic car. Could have performance out the *** and high horsepower, yet still get double the combined fuel economy of cars available today. All this, with no magical new technology needed.

But when consumers demand fuel economy, Detroit punishes them with anemic powerplants they don't want and dramatically downsized cars that they don't want. Aerodynamics are everything. Literally.

Powerplant? Not so much, unless you go 100% electric or B100!

[Sludgy]

[quote=The Toecutter] Aerodynamics are everything. Literally.

Not in my world: Vehicle mass and propulsion plant efficiency are more important FE factors in stop and go driving, which is how most Americans drive most of the time.

Sure, I love to get big numbers in highway driving, but my 10 mile commute has over 20 stop lights, none of which are synchronized. As a matter of fact, political pressure from residents along Wollaston beach has caused MDC traffic engineers to time the lights to stop at every one, regardless of pedestrian or side street traffic. I never get over 45 mph in my commute.

Aerodynamics won't help me much.

[JanGeo]

Sludgy - Sounds like you need a pure electric vehicle with really good regen braking. I built a scooter from a 6000 watt eCycle electric MG13 motor and mounted it on a Bladez Transport with 3 Hawker Genesis 26ah batteries and very seldom did I need to use the brakes in stop and go traffic or down steep hills.