Project: Geo Metro boat tail prototype - 15% MPG improvement @ 90 kph / 56 mph

[discovery]

It is amazing what a light boat tail can do to your MPG. I’m still in little disbelieve, but hey the numbers don’t lie. Everyone is improving their mpg by adding one. Just a keep up with info and may be one day I’ll do something like this.

[MetroMPG]

I was actually thinking of a tight form fitting closed cell poly "pool noodle" to fill the fender gap. Plus moonies.

I'd only radius the aft portion of the wheel arch with half a noodle. I'd extend the front/top surfaces out flat toward the tire. Probably minimal gains on an Insight though - they paid attention to the wheel arches in their design. (I'm assuming you drive an Insight from your username.)

The threads in question:

http://ecomodder.com/forum/showthrea...-0-a-5462.html

and

http://ecomodder.com/forum/showthrea...light=skirt%2A

[MetroMPG]

Originally Posted by Nerys

If your up for it (I KNOW its a ton of work) unless you already have the data?? ie what kind of improvement would JUST the tail make over a stock car? no belly no wheel skirts etc.. anyway to calculate that?

I couldn't really predict. Half to 2/3 as effective might be a safe guess, but it's just a guess.

IE big massive fan into a difuser array to straighten the airflow (think wright brothers wind tunnel)

Try it and let us know how it works out.

Originally Posted by JeepNmpg2

Is it still more effiecient to go full conical VS bluff boattail?

Yes, but there are diminishing returns the longer you make it. I know Phil has posted information about a Mercedes teardrop prototype with varying tail lengths.

[MetroMPG]

So, the last thing I'm going to do to the boat tail is document it: take a few more pictures and a bunch of measurements. Then it comes off, gets pulled apart and most of it goes out with this week's recycling.

If I had somewhere convenient and out of the weather to put it, I'd hang on to it until I have version 2 made.

But at least I have some hard numbers that are an incentive to make/improve the next one.

[Nerys]

are you kidding me? with those kinds of gains I would LEAVE IT ON TILL IT FELL APART :-)

[Johnny Mullet]

Blackfly needs window tint.

[Christ]

^^^ Darin could recycle some of those black plastic bags on the boat tail and make "Limo Tint"...

[Frank Lee]

Originally Posted by MetroMPG

Then it comes off, gets pulled apart and most of it goes out with this week's recycling.

Pull the plastic off then fiberglass it.

[3-Wheeler]

Originally Posted by MetroMPG

[B]Conditions:

Grenadier Island Past 24 Hour Conditions
... Pressure (kPa) ... Vis (km) ... Wind Chill
... 101.8 ...

Just wanted to mention that if your baro reading was from a weather station or radio, then the baro reading is 'corrected' for elevation back to sea level, and may need to be corrected for your current elevation above sea level.

For example, our TV station always reports our current barometric conditions as if we are located at sea level, even though our elevation in Wisconsin is actually about 1000 feet.

So for our location, the TV station would report a typical 29.9 inches Hg, but our 'actual' measured barometric pressure is really 28.9 inches Hg. That also means that our actual air density is lower than reported by the TV station.

Now when performing coast-downs, one should properly calculate the 'true' barometric pressure based on:

1) the TV station reading
2) your actual elevation above sea level
3) subtract one inch of Hg for each 1000 feet above sea level
4) from the TV station baro reading
5) now you have the actual baro reading at your location

Hope this helps, Jim.

Now back to our normally scheduled program....

[thatguitarguy]

Originally Posted by MetroMPG

So, the last thing I'm going to do to the boat tail is document it: take a few more pictures and a bunch of measurements. Then it comes off, gets pulled apart and most of it goes out with this week's recycling.

I'm all for recycling, but for the effort you put into this project, and for the interest you generated, I'd suggest pouring some of the gas you saved on it and ceremoniously burn it "Burning Man" style, or as a sacrifice to the Aero gods.

Or maybe that's just too American...