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

[MetroMPG]

Regarding the belly pan vs. exhaust bits:

- You can't see it well in the photo, but the front section is cut out where the exhaust down tube goes horizontal into the catalytic converter, and also a bit aft of it. There's about a 1 inch margin around the metal.

- basjoos often gets asked about his full coroplast undertray. He's had no heat related issues. Search his thread if you want specifics: http://ecomodder.com/forum/showthrea...0-a-290-8.html

[MetroMPG]

Ready to tuft test the top & sides, but it rained this afternoon.

And it's getting colder out. I think summer's finally over. Might snow this weekend.

[orange4boy]

The weather sure puts a damper on ecomodding. I was very lucky with the Prius work. It was a balmy 10˚c on the last day, since then it has dropped to around 5˚c which makes a big difference when you are wrenching.

Sweet belly pan.

I think you should make the permanent version in cedar strip. Simple eh?

[MetroMPG]

Oh, yeah - a varnished cedar strip boat tail would look fantastic on a black car!

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I get such a kick out of tuft testing. I could watch these videos over and over.



Top side observations: I can report that the tufts on the top lie very still. Makes me wonder how much more angle/curvature I could get away with. (Wish I had all the time - and warmer weather - in the world to keep on working on this!)



Details of camera set-up, above:

• The white line across the side of the car is the USB cable for the web cam, which is the little pod duct taped to the end of the "boom" (aluminum tube).

• I spiral wrapped the USB cable up the boom to alter its aero properties (minimize drag force)! Did it work? Who knows. You sometimes see this sprial treatment on smoke stacks.

• The white line from the cam to the roof of the car just is some string, pulled taut to tension the boom and minimize bouncing.

• The boom is attached (duct taped) to the aluminum tube frame of the boat tail. I cut a pair of flaps in the cardboard, top and bottom to access the tubes inside (you can see the bottom flap still open).

Driver's side observations: you can see for yourself even from this screen capture that there's more flutter - turbulence - on the side, increasing toward the bottom. No surprise there - probably the effect of the rear wheel.

Below: camera setup for the side shot. It sticks out about 3 feet from the side.



Next: I decided that since I've got this all set up already, before I pull off the tufts I'm going to CAD up a mini-boattail for behind the wheel, just to see what it does. (Cd will be happy to read that!)

Once I've done that (tomorrow, maybe), I'll put the tuft testing clips together into one video and post it.

THEN I'll watch for a good day to do the highway speed A-B-A on the entire boat tail.

[Cd]

Originally Posted by MetroMPG

I get sich a kick out of tuft testing. I could watch these videos over and over.



Next: I decided that since I've got this all set up already, I'm going to CAD up a mini-boattail for behind the wheel, just to see what it does. (Cd will be happy to read that!)

Yes, but only if it is made to match the varnished cedar stip !

[Cd]

How far does you camera boom stick out from the side of the car ?
It looks like a ticket waiting to happen ( yikes ! )

BTW, I like what you did with the belly pan in front of the rear wheels.

s-m-o-o-t-h

[RobertSmalls]

Originally Posted by Cd

It appears as though some of you guys are so bold as to have the Coroplast sitting flush against the engine.

Mine does. The oil pan is completely in contact with the coroplast. I also have coroplast in direct contact with my radiator. No damage yet.

Coroplast melts at 160°C = 320°F. Motor oil is expected to be a little bit hotter than coolant, so I figure no more than 220°F.

However, I have measured my cat at 560°F, and I'm sure it gets much hotter than that.

[RobertSmalls]

Originally Posted by MetroMPG

Next: I decided that since I've got this all set up already, I'm going to CAD up a mini-boattail for behind the wheel, just to see what it does. (Cd will be happy to read that!)

So will I! What kind of software are you using, and can it spit out CdA numbers, or just velocities and streamlines?

[aerohead]

Darin,the tuft images look great.They may be a little "nervous" in places,but they're mostly pointed "back" which means attached flow and no circulation.
That's about all one could hope for,and the base pressure in the wake should really be coming up closer to your forward stagnation pressure now.
Will be anxious to see your mpg although it's a rough time for testing,weatherwise now.
As to the maximum angle,it would appear that 22-degrees is the maximum for passive aerodynamics.Anything steeper and you'll need suction-slots.
Mair's boat tail R&D arrived at 22-degrees.The SAE paper on the Dodge Daytona reveals that Chrysler Aerospace arrived at 22-degrees.Many of the concept cars have "apparent" angles which are pretty steep until you figure what happens with their active suspensions,with dropped noses kicking their hineys up to a "shallower" angle.If I take a protractor to the back of the aerodynamic template it comes in at 22-degrees.
The trick is to maintain the progressively-increasing curvature,building up to the maximum that we see with the ubiquitous teardrop.

[MetroMPG]

Originally Posted by Cd

It looks like a ticket waiting to happen ( yikes ! )

You worry a lot about police!

FYI, the two runs with the boom out the side of the car were intentionally done on a quiet street where I saw zero traffic. No bikes. No pedestrians on the road. No wildlife darting from the brush only to meet their fate in the form of a lethal QuickCam Pro 5000. (Would have made for interesting video though.)

Boom stuck out ~3 feet - so the total width was about the same as a big truck.