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

[MetroMPG]

Passenger side and bottom left to do. Oh, and better not forget the camera boom before I seal it up.

Even only half covered, I'm cautiously optimistic about how rigid it already feels. I also did some cross-triangulating on the frame inside - will get a shot of that tomorrow before I finish the skin.


EDIT: also added another picture of the four bulkheads in place:
back here in post #74.

[tasdrouille]

That's one nice looking boattail. Keep it up! Are you going to do an A-B-A test of the CAD?

[MetroMPG]

My cruise control is still busted, so I can't do as-controlled-as-possible testing.

But I'll likely try it anyway - it'll also be a test to see how consistent & steady I can hold my speed.

I could just do coastdown comparisons (they pretty much remove the driver from the test - which is the goal), but I want to get an idea of the actual fuel economy impact, and coastdown runs don't tell me that as directly.

Before any of that, though, tuft testing to make sure it's got attached flow.

[Cd]

Are you going to see what the new drag coefficient is when you get everything worked out ?
Also, did you ever consider adding a trip strip on you rounded tail lights ? ( when you are in 'stock' configuration . )

[MetroMPG]

Yeah, once ALL the aero mods are done, I'll probably attempt to figure out Cd.

Trip strips: yes, I've thought about them - for the bumper as well. I had the idea that I could incorporate some hard edges on the bumper corners as a mounting point for the boat tail.

[wagonman76]

Good job so far. Yeah it doesn't take much for rigidity when you use sheets of material. Same way basically piece of painted cardboard keeps an entire entertainment center square. I braced mine to be totally rigid before adding any panels, to keep the load off them and prevent popping of welds. But if I had better welding equipment, I could have eliminated a lot of cross bracing and saved some weight.

[Cd]

Where do you plan to mount the camera ?
Besides the obvious views that you want, such as the sides of the tail, it would be interesting to see how much turbulence is on the very back and underside. ( like behind the wheels )
When do you plan to add minitails to your mudflaps ?
Also, I know that you didn't get good results with your bellypan test, but as you mentioned, the cardboard was drooping down during the test. Do you ever plan to redo the test ?

And one more thing - Do you remember the post about the U.C.Davis Taurus that they aeromodded ?
It seems like it would be a simple thing to create a concave area around the center of the back end. It can't hurt ( might even look better too, rather than have a totally flat surface ... a little style ) If you remember, the aero guy stated that the concave area created a small vacuum that resulted in a smaller wake.

[Nerys]

like one giant golf ball dimple. Interesting ....

[MetroMPG]

Not quite the same thing as a golf ball dimple. (Man, everyone loves golf ball dimples!)

Cd: will answer questions later on.

A couple more pics of progress:



Above: cross bracing the inside. (Yes, those white pieces are cardboard - really stiff "angle iron" cardboard.)

And below, two views of the completed driver's side and top... now with self-supporting goodness!

[Nerys]

hey man thats starting to look very cool. a quick shot of BLACK spray paint and it will even have a nice 20ft finish.