Boat Tail
 

Fashioned a boat tail out of cardboard and coloroplast. Did bi-directional runs North and South. Winds were 350@9 at the beginning and 360@14 after the end of the last run. Temperature remained steady at 45. Speed was 55. No cruise control but scan gauge showed average speed 55. Increase in FE 2.17%

With BT
N S
42.2 49.0
42.0 49.2
Avg 45.6

Without
N S
40.4 49.3
40.2 49.2
Avg 44.775

With BT
N S
42.0 49.5
42.1 49.7
Avg 45.825

Overall average 45.75 with BT
Overall average without 44.775

Total increase of 2.17%

Little disappointed with the results. Was expecting double what I ended up seeing. Although I am happy with the 45 MPG highway.:thumbup: I think that with cheap fabrications and crude attachment procedures that 3% is about it as far as mods go. Seems like every aero mods hit?s somewhere around 3%. Just proving that there is no silver bullet you just need to make sure your clip is full.

https://www.gassavers.org/garage_imag...kdrvjs3fuq.jpg

That's almost exactly what I saw with mine.

The new VW Polo diesel has a mini boat-tail. It's hard to see in this picture, but click the link below for a super huge zoom. You can see they added a plastic/fiberglass extension to the roofline & C pillar (it goes several inches past the back glass).


https://i.treehugger.com/files/th_ima...BlueMotion.jpg

super huge zoom: https://www.autobloggreen.com/photos/...motion/156660/

Nice work! So many hatchbacks could benefit from the boat tail. I think a longer boattail like basjoos' civic would yield a greater improvement in fe.

The porsche cayenne has a little thingy on the top back also
https://www.bilagentur.dk/images/Pors...20-%202005.jpg

Too bad the factory roof racks (which will likely never have anything carried on them) negate any gain from the roofline extension :D