Subaru Outback Prototype Boat Tail Test Results
 

http://lesbaru.com/stuff/lezzyboattail2.jpg
http://lesbaru.com/stuff/lezzyboattail3.jpg
http://lesbaru.com/stuff/lezzyboattail4.jpg

I put the plate on it and a light and went and tested it.

SADLY the only straight, high speed (35+ mph), low traffic, FLAT piece of road nearby was blocked off for construction work, and I went to the next best piece of road. Which was obviously NOT flat. However I did do several runs each way, and averaged them out with hopes of getting a more realistic number.

RAW DATA:

WITH BOAT TAIL:
1 22.2
2 50.3
3 22.8
4 53.9
5 22.9
6 54.1

WITHOUT BOAT TAIL:

1 22.5
2 48.6
3 22.6
4 49.2
5 22.6
6 49.6

With Average: 37.7
Without Average 35.8

Difference 1.9 mpg

Test was done by engaging cruise control at 55 mph, cancelled with the brake, and resumed with the resume command. Readings were averaged by scan gauge II which is usually within 1% for my tank average readings.

Now to get to work on my hitch basket based detachable boat tail! :thumbup:

Any chance you'll be able to get out and do a coast down test? Keep up the good work :thumbup:

Looks like almost the exact same gain I got with my original tail. A bit over 5%. I lost the gain when adding the piece to take the tail the rest of the way out. I need to get some more pics of it soon then take the piece off.

Glad to see the back-side view, it really helps visualize what you are doing. What did you use for wrapping? It looks like you might have used a shower curtain liner like I did.

Same here, it is nearly impossible to do a quick a-b test, with all the hills, wind, and potholes. I just use identical trips that happen to have the same temps and weather conditions and use that for comparison.

Nice work !
I'll be interested to see results at a higher speed when it becomes possible ( and perhaps that coast down test. )
Do you plan to tuft test the tail to see if you have any problem areas ?
With the clear wrap, you shouldn't need a spotter to drive along side you to see how they react.
It looks like the angles are O.K. from here, but I'm no expert.

It almost looks as if you just have the piping taped together with duct tape.

I'm really wondering how the police will react to this.
If you dont end up having any problems with the law, I might just think of building something similar.

This is really starting to get interesting :thumbup:.

It wasnt actually attached to the car in any way. At least the frame wasn't. The sheeting was because I didnt want it to parachute, but we simply connected it with clear tape.

The frame itself is attached by pinching the pipe ends in teh vice, creating a flat point, and stick it into wedges and bending the tips slightly. When building it, I made the pipes under tension to help give it a clamping effect.

The whole thing held onto the back of the car like a giant alligator clip. Looking for a basket hitch right now.

a quick helpful idea for you, if you want to make your boat tail removable why not use strong neodymium magnets, if you get them big enough your boat tail will only fall off if a car hits and and you'd need significant force to get it off your car! but it will be secure and 100% removable.

I was going to use hard drive magnets and some sort of gasket ish material on the edge, since theres no shortage of hard drives. BUT I still need to find a basket first.

Results
 

Kudos and congrats on the 1.9-mpg! Hope the numbers help your neck muscles recover quicker from the under car work.West Virginians will have more to talk about now.

When you say "the pipes under tension to help give it a clamping effect." are you talking just about how it attaches to the car or how the frame is held together. If that is describing how all the multi-angle frame parts are held together I am both confused and very impressed.