In the pics it is set on the car loosely, it is not clamped into place, so it looks clumsy. The tail is dragging, normally it is higher.
I found a way to cut tabs and bend them using heat to make tabs that fit into the door and trunk. Slam the door and the part stays in place. However it is a little tougher to coordinate all the parts so that the tail as a whole will stay in place. That is what I will be working on next. I have to work on the trunk tabs and wiring a bit, the trunk is not closing right. Then I will make the tabs for the doors.
The taillights are led truck trailer lights, red and amber.
There are some high spots and openings that have to be faired down somehow. I think I can bend it so that I don't need any additional support around the wheels but we will see.
The concept is a removable boxtail, with no permanent changes to the vehicle. I may have to ziptie the bottom panel to the bumper and drill some holes in the bottom of the bumper. Currently I am using binder clips (large paper clips) on the bumper which are pretty tight but may not hold up to gusts of wind.
The hole in the back is to get my hand in to open the trunk with the key. It will be covered with a removable piece.
I made this first mock up larger than needed. After a chance to look at it I will scale it down to fit the car. Also I will bend the sides in toward the middle to make the boxtail narrower than the car.
I like it. I wouldn't have thought of using the rear door openings to anchor the front end of it, but it is a great idea. Makes it easier, puts the attachment points out of sight, plus doubles as wheel skirts. Looks very simple and lightweight.
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Winter daily driver, parked most days right now
This was the "see if it falls off" test. It is very tight and will not fall off the car.
The tail is still pretty rough from an aero point of view. The "teeth" of the zip ties are all on the outside because I built it on the car and had no access to the inside. I can cut a few off at a time and replace them with the box of the zip tie on the inside.
There is some parachuting going on, the sides are not flush. I will have to put some filler in and fair it out somehow. I will also add tape to the edges and seams to try to smooth it out.
I think it still seems a little large but I'm not going to hack it apart again.
It takes about 10 minutes or less to install or remove, no fasteners other than binder clamps hold it on.
It seems to give me a few miles per gallon advantage as is.
Aggressive 30mph-50mph EOC gave 53.8 mpg. Thats pretty good, I don't think I ever got above 52mpg before.
Over a 7 mile course, I averaged 34.2mpg at 70mph, and 39.7mpg at 50mph. Thats is not much better than without the tail, although some of my previous measurements were before truing up the Scangauge.
I was wishing for a bit more but its not done yet.
Any chance you can tuft test it? That will tell you for sure what's going on.
I hate to "armchair design" someone else's work, but I have a sneaking suspicion that the slope of the top may be a bit steep - you need to ensure you've got flow reattachment (it would have detached at the trailing edge of the roof) before you can start your tapering.
While the shape of the sides may be OK, if the angle on the top and bottom surfaces is too steep, vortices may also be forming there. The sharp angle at the transition from "side" to "top" (and "bottom") would contribute to that effect.
At this point I have completed the tail to the point that it can be securely fastened to the car. The next step is to go to work with some white duct tape and try to fair it to the car's body and to cover the zip tie heads to try to smooth the thing out.
I don't expect that this box will be 98% efficient, since it has corners and is not rounded like a true aerodynamic form. But it is removable and was relatively easy to build. After I smooth the thing out a bit I will do more drive testing and see if it provides some benefit over the stock design. I am hoping for a 20% increase in fuel efficiency at highway speeds. That would get me from 30mpg to 36mpg at 70mph.
The Versa's a sweetheart! As we move into the warmer temps be really vigilant with your temp gauge.You sure don't want to cook that puppy.And remember,your highest ram pressure is to the center of the nose,so any unobstructed original grille opening there will be the place to go for more cooling if its needed.Really nice fabrication!
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