Quote:
Originally Posted by redneck
.
Instead of removing the existing roof rack, use it to incorporate the boat tail by building the roof line up to make it the new highest point as far forward as possible using the template. Then only a small portion behind the rear of the vehicle will then stick out. Think of it as a hump back whale.
You could use the existing side rails to flex a piece of coroplast or 1/2" insulation board in between the side rails to the shape required, attaching it with zip ties. Then use EMT or aluminum pipe to build a frame behind the vehicle to finish the tail.
|
At the moment I do not have access to a useful picture of a similar Forester, so I took my original boattail picture and put it back into the template machine. I need to redo it, first of all because that is not my car and I do not want weird differences throwing off my calculations, but I also realized that the picture was not level!
With the high point at the back of the roof, scaling the template to my car, that first vertical bar is 28.7" back and it only curves downward 3.5°, but if I make the front cross-member the new high point, it would curve 7° at that same point, and it would increase from there.
I know that everybody says to decrease the frontal area, not increase it, but I do not even see the point in doing a 4° Kammback.
If I extended my car three feet and brought in the roof 4°, the sides and bottom 3°, how much improvement would I see?
That would be 1 1/3" on top, 1" on the sides, and 1" on the bottom. My car is 68.3 inches wide, 65" tall, and the back of the bumper is 16" off of the ground.
First, will someone please tell me how to taper the sides and bottom?
Second, will someone please figure out how much improvement that would bring?
However much clearance I may have, I imagine that every bit of it is turbulent, so until I make it attach somewhere, I doubt the rest matters.
65x68.3=4,439.5 square inches
63.67x66.3=4,221.1 square inches, a 5.17% reduction. If that makes it 5.17% more aerodynamic, it would get 2.585% better mileage, although if the air is not attached, I will have completely failed.
How much is attached air worth?