I just finished the front skirts a couple hours ago. It took four hours. The first one took 2.5 hours, the last took 1.5 hours.
My main motivations for doing it this way:
1) Ease of construction - I know how to cut aluminium (shears), use a drill (to drill steel car body, you should spray some lubricant such as wd-40 on the drill bit before and sometimes during use) use a screwdriver, and cut rubber with boxcutters. Nothing fancy and you don't have to take the wheels off the car.
2) I was dubious about the elasticity of the rubber when faced with a wheel turning at full lock, either direction. For that reason, I wanted the rubber to be as long as possible, so the amount of stretch was minimized. Two reasons for this, one that the longer the rubber is, the less it will have to stretch per length of rubber. The other reason is that for small angles
, sin ~= tan, i.e. adjacent side ~= hypotenuse, when the adjacent side is large wrt opposite side, the adjacent side is roughly the same as the hypotenuse, meaning that the rubber will hardly need to stretch.
3) I didn't want the rubber rubbing at all during highway speed, so I estimated the maximum angle of the steering wheel from center position I'd steer at on the highway, and doubled it (basically 180 degrees from center position of the steering wheel). That's what the aluminium is for, to push the rubber out.
4) I could either put the rubber on the inside or the outside of the aluminium. I decided to put it on the outside, figuring that the ugliness of all the washers and screws would be counterbalanced by not having the aluminium visible. Note that the aluminium has a nice smooth curve where it could rub on the rubber, to minimize abrasion. If I put it on the underside, I'd have to curve the metal slightly outwards, which would be ugly aerodynamically and aesthetically.
I figure that the increase in frontal area will be counterbalanced by the fact that the the rear is curved in a shallow way. The front also is a smooth continuation of the front bumper until parallel with the side of the car. Although of course I'd anticipate a reduction in Cd, even using the old frontal area figure, because air is not being sprayed out to the front and side in a turbulent fashion.
I will test drive it tomorrow some time hopefully. I tried it with one side, it seemed to work ok both at speed and cornering at low speed.
Basic steps involved:
1. Make a cardboard/card template for the front and the back. (figure out ahead of time where you will screw it in (should be screwed in both sides for rigidity). Should flare out more at the bottom, very little at the top. Size it by estimating how big it needs to clear the wheel at highway type turns + safety factor.
2. Trace onto aluminium sheet (0.6mm is what I used, that's fine).
3. Attach strip weather seal to aluminium where it contacts metal. Chances are you will scratch the paint a bit anyway, this minimizes scratching over time.
3. Drill holes then screw in to attach.
4. Stretch pond sheet rubber (or inner tube rubber) over the frame you have made up, duct tape in place.
5. Drill, screw in screws (you will need washers so that the rubber doesn't tear).
6. Cut rubber with box cutters, be careful not to cut the paint.
7. Take for a test drive.