First, thank you all. I’ve been lurking for about 6 months, learning everything I can, and appreciating all the knowledge I can draft off of. Getting sucked along, knowledge wise, is a good thing and has helped me a lot.
I’ve wanted an aeroshell since at least the mid-eighties, when I realized that a shell could be shaped to dramatically improve mileage. Stumbling onto Eco-modder has increased that conviction and after gathering all the info I could, dove in.
I started with a used shell from Craigslist for $45. Someone suggested cutting one down and I believed that was a reasonable plan. Lesson #1 was that I should have pilfered it for the hardware and thrown the shell away. It has turned out well, I think, but I could have made it much lighter, with a faster build time by making a wood frame and covering it with FRP bath panel sheets instead of trying to repurpose an old one that really didn’t fit in the first place. But that’s for the guy behind me to profit from. A big reason I modified an existing shell is my wife had once expressed extreme hatred of the smell of Bondo/polyester resin permeating the house (I’m no fan either). The wood and FRP version would have needed extensive work in that vein.
There has been discussion about the ideal angle for airflow to remain attached on aeroshells boattails, kammbacks, etc. with angles from 12-22 degrees being mentioned as workable. The 12 degree number seems preferred but if I ran a straight line from the cab roof to the tailgate it was already 16 degrees. I wanted to wait until past the side window before dropping down (Lesson #2 by the way, and another reason to do the wood and FRP version, I wouldn’t have had the window frames to dodge that way.) The chosen solution was to incorporate a large radius and hopefully gently persuade the airflow to remain attached and head down at a 19 degree slope. I also cheated by extending the back of the aeroshell and raising it up, reducing the slope angle. As built it is 18 degrees and while the data is still incomplete and inconclusive it does seem to be working; now.
This week, after over a month of work, it was finished enough to mount on the truck and follow me on my daily commute. A quick test drive didn’t seem as smooth and easy as I had hoped but I reserved judgment until going to work. Arriving I checked the trip mileage on the scangage expecting an improvement only to find my average had actually dropped! AAuughhh! Much wailing and gnashing of teeth! What have I done? The cursed thing seemed a parachute behind me instead of coasting down gently.
It could be better than that, I had proved it could. I had it on earlier and with all openings paved with cardboard and taped shut I ran a test route and got 24.5 mpg, up from 20.2 with windows and cab-shell gap open. Now I’m note even breaking 20! Two days of sulking and inconclusive testing led me back to the side window frames and hatchback edges. Lesson #3, watch those edges! I hadn’t realized just how much a ¼” high plexiglass edge, running the full length of the hatch would trip and confuse the airflow. Taping those and the side window frames up put me back up to 23.7 mpg on the test route. Even better it would actually coast now, instead of throwing me forward against the shoulder harness. So last night I glued some ¼” moulding on either side of the hatch and caulked the window frames much better. This morning’s trip actually showed a decent improvement (I’m waiting awhile before posting numbers. The morning commute is tough to get good mileage on, especially since the school down the street restarted Wednesday.)
Overall I’m encouraged. There are more improvements to be made. I need serious help on my cab to shell gap seal for instance, anything short of duct tape just lets it flop madly. Follow my fuel log for awhile and we’ll both see if I know what I’m doing!
PS. It seems I'm unable to link to photos from my photo album on this site. Go there for a selection of photos showing what I'm talking about. Thanks,
Bruce