[orbywan]

Well, we took the RV on its maiden voyage with the new belly pans this weekend, with mixed results. I'm really disgusted with the belly pans at this point. After three weeks of serious work, the result was zilch. No gain whatsoever, and I wouldn't be surprised if I lost a tiny bit.

On the good side they didn't give me any grief, I had no idea how well they would hold up under various conditions. At one point I was doing close to 75 going down some mountains. Nothing flapped, fell off or melted. It was great being able to turn on the under carriage and roof cameras to check on things when I went screaming up and down those hills, gave me great piece of mind.

At one point on the first nasty hill I started smelling plastic (or something), had the quad monitor on in the split screen mode with the whole exhaust system area covered by two cameras, didn't see any problems so I kept going till I could pull over. The camera views were accurate, no problems at all.

The part that surprised me the most, I almost totally enclosed the exhaust system and had zero problems with heat. The smell was coming mostly from the adhesive on the metal tape I used to hold the fiberglass insulation in place on the exhaust system long enough to get some bailing wire around it.

I was confident I had done a serious amount of good under there, but apparently not. On the way to Phoenix I did manage to average 16.64 mpg, with the A/C on most of the time. Considering we had to pull off the road and
stop twice, and got in a 10 mph crawl for 20 miles on the freeway, not to mention a full load of water, food and gear, that's pretty good.

I'm sure that without the adverse conditions it would have been over 17 again. On the way back I duplicated the first Phoenix to Tucson test run. Had the A/C on all the way, and a slight tail/crosswind, and managed 14.95mpg. The previous test run under the same conditions with a slightly less strong cross/tailwind yielded 14.64 mpg. I believe the difference was due to the tailwind.

I believe the problem is two fold. I think I have restricted the air flow coming from the frontal area too much, creating or increasing the bow wave, and need to open up the pans in the front a little to let the air coming through the grille and front end out of the now enclosed undercarriage. The other thing that's hurting it is the departure angle of the boat tail is too steep, creating problems under the bottom of the boat tail. Our friends followed us for a ways and took pictures of the tale tells on the bottom. They said they are swirling in a clockwise direction which I believe means there is a major vortex where there should be smooth flowing air.

One interesting thing in that department. After 850 miles of
various road conditions, the sides, top and back wall of the boat tail are
spotless, not a hint of diesel exhaust on any of those surfaces. The bottom is
brown with exhaust. That tells me the air is flowing over the three other
surfaces pretty well I think.

Oh well, back to the drawing board. I've got too much work
and aggravation into this to scrap it without trying to make it better.

If anyone has any feed back or opinions I’m all ears. Thanks.