Aero RV Belly Pan(s)

[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.

[aerohead]

There's nothing I can say which will change your results or compensate for 3-weeks of slow-cooking under the beast.
Every wind tunnel investigation for Class-8 vehicles showed improvement with bellypans.
Cars and vans reacted similarly.
Fachsenfeld's Omnibus reacted very favorably.
Full-scale wind tunnel tests would give us immediate data.The real world may take longer.I see variability with the T-100 with no mod changes whatsoever.
I hope you'll consider long-term 'testing.'We all stand to learn a great deal.
I am especially thankful for the sacrifice.

[wyatt]

I will echo what Aerohead said. When I built and attached the SedanKamm to my car, I didn't see much difference around town, and even on the interstate I noticed little difference... for the first half of the trip! Overall, on interstate travel I saw a 6% gain in fuel economy, but that was over 1800 miles of 65-70 mph driving that it all averaged out. If I had gone with the first 800 or 900 miles, I would have been VERY discouraged!

[orbywan]

Originally Posted by aerohead

There's nothing I can say which will change your results or compensate for 3-weeks of slow-cooking under the beast.
Every wind tunnel investigation for Class-8 vehicles showed improvement with bellypans.
Cars and vans reacted similarly.
Fachsenfeld's Omnibus reacted very favorably.
Full-scale wind tunnel tests would give us immediate data.The real world may take longer.I see variability with the T-100 with no mod changes whatsoever.
I hope you'll consider long-term 'testing.'We all stand to learn a great deal.
I am especially thankful for the sacrifice.

Thanks Phil, I'm a long way from quitting, do you have any suggestions for testing besides redesigning the lower portion of the tail? The only other thing I know to do at this point is to cut a couple of vent holes in the second pan back to see if the frontal air is backing up in there. I'm blown away this didn't show some improvement, looking at it before and after, it is like night and day better, but looks obviously don't make it more efficient.

[orbywan]

Originally Posted by wyatt

I will echo what Aerohead said. When I built and attached the SedanKamm to my car, I didn't see much difference around town, and even on the interstate I noticed little difference... for the first half of the trip! Overall, on interstate travel I saw a 6% gain in fuel economy, but that was over 1800 miles of 65-70 mph driving that it all averaged out. If I had gone with the first 800 or 900 miles, I would have been VERY discouraged!

Thanks Wyatt, I guess I was somewhat spoiled by the great gains the boat tail showed. I expected to see some kind of improvement but it didn't happen. That's OK, I just have to figure out what is going on down under.

[JasonG]

Originally Posted by wyatt

I will echo what Aerohead said. When I built and attached the SedanKamm to my car, I didn't see much difference around town, and even on the interstate I noticed little difference... for the first half of the trip! Overall, on interstate travel I saw a 6% gain in fuel economy, but that was over 1800 miles of 65-70 mph driving that it all averaged out. If I had gone with the first 800 or 900 miles, I would have been VERY discouraged!

Is it possible the ECU needs time to compensate for the reduced load ?
I sort of doubt it on a '94, but I know newer cars do adapt to the driver. Transmission control units too.

[orbywan]

Originally Posted by JasonG

Is it possible the ECU needs time to compensate for the reduced load ?
I sort of doubt it on a '94, but I know newer cars do adapt to the driver. Transmission control units too.

I've been told there is a serious short between the steering wheel and the driver's seat, but I don't think the ECU is the problem.

[skyking]

Originally Posted by orbywan

I've been told there is a serious short between the steering wheel and the driver's seat, but I don't think the ECU is the problem.

I've been working on that problem myself for a while now
Seriously, keep on keeping on, man. Your big success was only a single trip. Build up some time and miles and see where it goes.

[grins2go_brett]

Originally Posted by orbywan

Thanks Wyatt, I guess I was somewhat spoiled by the great gains the boat tail showed. I expected to see some kind of improvement but it didn't happen. That's OK, I just have to figure out what is going on down under.

I've been lurking and watching this build thread with great interest. I have a 2007 Dodge Sprinter for my business. A boat tail is not an option for me since I have to open the back doors all the time. However, a belly pan is something I'm seriously considering. I've learned a lot from your trials, pains, descriptions, and pictures and I'm very appreciative of not only your effort to do the project, but document it so thoroughly for everybody here.

Now, my question is: what kind of MPG's were you getting before you made any aero mods? I'm just trying to put 15-17 mpg into perspective. I'm in the 16-18 mpg range myself. Thanks!

[jime57]

I think you may be a bit hastey to judge the results. Testing is difficult as you recognize by now. You admitted some stop and go traffic, and just a little of that is a killer. See what the longer term looks like. You have done some great work!