Help Analyse my Ford E350 Teardrop RV Concept

[Poodwaddle]

As a new (and amateur) student of aerodynamics I would like some feedback on a concept I have banging around in my head. I want to travel and camp around America for 6 months to a year. I have a family so I can't exactly drive a metro, but I still want to maximize my MPG. Driving an RV is out. Those boats get 5-8 MPG. I have build and welding experience to the months of fabricating would not be difficult. I am debating buying a 2003 or older Ford cargo van with the 7.3 diesel, cutting down the cargo box and welding up a pivoting roof that would fold down to form a teardrop-ish shape. The construction details are already pretty well formulated, but what I am wondering is whether it is worth the trouble. Would the semi-teardrop give enough benefit to warrant the extra effort and cost of the folding roof? The pivoting roof would have to be framed in aluminum and the entire construction would be much more complex and more expensive than a solid build. I figure that a 7.3 diesel in a typical Ford van gets 18ish MPG to start with when driven by a typical lead-foot truck driver. Clearly I can improve on this with some good driving habits, but more important to me is estimating how much the drop roof will improve the fuel economy. It has to be better than a 5 MPG improvement to pay for the extra cost of construction. As you can tell, the inspiration is a gypsy caravan. I haven't bothered yet to draw the interior, except a few scratchings on restaurant napkins. Yes, I realize that the shape is not a true teardrop, but aesthetics and livability do have to be factored in as well. Give me your opinions and ideas. What would my MPG potential be? What other ideas can you suggest to improve efficiency?

[Hersbird]

Looks cool. I don't think it improves on a stock cargo van at all, it's wider and taller. Better then a class C RV but similar to an airport shuttle van. I think just adding a pop top to a stock cargo van would be more aerodynamic but with a little less floor space. I also disagree the average employee driving the bosses 7.3 van gets anywhere near 18 mpg. No doubt you could, but an average nut behind the wheel Wilmington be lucky to see 12-13, probably less then 10 on an airport shuttle van.

[Poodwaddle]

Originally Posted by Hersbird

I also disagree the average employee driving the bosses 7.3 van gets anywhere near 18 mpg. No doubt you could, but an average nut behind the wheel Wilmington be lucky to see 12-13, probably less then 10 on an airport shuttle van.

I am not sure on the 18MPG but the gas vans get 12-13. gas powered box vans get 8-10. The 7.3 diesel is a real monster and is used in quite large shuttle buses with plenty of power to even tow a trailer behind. Even some drivers of the smaller shuttle buses claim to get 17MPG on the highway, 11+ in town. Unmodified, the diesel van gets 17-22. Even people who have added a power chip say they get 18, so I think 18 is a reasonable claim...and of course as an RV most driving will be highway.

I think that you are right about the greater frontal area. Squaring off the corners and raising it up a bit will, no doubt, reduce aerodynamics. A pop-top on a standard van is just not reasonable. My family needs more space, and I will not be taking my family around the country in a tacky pop-top van. Sprinter vans are a bit less tacky and a bit better on fuel. They might tempt me, but most are unibody so they limit the modifications possible.

[Hersbird]

I know what some people claim on mpg, but fleet managers who count every bean say the diesels seldom do much better in the real world, and never good enough to make them cost effective. They deal with drivers who go pedal to the metal when moving, and then let it idle for 2 hours at stops. They only buy them because the workers ***** if they don't get a diesel to trim trees or whatever. I bought a 2005 Duramax because of such MPG hype but never saw anything worthy of writing home about. Power was great but mileage just a few ticks better then my 454 gas, no better then my 5.7 hemi, and I actually was/am trying to get good mpg. I would go with a 7.3 in the Ford world, stay away from used Sprinters with the modern DPF systems, fleet guys will tell you the big maintenance problems they get at 150-200k probably when you will see them used. I personally love the new Promaster because of its FWD and low floor in back. The 3.0 ecodiesel does get good economy compared to gas. Some Ram drivers get over 30 and I do actually believe them.

[vskid3]

How big of a family? How much driving would you really be doing? Do you plan on keeping it after the trip?

In my opinion, your design wouldn't be big enough for more than 1 or 2 people for such a long trip unless most of the family will be sleeping in tents. Fuel costs, while high, might not justify the cost of doing such a mod (that's up to you, though). Along with that, there's the resale value if you plan on selling after the trip. Your modified vehicle could end up being worth more to the right buyer after modding it, but there's no guarantee. You could buy a 10-15 year old Class C RV, drive it for a year, and likely be able to get out about what you put into it. You could even add some aeromods to improve the mileage (which isn't quite as low as you think). http://ecomodder.com/forum/showthrea...d-e-18151.html

[mwilliamshs]

Shuttle bus mileage is a horrible suggestion for comparison to what a motorhome owner might see. Shuttles idle for hours on end to keep their interiors warm or cool depending on climate/season and generally get driven hastily to airports or conferences to make up for clients running late. I've driven shuttles locally and have a friend who drives a ~150 mile loop in Texas to and from the Houston airport. He's had people board the van 30 minutes before take-off and 90 miles away, who offer him a couple hundred bucks to get them to the airport on-time...basically asking him to do in a 10,000 lb shuttle what couldn't be done in a Viper. Believe me, if a shuttle got 18 mpg it'd be a genuine miracle and if it did, a conscientious owner could expect 25 mpg...neither is gonna happen.

[Hersbird]

Sometimes I think people make a MPG claim based on a best case scenario. "I get 18mpg on the highway" really means they got 18 mpg one time, when they drove slow and reset the computer once up to speed. Their actual whole tank, hand caculated mpg is probably 13mpg. Our van on a 360 mile trip got 29 mpg hand caculated, round trip, last week, which means we had ling streatches of 35 mpg. We only average 19 total over the last 2 years, albeit 80% city. So should I tell people a 2011 Town and Country gets 35 mpg highway? Even saying 29 is a bit misleading as it's outside the norm. I wouldn't technically be lying either way, just 26 is more realistic.

[Poodwaddle]

The shuttle bus mileage estimate comes from people who have purchased them for use with handicapped family, not from fleet bus usage. It is, no doubt highway mileage of a mostly empty bus of the shorter type.

My mileage estimates were based more on my own driving expectations for this trip. It makes little sense for me to calculate people's commute mileage when I will be highway driving. My driving (me, wife, and young son) would be mostly smaller highways since I enjoy seeing the sights. I have little interest in cities and on interstates I drive no more than 60 (65 if I feel pushed by traffic). I have been toying with similar designs for a Mitsubishi Fuso as well, which would have the added benefit of extra space. Yes, this van design might get cramped at times. We will probably stay in a hotel once every couple weeks just to stretch our legs. After the year I will probably give the vehicle to my parents who love traveling.

[Poodwaddle]

Originally Posted by Hersbird

Sometimes I think people make a MPG claim based on a best case scenario....

Mileage quotes are like winners in Vegas. Gamblers will always tell you what the won, "I won $1000 last weekend!" They conveniently forget that they let it ride and lost it all 5 minutes later.

"I got 70 MPG coming down Donner Pass the other day... but I got 5MPG climbing up the other side."

That all said, there are subtle differences in vehicles. These full sized vans with the 7.3 diesel are not all the same. The rear end might be geared low for work and acceleration, or high for highway speeds and MPG. Some might have big fat work truck tires with 40 PSI. Others might have street tires that pump up to 80PSI... and are completely worthless on snow. Some are driven by morons who think the accelerator is an on/off switch. So I suppose one could honestly say that highway mileage of a Ford E-250-350 with 7.3 diesel is anywhere between 10 and 20. Some claim higher and are probably lying. Some claim lower and are probably idiots driving a poorly maintained POS... or I could be wrong... it has happened once or twice before.

[Hersbird]

So back on topic then... Is there a reason for the cab over portion? Is that going to be big enough for a bed there? Losing that harsh aera above the doors would be nice. Putting a radius down the side of the roof also is important in cross winds. Basically like the back part but make the whole top that way. Just cut the bottom lower and run a flat portion down from the top after the radius ends. I wish my Hi-Lo camper had better radiuses, an Airstream top on a Hi-Lo bottom would be perfect. Just so you know the seal between the 1/2s of my Hi-Lo is far from perfect. It does OK in the rain, but take it on a dirt road far and it's a mess inside. I wish instead of an overlap seal, the top just rested down on a plate and made a seal, more like a tent pop-up camper. Our new camper has tip out tent beds. If you could work one of those in there you get a big jump in floor space as the bed no longer takes up any room. One queen tip out, and one couch bed would be perfect for 3.