Help Analyse my Ford E350 Teardrop RV Concept

[Poodwaddle]

Originally Posted by ennored

Have you considered towing a small car to do your exploring with?

The back porch is sized to fit a couple bikes, perhaps a scooter if I decide to build it solid/ without the drop top.

[slowmover]

Originally Posted by Poodwaddle

ecomodder is all about reinventing the wheel. We aren't satisfied with simply purchasing the newest, most fuel efficient vehicle. We mod.

I built a teardrop trailer and it worked so well I want to step it up to the next level. Yep, I want to reinvent the wheel.

As far as an airstream goes they are beautiful beasts and have their appeal. But they are designed for the masses. Their layouts do not appeal. Perhaps a remodel would be better, but it would never be mine.

Space efficiency. A Moho of any sort is inefficient. Rather like a pickup versus a car pulling an open trailer.

And the layout of the aero all aluminum travel trailers is proven. Weight over the axles dictates interior, for the most part. Can't screw with physics.

The engineering exercise is commendable. But will prove difficult. Easier (better) to spend time camping and learning more about what constitutes overall economy. Fuel burn is less than half.

Not to mention the reason for camping in the first place. Backing into details too far is counterproductive.

.

[rmay635703]

Look at a motor home called A Vixen, it's not boat tailed and gets 30mpg

I would love one myself but their hard to find and I haven't found much in reliabily and maintenance needs.

I would love to drop a 6.2 c-code diesel in one and upgrade it for towing

[Hersbird]

Originally Posted by rmay635703

Look at a motor home called A Vixen, it's not boat tailed and gets 30mpg

I would love one myself but their hard to find and I haven't found much in reliabily and maintenance needs.

I would love to drop a 6.2 c-code diesel in one and upgrade it for towing

There was one here on Craigslist for about $20k. Guy had a 10 year mileage log with lots of high 20 mpg fill ups. There is this really nice one near Bozeman Montana as well, I bet they are looking for around $20k as well.
Vixen-td-Vixen21-21-BMW-diesel-524TD-turbo

[Poodwaddle]

Originally Posted by rmay635703

Look at a motor home called A Vixen, it's not boat tailed and gets 30mpg

I have looked at those. I like most everything about them. They are clearly designed by a hypermiler and could use a few modern tweaks but are amazing vehicles. I am not, however, shopping for something that looks like a vehicle. I want a platform to build my own design and that limits my options to framed trucks with beds over 10 feet long. Mostly this means vans built by the big 3 who put in overpowered engines like the 7.3

As a hypermiler I much prefer the small BMW Diesel in the Vixen over the monster 7.3 that is the only thing Ford used that was worth getting. I am starting to seriously lean toward a Mitsubishi Fuso and studying what mileage it can be tweaked to get. It is very difficult to find info on them because drivers have so many different boxes and loads. Their aerodynamics are pathetic and the frame is built high and heavy, but the engine is excellent. The choices all kinda suck.

[rmay635703]

Might I recommend a 6.2 diesel?

It (like the 6.9 diesel) was designed for fuel economy not power.

The vixen was just a GM c20 extended cargo van with a full fiberglass shell and extended control arms.

Couple appropriate rear end gear ratio, with a c-code motor and a 5speed stick and the 6.2 achieves 30mpg in an oversized boxlike vehicle.

Some bread trucks came in a stick shift form with a 6.2,

6.2s may only drive 200k under heavy use but the blocks can be had for as little as $50 and rebuilds top to bottom start at about a grand.

You will find GM platforms are easier to locate and cheaper to maintain despite motor issues.

Having owned an oversized 7.3 casino bus, never again comes to mind, everything but the motor was garbage and rednecked.

Just my 2 cents

[Poodwaddle]

Originally Posted by rmay635703

Might I recommend a 6.2 diesel?

Thanks for that. I did not realize the Vixen's heritage. The GM diesel seems quite hard to find and reports on it's fuel efficiency suggest that it might be slightly better than the 7.3

I have also considered something with the Cummins 4BT like a Dodge 1500 or a cube van. Those things are simple to work on, offer lots of tweaks, and look like they have the potential for great mileage (the engines, not the cube vans)

[freebeard]

I want a platform to build my own design and that limits my options to framed trucks with beds over 10 feet long.

You asked for a critique of the design and the conversation has drifted to diesel engines.

I like the lift-up top. The hinge line might even overhang the windshield, like a sun visor.

I'm looking at the covers for the front edge that changes angle as it lifts. Aerodynamically you want a radius in the front edge. Actually you could pull the curve back toward the door and then taper the sides behind the rear axle. Give it a continuous curve from front to back. The joinery gets more complicated.

What are your fabrication skills? What materials will you work in? What level of surface finish?

[Poodwaddle]

Originally Posted by freebeard

I like the lift-up top. The hinge line might even overhang the windshield, like a sun visor.

The overhang presents an interesting question on aerodynamics. It will be easier to draw than to explain so here is a photo of a Ford bus.



How does the air flow over a Luton bump? Does it (A) create a parachute effect, or (B) create an air pocket that pushes the air over efficiently? Obviously the sides release air and this might cause more of A than B, but if we ignore the sides (pretend that they are enclosed as well) then what does the air do? Parachutes (the old type) have a hole in the middle. Without it the parachute would rock back and forth as the air spilled over the sides - essentially an air pocket is being held in the chute. Would it be the same on a bus?

I suspect that the air is captured by the bump to some degree and so is a big aerodynamic no-no...but then I would have thought that tailgates down was also more efficient. Visors/cab shades might be the same... in theory.

I would prefer to build out of steel square tube for several reasons. For one thing I already have the equipment and experience. Steel is just so easy to work with. But if I choose a hinged top then I would certainly want aluminum. I also have experience in wood and fiberglass and have even debated building the top like a cedar strip kayak (fiberglass-wood core-fiberglass sandwich). This can actually be quite light and very very beautiful. I built a kayak many years ago and found the technique both strong and light. But if I chose to keep the surface unpainted then it would be high maintenance (resins yellow over time and need to be recoated by varnish each year).

The one thing I have little experience with is sheet metals. The corners would require folding or even rolling depending on the design. The simplest solutions would not be the most aerodynamic.

[freebeard]

How does the air flow over a Luton bump? Does it...

Neither. Any surface exposed in the direction of travel experiences a positive pressure gradient. The air sitting undisturbed at A or B has only two choices, sideways or up. Start with 20 streamlines that are all put into competition. Air under the bump is going to move sideways and wrap around the A-pillar. Within a fraction of an inch the air is gripping the body. That's skin friction. At the distance you've drawn the streamlines air is interacting with air is interacting with air, in a [diminishing] fractal recursion. Wind tunnels want 8-10% blockage to get an accurate rendition close to the body.

The only time air moves forward in relation to the body is in the wake, within recirculating separation.
_________

How would you get from square tubing to a finished surface? Sheet metal seems logical. When you built the Kayak was there a lot of tapering the strips necessary? I guess you could do them in bulk. I've known a person who breathed a lot of resin fumes and then croaked.

All four edges of the roof need some radius. Forward facing edges a minimum of 4% of the gross width, typically about 4". 1/4-round down the sides. At the back it makes no difference, but you might as well do that too so it all matches.

Here are some experiments I did with a material called Polymetal. It is an aluminum/plastic/aluminum sandwich. The same joins could be done in sheet metal. Rolling sheet materials is actually easy, the problem is finding rollers long enough for big pieces. Three 10' steel pipes and six skateboard wheels jammed in the ends would suffice.



Note the bottom one has a radiused edge with no framing. It could be sandwiched around a piece of angle iron if that's needed.