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-   -   More aerodynamic class C sleeper? Angled roof? (

capturedbyrobots 08-08-2014 01:05 AM

More aerodynamic class C sleeper? Angled roof?
So my new touring vehicle is bought, and I'm starting the planning on how to
eventually get it comfortable for me, and as aerodynamic as I can.

It's a 10ft box truck, single rear wheels, almost no additional width in the box more than the front van width. Single rear wheels . Curb weight unloaded 6k lbs.

I'm going to have to make myself a sleeper for it, because the box will be used to store my robots and gear when on tour. Not much room for living after it's loaded.

So my question is this.
I plan on raising the roof from the end of the windshield above the height of the original box roof, then taper that high point at an optimal angle and curve back to the rear (then have a fold up boat tail to continue the taper.

The q is regards to height? If it tapers back at a good angle, and the air doesn't hit a flat wall up front, will the added height cause me to raise FE much?
Just will have a lot of time to think about this, and want to do it right to gain me the most extra space without turning it into a class C sail. How high can I go?
I'll post a pic of what I'm thinking in a few minutes.

I'm already going to do side skirts and a front air dam and boat tail, it's mostly the top that I'm unsure of. I know the template shows it should be a rounded roof, that's not a problem. It's just the amount of roundness that I don't know. Thinking about using steel sheet metal and maybe conduit for framing on the roof and welding or brazing the seams to stop any leaks.

So has anyone fooled with big vehicles like this from a roof modding perspective? Would there be a substantial difference if I stayed flat roof but tapered to the rear rather than curved?

Oh my brain....

capturedbyrobots 08-08-2014 01:31 AM

1 Attachment(s)
Kind of like this additional area I added.

capturedbyrobots 08-08-2014 01:34 AM

Or would there be a way to extend something off the front and still have it be somewhat aero....maybe a wedge like those newer trailers?

aerohead 08-08-2014 05:52 PM

*Hucho's recommendation is to never do anything to add frontal area.
*The added frontal area adds drag arithmetically.
*If you add 10% frontal area,your drag increases 10%,all else being equal.
*Don Bur,in the UK has been able to add frontal area to create roof camber on his '18-wheelers' ,and realize a net drag reduction.
*If you're absolutely committed to the roof addition,you should study their work closely.
*Having roof camber,without side camber is a setup for creation of vortices if not integrated perfectly.
Also,you owe your self a look at 'NOSECONE' fairings.These are undisputedly the best solution for the front of the box.Truck salvage yards might provide you with a used one which would fit the truck.I worked for a local moving company and we added a nosecone to a 35-ft, Ford chassis,gasoline-powered, moving van and realized 8-mpg with it.Something otherwise impossible without it.
I've been working on commercial vehicle stuff during the heat of the day and will try and post some truck aero stuff Saturday (tomorrow).
If you haven't seen the NASA truck aero link yet,check it out.It's way out ahead of nothing.:)

chillsworld 08-08-2014 05:55 PM

If you mean a wedge off the front of the box (above the cab and not connected to it), then I would assume that would lead to a lot of wind resistance if not done correctly. It's an issue that overland and expedition guys face when building their campers. And if those DIY guys notice an issue, with their blatant disregard for FE, then I can only assume it most be bad :eek: I would think raising the roof of the cab idea would be better. Then again, I might be misunderstanding what you are referring to by "wedge".

Also, I can't tell in the photo... But if the cab isn't attached to the box, and you create this high cab extension that is molded the length of the box, you are in for some serious issues due to body/frame flex. You might be even if the cab is already attached. I know this is a consideration/issue when designing campers/RV's on medium and light duty trucks. I'm not an expert on ANY of this though.


jedi_sol 08-08-2014 06:39 PM

chillsworld 08-08-2014 09:44 PM

Aerohead, that stuff by Don Bur is phenomenal! I had never seen his work before.

capturedbyrobots, I was sitting here watching netflix and I was wondering if it wouldn't perhaps be easier to build on to the rear of the box as opposed to building up for a sleeper birth. Rather than adding frontal mass, use the idea of the tear drop shape to build an aero unit on the back to hold a bunk and your personal gear. Figures below, design 1 and 2, from the NASA link provided by jedi_sol. Design of the sleeping quarters would be dependent upon the adoption of egg or aero back... Then it would be a simple matter of accounting for the space above the cab from an aero standpoint rather than the addition of space standpoint. One could heat/cool the whole box since it's small, or simply control the back add on. The unit could hinge, allowing it to swing out of the way for loading and unloading. Or one could cut a door in the side of the box allowing the rear unit to be more permanent and allow for easier design and installation.

One need only look to small teardrop campers and overland/expedition resources for ideas on small and efficient sleeping quarters. Better yet, boat design!


Design 1:

Design 2:

freebeard 08-08-2014 10:35 PM

Embrace the box—and then think outside it. These exist, or you could make your own.

As chillsworld, says, boattail it. Here's a sketch I did for my VW van. It has a vertical tail in the back and an horizontal wedge in the front to lower tha stagnation point.

You could hinge the tail at the top and have power jacks. Then it would open up into an 8' long Gothic roof over a fold-down floor section.

California98Civic 08-08-2014 11:09 PM


Originally Posted by capturedbyrobots (Post 439011)
Kind of like this additional area I added.

That seems like it will add a lot more frontal area than it is worth. Tapering is a good idea. Rear wheel well covers would be good too. And there are many other suggestions in the links jedi-sol provided via aerohead.

skyking 08-08-2014 11:10 PM

The money is all in the tail. Add a foldable tail and you will get the most gain possible.

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