Why there isn't an aerodynamic shaped RV
 

They are all rectangle boxes, really about the worst they can be.

Living/Storage space is highest on the priority list, and tops the efficiency,
so a rectangle is going to give the most space.

Lots of disussion about streamlining an RV, has anyone actually done it and how much efficiency improvement do you get after losing all the space?

I'm looking at 33ft motorhome with some rear side damage, and the back 24ft body could be totally redone.
I'm thinking the easiest most cost-effective way is to make the roof pop-up hinged on the front section, so it hinges down to give a nice slope while driving, and hinges up to give a big roofline and living space inside.
I'm planning to use for storage really, but if I rebuild the rear section, might be interesting to see how efficient I could make it while still having lots of storage space when hinged up.

The Toyota Prius is popular, but it seems like many people purchase it for the smug superiority, while other cars are slowly trying to sneak in aerodynamic tweaks, like tapered cabins. I would be kind of surprised if you could not find an RV with some tapering, but I think there is a big difference between head and shoulder room and being able to walk around inside, store things in cabinets, etc.

People seem to think that actual aerodynamics are ugly, but it could just be that if you can afford an RV, you can afford to haul around a box.

If you found a superficially-totaled PriusV, could you turn it into an RV? :)

Prius is not really big enough.

I would like to see a minivan sized RV camper.

Make it 4 cylinder fwd and add a rear hybrid drive. The beauty of such a system would be good performance/efficiency as well as a nice sized battery pack that could easily run the AC/misc electrics while parked for hours without a noisy generator

You don't buy an RV for the driving characteristics.

There are a couple of members here that have done aeromods to their RV.
As others would say " It's fruit ripe for the picking".
I think of it this way : the worse off something is aerodynamically, the more easily you will see a noticeable change when doing aero mods.

A boat tail is a mod that should make a big difference while not impacting interior space. This one increased mileage from 13MPG to 16 MPG according to preliminary tests.

I see it from the other side, call it an 'obversation', an aerodynamic shell with the same drag as that little box would be immense. As a vehicle, it has legally defined length, width and height — a box. An ideal dwelling will be a circle. :thumbup:

This 33-footer, is it a class A- or class C-motorhome? Would you be willing to extend the length (and licensing cost) to increase the fineness ratio?

Consider all the side taper you can pull off, with a flat roof. If it has a radiused edge to avoid vortex generation wouldn't a Tropfenwagen shape give space without needing pop-up/outs.

Unfortunately, advanced aerodynamics wouldn't improve the space-savings in a motorhome so much as a boxy layout does. There is always some compromise. Anyway, I would eventually consider a platform with the engine closer to the driven axle such as the FWD Ram ProMaster in order to get a lower floor, since it would lead to an improved internal height even if the external height get lower than a comparable front-engined RWD van.

Here is the front wheel drive motor home I had. Sold because I lost my parking space. :(

http://ecomodder.com/forum/member-fr...2-p1010018.jpg

It was 18.5ft long. Here is a proposal for a new body with the same drivetrain.

http://ecomodder.com/forum/member-fr...-w-caption.jpg

At a fineness ration of 4:1, it would be 32ft long; with similar interior volume but 50% higher licensing fees. But it would have gone from worst to best case for aerodynamics.

The Clark is gone, but I still have a Lexus motor-generator* that could power an electric version about the size of a Dodge van or VW microbus. So it still could be built.

Edit: *Now that I think about it, the folks at EVTV are reverse engineering the Tesla drivetrain CAN Bus messaging. That would be an appropriate size for a motor home, about 400hp.

What's its driveline? The same of the FWD Cadillacs from the 70's?

http://ecomodder.com/forum/member-fr...istory-087.jpg

225cu in Chrysler slant six on a (four-speed manual) Clark fork-lift transaxle. Mine had a Carter single-barrel side-draft carburetor, same as the '53 Corvette six.

Later models had a 454 Olds. I don't know if it had the same transmission. The non-CV u-joints are a weak link. Crank the wheel and floor the gas and they go Pop!

I don't remember when was the last time I saw a forklift with a manual transmission. Anyway, this setup doesn't really seem to inspire so much confidence to use in a motorhome.

When's the last time you saw a motorhome with a chrome floor-shift lever?

For Cd, perhaps, but reducing a rectangular vehicle's Cd comes at a cost to crosswind stability. Do you really want an RV that steers off the road in a crosswind? Hucho includes a study of crosswind stability vs. body shape, showing the progressive reduction in stability as Cd is reduced.

That's why RV's are all rectangular boxes, and all 911's have rear wings, too.

Have fun,
Frank

Cd vs crosswind stability
 

I believe that Professor Alberto Morelli's 1978 research at the Pininfarina wind tunnel gave us an out with respect to low drag and directional stability.
He found that he could straightforwardly tune the center of pressure to compensate for center of gravity bias.

Where's all the examples? ;) Are we talking about the banana car? Airplane type rudder?

Ah, the one with Batman fins on the roof.

talkin' about
 

For Morrelli it would be the CNR 'banana' car of 1976-78.
The shape is zero-lift and very stable in crosswind due to the fins placed behind the rear tires,placing the CP behind the CG.
http://i1271.photobucket.com/albums/...ntitled2-3.jpg

You don't need aerodynamics for a storage unit.

I suggest getting rid of junk instead of storing it, and camping or getting a motel instead of bringing your house with you on your travels.

smoothing the rectangle
 

http://i1271.photobucket.com/albums/...titled5_11.jpg
http://i1271.photobucket.com/albums/...titled1_14.jpg
http://i1271.photobucket.com/albums/...titled2_14.jpg

Really like the shape of that. Don't know about the trike layout though

I would think that a TDI drivetrain up front with a rear wheel tesla style EV drive would give it plenty of power. Give it enough battery to allow a few days of no generator house power.

I would think that such a vehicle could crack 30 mpg highway, without breaking a sweat.

Yep.

Overall, its purpose is to be a cavernous space, the exact opposite of aero efficiency. Making it less so is too much of a design compromise- to succeed in that at all, you need either a tent in the trunk or a smaller "as much volume as I can cram onto this size frame." My compromise is a pop-up, but if you want more space you have to accept horrible mpg. Accessories need to be modular- AC systems and the like. Camper manufacturers aren't AC manufacturers, and cost & effectiveness are more important to camper companies and buyers than incremental decreases in drag.

Of course, if it were mostly about driving then you'd have a tent in the trunk. Campers are about how much space you have when you're parked, how much choice you have in parking spots and how quick/easy it is to set up once you park. Mod away to snag an extra mpg or two (huge % bump!), but they're not going to design one from the ground up for aero. Well, they already have, and those are the tiny ones.

We don't usually go places where there are hotels. We also spend very little time in the camper. A warm, dry place to sleep, a bathroom, a place to store some gear,and a place to store and cook food. An external kitchen would be best in my book. Total hards sides are a plus in bear country, not so much for sleeping but so you can leave it setup while you are away from camp andbit likely won't get bothered.

I could bet that FWD Ram van is going to be very popular among RVers, due to its lower boarding height allowing it to provide more internal height in a lower and predictably more aerodynamic package.


Floor-shifters have been more frequent in my country than in the U.S., but I haven't seen any motorhome with a chrome shift lever. Black had always been more usual. Anyway, since the majority of the motorhomes back here are based in commercial truck and Euro van platforms, manual transmissions are also prevalent.

With a high-voltage AC all-electric drive train I'd hope for the equivelant of 40-45mpg. And three-wheel steering.

An electric car and a house have a similar power requirement.

A cube and a prolate spheroid have the same volume on a per cubic foot basis (squaring the circle), the spheroid does better on a per sq ft surface area basis, but the cube wins trying to stuff it through the hole in the DMV regulations. If the regulation was cross sectional area instead of max height and width, the spheroid would win [in Cd]

The next revision of my tricycle design will replace the slide-back door with dual gull-wings. With a fold-down rocker panel and deployble awnings.

Ease of construction is a consideration for the manufacturers as well. They don't need to tool up for expensive metal stampings when they use sheet stock for all but the front and rear endcaps which are plastic now and were 'glass in the past.

Take the flybridge off the Deco Liner and it's pretty aero.
http://cdn.celebritycarsblog.com/wp-...eco-liner.jpeg
http://image.hotrod.com/f/41307529+w...r-overview.jpg

Deco Liner's daddy
 

Here's something that I ran across online.
http://i1271.photobucket.com/albums/...titled27_3.jpg

bowlus [Tin Can Tourists Wiki] That's the Bowlus Motor Chief. According to the linked site, only 2 years of production for all models. I wonder how many were built.

The Decoliner has pontoon fenders and multiple axles, echoing Norman Bel Geddes.

https://upload.wikimedia.org/wikiped...lGeddesCar.jpg
https://en.wikipedia.org/wiki/Norman_Bel_Geddes

That looks nice. What's its GVWR?

Due to grandchildren traveling with us from time to time now we have a motorhome. Our RV of choice is our 35' Avion pull trailer it is very aero, it has been referred to as looking like a big Twinkie. After the grandchildren outgrow traveling with the old people it's back to the Avion for us.

With an RV, space is what's inside, and how close you are to the RV in the next space. With a tent, I can easily go places where it's 10 miles or more to the nearest human :-)

I own a tent myself.

I had the kids out on a few hikes this summer, one was at night and one was to the top of a small mountain. I also started them on sleeping in the tent. Next year I'm looking at getting them up Chocoura.

But this isn't about camping, it's about vehicle design requirements. And I really do prefer being out there and not sleeping on the ground. :)

35'
 

I've been chipping away at RV drag stuff,and Hucho published a work by R.Barth in Germany who tested a series of 'Twinkies' in the wind tunnel.
If you consider them as the body of an AVION,then:
*an 11-footer is Cd 0.38
*an 18.5-footer is Cd 0.230
*a 27-footer is Cd 0.205
*a 38-footer is Cd 0.200
*and a 45.5-footer is Cd 0.205.
So your 35-footer is near the bottom of the drag bucket for these shapes,making it the lowest drag length.:thumbup:

Neat! My 35-footer is the most aerodynamic thing I own. Too bad it's been up on blocks and skirted since possibly 1962.

That's just the basic body shape, correct? Real numbers would be higher?

I can see that. OTOH, I see a lot of RVers who park the thing in the (not so) wide open spaces of a campground, then spend their time sitting inside watching TV - which suggests that someone is kinda missing the point :-)

basic body
 

Yes,he tested a smooth rectangular cylinder with all edges softened to a radius equal to 10% of body height,in ground proximity,from almost a flat plate,out to a fineness ratio above 10.5:1.
*No features
*no cooling system
*no wheel openings
*no wheels
--------------------------------------------------------------------------
He tested 5-different shapes,all have a 'sweet-spot.'
This has been important to me as I do the geometric comparisons.It's easy to fall into traps without this sort of data.:o

It does not sound like you are wasting much gas fighting drag. :)