Class a motorhomes aerodynamics
 

I know it's hard to make a box aerodynamic but just wondering if anyone knows of any links where people have made the attempt.

...also lookup what the trucking industry does with their long and short trailers.

What he said. Mainly, deflect air away from the wheels and the rough underbody, and taper the back end.

Tapered rear end
 

I liked the Prototype tapered rear on the home page. A class A motorhome with a taper in scale with that car might be 15 feet long. The undercarriage of a class A is huge so smoothing it seems impratical. I was thinking of the underside of the front being streamlined and streamlining in front of all wheels. Coming up with a proper shape to streamline the wheels I'd rather copy what has been tried. I will be making wheel skirts. I looked at air tabs for the rear. Seems tapered rear would be better. I don't tow a car like most Class A owners do.

So anyway, if anyone has seen anything done to a big fat motorhome....

I will take a look at the trailer stuff again. Some of those truck sites focus upon the gap between the tractor and the trailer.

There are some "aerodynamic" mud flaps out there. Supposed to smoothe out the spray with slots in the mudflap surface.

motorhomes
 

I've not yet seen any streamlined motorhomes except for earlier efforts by GMC and Airstream,plus one-off units built from aircraft fuselage.
The motorhome would benefit from anything which improves a typical van.Hucho's thing is to add length while carefully reducing the cross-section to maintain attached flow,which is the "boat tail."
If I had a motorhome,I'd construct a trailer which forms the boat tail,with complete gap-fillers.( the accordian-bellows material used with articulated buses would be a great way to go ).
I've had good success with a van,coupe,and pickup truck,using boat-tails.NASA has some images of their boat-tailed van research at Edward's Air Force Base.This is one of the 'bird-in-hand' low-drag technologies.
Last December I attempted a road test of a boat-tail trailer without the gap-fillers.I lost a wheel early on and had to abort the trip and limp home with my tail between my legs.
Considering that the trailer shouldn't work without the gap closed off,I was relatively pleased with the 30-mpg under the winter driving conditions and undercarriage damage.Until I can repair and re-test,she remains an unknown quantity,so I can't give you any 'real' numbers until then.On paper,the trailer will increase mpg.

Have you got any pics ?

It also helps if you only add part of a boat-tail.
On trailers, flat plates angled inboard and around 1m / 3' long already help.

If it's huge with a lot of stuff sticking out underneath, it's also an area where serious improvements can be made ;)

Fairing any big external fittings on the roof (vents, windows, airco ?) would also help.

Truck fuel economy is pretty well cast-in-stone. Still, the the difference between drivers of otherwise identical rigs (big trucks) is 30%. That's a huge spread. Some drivers just get in and go. Others (the winners) know the details of the day in advance.

Trip Plan is the truck industry name for best utilization of equipment in re time & distance. It involves the use of different analytical tools. Most parameters are absolutes (staying on pavement, obeying traffic laws), so the margins are exploited to gain small increases that accrue over time.

Were I using a motorhome (and I have, going back over 30-years) my first thought is that the shortest engine-on time is a goal to post. Second is the distance to be covered (where the origination and destination are both known). Third is weather. Fourth is daylight hours available.

Within these are the items which can affect total mpg: best roads (even if a bit longer), estimated fuel burn (where do I re-fuel; consequently, where/when do I eat & rest); what major metro areas must I traverse (they tend to be at least 100 miles wide on any road), what temps, winds, conditions will I encounter? Altitude changes? Etc.

One needs to know the point-to-point distances to correctly estimate driving time on a daily basis. 50 mph for all hours is a standard, to include moving or stopped. But, as you are NOT on a schedule in the same manner, a different numbers may work, but you MUST keep a log of how things go in order to isolate and improve.

In other words, before the key turns one must know not only routing, but EVERY stop beforehand; right down to how to enter and exit a particular location (GOOGLE Street View). Some choices are far better than others, as all truckstops or rest areas may not be open, or be unpaved, or exist after three turns and three controlled intersections away from the highway, etc.

Motorhomes are notorious for terrible steering (sloppy, huge dead-center) so that is where I would expend any funds prior to aero aids. Second is brakes. Then FE alignment. Depending on year model, ignition, exhaust and fuel delivery if gasoline. A close eye on hub & tire temps/pressures, etc.

The fewest stops/starts is key. The smoothness of each is secondary, yet additive.

Within this, aero starts to work. Unlike a car one cannot just follow the front wheels around and keep gains consistent. The percentage difference of a 1/4-mpg on a moho are huge (and practically meaningless for a car), and easily, easily lost.

The trip plan means all contingencies have been addressed (takes experience, too). If high winds are expected in the afternoon, one might be advised to avoid same by a late, long, lunch and an early stop to the day (campground), for example.

The "aero" motorhomes are low to the ground in their class: VIXEN, FMC, GMC. Note mirrors (big deal) and other items hanging off body. Chin spoilers seem to have been attached to some Class C types since the 1970's.

Modern motorhomes (SPRINTER-based) rely on excellent drivetrains/gearing to achieve high mpg. A boat-tail on one of those would likely be the "capacity" (motorhome abilities) versus fuel burn champ.

accordian bellows articulation
 

I found this image online and finally got it into Photobucket so I could share it.
This modern CIVIS concept bus has this real clean gap-filling bellows,akin to Walt Disney's, Disneyland Monorail in Anaheim,California.
http://i1271.photobucket.com/albums/...ad2/scan13.jpg
What's old is new again
http://i1271.photobucket.com/albums/...ad2/scan15.jpg
http://i1271.photobucket.com/albums/...ad2/scan14.jpg

I know this is a really old thread...
 

...I found something that could be applicable in more than this.
A german company was testing what is called a Trucksack. Company seems to have moved on, but here is the youTube showing the test run.
youtube.com/watch?v=SCKbQ8irR3A

20% really?
it inflates by the air being forced into it while moving. When it collapses(stop a traffic light) could be a problem.

CW 'value' 0.58. A or B?

(fuel consumption) -20%

Lots of pix on the highway, none at the loading dock.

Hi guys, no the company is still running, belongs now to Trailer Dynamics/Krone Commercial Vehicles. located at the RWTH Aachen University campus.

Welcome to Ecomodder.

Time is either speeding up or stretching out —I don't remember the post at #10 at all.

I watched the video again and what stood out this time was the inflating mechanism standing proud of the sidewall. I proposed a design that has a rigid floor, but was to use a passive inflation system. Those scalloped openings are apparently overkill. More recently I considered retractable fiberglass rods.

https://ecomodder.com/forum/member-f...pe-ii-boat.jpg

Third phase of development and homologation
 

Looks very good freebeard. We actually carried on with the work and are now in the third iteration phase.

Fortunately for us, we also prevailed with our patent and were granted the patent this summer.

Unfortunately I cannot send any pictures via ecomodder at the moment, but if you just google under "Alpha Team Aachen" you will be able to see a few pictures

Do three more posts and the restriction is lifted.

My design has a rigid floor (diffuser roof) but I know that that wouldn't play nice with a loading dock.

Robust and user-friendly
 

yes, probably true. anything that blocks the rear portal is always a problem for the operators.

It was suggested to us that the solution must be cost efficient, light and robust. In addition, the aerodynamic solution must comply with the approval rules.

freebeard,
I have reviewed the NASA aerodynamic data... and it is clear that a boat-tail or folding semi trailertail or Rocketail would get a 11.5' X 8'+ rounded nose brick a more fuel efficient exit.
Ours is a '02 Rexhall Aerbus XL3100. its a measured 32' long. w/44,000miles. It was cheap used, & its nice sitting up front watching the world go by.
I've done some weight reduction. and added vortex generators to the rear, so far.

Honestly I've been a little "abashed" ... most here are projecting on 30mpg autos up to 50 & 60mpg. The first thought why bother chasing a +10% goal of 9mpg. when the newer class Bs might be getting 21mpg. of course those are selling for 10xs what I have in Moby.

https://www.rvtrader.com/listing/199...100-5016435059https://cdn2.rvtrader.com/v1/media/6...ef3288e19.jpg?

Is there a question? I don't see a lot of opportunity -- delete the step and awning and it's arms, and blister the rooftop air conditioner.

Possibly the best opportunity would be skirts or air curtains over the front wheel wells. At 32ft the boat tail better be deployable at speed.

If you've got random tires on it, you might gain 10% mpg just from switching to the loweat rolling resistance models. Michelin has a calculator to see what percentage change in rolling resistance you'd get between various tires: https://indus.michelintruck.com/tool...ce-comparison/

I imagine you could get noticable gains by covering most of the undercarriage with smooth panels.

Pretty close ...ours is a 2002. little different headlights
the awning was removed before I bought it, by a wind gust I think. I have no interest in putting that back on....and our stairs tuck in better.

A complete under belly pan, including a diffuser? I'm ready to put a security plate under the catalytic converter. Oh and skirting the rear wheel wells., ala newest Mercedes commercial trucks. I've got lots of old road signs, made of aluminum.
:p
I know.... kinda silly.
1st step is figure out if an UltraGauge or ScanGauge will work on a OBD 1, as that's the label on the V10

There are the 2 sections of driveshaft, 3 u joints between the transmission & the rearend. Lots of room for an on demand electric, and batteries(more weight) or capacitor(s)

I mentioned the Rocketail... I think earlier... which seems to have lost much of its support from retail.
I think is pretty compact, and has interesting flow data.

"https://uspto.report/patent/grant/10,442,478#D00005"

I couldn't find my Yokohama tires listed in the Michelin site.
Thank you... I've bookmarked the website for the future.

Mercedes IAA concept:
https://i.kinja-img.com/gawker-media...6742354834.gif
theodoretziegler.wordpress.com/2015/09/15/heres-mercedes-transforming-afterburner-tail-in-action/

It's hard to see from this angle, but the extension panels are fairly straight so the extrude from a body that tapers back to the separation edge.

...and the way the wheel covers change shape is cool too.

Yokohama has a calculator of their own: https://www.yokohamatruck.com/tire-t...ngs-calculator

Looks like they list their 023, 101, 108, 109, 114, 517, 617, 703, 709, 712, and 715 tires on it...

Thank you for the Yokohama site.

I've thought an inflatable aero treatment made the most sense.

Make it so it's foolproof and easy, that lazy slobs will still be compliant.

Make it with relief valves so lazy forgetful slobs don't break things when they back into a loading bay without deactivating the system.

Maybe make it out of the type of rubber used in high end rafts (PVC?). Tolerates higher pressure and abrasion resistant.

Perhaps it could be made so that when the pump is reversed, the thing sucks back into a minimal storage compartment out of the way.

*Not implying all or even most truckers are lazy slobs

it definitely has possibilities. And a way to get it to "deflate it" would be important, even for a RV.
Here's another one...neither really address this
youtube.com/watch?v=dm-Euo4yS6M

inflatable
 

I can testify that even 'mediocre' inflatable tails will show at the gas pump or charging station.
I'd link a photo, but the 'manage attachments' no longer exists.

I've never understood the attraction of attachments. I raided your albums:

https://ecomodder.com/forum/member-a...ilkisons-t.jpg
ecomodder.com/forum/member-aerohead-albums-pickup+images

raided
 

Last two times I attempted to share images, there was no longer the 'MANAGE ATTACHMENTS' button to use.
Not sure what's happened.

Thank you Aerohead & Freebeard & MetroMPG for your interest in this project...of mine.
Our last couple treks have been from Virginia City, NV(6000'ASL) via CarsonCity(5360'ASL) over the Sierra Nevada(7780'ASL) to near Yosemite(4000'ASL) to spend camping trip with Grandkids, and back. <5% @55MPH, 45MPH on the uphill grades = 7.9998 mpg. I've been hypermilling as much as is practical, but its a little scary "letting her go" downhill on a 2 lane highway.

I re-read the Aerodynamic Seminar(s) ...#5:
"It was Klemperer of the Zeppelin Werks who discovered the low drag 6 to 1 length to width ratio which gave the airships a drag coefficient of Cd0.04 in 1932."

.... with a 32 foot MH... 8 foot wide(...11' tall)... that means I could?have a potential 16' long boat-tail(48' overall). Yikes, I was thinking more 2-3 foot "fleetaero.com/rocketail/" .

16-feet
 

I believe that boat-tail length is capped @ 48-inches, unless its inflatable, then you've got 60-inches to work with.
Since the MH has the more narrow 'width' dimension, all geometry for the tail could be based upon the 96-inches.
The W.A. Mair contour is a known quantity.
NASA used a tail very similar to it for their van / 18-wheeler experiments.
GM had an 'Optimum' boat tail in the 1980s, which, while it had no compound surfaces, it did have generous edge radii, which helped kill vorticity before it ever got a chance to form.
I'd give you a link to an image, but I can't.
Texas Tech University's Dean of the Mechanical Engineering Dept. office could probably provide a reprint of ' Project Tailwind, which Professor Carver participated in. It could be of value.

The Zeppelin aeroform is not as pertinent as the work Mair did on torpedoes.

https://ecomodder.com/forum/member-f...1215134663.jpg

You have fineness ratio going for you.

A series of 3- 12+" sections ..ala "Mercedes IAA concept:"or tri-fold closet doors- seems a bit complicated...problematic
...which brings me back to Freebeard's original idea (Post#12).
The MH has no need for access to a "loading dock"..unless a toy-hauler. So design with rigid flat bottom(Naca vent to inflate?), would close(w/cable & pulley) to conceal the "fabric" upper, only need to consider taillights.

rigid bottom
 

1) It will help stabilize the entire envelope.
2) A light-kit could be integrated into it. Traffic near you need to see your functions from all vantage points.
3) And likely, the rear license plate.
4) A passive-inflation tail has been patented and tested. Mine was forced-air, using a 12-VDC Bosch heater blower off of a VW Westfalia Camp Mobile. Many of today's inflated, outdoor advertising displays use a small, high-static-pressure air handlers to keep the envelope taught.
5) I designed a two-way, reversing 'valve' which allowed the inflation fan to also evacuate the envelope. It's a simple guillotine, slide-port mechanism.

Like this?
partsgeek.com/gbproducts/WC/7229-01050292.html

partsgeek
 

I made it to their home page, but they couldn't find the page for what I typed.

Try this one: put 3xW before it... ".mk1autohaus.com/assets/images/251819015.png"
I'm on Post 14... hope this gets easier soon

I was thinking of attaching the flat bottom just above the lip above the taillights.
http://www.rogersworx.com/images/IMG_1977.JPG

3xW.............
 

It shows an unsecure site and won't let me in. We'll succeed at some point.