New and seeking aero advice for my "brick"
 

Hi Everyone,
I have a camper I built from a 1994 square-box-style ambulance. It has a 7.3 IDI diesel and get about 13mpg at 55mph. It has a huge flat front area that just grabs the wind and I keep thinking about putting something up there to make it more aerodynamic. I am trying to find a way of figuring out the benefit I might see with a more sloping front...and what other mods I can do to benefit mpg in a cost effective way. I'll try to post a pic but imagine any box ambulance you have seen before.
Thanks for any help/advice (accept "sell it")
FR

https://ecomodder.com/forum/attachme...4&d=1538852832

The classic response to your inquiry is that drag is created at the aft section of the vehicle, after the high point in the roof (at the rear).

However after looking at your "brick" I see there is ample opportunity at the front where attachment of the air built up from air pressure occurs.

The air pressure build-up after the cabin as it hits the box is off the scale, those rounded corners help, but I cannot but help to feel your pain.

Let me try and sketch something up, a picture is worth a thousand words.

EDIT:
I marked up eight things off the top of my head, looks like a lot of work. If you are going to do that much work, look at the Ram-Aero camper thread of a few days ago.

Link:
https://ecomodder.com/forum/showthre...udy-36886.html


https://ecomodder.com/forum/attachme...5&d=1538858550

brick
 

There's great paper available online from NASA and their 'Shoebox' project from the 1970s at Edwards Air Force Base,California.
Maybe GOOGLE NASA truck aerodynamic research.

I was thinking of the Dryden projects, but found this under scholarly articles, it's a book more than a paper I think, and I have not seen it before. And it seems to go on forever, keeps loading more pages and more images every time I scroll.

https://books.google.com/books?hl=en...search&f=false
https://books.google.com/books/conte...SYpasxgp4689CA

Here is the NASA Dryden project page: (a fragment of what's out there)
https://www.nasa.gov/centers/armstro...-100-DFRC.html

EDIT: Speaking of books, this is new to me as well.

https://www.amazon.com/Fairing-Well-Aerodynamic-Monographs-Aerospace/dp/1780398999
https://images-na.ssl-images-amazon....4,203,200_.jpg

Click "LOOK INSIDE" in the upper left hand corner of the page.

Spoiler: Lifting-Body content in preview.

Here ya go, some numbers to go with the theory and forms.

Aerodynamics Research Revolutionizes Truck Design
https://spinoff.nasa.gov/Spinoff2008/t_3.html
https://spinoff.nasa.gov/Spinoff2008/images/t-8.jpeg
https://spinoff.nasa.gov/Spinoff2008/images/t-9.jpeg
There is half-hearted acceptance of Airtabs in the forum in my opinion, speaking for myself, I was curious but cautious about jumping on any bandwagon I didn't completely understand. Maybe I will take a second look now.

Farraider, as far as adding a #9 to the sketch for Airtabs I will leave that up to you.

Accept ≠ except. Sorry, but you asked.

One of our forum members has had success implementing this design as a way to radius a square corner without cutting into it.

https://ecomodder.com/forum/member-f...01-2-04-41.png

At the doors, it might need a concave inner half. I've had less success with this:

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

But modern bus design follows the principle of this stap-on:

http://www.icbus.com/~/media/Navista...CD441CBC1E15A6
https://ecomodder.com/forum/showthre...tml#post494966

So maybe you could add a cab-capper with a little added frontal area and show a net gain in Cd. Would you be interested in a retractable boat tail back porch? What's the use case anyway?

Why add the frontal area? :confused:

If those protruding radii at the vertical leading edges of the camper work, why not turn 'em horizontal and slap one on the forward leading edge of the windshield/roof junction with no added Af?

That whole ****ing Greenshield thing makes me want to puke.

I posted that graphic and the comments that disputed it's working. I also said something similar to what Frank Lee just said.

Just clarifying that is a bad graphic, hence it's inclusion into the "Random UnAerodynamic Cars and Trucks Thread".

If newer buses do have this feature built-in I question if it's just a marketing gimmick.

Bad example. I found it first when I was looking for this:

http://www.oxford-chiltern-bus-page....%20Francis.jpg
https://ecomodder.com/forum/showthre...ics-17717.html

Adding interior volume. So long as the curve respects The Template, flow can reattach to the (admittedly short) flat top. There's normally a low pressure area behind the top edge.

Alternatives would be a row of vortex generators or a blown slot.

Thanks for the sketch Kach, great looking ideas. Freebird, I rushed the post and caught the error right after I hit submit but had to head out the door. Or may be I meant to have to accept selling it, hmmm, that's it!

Anyway thanks all for the ideas & suggestions but I'm trying to get an idea of my cost and effort for reward ratio. Is there a site to help me compare different modifications and what the energy savings would be? I'm sure I could spend $10G making it look like a rocket but I'm not going to do that. Im trying to find that sweet spot in the ratio (effort<=reward) and what to expect.

Question: If I have a square meter box, what is the aerodynamic reduction of force required to push that through air at 60mph if I instead it had a 45 degree leading edge? Is this an applicable question for the front box of the truck?

If that greenshield thing works, maybe I could mimic the idea and use it to hide my spare up there. Reasonable?

Thanks again everybody.
FR

That would be Ecomodder. :) It's all anecdotal, because each owner and use case is different, but there are accepted principles based on both hearsay and evidence.

https://ecomodder.com/forum/member-f...ntitled-3b.jpg

Every element has a Cd. Those are both summed and interactive.

It needs to be moved forward over the cab to maximize the length of roof behind it. Davits for storing and retrieving the spare? That's the style with [the decidedly unaerodynamic] Dekotora trucks. They started out as a place to store tire chains, etc. Colani's trucks use a tilted oblate spheroid:

https://upload.wikimedia.org/wikiped...signTrucks.jpg
https://en.wikipedia.org/wiki/Luigi_Colani

Here is a sketch I did for another thread, some of it might transfer to your case. Half-round front corners and a deflector ring at the rear.

https://ecomodder.com/forum/member-f...-1224-copy.jpg

Rear-view mirrors are also impotant.

I just discovered the archive view of the Aerodynamics sub-forum. Scan this list for item of interest:

https://ecomodder.com/forum/archive/f-6.html

Here's a list of relevant threads from here.

https://lh3.googleusercontent.com/d8...=w1135-h638-no
https://ecomodder.com/forum/showthre...uck-34674.html

1. How much can you get for your vehicle today? It would make a great work truck for a builder.

2. I so much more favor a Diesel Sprinter as your starting point as myself and others have been leading to towards.

Will you ever get it this nice?

Winnebago
https://winnebagoind.com/products/cl...avato/overview
No, but it can be a nicer end product with less effort and money than if you start with your ambulance.

2006 Dodge Sprinter - $7200 Diesel 5 cylinder
https://seattle.craigslist.org/see/c...717993528.html
2013 Mercedes Sprinter Bluetech Long-wheel base One owner - $1 (NE Couch st)
https://portland.craigslist.org/mlt/...713535697.html
06 sprinter van high top short model runs perfect very reliable 24mpg - $4900 (Turbo diesel 5 cylinder Marysville)
https://seattle.craigslist.org/sno/c...710593951.html
https://images.craigslist.org/00N0N_...gm_600x450.jpg
Oh my God, 400,000 miles................dang, those other ones at 250k are just babies. :D

What a mule that thing is, in a good way.

https://images.craigslist.org/00k0k_...k_1200x900.jpg

The artwork I would do for one of these Diesel Sprinters would be far less involving, that much alone tells you what a superior starting point they are.

The 8-point list would be down to less than half.

Chin spoiler, rear box cavity baffles and pizza pan wheel covers with zip ties - DONE!

Welcome !

Never going to return great mileage with a huge engine and boxy bodywork.

Do you plan on doing many miles /year ?
That'll mean wether the improvements have any true value (saved fuel minus your investment)

Driving 5mph slower may be an option.


Air dam underneath up front

Sideskirts

Cover the rear wheel arc

Wheel hub caps

Close the gap between cab and box, if any, including underneath.

Bigger / wider & higher deflector on the roof of the cab.

Bigger radius on the corners of the box
(by adding a half-pipe - can be used to store long thin items)
or
turning vanes on the corners
https://www.hyundai.com/content/dam/...s-original.jpg


Rounding the rear corners too much, will decrease stability though
(google coanda effect http://www.formula1-dictionary.net/I...fect_paper.gif

You would need something like this to reduce drag aft:
https://www.ttm.nl/wp-content/upload...1/1591_279.jpg



Lighter color than black will keep it cooler

Good points and nice graphics euromodder.

There are nice camping sites on a lake less than 30 minutes from my house, in that situation this ex-ambulance would be just fine.

Then again I could drive half a day and still be in Michigan and on a really big lake, some would call it a Great Lake. In that situation something with better MPG would be nice.

Farraider , could you share some more details?

It's going to come down to some simple math.

If it manages to reduce the drag coefficient more than it increases area, it works ...

Thos bumps are found on small European vans, busses seen above, trains, ...

Don-Bur trailers work
Despite the added area - c an't reduce internal trailer height
Aerodynamic Teardrop Trailer

There is a simple diagram from the late 1970's (I presume) that I find once in a while on the Internet. It shows a boxy sedan with a 90 degree angle between radiator and hood and some rotational arrows illustrating turbulence at the plane change. This is not a real life condition found in the last 30 years on vehicle design but even back then I suspect it was a misrepresentation because the high pressure wave in front of the vehicle directs air flow just above it up and over the hood.

I think you are right that it comes down to in field or in lab testing of individual conditions, and no two will be the same.

In the link below "radius of curvature of a fairing sitting on top of the caravan" seems to be an important element in the CFD studies. maybe there is something in the article that sheds light on our related topic.


Posted By LEAP CFD Team on Jun 21, 2017 | 0 comments
https://www.computationalfluiddynami...l-consumption/
https://www.computationalfluiddynami...ld-image-2.png


The Don-Bur Aerodynamic Teardrop™
Aerodynamic Teardrop Trailer
http://forums.pelicanparts.com/uploa...1539094718.jpg
http://forums.pelicanparts.com/uploa...1539094718.jpg

Of course there can be other problems with going higher, like not fitting into your garage, or worse.

http://forums.pelicanparts.com/off-t...pics-4597.html
http://forums.pelicanparts.com/uploa...1539033916.jpg

I passed a similar ambulance on the highway yesterday, dang those things are wide.

I can see the attraction of starting with a wider box than a Sprinter type van.

One thing a bit unclear to me, is the former ambulance already outfitted as a camper?

I can see why you would want to hang on to it if already made into a camper.

Hi Guys,
Yes it's already a camper and we drive it down and around Mexico in the winter to escape the snow/cold and go rock climbing, eat cheap tacos and soak up some sun. Probably 10-15K mi/yr.

Regarding Sprinters, they're too common and have no character IMO - I like this vehicle and I did all the work myself.


I just seem to be making the aero worse. Today I installed a hitch on it so I can also carry my dual sport bike down this year too. There's an extra 400lbs to carry. Ugghhhh. Maybe that will encourage me to take the "5mph slower" advice.

Euromodder, your suggestion about rounding the corners more with half pipe. Half a 6 or 8 inch pvc pipe just mounted down the corners? With middle of the curve directly over the corner? I wonder how much that would help? It probably pales in comparison to fixing that huge flat front and rear drag.

Thoughts?

Then get started.

If you just want to get your feet wet, the conveyor belt chin spoiler is a weekend project if you get all your supplies together the weekend before. There is a link in my signature for some tips on how to do this. Lawn edging is fine for a year or two or until someone backs into it with their bumper and should be considered temporary.

The roof deflector fairing is at least a two week project unless you can repurpose a found item and make do.

The most beneficial item is the longest most time consuming and challenging, the rear box cavity as it may have moving parts. Maybe there is something on the market already or a damaged semi-truck unit from a junk yard can be modified. Point is, it's just big and requires some engineering.

I would proceed in the order above and knock out the other items along the way.

Take a look at this picture from Permalink #4

https://images-na.ssl-images-amazon....4,203,200_.jpg

The dust in the air shows your areas of concern. The dust suspended abaft the top edge is heavier than the sides because the step is 2-3ft instead of 6-8". The dust over the cab is similar to the cap you have already.

I'd make a bullnose cap that extends above the windshield as a visor. I'd also make it clamshell open reverse-alligator style to make a roof-top tent, but that is optional.

For the sides, what is the dimension of the front face of the van, the depth of the door pillar and the distance from the van edge to the opened door's edge?

In the rear, would a box cavity (Trailer tail™) enclose the sport bike?

I'd be remiss if I didn't repost this one. It is a unibody isn't it? I apologize for not Photoshopping this into something comprehendible:

https://ecomodder.com/forum/member-f...56-aerobug.png

If you find a derelict cab that uses the same door you could cut the door frames down into a pie-shaped piece and slip it inside the half-open door and weld 'er up.

If its american ambulance, it will be conventional truck frame & cab, probably a standard box also. Lotsa parts available. Worst case pick a part is your new friend

I found this.

12v Cummins with stacks & fairing
https://www.youtube.com/watch?v=nOYSTMub8Ww
https://i.ytimg.com/vi/nOYSTMub8Ww/maxresdefault.jpg
New FWC camper, wind fairing suggestions
http://www.wanderthewest.com/forum/t...g-suggestions/
http://www.wanderthewest.com/forum/u...934_607199.jpg

http://www.airodyne.com/collapsible.asp
http://www.airodyne.com/P2-9%20T680_flyer.jpg

One could set up some temporary plywood forms and wire fanfold insulation to them, then resin and glass over it. However a found item that is modified could also work.

I looked up basement window well covers, but could find nothing wide enough, was thinking one could fiberglass cloth and resin over it.

Bouyancy blocks (big chunks of rigid insulation) for floating docks could be glued and carved up to desired shape, but those blocks can get expensive and it's going to make a great mess.

If you don't look forward to tiny fiberglass needles in your skin and breathing toxic vapors, consider Nudo Polymetal or Grimco Max-Metal as a material.

https://ecomodder.com/forum/member-f...1-100-0866.jpg

These samples were sheared, rolled and braked with a hand operated tool with an 18" lever arm. Braking the short edge ruptured the metal skin on the outside. Scoring the inside first might alleviate that.

The result is pre-finished, no filling and sanding needed.

Great idea, I saw that being used on a job site sign ten years ago and thought it had great potential as an ecomodding material.

Limited to 2D bending, but that's what folding tabs and joint fillers are for, right?

I've only bent the non-alum skin version before.

https://www.boatdesign.net/threads/t...ruction.21403/

Remember the accepted roundness for leading edges is a radius of 4% of the width. That'd be 4" for a 100" wide box. Looking at picture of the ambulance, it appears to already have that on the box. Can't really see it much though. OP?? If it's already radiused, I'm not sure there's anything to be gained there.

OP posted three times total, but not in the last 48 hours, FWIW.

U-Haul trailers are optimal, the example in the one photo we all struggle with looks a little tight to me. Maybe 3"?

Good point, but just rounding the corner edges to the optional roundness isn't the same or effective and a whole body approach that includes a massive roof top faring.

No one is going to claim that a cube with radius edges is as aerodynamic as a teardrop shape for instance.

He has one good detail on the truck, but as a whole it is flawed in every way possible.

It makes for an excellent ecomodder challenge though.

EDIT:

Look at the big rig fairings I posted, if just rounding the edges of the tractor trailer boxes was truly optimum then why would anyone strive for a better fairing?

https://upload.wikimedia.org/wikiped...Colani-LKW.jpg
https://upload.wikimedia.org/wikiped...Colani-LKW.jpg

Tilt the Colania bubble back as appropriate. The three-bladed wiper might need cyclic pitch control.

OK, but that character is gonna cost ya ...

No, that would make the box even wider
You really don't want any more frontal area when you can avoid it

With the half pipe entirely on the front of the box

Doing the same on the roof might work too, despite a bit more frontal area
(the area of 1 pipe diameter)
Essentially creating a channel guiding the air aft.
With less air spilling over to the sides along the length of the box.
And what spills over, goes over more smoothly due to the bigger radius of the pipe than the box's original corners.

To be combined with a cab roof spoiler guiding the air to that channel


It won't be the miracle solution, but your box could use any help :rolleyes:


Not much of a creative talent here, but these quick drawings may give you the idea :

I agree strongly with the wider & higher deflector on the roof comment that I highlighted in dark red (above).

On the second point of radius box corners that he already has, there are other areas much more deserving of attention, and that is probably the least of them.

Those European cab over engine air curtains are a fascination of mine as well, but here those giant rear view mirrors that he has are air flow interrupters and concept killers, that beautiful illustration will probably not work here.

A fine example of huge roof top fairing combined with curved leading edge box corners has already been posted, it helped me to look at it closer a second time. We need to get over that it's a Sprinter example, and focus on the details, these are details similar to the ones I sketched up early on and that we all seem to be in agreement on lately.

EDIT-1:

Regarding the below comment, sounds expensive and heavy compared to gluing some foam wedges to the door and painting them black. Neither idea is bad, just that there is just so much more low lying fruit to pick and these would be the very last things one would do if at all.

Good info I am trying to improve aero on this

That is a much cleaner starting point, although not 8-feet wide like that ambulance.

Interesting.

Good fineness ratio and taper in elevation. You could panel in the sides and put pontoon fenders over the three axles.

Having just read through the thread, I don't see that anyone has mentioned some of the obvious improvements; that being the underside of the truck.
As is, it seems to be slightly nose up, and this won't improve with a trailer in tow.
Depending on the needs demanded by usual roads, drop this down to no more than 6", give it a bit of forward rake, put on a front air dam, and try and smooth the underside as much as possible, then repeat MPG test.
cheers

So many other things going on with that project, why not add a belly pan indeed.

That should cover his "to do list" for the life of the vehicle. :D

I see that the trailer caught your attention, a work of art isn't it?

I assumed he was talking about the white van.

I would start, by changing air and fuel filters, and go to a lighter grade synthetic oil.
Aerodynamics will do very little below 55mph. It appears to me your engine is just horribly inefficient.
At that cc, your engine should be running at 1500rpm. If it's doing 2k or more, gearing is also to blame for it.

Perhaps time to change piston rings, as well as change the head gasket, and check the cylinder bores.

If the piston rings create blowby, your oil is very black every oil change, and new piston rings will do most of the mpg gains.
But if they're good, and air and fuel filters are good, I figure you probably can gain 2 to 5 mpg at best, by tuning.

It has an overly large engine, that produces the same amount of power (or less) rhan a 2.6 liter Ecoboost engine from Ford, which is half the size, and double the mpg.

Sorry I missed this earlier.

The 53’ trailers I pull with an aero Class 8 tractor vary from no aero mods, to those with full skirts and tail. The difference is somewhat slight, but telling as to the extra work I’ll have to do that day. I’d always prefer full aero.

The biggest change would be to have a flat-front trailer hooked to a non aero tractor. It’s unreal how much force is necessary to pull that down the highway. I speak of how noticeable this is to the driver. How hard it is to show decent FE on the gauge.

Some cattle-haulers prefer this set-up as it’s literally an aid to braking (moving livestock a world of its own).

I see that ambulance and the first thing I think I’d do is to add (brand name) Nose Cone to the body. Get that problem out the way and the feel to the vehicle changes rapidly.

Steering slop and old shocks can’t be tolerated. Same for worn body bushings. Steering corrections per 100-miles is a measurable FE effect according to industry. Aero won’t help much until your steering degree of angle and duration x corrections is minimized.

Until you’ve minimized the flat front effect with some aero, and made steering AND handling brand-new, don’t expect aero band-aids to do much for you. That comes AFTER the driver can feel what’s happening thru the wheel. Sensitivity.

As to the rest, ORBYWAN modified a Class C motorhome on these pages a while back. Read all those threads. (Great stuff above in this thread).

For the vehicle rear, a custom trailer that followed the lines suggested by Aerohead to cause a passenger bus to be able to run 100-mph on the same fuel would be the right approach.

Or study the design of a (brand name) Trailer Tail.

Straight trucks (non-articulated) are terrible on the highway. It’s the wind that is not released by the body until passing AGAINST the air moving cross-ways underneath. I feel certain that an air dam and side skirts are a worthwhile investigation at a low cost and are easily removed. Will smooth the vehicle passage so that nose cone and trailer tail devices can more easily be evaluated.

1). Steering
2) Handling
3) Body to ground mods
4) Entry & Exit Mods

One has to have great feel at the wheel. Like locating the direction of a sound.

As to the RV as RV:

A motorhome is inefficient in all respects. It’s weight, complexity, and shape keep its initial cost and operating costs high and camping utility low. Only newbies love them.

If my 63’ combined rig RV can average 15-mpg (17,000-lbs), sleep six with far more storage, capacities and features, where is the advantage of a commercial truck-based RV?

As 13-mpg isn’t bad. If driving a few extra feet off-road is really worth it.

The formula for total cost is annual nights aboard into years of service. Answer that for relative cost and the balance falls into place. Value.

.

From leaving the pavement to the camping spot. With that vehicle, it’s that distance that kills fuel economy.

Over a years time, what is that distance?

Over on Airstream Trailer & Motorhome Owners Community is contributor, “Moosetags”, with a diesel 4WD pickup plus camper pulling an Airstream. A big budget vehicle for most of us as it was new. This is the third generation as I recall. He and his wife travel for months. The travel trailer gets left behind as the truck ventures off-road.

That would be the “better” approach as to flexibility and fuel economy. The template. His FE not that exciting, but no off-pavement use vehicle will ever be so.

Dirt = Drag.