Ambulance Aero
 

Hello All.

Question: Do you think the larger cab on a medium duty ambulance will give better aero than a light duty ambulance?

Below is Freightliner M2 106 next to a Ram 4500 with the same size box. I know box trucks and Class C RVs have horrible aerodynamic due to the large flat profile on the front of the box. The MD ambulances have much less of the box exposed and I'm thinking that might be why I'm seeing similar mileage claims for medium duty ambulances as for light duty ones.

https://i.pinimg.com/originals/81/52...aaa82fd3a4.jpg

The back-story:

As some may know my wife and I are looking to travel full time in about 2 years. Our current campervan is too small and we are looking for something bigger. At first I was looking at high roof Transits or a box truck.

Then I got turned on to ambulances which are basically a box truck with a MUCH better built box on them. All aluminum construction with lots of lockable storage already built in. The only down side is most are van based and after 2 decades of helping my father wrench on Econoline vans I have no desire to own a Type III ambulance built on a cutaway van chassis.

There are Type I ambulances built on truck chassis. Those have some benefits like easy suspension upgrades and more room to work under the hood. (Although if a turbo goes out the cab has to come off!) The big downside is that Type I trucks built on a F250 - F450 chassis rarely have a walk-through to the cab. That is a must have for us

Then I starting thinking about Medium Duty Ambulances. At first I though they would be WAY to big but the box is the same size. The major difference is the size of the cab....

Holding a straight edge up to the screen suggest that the hood height is the same but the box on the left is taller. Does it have a higher floor level? I'd guess the medium duty has the advantage aero-wise.

Not having a walk-through sounds like a solvable problem.

The finnish way to build them:
https://www.profilevehicles.com/en/s...rez-ambulance/

Yes, a MD has a higher floor height and cab height. The higher cab and lower front of the hood makes for better forward sight-lines and smaller blindsports in front of the vehicle. (The tall long hood on the GMC I recently rented made for HORRIBLE sight-lines)

Top of the frame rails to the top of the cab:

47 inches - F450
58 inches - E450
68 inches - M2 106

I suspect this is why most pickup based ambulances do not have a walk-though. It would be more like a crawl through.

Yes, given enough effort just about anything can be done. However, ambulances have a LOT of wiring. Type I ambulances without a pass through put their wiring at the front of the box under the window. So to make a pass through I would need to relocate all of this

http://www.hatzalahchicago.org/wp-co...ruction-05.jpg


We call that a Type II ambulance. Just a high top van with medical gear added. If I was going to go with a van there would be no reason to buy an ambulance - I would just buy a high-top Transit van.

https://www.fedextrucksforsale.com/w...n-for-sale.jpg

The walkthrough is a local option. Class C camper cabs have it. Why not just use a box truck? Them 16 ft Isuzu things get flogged to death and keep on trucking.

Yes, Class C RVs build on truck chassis have a walkthrough. They also have a living space overhead that ties into the cab that make it easier to make a large vertical opening.

I started off looking at box trucks. Specifically, something like a Penske 12 foot built on a van chassis. I was drawn to the rectangular shape that make upfitting the interior WAY easier than trying to match the interior profile of a van. (Lesson learned from building our first campervan)

https://personalspaceministorage.com...12ft-truck.jpg

A typical box truck has a flimsy wooden box on a flatbed covered with either fiberglass or aluminum. They are prone to leaks and rotting of the wooden core. I also doubt most would survive long if subjected to a steady diet of rough forest service roads. Most box trucks are also made to back up to shipping dock 48 inches off the ground so the box is too high. (Bad for Aero, bad for getting in and out of the box, bad for overhead clearance)

Ambulance boxes must be crash tested and certified. They are made of welded aluminum tubing and some have the seams of the exterior aluminum welded. Most are insulated from the factor. They also come with a bunch of external storage compartments already made that are lockable and watertight.

Ambulances have:

• Rear Heat and A/C
• Shore power
• 110V power with a quality invertor designed to work with sensitive medical equipment
• Dual alternators
• House batteries (Usually 2-4)
• Air Ride (Which can also be used to level the box when parked)
• Onboard air compressor to air the tires up and down
• Certified seats with seatbelts to allow people to legally ride in the back.
• Lots of the wiring already done (and individual wires printed with the circuit info)

Then there is rust or lack of rust. A M2 ambulance has an aluminum cab with an aluminum box.


They do. They also have cramped cabs with the passengers sitting right on top of the front axle. I’ve spent some time on expeditors forums and the general consensus is that cab-overs great for maneuvering around town but miserable to drive long distances on the highway. The requirement for the cab to swing up for service also makes doing a walk-through to the box harder. I haven’t seen any with a low entry box.



Back to aerodynamics.

I would likely do an air deflector on the top of the cab (factory option so easier to find / install than some custom fabrication)

Medium Duty side profile

https://d2uhsaoc6ysewq.cloudfront.ne...6-17956970.jpg

I would likely do an air deflector on the top of the cab (factory option so easier to find / install than some custom fabrication)


Pickup side profile

https://arrowambulances.com/media/IMG_6134-900x675.jpg

What's the difference in rated fuel economy?

If the medium duty has a passthrough cab, then there's no comparison. They're both a wreck, aerodynamically, but a nicely curved deflector looks easier on the medium duty cab. Also less side overhang

Passthrough cab over all.

I mean, it's the squared off rear-end that's the biggest problem; and probably not easily solvable while maintaining the ease of access.

There is no rated fuel economy for vehicles over 8500 lb GVWR so all I have to go on is various forum posts from different websites. I’ve seen claims anywhere from 6 mpg to 18 mpg for ambulances in general. As I said in the OP - I’m seeing very similar numbers claimed for medium duty vs lighter duty vehicle.

I’d be happy with 15 mpg at 60 to 65 mph. That is more for personal satisfaction than economics. At 20K miles a year and $3.50 a gallon the difference between 15 mpg and 10 mpg is $2333 per year or $195 a month.


They are a wreck but much better than this:
https://www.kloompy.com/oc-content/u...128/188504.jpg
Some friends of ours have an RV like this with the Ford V10 and get 6 mpg at 60 mph

The shipping industry has that covered. One of the benefits of going with a square vehicle instead of something curved like a van.
https://base.imgix.net/files/base/eb...op&h=432&w=768

The back doors won’t be used to get in and out of the vehicle. Ambulances have a side access door on the right side. I plan to have a bed across the back of the vehicle with a “garage” storage below.


I jumped in a M2 106 at lunch and the sightlines are night and day different compared to a full-size truck. Nice roomy cab too. That is another check in favor of a Medium Duty.

I spotted a '08-'09 Dodge Ram 2500 with a coachbuilt motorhome body this Sunday, and its proportions reminded me of an ambulance, even though it had a sleeper over the cab that smoothed its frontal area a little. Maybe getting a light truck instead of medium-duty can be beneficial, as the lower cabin may keep room to add either more storage or sleeping area without increasing the overall height.

An inflated half-round on the vertical edges would help as much as the deflector. Assuming they run all the way to the top.

Are you talking about the front or the back of the box? The industry has gotten more creative in recent years to improve aero without the inconvenience of requiring the driver to fold in rear flaps. (Innovation driven by recent federal mandates for trailer manufacturers to reduce drag - both aero and rolling)

So in addition to flaps there are little fairings like Michelin uses:

https://aecbmesvcm.cloudimg.io/v7/ht...c-feature3.jpg

I also won't have a smooth top to the ambulance. I'm planning about 1400 watts of solar and at least one powered vent.

and also little turning vanes like Rockettail

https://h7f7z2r7.stackpathcdn.com/si...?itok=v2QAJuEI

The problem (for me) is that they are generally tested as a complete kit with underskirts, wheel covers, and other aero aids.

I also won't have a smooth top to the ambulance. I'm planning about 1400 watts of solar and at least one powered vent.

Thanks for the reasoning on why not a truck. Low access height does mean you will have wheel arches to contend with.

You need to check on jurisdictions, our ambulances sometimes have the side door, but always have the pass through. Everyone specs out their needs differently.

6mpg isn't bad for something driven with two pedal conditions: full on and full off. I suspect they would get 12-13 driven sanely which is what I got dragging my big boxy unaerodynamic toy hauler.

Solar on top shouldnt add to much friction drag as compaired to a/c and emergency access mandates.

better
 

From what Hucho shared in his chapter on commercial vehicles, and NASA's reporting, the Daimler-Benz Freightliner would have the advantage.
Daimler's design blows a bigger hole for the box to trail behind, and that added width and height better takes more of the leading edge hit, than the horrible face of the box.
Ideally, the cab would be just as big as the box, as with Tesla's Semi/ NASA's semi, most current Class-8 rigs operating at a profit.
It's the difference between Cd 0.89 and Cd 0.41.

The Finnish way
 

You're people are smarter than our people!:p

air deflector
 

For sure!
If you could seal as much of the gap between cab and box, that would also show. ( delta-Cd 0.016 on my pickup )
Also, extend the box sides down even with the bottom elevation of the running boards / step.
Wheel arches?

I'll point out that the purpose of an ambulance isn't to get great fuel economy.

Yes, I will have wheel arches but I’m willing to put up with them for a low step-in height. One design I’ve seen that seems to work well is to leave the two jump seats over the wheel wells in the final conversion with a flip up table between them for dining. That not only gives seating for eating but also gives two certified seats with seatbelts to allow passengers to legally ride in the back.

Attachment 31051

Some ambulance layouts work better than others for camper conversions. The ambulance above isn’t ideal due to the tall vertical outside cabinet with the yellow X. That would need to come out to put a bed across the back.

Yes, every ambulance is a bit different. The only ambulanced I’ve seen for sale without a side door are Red Cross vehicles. There are a bunch of these trucks for sale right now (Mid-2000 Fords with the 6.0L Powerstroke) Although advertised as ambulances they aren’t really. They are ambulance bodies that are basically empty inside and used for delivering disaster supplies.

https://i.imgur.com/teRbDK4.jpeg

This friend does not drive with the gas pedal as an on / off switch. That MPG is getting on I-75 and setting the cruise at 60 mph. That early Ford 6.8L V10 2 valve was pretty legendary for bad fuel economy. It doesn’t show up in vehicles small enough for EPA rating much but a 2012 E350 passenger van with the more advanced 6.6L V10 3 valve is rated at 10 mpg city / 13 mpg highway. makes 6 mpg seem more reasonable in a huge RV

True. When I added solar panels to my current van I didn’t see much of a fuel economy hit. (Mine are framed in 80/20 and set underneath a ladder rack) I do think it might disturb flow enough to make something like the Michelin top fairing worthless.

Front. In accordance with aerohead's suggestion, the 'inflatable' part was to fill the van/cab gap.

You last example has the overcab deflector already but no opportunity on the edges. It would need the doors reframed or padded out.

I'm actually looking at raising the steps or increasing tire size. This will not be a on-road only vehicle. I'm not looking for a rock-crawler but it needs to be handle forest service roads

http://3rd-st.com/Darpa/rough_road2.jpg

M2 ambulances come standard with 19.5 inch wheels. I'll have to see what is required to fit 22.5 inch wheels. Nothing extreme like this truck

https://www.ambunet.com/wp-content/u...river-Side.jpg

That example would need an ogive curve that follows the sweep of the opening door and then goes convex at 4% of the overall width.

Treat yourself to this

https://i.insider.com/5eb18814144192...36&format=jpeg

Seriously though, I'm getting excited for your retirement plans. Swing by and visit Silverton when you embark and I'll send some beers along for your travels.

$700K !!!! I could buy 6 rental houses with the difference in vehicle costs.


Thanks. I do make it down that way every now and then but usually on short notice.

Everything seems to be more expensive when it's meant for motorhomes and campers.

a look at Cd 0.38
 

https://ecomodder.com/forum/member-a...here-money.jpghttps://ecomodder.com/forum/member-a...nt-attacks.jpghttps://ecomodder.com/forum/member-a...-windkanal.jpghere's a link to a dated Mitsubishi box truck worth looking at. Some box truck at the time were near Cd 0.90.
https://ecomodder.com/forum/member-a...aero-truck.jpg
You can get away with murder at the front, but gaps are expensive, and transitions to the 'roof' need to be 'tuned'. You'll notice flow separation on the roof of the trailer van.
On the way to see the Dynaxion Car, at Harrah's Auto Museum, Reno, Nevada, I snapped this shot of leading-edge 2-D flow separation on a bridge abutment under a bridge over the Truckee River. It offers a clue as to aerodynamic challenges with 'hard' edges.
Finally, Hucho's iconic image of a squareback wake, which you'll never find used in nature.

https://ecomodder.com/forum/attachme...1&d=1627058664

We'll cheap out on the formwork for the abutment, but people can see the brackets so we'll make them Art Deco Streamlined.

And those forward-control trucks are quite harder to streamline than the average American truck with a conventional cab.

A Freightliner FLD - that is step back in time! (Produced from 1987 - 2010) Freightliner's first "aerodynamic" truck build before Freightliner had their own wind tunnel.

Which is part of the problem. Plenty of things that "look" like they should be aerodynamic aren't actually. For example you may think extending side fairings on a truck back to the rear wheels would be better than a short fairing. However, that isn't always the case. The early full wheel to wheel fairing on a Cascadia is less aerodynamic than the later model short fairing that stops even with the cab extenders.

https://orion.soarr.com/photos/16019...cascadia.3.jpg

https://www.imanpro.net/pub/co/dot/p...20200316104950

Well - I have an ambulance.

2011 Chevy Express 4500 with the 6.6L Duramax and 6 speed auto.
110K miles / 4200 hours

Now I just have to get it home. (It is in North Carolina)


https://ecomodder.com/forum/attachme...3&d=1647478971

What's the plan?

Sure that box would be a good base for a tiny house conversion. I guess you could take some good inspiration from those people who convert prefabricated sheds into tiny houses.

I've got paternity leave pending...

To get it back to OR? It will be up on a shipping load board tomorrow. The dealer thinks it will cost about $2500 to ship which is less than $1 per mile. That would be about what it would cost me to drive it back solo and less than flying my dad in for another father / son cross country drive.

If it doesn't get picked up I'll be back in NC in a month and will drive it back. I still have a week of vacation to burn by the end of April. That is just a poor use of vacation days

Buck a mile sounds right based on all the vehicles I had to arrange but never with a freight company, it was all vehicle transport on an auto carrier. Gonna suck up 1/2 or more of a flatbed, lowboy cross country, I dunno. Any prices on specialized auto transport and how flexible are you on delivery city like perhaps SACTO

The dealer I bought it from buys a lot of class 4 - 8 trucks out of the Southwest. He ships to all 50 states so he knows the shipping game

(This ambulance came out of California).

[the movie Vanishing Point]

I suppose it would be obvious to have it delivered out of CALI then?

The truck physically sits in North Carolina today. This dealer bought 3 of these ambulances last fall and had them shipped from CA to NC. (He said it cost $1600 per vehicle back then)

I am very hesitant to buy a truck like this sight-unseen. I didn't expect to buy this truck due to the location but it was in too good of shape to pass up. Not only is this truck immaculate outside - it is fantastic underneath as well. Looking at it up on a lift this is the most rust free vehicle I've seen. No fluid leaks either. The dealer also runs a HD truck shop and it has all new fluids, filters, brakes, and 6 new tires.

It is also the lowest hour ambulance I've found in my ~ 1 year search. Most low mile ambulances have very high hours from the crews idling them all shift. It is crazy to see how many ambulances with 200K miles or less that are advertised with replacement engines.

EDIT: It was also easy to insure. One thing that always pops up on campervan forums is how hard it is to get insurance on an ambulance insurance companies refuse to write policies for them. The general advise is to insure convert the title to an RV. That is not the case. I called Progressive, told them what I had, they said I couldn't get a personal policy but their commercial group would be happy to insure it, they transferred me and it took about 15 minutes.

I am aware of where it is currently, I completely understand the complexity of getting it to where you are, in addition to purchasing it without a good level of trust. One van I had paid transport for Jobcorps had a tree growing out of the engine compartment which wasn't in the picture on the sale. Try getting a tree trimmer onto a secure military site sometime from across the country, then rescheduling that transport for an unspecified pick up date but with a drop dead delivery date a week in the future.
Oh and if you miss your targets, your organization gets suspended from further procurement for an unspecified time.

You don't agree it would have been nice if it was still in socal, that's OK.