Bus roof raise aero
 

https://static.wixstatic.com/media/7..._1570_s_2.webp

https://www.washingtonpost.com/wp-ap...6JJA.jpg&w=916

I'm doing a bus build and I am raising the roof about 22"

Now the first image is what most people ha e been going to here lately. And leaving the back a strait up lift. I'm thinking I like the second strait up blunt raise for the front and will slope and transition the rear over my bed room. Or would sloping both front and rear be beneficial?

As I take it the rear would be much more important than the front. A blunt raise would alow my to mount a big screen TV above the driver head. But if its beneficial I could slope the front as well and live with a small screen.

Thoughts?

How much are you going to drive it?

Quite a bit probably. This won't be a "tiny house" its an rv/tow rig ill be using at least once a month to pull my rock crawlers to offroad parks.

Just wondering if the strait up roof rasie would hurt me at all.

Define hurt — 10mpg vs 11mpg?

A lot depends on the floor plan of the interior, but your first example has a saddle-shaped curve. The ideal is a bluff prow that transitions smoothly into center section. It's not really bad it's just pointless and robs interior space.

Make it like an Airstream or U-Haul trailer.

Since you posted in Aerodynamics note that the front is only 25-30% of the total drag.

https://ecomodder.com/forum/member-f...dynamics-c.jpg

Tow vehicle you say?

https://ecomodder.com/forum/member-f...99-cvwihdt.jpg

I'm no expert (hehe), but I'd assume a completely flat front end would just push all the air straight up, rather than guiding it over the roof or down the sides. Rounded transitions would make a lot of difference at speed. The larger the better.

See the attached rough concept.

If this is for an RV, have you studied or given thought to gutting the raised floor system?

I'm not sure how all the working parts are organized under there besides dedicated luggage areas between the wheelbase, but it seems lowering the floor could be just as labor intensive as raising the roof, plus the "A" in CdA is the same or lower should you taper off the back as shown in concept sketch.

In between the wheels the lower half of the coach interior would be "U-shaped" in cross section but the rest of the time it should just be a rectangle.

Don't think of this as removing the floor, think of it as lowering the floor.

I'm guessing that you are running electrical and plumbing under there for your new layout, leave a service utility cavity but instead of 36" make it 12".

Drive shaft and exhaust pan tunnel raises will be the immovable fixtures to work around.

Do you already have the bus? If not you may consider the round top bluebirds which generally went further between refuels than the flat nosed dittos that I drove.

You might not be able to lower the floor as much as I was wondering about.

See attached image.

https://www.pinterest.com/pin/356488126734879948/

Maybe there is wasted room in there anyway?

Flat floor?

Minimization of wheel arches in passenger compartment?

There might be as much as a foot of suspension travel you can ignore because youre not dividing time between preschool and high school load weights.

Nor I (I just parrot back what I've heard here) but I'd wager that an air (particle/voxel) is going to the nearest edge, there's twice as much sides as top and the bottom will exhibit vena contracta.

No need to correct kach22i, he did himself. I'd strongly consider shortening the roof to leave a back porch.

https://ecomodder.com/forum/member-f...box-cavity.jpg

I say go big it's not like your driving it to work every day.

This is from my Christmas card in the 1980s

https://ecomodder.com/forum/member-f...4-1st-copy.jpg

That's a sliding security grating at the bottom of the steps, there was to be an oak entry door at the top.

edit:
Wait a minute! I just realized Randy Grubb stole the Type II over White 300 design for his Deco-liner. Since it's all a fantasy, the engine is a flathead flat 12 amidships under the living-room floor.

https://ecomodder.com/forum/member-f...icle38to39.jpg

Yes. 40' international, dt466 pusher.

Can't lower the floor. Will be adding side skirts.

I have allready stripped the windows out and working on stripping the interior.

I can't lower the floor. Actually the floor is getting thicker because of the insulation.

I will be adding side skirts and sloping the roof in the rear. Just dont know what to do with the front.

Given the tow vehicle status does it make more sense to raise or lower it? Air bags? It would be cool to be able to lay frame in a school bus.

But whatever, ditch that fiberglass end cap with the red and yellow lights for something that sweeps back from the windshield. There is a smallish radius on the front edges, look to European trucks for their aero add-ons. Review bluebunny's thread here: canard for bluff bodied box

The rear view mirrors project forward which is good. Ditch the bumper mirror.

"95 metro 3cly 5speed 45mpg" :thumbup:

The degree of rounding the front needs is actually quite small. A radius equal 4% of the width has been mentioned before. That's a 4" radius on a 100" wide vehicle. Just need to get the air to flow smoothly to the sides and top.

Add some rear taper and you're about as good as you can get. Look at a Monaco Vesta, or Vixen motorhome. Both were designed in a wind tunnel. The Vesta had LOTS of resources behind it, way more than you have I assume, and it really doesn't have an unusual shape or features. You probably shouldn't either.

Oh yeah. Slow down.

thoughts
 

* With no leading edge radii a bus will be Cd 0.88.
* With leading edge radii equal to 5% of the square-root of the frontal area, the drag will be Cd 0.36.
* With the 'Stromform' front, Cd 0.34. And the most difficult and expensive build.
-----------------------------------------------------------------------------------
* Test data exist for buses with 5-degree boat-tailing, at top, sides, and bottom. The further back, the lower the drag. Diminishing returns at some length.
* If 'soft' edges are incorporated into the tail, you can kill off any potential vortex drag.
* If boat-tailing is done as an 'add-on', the legal limit is 60-inches of added length.

rough concept
 

The rough concept is NASA-esque. The air would like that.:)

Keeping the area low would probably do just as much as improving aerodynamics, yes?

https://www.pinterest.com/pin/745768.../?d=t&mt=login
http://forums.pelicanparts.com/uploa...1605730854.jpg

EDIT:

Attached a second concept where the roof is tilted back. Same original roof, just tilted because side windows are removed.

Mattress near floor, with enough room to sit up in bed, but not stand or jump on bed at about 5 foot ceiling.

Shower just enough headroom a +6 foot (allowed in building code at one time), dining area at 7 foot, living area at 8 foot proper.

Think like a yacht designer.

The thing that ruins it for RV's is all the junk they put on the roof like air-conditioners etc.

Stuff the A/C unit in lower part between the wheelbase in a well ventilated chamber, louvers or mesh screen panel covering.

I like the box-cavity rear porch area Freebeard mused about, would totally work. Heck, put a yacht-like balcony in there like a train car.

https://www.pinterest.com/pin/440226932301129829/
https://i.pinimg.com/originals/15/27...0acbd9ec7b.jpg

I guess you would want to take a look at the current generation of Marcopolo urban transit buses in order to get some inspiration for aero mods.

Hotsite - Comienzo - MP 60 BRS - Marcopolo Ônibus

I was hoping for more from them, no box cavity, still has wheel flares, and those front corners could stand to be more rounded in my opinion.

Is that a city bus or a highway cursing bus design?

We should perhaps be looking a long distance highway cruisers, yes?

I did find the below doing a search on the topic, looks like they did more to the fronts than the rears, which is not very encouraging.

Aerodynamic Exterior Body Design of Bus
https://www.ijser.org/paper/Aerodyna...gn-of-Bus.html
https://www.ijser.org/paper/Aerodyna.../Image_001.jpg
EDIT:

This is cool.

Teardrop Cars
CLASSIC CARS
Aerodynamically, the shape of a drop of water faces the least air resistance, so in the years running up to the Second World War, numerous ŠKODA vehicles strove to replicate this “teardrop” look.
https://www.skoda-storyboard.com/en/...teardrop-cars/
http://forums.pelicanparts.com/uploa...1605981642.jpg
AUTOCULT - SKODA - 532 AUTOBAHNBUS CZECH REPUBLIC AUTOBUS 1938
https://www.carmodel.com/autocult/at...us-1938/128098
http://forums.pelicanparts.com/uploa...1605982045.jpg
http://forums.pelicanparts.com/uploa...1605982045.jpg
http://forums.pelicanparts.com/uploa...1605982045.jpg
http://forums.pelicanparts.com/uploa...1605982045.jpg

These are all nice, but is it known how much length can be added to a 40ft bus? Maybe five feet?

The hardest limitation is the right front corner. Maybe the door could be modified to something like the GMC Motorama trucks.

https://i.pinimg.com/originals/aa/29...2d8fd75252.jpg
https://i.pinimg.com/originals/aa/29...2d8fd75252.jpg[/URL][/URL]

https://ecomodder.com/forum/showthre...ure-33061.html
Apparently, they are eliminating the vertical foils at corners and or scoops normally found on European racing trucks (see below).

https://www.eurotransport.de/artikel...-11170089.html
http://forums.pelicanparts.com/uploa...1605989291.jpg
http://forums.pelicanparts.com/uploa...1605989291.jpg


May 8, 2013
Scania - Streamline Aerodynamics
https://www.youtube.com/watch?v=uXF3meOHr08

Leading Edge Radius
https://www.sciencedirect.com/topics...ng-edge-radius
https://ars.els-cdn.com/content/imag...0750651318.gif

https://www.jstor.org/stable/44718757?seq=1
https://encrypted-tbn0.gstatic.com/i...Eb2iQ&usqp=CAU

Legally I think it's 65ft for any vehicle. 40ft is the arbitrary length for non articulated to make typical street corner right turns in a city without running onto the opposing traffic lane, left turns in Britain.

No doubt it varies by jurisdiction, my recollection is 45ft for a single vehicle and 65ft for any combination, up to three trailers.

That's a city bus, yet it seems to have been inspired by the Marcopolo highway cruisers.

Some retro inspiration.

Random TRANSPORTATION pictures - Page 2412 - Pelican Parts Forums
http://forums.pelicanparts.com/uploa...1606435671.jpg

magic radii
 

Hucho commented that, during development of the VW Vanagon, in 1969, when tested at full-scale, flow could remain attached with smaller radii than in scale-model testing. 4.5% of the square-root of frontal area was sufficient.

Thank you.

It can be more complex than that with side view mirrors, visors, radiator grilles and so forth mucking things up, at least that's my walk away from the video.

And what ever you do, don't crack open a window.:D

Worse yet opening a window and popping open the door. Can you say tornado?