bus aerodynamics

if money were no object, i've been dreaming up a boattail i want to try to lessen the drag
 
turf said:
if money were no object, i've been dreaming up a boattail i want to try to lessen the drag
Click to expand...


According to that article, you do not need a full boat tail, just 24-32 inches. Heck, you have probably seen tractor-trailers with those "box-kite"-like farings on the back end. That is what they are for ... to reduce the drag on the end.
 
this isnt a new article.

i believe it states that about half of the drag comes from the front, and half comes from the back. a tail only should be 5% fuel savings. wheel covers will get you another 2-3%
 
I've been thinking that a 10% fuel saving would amount to a lot of money in the end - I doubled my mileage from 3 1/2 mpg to 7 mpg by adding a concave scoop to the front of an awkward load on one truck I had, so I know from experience how much an afternoon's work can save in fuel - I'm likely going to be doing a roof raise when I get my bus and I'll seriously consider getting rid of the typical flat forehead of a school bus and do a nice swooping roof line up to the transition, perhaps over an area 10' long - an air dam under the bumper , plus some hub caps ( who doesn't like a shiny set of hub caps on an old vehicle? ) - I haven't looked in to a fairing at the back yet, but if it can save even 1 or 2%, long term, would be worth a bit of fabrication - I don't know if a 'bug shield' on the hood would help or not, but it might help direct the airflow past that flat sail of the windshield - apparently mirrors can add significant drag, so perhaps a bit less ambitious set of mirrors would help along with one or two back up cameras - I recently put a new set of trailer towing mirrors on my pickup - they extend outwards when you need them and give a nice area of view - not as good as a set of West Coast mirrors maybe, but pretty good and certainly less drag than the West Coast mirrors - so if all that gets me a 10% saving, I'll save a couple hundred dollars each time I travel north in the winter
 
Sleddgracer said:
I've been thinking that a 10% fuel saving would amount to a lot of money in the end - I doubled my mileage from 3 1/2 mpg to 7 mpg by adding a concave scoop to the front of an awkward load on one truck I had, so I know from experience how much an afternoon's work can save in fuel - I'm likely going to be doing a roof raise when I get my bus and I'll seriously consider getting rid of the typical flat forehead of a school bus and do a nice swooping roof line up to the transition, perhaps over an area 10' long - an air dam under the bumper , plus some hub caps ( who doesn't like a shiny set of hub caps on an old vehicle? ) - I haven't looked in to a fairing at the back yet, but if it can save even 1 or 2%, long term, would be worth a bit of fabrication - I don't know if a 'bug shield' on the hood would help or not, but it might help direct the airflow past that flat sail of the windshield - apparently mirrors can add significant drag, so perhaps a bit less ambitious set of mirrors would help along with one or two back up cameras - I recently put a new set of trailer towing mirrors on my pickup - they extend outwards when you need them and give a nice area of view - not as good as a set of West Coast mirrors maybe, but pretty good and certainly less drag than the West Coast mirrors - so if all that gets me a 10% saving, I'll save a couple hundred dollars each time I travel north in the winter
Click to expand...

I doubt there is a 10% difference, but a 4% difference over 1,000,000 miles would be substantial. Probably negligible results for the mileage we see. At $3/g you would spend $300000 in fuel at 10mpg. 4% over a million saves you $12k, 10% saves you $30k
 
o1marc said:
I doubt there is a 10% difference, but a 4% difference over 1,000,000 miles would be substantial. Probably negligible results for the mileage we see. At $3/g you would spend $300000 in fuel at 10mpg. 4% over a million saves you $12k, 10% saves you $30k
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I just spent too much of my day reading about improving aerodynamics ( thankfully it's been a slow day here at the kennels ) - sites about improving a semi's mileage, a couple of old skoolie threads about the subject of improving air resistance on buses - I'm planning on a roof raise and that will give me the opportunity to alter the profile of the roof line, rounding off both front and back, at no or little extra cost ( labour not taken into account ) -using conveyor belting to make a front air dam, side skirts, and an abbreviated tail to reduce wind turbulence at the back, will make quite a difference - belting can be low to the ground for maximum effect and is flexible if more ground clearance is needed - I'm pretty sure I can get all the belting I need for a case of beer - so the cost of going for some aerodynamic improvements will be small and going by the improvements in mileage I achieved with a simple scoop on the awkward load I mentioned before, I think a 10% improvement is reachable - with the $6.40 we are paying here for an Imperial gal of cheap gas, that 10%, or even less of an improvement, will make quite a difference on a 2000 or 3000 mile trip - if it's only 10%, I'll could save $240 on one 3000 mile trip
 
Ronnie said:
I wonder how much difference the tails on trucks actually do? a few percent, 10%, 20%?
Click to expand...


The study did not break down the effectiveness of the boat tails alone but in conjunction with gap closure devices (busses have no gap) and skirts (some have low skirts). The total the study quotes is up to 14% fuel savings.
 
Thanks for the discussion. Google did not show me what a "boat tail" is. Can someone post a pic? I want a RE type D because it provides the greatest amount of underfloor storage, but gives the aerodynamics of driving a brick. Is handling also a byproduct of aerodynamics? i.e. will a vehicle with better aerodynamics have better handling characteristics? Hub caps sound like an easy to do thing. I remember during the "oil crisis" in the 70's there were car designs that covered up the top half of the rear wheels in an attempt to get better mpg. Has anyone considered enclosing the bottom of the bus completely (maybe its called a belly pan)? While reading about vans I heard that this gives 5-7% better mpg. If you compare the Greyhound buses with our skoolies, you will find that the windows don't open on the GH busses and provide a really smooth, slick surface down the side. It is not something that most people would address if you have finished a conversion, but if you are going to be putting significant miles on the bus and are at the beginning of your conversion, it might be something to consider. A lot trucks and cars come with wheel wells lined with hard plastic...is this helpful?


Maybe people raising the tops should think about this:
serveimage



I know it is not reasonable to compare Greyhound with our skoolies. GH buses use something like unibody construction, which makes it lighter, uses aluminum in a lot of places, so also is lighter, etc. I sometimes "go greyhound" and the service people tell me that their buses get 10-11 mph at highway speeds, usually 65mph or more. Still maybe there is something to learn from them.


I am not an autocad person, but a long-time-ago friend of mine could speak "Autocad" better than he could speak English. He had some kind of add-in to AC that measured drag of an object....is anyone familiar with this?
 
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Did you notice it said flat front was better then dog nose? I saw that and been thinking about it since. I really do not like the look of flat front. A Crown bus yes or an old GM.

I have an old "Silver Streak" camping trailer and it is build with a full belly pan. From a maintenance standpoint seems like a lot of trouble for a bus. An airdam might be better, and bring the side skirts lower?

Must say looking at my skoolie it is not clean, ie two rooftop a/c, two roof vents, solar panels, low railing around a deck area, and plumbing vent pipe.
 
'was doing some more searching last night and came across some new technology being used on heavy trucks - one is a guide installed under the truck that steers the air past the outside of the rear wheels - it starts narrow and gradually widens giving sort of a funnel effect it looks like - truckers claim it adds stability in cross winds and better handling on the road - another idea was an air dam installed in front of the rear axle that forces the air to the outside of the dual wheels
 
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