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Old 12-19-2015, 08:41 PM   #71
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Originally Posted by somewhereinusa View Post
I'd like to keep this post alive...
Yeah, me too. I'm not sure though if reviving an 11 year old thread will be frowned on, but I'll risk it. I was doing some searching and the only really good thread that came up was this one, so I figured why not keep everything in one place.

One of the pages I came across was this one. Mostly focuses on trucks, but there's some decent info on busses.
https://www.tc.gc.ca/eng/programs/en...-eng-2939.html

I also came across this.
https://www.google.com/search?q=gree...6oBaYQ_AUICCgC

This seems kind of a 'no-brainer', as every image of bus aerodynamics (thermo, CAD, or whatever) seems to show massive turbulence above the front window, and smoothing that turbulence is the goal.

However, I was remembering an article I read in some car magazine years ago, and they were interviewing some powertrain engineer at one of the major auto makers. The quote was something like "Every engineer I know would sell their mothers soul to the devil to get another 2 miles per gallon." It seems to me that if a specific product or design worked, why wouldn't manufacturers incorporate it in their design? If you can give your product a mpg advantage over your competitors product, at a negligible cost, wouldn't that help you sell more busses to cash strapped school districts? Selling long term savings would be a good thing, wouldn't it?

So it's been a year + since this thread was active, and lots of ideas had been thrown around previous to that. I'm wondering if anybody had experimented further with any side skirts, air dams, under-body stuff, or whatever. Bumper modification was mentioned, and there are a lot of newer trucks on the road with aerodynamic bumpers...maybe a retrofit?

Anybody got anything new?
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Old 12-20-2015, 06:40 AM   #72
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You will notice all of the newer motorcoach designs incorporate pretty smooth lines with a lot of slope to the front ends and windshields.

School buses are also a little bit smoother than they used to be.

But the reality in the school bus world is they spend 95% of their service life on surface streets at speeds less than 35 MPH. At those speeds aerodynamics really don't come into play.

I own two different Avion travel trailers. One is a 26' tandem axle and the other is a 34.5' tri-axle. The tri-axle weighs about 2,000 lbs. more than the tandem axle.

I have towed both with two different tow vehicles. One is a 1965 Travelall with the SV304 and four speed and the other one is a 1993 Suburban with the 5.7L and 4L80E. I have towed both trailers enough miles to know that the fuel to tow them is virtually the same. Yes it takes a little longer to get up hills with the larger trailer but the difference in fuel use is so little that it could be considered statistically the same.

Since both have the same frontal area and the same drag on the roof and sides (A/C, awnings, etc.) I have decided that frontal area has more to do with fuel consumption than weight.

In a vehicle or a combination that weighs in excess of 14,000 lbs., reducing weight by 100 lbs. is not going to make any real difference in fuel consumption.

Even if you do reduce some of the excess drag and clean up some of the skirt areas to improve air flow the improvements would be minimal in relation to the cost.

I have also discovered that reducing my speed from an average of 65 MPH to 55 MPH increased my fuel mileage by almost 20%. Which is all driven by the frontal area. When you are pulling or pushing a brick it takes a lot of dead dinosaurs to move it. The faster you go the more dead dinosaurs it is going to take to move it.
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Old 12-20-2015, 12:36 PM   #73
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Originally Posted by cowlitzcoach View Post
You will notice all of the newer motorcoach designs incorporate pretty smooth lines with a lot of slope to the front ends and windshields.

School buses are also a little bit smoother than they used to be.

But the reality in the school bus world is they spend 95% of their service life on surface streets at speeds less than 35 MPH. At those speeds aerodynamics really don't come into play.

I own two different Avion travel trailers. One is a 26' tandem axle and the other is a 34.5' tri-axle. The tri-axle weighs about 2,000 lbs. more than the tandem axle.

I have towed both with two different tow vehicles. One is a 1965 Travelall with the SV304 and four speed and the other one is a 1993 Suburban with the 5.7L and 4L80E. I have towed both trailers enough miles to know that the fuel to tow them is virtually the same. Yes it takes a little longer to get up hills with the larger trailer but the difference in fuel use is so little that it could be considered statistically the same.

Since both have the same frontal area and the same drag on the roof and sides (A/C, awnings, etc.) I have decided that frontal area has more to do with fuel consumption than weight.

In a vehicle or a combination that weighs in excess of 14,000 lbs., reducing weight by 100 lbs. is not going to make any real difference in fuel consumption.

Even if you do reduce some of the excess drag and clean up some of the skirt areas to improve air flow the improvements would be minimal in relation to the cost.

I have also discovered that reducing my speed from an average of 65 MPH to 55 MPH increased my fuel mileage by almost 20%. Which is all driven by the frontal area. When you are pulling or pushing a brick it takes a lot of dead dinosaurs to move it. The faster you go the more dead dinosaurs it is going to take to move it.

Good post. So what you are saying is I should drive faster to take advantage of the aero mods I have made? Just kidding.

When I had a Dodge 3500 crew cab with a 5.9 Cummins, the mileage went from 22mpg @70mph to over 28mpg @ 55mph. I just couldn't drive that slow back then.
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Old 12-20-2015, 12:50 PM   #74
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Aerodynamics aside...most diesels will get the best mpg when kept close to their RPM "sweet spot". Typically about where they produce peak torque. On my 4BT, that is between 1700 & 1800 RPM. Add in some aero effect and you can boost that.
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Old 12-21-2015, 10:03 AM   #75
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Originally Posted by mudpie View Post
The quote was something like "Every engineer I know would sell their mothers soul to the devil to get another 2 miles per gallon."
As an engineer, I thought it'd be interesting to evaluate this claim. See the chart below. It's a little hard to read, so I'll provide a summary and example below. An interesting point on the graph is shown by the yellow and red dashed lines. Apparently going from 6-8 mpg @ $2/gal saves the same amount of money as going from 10-12 mpg @ $5/gal.

Assuming someone is willing to sell their mother's soul to the devil for 2mpg, the best price would come by manipulating two variables. You can either assume a very poor initial fuel economy, or very high fuel prices.

Going from 6mpg to 8mpg at $5/gal means that you'll save $1,000 for every 4,800 miles driven.

If you were to go from 12mpg to 14mpg at $2/gal, you'd have to drive 42,000 miles to save $1,000.


For a more personal example, my bus gets about 10mpg. For the sake of this example, let's hope and pray that diesel prices get back up to $4/gal. I only plan on driving my bus about 5,000 miles per year. I'd say my mother's soul is worth quite a bit, but for the sake of this example let's assign her soul a value of $10,000. I'd have to drive 150,000 miles at $4/gal to get $10,000 in fuel savings with a 2mpg fuel economy increase. That'd take 30 years at 5,000 miles/yr.

If I wanted to get my $10,000 value for her soul in one year (2016), either fuel prices would have to average $120/gal in 2016 or I'd have to drive the bus 240,000 miles in 2016 (assuming $2.50/gal). 240,000 miles is slightly more than 5 times the length of the interstate highway system. Averaging 60 mph, I'd have to drive nearly 11 hours a day for all 366 days of 2016 to get my $10,000 worth of fuel savings for my mother's soul.





So, in summary, I don't really think every engineer would sell their mother's soul to the devil for 2mpg in their skoolie. But people who have poor fuel economy to start with and people in times of very high fuel prices (and people who don't place much value on their mother's soul) might consider it.

Maybe the 2mpg quote was about truckers? Truckers drive a lot of miles and get very low fuel economy. Going from 5mpg to 7mpg for a trucker that drives 150,000 miles per year paying $3/gal on average saves him nearly $26,000 per year.
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Old 12-21-2015, 10:09 AM   #76
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If you want fuel efficiency, look towards the trucking industry. All of your large corporation otr trucks have sleek lines, low profile hoods, super single rears, skirting along the trailer, those goofy wind things on the back of the trailer, and the inserts to go in the tire rims.

Last I heard, one of the regional outfits in the south east(name slips me) was getting a little over 10 mpg average with all of the aero touches, and a speed limit of 55 mph.

Here is a neat article if you want to read more. Cummins and Peterbilt Build a Super Truck - Cummins Peterbilt Tractor Trailer Gets Good Gas Mileage
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Old 12-21-2015, 10:22 AM   #77
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Originally Posted by austin1989us View Post
So, in summary, I don't really think every engineer would sell their mother's soul to the devil for 2mpg. But people who have poor fuel economy to start with and people in places with very high fuel prices (and people who don't place much value on their mother's soul) might consider it.
You're talking one bus. Imagine if you were an engineer at peterbilt, or cummins, or whatever flavor in the trucking industry you wanna choose. IF you could go to your bosses with something with a 2mpg increase, and they could back it up with testing, that would be huge for the company. They would sell a boat load more trucks because while the 8,000 dollars a rig savings isn't worth your mother's soul, multiply that by 1000, 5000, or even 10,000 trucks, and you'll begin to understand where that saying has merit.
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Old 12-21-2015, 10:41 AM   #78
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You're talking one bus. Imagine if you were an engineer at peterbilt, or cummins, or whatever flavor in the trucking industry you wanna choose.
I'd added a bit about truckers in my original post as an edit as you were posting your responses.

2 mpg is a big deal when you go a lot of miles. Most skoolie people don't. I guess I originally was looking at the statement through the lens of a skoolie person and not a fleet manager.

If someone were running a fleet that does 5,000,000 miles per year and is paying $3/gal on average they'd save $1,000,000 per year if they went from 6 mpg to those fancy 10 mpg trucks. The added cost might be worth it, but that'd be up to the company to decide. Assuming 25 trucks going 200,000 miles a year each that they replace in the fleet after 1,000,000 miles. The 10mpg trucks could be $200,000 more expensive than 6mpg trucks and they'd break even at $3/gal provided the trucks performed as advertised and maintenance costs were the same.

If I was running it, I'd do my analysis with $2/gal diesel and divide by at least 2 just to factor in possible increased maintenance costs and mpg not performing as advertised. I wouldn't pay more than $65,000 extra for the fancy trucks.
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Old 12-21-2015, 10:50 AM   #79
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I never was very good at math, but with any luck at all, the diesel engine, tranny and rear axle transplants I have made should take me from about 5 mpg to around 25 at a cost of 15 grand.

So...how far do I have to drive just to break even at say $4 bucks a gallon. And...just how far is the Moon anyway?
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Old 12-21-2015, 10:57 AM   #80
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I never was very good at math, but with any luck at all, the diesel engine, tranny and rear axle transplants I have made should take me from about 5 mpg to around 25 at a cost of 15 grand.

So...how far do I have to drive just to break even at say $4 bucks a gallon. And...just how far is the Moon anyway?
Going from 5 mpg to 25 mpg at $4/gal you'd have to drive 23,437.5 miles to save $15,000 on fuel. The moon is about 238,900 miles away, so that's about 1/10th the way to the moon. The circumference of the earth at the equator is about 24,902 miles. So you're about 1,500 miles shy of driving around the earth on the equator. 1,500 miles is about the distance from Downtown Houston to Downtown Los Angeles if you take I-10.
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