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David Evans (Dmd)
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Post Number: 654
Registered: 10-2004
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Posted on Saturday, December 10, 2011 - 10:28 pm:   

http://www.sti.nasa.gov/tto/Spinoff2008/t_3.html Been doing some site surfing and always interested in better MPG. our late 40's design is pretty slippery for a bus and i think it has alot to do with the good fuel milage. I also think when we had the 4-71 the cruising speed of less than 60 was a big factor. now that we can go quicker, we dont. Mostely. I wonder how towing a trailer will affect our milage? Also google MAN buses/trucks areodynamics.
les marston (Les_marston)
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Posted on Saturday, December 10, 2011 - 11:48 pm:   

It would be very interesting to put these airtabs on a coach just to see what difference they would make. I wonder what the return on investment would be.
thanks for this article
FAST FRED (Fast_fred)
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Posted on Sunday, December 11, 2011 - 7:05 am:   

"I wonder what the return on investment would be.'

Close to zero in terms of fuel savings , at 5000-10,000- miles per year , rather than 100,000+ for an OTR truck.

However the added stability claims are interesting.

FF
Bruce Henderson (Oonrahnjay)
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Posted on Sunday, December 11, 2011 - 9:21 am:   

I clicked on this thread, not thinking that I'd find anything useful, but just to see who would put the words "bus" and "aerodynamic" in the same sentence!
les marston (Les_marston)
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Posted on Sunday, December 11, 2011 - 11:39 am:   

Fred
Lets see
6829 gallons per year based on 100 k miles traveled by trucks vs. 680 gallons for 10 k traveled in a coach... that is still 680 gallons less fuel per year
680 gallons times $350 per gallon= $2380 per year.

I see your point about there being no return on investment

Bruce
Yup we drive bricks on wheels
Sean Welsh (Sean)
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Posted on Sunday, December 11, 2011 - 6:21 pm:   

Les, I'm not sure I understand where you are getting your numbers. My coach burns just under 1,600 gallons to go 10,000 miles. No way Airtabs or anything else is going to save 680 gallons and bring that number down to 920 gallons. That would take my mileage from 6.3 mpg to 10.9 mpg.

The article said many of the gains came from decreasing cab-to-trailer gap and fairing the enormous open area under the trailer -- gains that simply do not apply to motorcoaches in general. So you can't just take the 100,000 mile number they tossed out for the aggregate improvement in tractor-trailer mileage and divide by ten to get coach improvement...

-Sean
http://OurOdyssey.BlogSpot.com
les marston (Les_marston)
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Posted on Sunday, December 11, 2011 - 7:11 pm:   

On reading the article again, I am sure you are right.
At the price of fuel it is a happy thought to even gain a small percentage of fuel economy.
I have often thought that if there was some way to funnel air to the back of the coach to reduce the low pressure drag that it would have to have a positive effect.
Gus Causbie (Gusc)
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Post Number: 1407
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Posted on Sunday, December 11, 2011 - 7:59 pm:   

It is amusing to read about aerodynamics concerning a vehicle with a flat front!!
David Evans (Dmd)
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Posted on Sunday, December 11, 2011 - 10:12 pm:   

I think after the war, there were a bunch of engineers with lots of steel and time and newfound knowledge. Our front is rounded both ways, the rear is sloped teardrop style. some airdams and some shrinkwrap panels underneath, 50 mph and i am breaking 11 mpg!;) cant post the front end shot.
FAST FRED (Fast_fred)
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Posted on Monday, December 12, 2011 - 6:52 am:   

On the Euro trucks they use loads of axles with only a single tire on each side.

Any fuel savings $$$$ would be confiscated at every toll booth.

FF
Brian Evans (Bevans6)
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Posted on Monday, December 12, 2011 - 2:01 pm:   

I have Airtabs on my trailer, I had them on the previous trailer as well. True story - I did a run from Nova Scotia to Ontario this summer, pulling the brand new trailer empty. I got horrible gas mileage - around 7 to 7.5 mpg. I had a seriously hard time maintaining 60 mph, I did most of the trip in 4th gear around 55 mph. I just could not understand this - I had gotten lousy mileage on the way out, but I put that down to a 3,000 lb load and some head winds. I had towed my previous trailer, even bigger and heavier, for many thousands of miles and averaged around 9 mpg. I ordered and installed the Airtabs as soon as I could. Three weeks later I took another trip, to deliver a car to Kingston, around a 2,000 lb load. I got 9.4 mpg and I was able to run 60 mph in fifth gear for most of the trip. No funky winds either trip, pretty honest back to back comparison. 25% improvement in fuel mileage. There is a reason for that rather astounding number - it was obvious that the increase in drag from the new trailer - which while lighter and shorter was a foot taller and therefore had a larger cross-section - had take the load past the point where the engine was able to pull it, and had taken the fuel curve of the engine to a place it didn't want to go. I was literally full throttle, fourth gear, 2500 rpm for 50% of the 7 mpg trip. Hills, and there are a lot of them between Quebec and Moncton, had me in third gear, full throttle, 50 mph.

Bottom line - I saw a real 25% improvement in fuel mileage with the addition of air tabs, even if that is not going to be matched by many, or by me on other trips, probably. My previous trailer saw a solid 15% improvement over tens of thousands of miles. Rocket science that works!
Brian Evans (Bevans6)
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Posted on Monday, December 12, 2011 - 2:29 pm:   

Just for fun I did the ROI. $225 for the air tabs. $4.75 per US gallon of Canadian gas. $0.505 per mile at 9.4 mpg, and $0.678 per mile at 7 mpg, difference of $0.173 per mile, so the $225 gets paid back in 1300 miles.

Again, not suggesting this works for anything other than a tallish car trailer being towed by a Dodge Ram with a Hemi, but I do think that gains of some sort are expected, probably in the 10% range.

Brian
David Dulmage (Daved)
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Posted on Friday, December 16, 2011 - 3:27 pm:   

Not unlike the aerodynamics work done by Chrysler Corporation in the early 1930s, when they determined most car designs of the period had less drag with the bodies mounted backwards. Hence the Chrysler Airflow which didn't sell. Glad to see NASA confirmed the information.
Buswarrior (Buswarrior)
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Registered: 12-2000
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Posted on Friday, December 16, 2011 - 11:58 pm:   

Wasn't there a busnut who was a distributor for Airtabs?

happy coaching!
buswarrior

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