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Old 10-14-2019, 02:23 PM   #181 (permalink)
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A couple questions

Hi Orbywan,

I am trying to do a similar boat tail on a short bus that I have. I know this is an old thread but if you were willing I would love to know:

- If the fuel savings seemed to pan out over the long run?
- And do you know the actual degree taper of the boat tail you built? I tried to calculate it from the photos but I am not sure that is accurate.

Thanks, Bill

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Old 10-14-2019, 11:17 PM   #182 (permalink)
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Quote:
Originally Posted by stcyrwm View Post
Hi Orbywan,
- If the fuel savings seemed to pan out over the long run?
- And do you know the actual degree taper of the boat tail you built? I tried to calculate it from the photos but I am not sure that is accurate.
Thanks, Bill
Hey Bill, as i recall he had about 17' of taper to the BoatTail.
As for his mileage gains, i remembered he also slowed his speed down around 55 and traveled a lot of older state hwys and such so he could maintain the gains and stayed off of the interstates as much as possible.

Good luck with yours. You can also use the template here in the tools and get the degree of angle that best fits your vehicle...

:{)
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Old 10-14-2019, 11:57 PM   #183 (permalink)
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Quote:
You can also use the template here in the tools and get the degree of angle that best fits your vehicle...
Oh, noes. Not again.
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Old 10-15-2019, 12:19 AM   #184 (permalink)
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Quote:
Originally Posted by HHOTDI View Post
Hey Bill, as i recall he had about 17' of taper to the BoatTail.
As for his mileage gains, i remembered he also slowed his speed down around 55 and traveled a lot of older state hwys and such so he could maintain the gains and stayed off of the interstates as much as possible.

Good luck with yours. You can also use the template here in the tools and get the degree of angle that best fits your vehicle...

:{)
Thanks for the confirmation of that. That matches my calcs based on his photos and of the NASA aerodynamic van boattail also!
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Old 10-15-2019, 12:30 AM   #185 (permalink)
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very cool! looks like it was built to perfect spec!
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Old 10-16-2019, 12:39 PM   #186 (permalink)
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very cool! looks like it was built to perfect spec!
A pair of notes on use:

1). Baseline MPG: a loop outwards from a truckstop about 45-miles from home. Top the fuel, scale the beast, correct the tire pressure according to actual load. An RV also needs fresh water supply and propane filled to capacity. The drive needs be 50-100 miles outbound from that point (as warmup is complete) and choice of turnaround ideally with no stops.

Full-time use of cruise control. 59-mph. Top off fuel second time at same pump, to first auto shut off. No variations to this from test to test. Only season/weather.


2). A trip plan always must include the time of departure. Traffic volume increases nationwide on the Interstates thru 1100 and doesn’t dissipate enough to be a non-factor until 2300. Past road choice it’s the single most important factor for highest average mph (and mpg) for a given cruise control set speed.

IOW, I’ll leave at 0400. You’ll leave at 0900. With ZERO changes, the early departure will ALWAYS see higher mpg. Fewer changes from steady-state in a single lane. That’s the goal.

RV’ers are notorious for leaving after work and traveling into the night. Wrong choice. Safety & FE.

The machine is in important. But driver and actual use can trump it. Aero won’t overcome bad choices.

I do it for a living. Constant reminders of the penalties. There are times when with an additional TEN TONS in the trailer my mpg can be higher. And I don’t mean a few tenths.

.

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