Quote:
Originally Posted by stcyrwm
In the next week I am planning on building a boattail on my 2004 GMC Savana 3500 Shortbus Camper. I am looking at doing something in the 2 to 4 foot range for length. I would like to keep it on the shorter side but could be swayed based on fuel savings. At the moment I am leaning toward a compromise of 3 feet or so.
I am currently getting 11.25 mpg. The engine is the Vortec 6L Short Block V8. Overall length of rig is 20'.
I guess my main question has to do with whether there is an ideal taper for roof, sides and base? My memory from reading through a lot here in the past is that maybe 10 or 12% would be ideal but I wanted to double check that number.
All other factors being equal I would lean toward a smaller taper for storage space reasons but that is definitely secondary to potential fuel savings.
Any help here would be greatly appreciated!
Thanks,
Bill
PS
I did read the "Aero RV (custom boat tail for '95 Ford E-350 Class C motorhome)" thread and noted that several folks thought his taper was too aggressive but I couldn't find what would have been better % taper in that thread.
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1). How many miles per annum will this RV be used?
2). At a 12% improvement, what is the annual reduction in gallons used? (45?)
3). Even at $3/gal, and the RV’er average of 5,000-miles per annum, it’s maybe a little over $100 in savings.
A bus like that really isn’t a highway vehicle. Metro loop, point to point, is about it.
Look at the differences in school buses and highway passenger service buses. What sticks out is ground clearance. A school bus doesn’t benefit from lower cladding . Adds weight and makes inspections more difficult.
A Trailer-Tail has a LOT of force being applied to it while underway. Find a truckstop and walk up to have a look at the structure. It’s the right idea, but to have it stay attached may preclude use of rear emergency door.
Straight trucks (26’ Penske rental as example) have some of the very worst aero imaginable. And it’s that exposed underside that does it. The Fed-Ex Custom Critical guys blow everyone off the road (find a pic).
The key to lowering motorhome fuel burn is planned use. I can show that a 5-mpg Moho can use less fuel on a trip than something that gets four times that much: it’s about capacities for propane, water & food.
The important question to answer is: How many nights aboard before a re-supply run is necessary.
That’s the fruitful avenue.
The
genuinely low transportation fuel cost route is where the family car is used to tow an aero travel trailer. Again, capacities matter. But the real savings is reducing the headache of a second drivetrain to maintain & repair. Not enough annual miles accrue to stave off dry rot with Mohos.
The cost of an RV is the total expenditure over (X) years divided by nights aboard (Y) in that period.
Step back for the big picture.
(If you keep it, see Roger Marbles site on RV tires. Mandatory reading).
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