Wednesday, September 26, 2007

Still on the road

Yesterday at Jekyll Island, Georgia. Last night in North Carolina, back to Virginia or Maryland tonight.


stronger said...

The girls look so much older in this picture! How did that happen? :)

Brian said...

what do you think of the rv?

Nancy Toby said...

This particular model? Or in general?

This is a 24-foot 7.5-foot wide diesel model. It used a lot of propane when not plugged in for the A/C, which was a pain to get filled. Diesel is a slight pain to locate while on the road, not bad. Otherwise it drove and handled quite well compared to the wider models. But it's quite expensive compared to them too.... I think the cheaper gas models are a better value, myself, but this was a good one to try out.

SToby said...

On returning, I added up the cost of the RV and calculated fuel economy for most of the trip (records for most of the outbound leg fell victim to grabby little hands that defaced our notebook with Magic Markers and tore out a few pages. After that I made the cab of the RV "off limits" to the children). The fuel economy was 14,13,13,14.2, and 16.1 mpg of diesel for the last 5 fillups. Aerodynamics was the deciding factor -- the last fillup included some 40-mph time and no speeds over 60; earlier fillups included 70-mph cruising on Southern Interstates with high speed limits. As we engineers know, diesels operate unthrottled so their efficiency decreases barely at all at light load, while the aerodynamics of an RV are poor; it's your basic brick. This physics naturally leads to a dramatic drop in mpg with increased vehicle speed. For a gas engine the mpg penalty of higher speeds would be less, since their efficiency drops off more at low power.

The bottom line fuel cost for the entire trip, almost exactly 2400 miles on the odometer, is about $500; the rental cost about $2600, including an annoying, $300-plus penalty for extra mileage. Our rental company allows a certain number of miles per day, with a punitive charge for miles driven beyond that.

The diesel engine was a 6-cylinder turbocharged model whose operation was practically transparent, sounding and responding no different from a gas engine. Diesel fuel cost somewhat more than gas on our trip, about $3 per gallon. (Gas varied more but was around $2.50).

Anyone have real-world data on the efficiency of gasoline powered RV's? We failed to keep good records on our earlier trips and I'd like to know how important the difference really is.