RV Fuel Issues & Prices - Post 'Em Here!
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Forum Discussion
cekkk wrote:
Living where we live means dropping 3 to 4k feet every time we go to I-25. Miles per gallon are pretty darn good going down. But then we have to come home. The mileage is poor going uphill, but once at the top, well, now you're coasting. DW's Toronado and STS had instant mpg readouts and they'd show 80 some mpgs when coasting downhill and various high numbers when under reduced power on the downhill side. On a trip using a tank of fuel, I'm convinced it comes out more or less a wash.
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More or less. The uphill/downhill is a gravitational conservative field so that's a wash (ignoring friction in bearings which is non-conservative). But wind effects are more complex since they are non-conservative and non-linear (usually some kind of power law, like square law, is used at such speeds) and then there are losses in the irreversible carnot cycle of the engine (the air brake made George Westinghouse a billionaire because of that). But the overall Hamiltonian is dominated by the potential/kinetic energy of the mass, swamping out the other terms.
