04-02-2016, 05:43 PM
MountainMan, I think that the answer may be found in the words Altitude and Capital Cost.
Firstly Altitude, from my reading of World War Two aircraft books, I know that 10,000 feet is generally considered the height at which aircrew in non-pressurized aircraft had to be fully using the oxygen supply to prevent anoxia [the lack of oxygen to the brain] thus impairing cognitive thinking. This height is also relevant to Internal Combustion Engines [i.e. propeller aircraft] as the performance of the engine and thus the aircraft falls off significantly using normal aspiration and the solution is to use single and then double stage superchargers to attempt to maintain performance levels.
Now a steam locomotive is an open combustion engine so the fire is drawing in oxygen from the surrounding air which is thinner than the air at sea level, so the fire does not perform as well along with the poor fireman tending the fire.
We also encounter a problem with the generation of steam at altitude called an Adiabatic or Isothermic reaction [not sure which at the moment writing this in a rush] whereby the lowering of air pressure also lowers the temperature at which water boils, which causes problems because the boiling water is not receiving enough heat to create the steam pressures we normally require for an operating steam locomotive. This phenomenon has been shown where we can boil some water at altitude yet not be able to cook potatoes, so the problem would be far greater for a steam locomotive[s] struggling on a steep grade with a heavy train. As we all know a successful fire requires all three sides of the equilateral triangle to work properly.
I think that this last point is the most likely explanation for the double heading question.
There is also the possibility of a geared locomotive having a greater capital cost than a standard narrow guage loco, which would be relevant to a start up railroad, but I dont think that issue is as important as an out of breath loco.
Mark
Firstly Altitude, from my reading of World War Two aircraft books, I know that 10,000 feet is generally considered the height at which aircrew in non-pressurized aircraft had to be fully using the oxygen supply to prevent anoxia [the lack of oxygen to the brain] thus impairing cognitive thinking. This height is also relevant to Internal Combustion Engines [i.e. propeller aircraft] as the performance of the engine and thus the aircraft falls off significantly using normal aspiration and the solution is to use single and then double stage superchargers to attempt to maintain performance levels.
Now a steam locomotive is an open combustion engine so the fire is drawing in oxygen from the surrounding air which is thinner than the air at sea level, so the fire does not perform as well along with the poor fireman tending the fire.
We also encounter a problem with the generation of steam at altitude called an Adiabatic or Isothermic reaction [not sure which at the moment writing this in a rush] whereby the lowering of air pressure also lowers the temperature at which water boils, which causes problems because the boiling water is not receiving enough heat to create the steam pressures we normally require for an operating steam locomotive. This phenomenon has been shown where we can boil some water at altitude yet not be able to cook potatoes, so the problem would be far greater for a steam locomotive[s] struggling on a steep grade with a heavy train. As we all know a successful fire requires all three sides of the equilateral triangle to work properly.
I think that this last point is the most likely explanation for the double heading question.
There is also the possibility of a geared locomotive having a greater capital cost than a standard narrow guage loco, which would be relevant to a start up railroad, but I dont think that issue is as important as an out of breath loco.
Mark
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