Steam

[NW Mailing List]

>   Unlike a diesel-electric, whose ability to haul "X" amount of tonage decreases as they go faster steamers don't have that problem.  If you were to look at a traction effort curve for a diesel you would see that at very low speed they can pull a great amount of tonage but as speed increases they loose that ability, with the curve dropping way down.  On curvy right-of-way and on lines with heavy grades, diesels loose their ability to keep a train going at higher speeds, except that they pile on more diesels.  The H.P. of a diesel is less effective at faster speeds because more electricity is needed to keep the traction motors spinning at the higher speeds.  This is why there are many a photo of trains from out west that have five, six and seven locomotives on the point, so that they can maintain the higher speeds  

>    

>   Steam on the other hand maintains their tractive effort through out their speed range.  As long as there's sufficient steam presssure a steamer can pull the same load at 60 m.p.h. as it did when it was at 10 m.p.h.




>         jerry 

> 




Speed is dictated by horsepower per axle, not by unit count.  Given equal factors, i.e, gear ratio, adhesion factor, etc, one diesel will go just as fast as one hundred... the only difference more units make will be amount of tonnage able to be pulled at that speed.  Steam engines do not maintain TE as speed increases... it also falls off.

Robb Fisher
RFDI