Steam

[NW Mailing List]

 A: Until the SD70 no diesel could make as much tractive effort on a
 per axle basis as an N&W Y6.

 B: If under 10 mph the maximum boiler output is not required to produce the
 maximum TE then that is an advantage over the diesel which requires the
 maximum prime mover output and fuel consumption to produce the maximum TE.

 C: The Modern Steam Locomotive has no restriction on continuous TE versus
 starting TE. No traction motors to burn out and produces just as much TE at
 10 mph as it does at 0 mph,  a diesel cant do that.

 D: Not hardly.  The max DBHP on a Diesel-Electric is 20 MPH and it falls at
 around 150 DBHP for each 10 MPH till it gets close to the max speed for the
 locomotive.

 John Rhodes



A:  Not really a fair comparison though, given that the Y6 had some 25% more weight on it's drivers, by virtue of having more axles and larger bearings and wheels.  Max TE is ultimately determined by weight on driven axles * adhesion factor.  Adhesion factor is ultimately determined by mu sub k, the static coefficient of friction of steel on steel.  Truck and motor design also affect adhesion factor, but it can never be higher than mu sub k.    

The Y6s' had 522,850lbs on the driven axles, with a max TE of 152,206lbs simple, or a 29% adhesion factor...  an SD70 has 396,800lbs on driven axles with a max TE of 163,142lbs, or a 41% adhesion factor... both of those are at max optimal conditions, so you can reduce each by 3% or so, if not more, to get a more realisitc max TE number in everyday operations.  

B:  Max TE is not determined by power output (a diesel, nor any other locomotive type, does not require full power output to get max TE... )... continuous max TE is.  At continuous max TE, a diesel does require its full power output.   

C: Not only can a diesel not produce as much TE at x speed as it does at start, nor can any other locomotive of any type ever built... I'm curious as to the physics equatinos you used to arrive at your hypothesis, as the ME in me says it's not possible to do so.  Are they in your paper?

D: While drawbar horsepower will fall as speed increases (darn that physics), the diesel is applying full power to the rail throughout it's speed range.  A mechanical steam locomotive has the advantage of being able to increase horspower as speed increases, however, becuase of this mechanical system, it simply cannot create that rated power at lower speeds.  No mechanical engine in the world is capable of a constant hp curve... this inabilty to start or move trains at lower speeds that it can move at higher speeds is the greatest pitfall for a steam locomtive.   

Robb Fisher
RFDI