From Facebook, Jared Childress: It is an odd question that I could not find an answer to online. Does anyone here know what a 4000 class Heavy Mikado was rated for (tonnage) northbound out of Ft Smith/Van Buren on the Central Division? If my memory services correctly these were the heaviest class allowed in the steam era over the bridges on this sub, correct?
Karl Brand's response: The the bridges on the Frisco’s Central Division between Monett and Paris had Coopers Rating of E-53. The Frisco’s 4000-4032 were USRA Light Mikados. As built, the class were given a Coopers bridge class of E-51, except for those which were equipped with boosters; those had a bridge class of E-53. By the end of steam, betterments to this class increased the bridge class rating. Those locomotives with an E-53 rating include: 4000, 4002, 4010, 4010, 4014, 4017,4020,4022,4026-4027,4032. Those with an E-53.5 rating include: 4001, 4003-4006, 4008, 4009, 4011-4013, 4015, 4021, 4025, 4031. The heaviest of the light Mikados, 4007, 4016, 4018, 4019, 4023,4024,4028-4030 carried a Coopers rating of E-53.8. Eastbound from Ft Smith the light Mikados were rated: North Yard-Rudy 2110 tons Rudy-Chester 1895 tons Chester to Winslow 950 tons Winslow to Fayette Jct 2510 tons Fayette Jct to Seligman 1750 tons Seligman to Exeter 2190 tons Exeter to Monett 2740 tons
Jared's follow-up: Karl Brand is this Coopers rating valid still to today or would the bridges have received a modern railcar weight upgrade while still under the Frisco? In that case of your reply above were all engines with a 53.5/53.8 excluded from service on the Central Division? Or was there some kind of tolerance allowed?
Karl's response: I have attached 3 pages the last Central Division ETT, Number 4, issued by the Frisco on April 22, 1979. You can see that the Coopers rating was little changed. The ETT also placed a maximum car-weight restriction of 263,000 lbs. In theory, any locomotive whose bridge class exceeded the Coopers rating of the bridges would not be allowed. I can’t say with certainty to what degree that was fudged, if at all.
"Chester to Winslow 950 tons" Interesting to note, that aside from the 1-A-1 truck equipped E's, no six axle diesel power was used on the FS Sub. I remember hearing from the Frisco guys I was around that the Frisco tried the SD45's on the line, but they were bad at spreading the rail on some of the tighter curves the sub had. (Like Lancaster Curve.) Seeing as 6-axle power wasn't used, then one can see that a 4-axle Class 52 engine could very likely lay down trying to do what one 4000 could do on Boston Mountain Grade between Chester and Winslow. (4000 = 950 tons, Class 52 = 945 tons.) It's also interesting that the little GP7 (or F) was only good for 770 tons on Boston Mountain Grade. IF the SD45/SD40-2's were allowed, they could have beaten the 4000's with 1415 tons per unit up Boston Mountain Grade. Pretty impressive, but their ability wasn't able to be capitalized upon on that particular grade.
See this thread about SD-45’s… http://www.frisco.org/shipit/index.php?threads/frisco-sd45-question.12981/#post-84726
