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| Re: Amtrak's ACS-64 (1170065) | |||
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Re: Amtrak's ACS-64 |
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Posted by Jace on Thu Aug 2 11:18:11 2012, in response to Re: Amtrak's ACS-64, posted by Jersey Mike on Tue Jul 31 14:55:44 2012. Thirty years later, there are still all kinds of stories about the SDP40's! Amazing. The HT-C's had a hollow bolster that somehow performed differently. They had a high CG with no baffles in the SG tanks. They were unstable only when coupled to baggage cars. They were unstable only when running elephant style...These factors above may have contributed in some cases, maybe not (the accident reports suggest not), but if any of these come into play at all, then the units were clearly marginal at best. So why were they marginal? Because they were heavy six axle locomotives running at high speeds on track that was inadequately designed and/or maintained. This problem was definitely not limited to the SDP40's, it was a problem of the times. This is why the SP had derailments on their SD45T-2's, so much so that they limited their speed while they conducted a nine month dynamic study of their own ("Dynamic Performance of the HT-C Suspension under Six Axle Locomotives", July 1977). The same issues were found on the U30CG's (no longer in passenger service after the February 1969 derailment of the Grand Canyon), and the pooches and the E60's. I should also add that four axle units weren't immune: the Empire Builder derailed in 1980 on the BN (how ironic!) due to the locomotives rolling the high rail on a curve. The locomotives: a couple of brand new F40's. SP's findings in their report were inconclusive but the were able to convince EMD that by going to a softer elastometer in the secondary springs and changing the dampers on all HTC trucks then dynamic performance would improve. The idea was to make the suspension less stiff going into curves as all of these derailments were due to excessive lateral force on the high rail. These changes were implemented on all HT-C's by 1978 yet there were still derailments. So what about the track? It seems that if you're going to be putting a lot of force into the high rail (which due in part to super-elevation is directly proportional to the mass - and speed - of the locomotive) then you've got to have a track structure that can withstand the load. If you knock down the high rail, the track structure was inadequate. Up until the 1970's the FRA specified the minimum number of spikes required for different classes of track. These minimums had not changed for many years despite significant increases in car and locomotive weights/axle loads, especially through the 1960's. Most railroads followed the minimums and that's it. Others (MP comes to mind) used more spikes in curves. (And note that the MP SD-40-2's were among the heaviest out there, heavier even than the SP SD45T-2's). This is why the derailments occured on some railroads and not on others. After all of these derailments, the FRA changed their rules. Instead of specifiying spike minimums, they now had a statement that said, in effect, that the track structure and specifically the number of spikes used has to be adequate for the trains operating on the track. Once track was designed and maintained to the new standard, these types of derailments disappeared even with all those thousands of HT-C's out there. |
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