One day last week - I'm pretty sure it was Weds., Nov. 25th - during a strong drizzle/ light rain in the early afternoon, an apparently heavily loaded westbound NS general/ mixed freight train was truly 'down on its hands and knees' as it struggled up the grade on the Reading Line from the S. 12th/ Vultee St. crossing towards MP 32 here in southwest Allentown. Per a 1999 ConRail Track Chart, that grade increases from 0.28 to 0.31 to 0.50 to 0.81 per cent. I was able to pace directly alongside it for about 1/4 mile along the parallel and adjoining Industrial Ave. up to the 31st St. SW grade crossing, so between my car's speedometer and my estimation, I can confirm it was not going more than about 10 MPH. From how slow it was going past the Wawa store at Downyflake Lane, I expected it to stall.
The motive power was all NS - an SD60I leading, with a pair of D8-40CW's (I think) trailing. Aside from the slow speed, what was noticeable was the wheel screeching that appeared to be coming from the SD60I. Also, the engine seemed to be cycling - loading and unloading - at a rate of maybe 3 times every 2 seconds or so. At one point it seemed as if the engineer tried to get an extra notch on the throttle, but that ceased quickly. I couldn't really tell if sand was being applied or not. As the head end got over the 31st St. crossing, the speed seemed to pick up a little bit, so I suppose that the crisis had passed.
I surmise that the screeching was from the wheels slipping and 'creeping' on the rail briefly before the wheelslip control took over and slowed them down, and that the 'cycling' that I was hearing was also related to that. Is that correct ? Is it normal for those conditions ? What else was going on that I should have noticed as well ?
Thanks in advance for any answers or insights.
Paul_D_North_JrOne day last week - I'm pretty sure it was Weds., Nov. 25th - during a strong drizzle/ light rain in the early afternoon, an apparently heavily loaded westbound NS general/ mixed freight train was truly 'down on its hands and knees' as it struggled up the grade on the Reading Line from the S. 12th/ Vultee St. crossing towards MP 32 here in southwest Allentown. Per a 1999 ConRail Track Chart, that grade increases from 0.28 to 0.31 to 0.50 to 0.81 per cent. I was able to pace directly alongside it for about 1/4 mile along the parallel and adjoining Industrial Ave. up to the 31st St. SW grade crossing, so between my car's speedometer and my estimation, I can confirm it was not going more than about 10 MPH. From how slow it was going past the Wawa store at Downyflake Lane, I expected it to stall. The motive power was all NS - an SD60I leading, with a pair of D8-40CW's (I think) trailing. Aside from the slow speed, what was noticeable was the wheel screeching that appeared to be coming from the SD60I. Also, the engine seemed to be cycling - loading and unloading - at a rate of maybe 3 times every 2 seconds or so. At one point it seemed as if the engineer tried to get an extra notch on the throttle, but that ceased quickly. I couldn't really tell if sand was being applied or not. As the head end got over the 31st St. crossing, the speed seemed to pick up a little bit, so I suppose that the crisis had passed. I surmise that the screeching was from the wheels slipping and 'creeping' on the rail briefly before the wheelslip control took over and slowed them down, and that the 'cycling' that I was hearing was also related to that. Is that correct ? Is it normal for those conditions ? What else was going on that I should have noticed as well ? Thanks in advance for any answers or insights.- Paul North.
- Paul North.
All EMDs starting with the "50" series have a "Creep" type adhesion control software. Research discovered that maximum traction is achieved with the with a controlled "creep" or slip of about 7% faster rotation speed of the wheels than is required for the current ground speed. This is the reason that all EMD locomotives fitted with the "Super Series" adhesion control use Doppler Radar to measure Ground Speed. Older locomotives simply try to keep the wheels from slipping. With creep type adhesion systems you want the wheels to slip in a very controlled fashion. With DC motored locomotives this is difficult to achieve reliably, with the newer AC motored locomotives it is much easier. With the SD60 there was likely a problem with the system, the radar might have been out of calibration, or some other problem. The Creep type adhesion controls are the reason that modern locomotives both EMD and GE are screechers.
beaulieu -
OK, thanks much for that confirmation and explanation. I knew about the 'creep' phenomenon from the article in Trains back in the 1980s sometime about 4 new EMD diesels for the Foster Yeoman stone trains in Great Britain, and Bruce Meyer's trials and tribulations with getting that wheelslip control calibrated and trouble-shot:
EMD's British bridgehead Trains, March 1987 page 52 Electro-Motive diesels at work in Britain ( "ALLEN, G. FREEMAN", BRITAIN, EMD, TRN )
That principle of maximum adhesion with just a little creep also applies to braking action and forces, I believe. But I do not recall ever seeing the 7 % figure for that before, so that much is new to me.
I should have also mentioned that all of the involved track is tangent, so that much screeching could not have been from curves - and they were going so slow that truck 'hunting' from side to side that could also cause that kind of noise wasn't happening either. I recall reading about 30 years ago that the screeching of railroad wheels when going around curves is mainly due to the creep of one wheel or the other with respect to the railhead, due to the conicity from the typical 1:20 AAR wheel tread taper and the differing distances of each wheel's path around the curve resulting from the different radii of each rail, and since the wheels are rigidly pressed on each axle so they can't rotate there either to relieve that difference, etc.
Thanks again for your time and insights !
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