Youtube! UP Big Boy 4014 shoves stalled Manifest over Blair Hill (6/29/2023)

[dorin]

Wow!
https://youtu.be/icgH_3dXdOU

[Harold_V]

Wow!
https://youtu.be/icgH_3dXdOU

Indeed!

H

[Greg_Lewis]

Too much fun.

I've heard that a single large steam loco has more drawbar pull than a single diesel unit. I've also heard that a steam engine has maximum torque at zero rpm. Sounds logical to me.

[Charles T. McCullough]

I hope I get this right:

A steam loco can start a train it cannot pull;
but a Diesel can pull a train it cannot start.

[Steggy]

I hope I get this right:

A steam loco can start a train it cannot pull;
but a Diesel can pull a train it cannot start.

Old wives’ tale.

A steam locomotive is a constant torque machine. The constant torque nature of a steam locomotive implies that the faster it runs, the more horsepower it will produce...until the boiler’s steaming capacity is exceeded. Therefore, it theoretically will generate the same drawbar pull whether near standstill or highballing.

A Diesel-electric locomotive is a constant horsepower machine. Therefore, it will generate its highest drawbar pull near standstill. Since the Diesel’s horsepower is constant, drawbar pull will decrease as speed increases. Disregarding possible adhesion issues, a Diesel-electric locomotive will be able to start any train that it can pull.

As for the Big Boy, at 135,375 pounds of tractive effort, it isn’t as powerful as an EMD SD70ACe unit, which is rated at 157,000 pounds continuous tractive effort. However, the Big Boy is much more interesting to watch as it goes about its business.

[ALCOSTEAM]

back in the steam engine days it was not uncommon to have a helper push a heavy train out of town to help them get going and there were helper districts even on some fairly flat railroads. A steam locomotive could pull a train over the road that it could not start from a standstill, of course most road type steam engines had non powered wheels dividing weight off the drivers and that takes away TE. Most road type steam locomotives if you look at the drawbar charts during dynamometer testing would commonly put out maximum power in the 40ish mph range. Many of the more modern steam locomotives like the NKP Berkshires and others of that era were considered super power locomotives, with all the most modern refinements, stokers, big fireboxes, and they had a steaming capacity that if the fireman was keeping up there was virtually nothing the engineer could do to run the boiler out of steam.

Early diesels with their DC generators and DC traction motors were a sizable step backwards in power compared to late steam and if it had not been for the massive reduction in maintenance mainly shop forces early diesels would have been much slower taking hold. Again power charts for early diesels such as the EMD 1500hp locomotives like the F7, GP7, Alco's RS line and others show as speed increases the TE decreases of which there are several factors for this but the end result is what the drawbar pull is. It was common for an early diesel that say had 45,000 lbs TE at a few mph to fall into the 15,000 range at 35 mph. So a train a set of diesels could start out pulling they might never get over the road at least in any timely manner. As diesel locomotive technology improved so did the TE and then came the AC alternator with diode rectification and today many road locomotives have AC traction motors with the associated frequency drives. These modern AC locomotives have a power curve that has very little drop to it and its apparent when one 4400hp 425,000 lb locomotive has more continuous TE at 50 mph than three 1500 hp 245,000 locomotives had at 35 mph.

So in general terms a steam locomotive can pull a train it cannot start and a diesel locomotive can start a train it cannot pull.

I have watched a few of the youtube video's of the 4014 doing that bit of helper service and its certainly working as in one of the video's you can hear the engine slip a bit and the engineer catches it and brings the power back on.