Define “drag freight”

[SD70Dude]

The minimum continuous speed of 10-12 mph also conveniently translates into the lowest speed where the locomotive can use all its power without slipping excessively.  

That unit I saw with the failed blower was a mid-train remote in a 220 car 30,000 ton grain drag.  Not easy to replace if it failed completely, and as it was still making power I don't think the crew knew about the problem, as you only get a generic trainline alarm message without any details if something happens on a remote.   

The Diesel Doc called them a few minutes later and asked them if it was giving any alarms or only putting out reduced power, apparently it had thrown a code when the blower failed.  He told them to keep using it and to call back if it stopped pulling properly.  

[wjstix]

DR DENNIS GORDAN

I am late to the discussion, but note that all comments relate to diesel electrics, while "drag freight" started in the steam era, when there was no issue with overheating at low speed, so slogging along with the least power that kept things rolling was safe and economical.

 

 

Apparently you missed my earlier post.

 

In 1900, the strongest mainline freight engine, like a 2-8-0, could pull maybe 30 or so freight cars. If you wanted a longer train, you had to add another engine and crew. When Mallets / Articulateds came along, they were basically two engines in one, so now mainline freights could be much longer and still need only one engine and crew.

 

However, steam engines can't change gears like a car or bicycle. The diameter of the wheels determines how much the engine can pull and how fast. An engine with 80" drivers can go very fast, but will tend to slip badly when trying to pull a heavy train. An engine with 51" drivers can dig in like a car or truck in low gear, and pull a very heavy / long train, but can't go very fast (partly because the smaller the wheels, the harder it is to properly counterbalance them). So a c.1920 2-6-6-2 or 2-8-8-2 could pull a very long train - probably comparable to what in the next generation could be pulled by an A-B-A set of F-units - but only at about 10-20 MPH. That's a "drag freight", a long train running slowly pulled by the largest most powerful engine of the time.

 

By 1930, engines were developed that were large enough to pull long trains, but had larger drivers so they could go much faster: 2-8-4s, 2-10-4s, 4-6-6-4s...'supersteam' engines. Those engines brought the end to the drag freight era.

[BaltACD]

wjstix

By 1930, engines were developed that were large enough to pull long trains, but had larger drivers so they could go much faster: 2-8-4s, 2-10-4s, 4-6-6-4s...'supersteam' engines. Those engines brought the end to the drag freight era.

Until the era of PSR, where except for 'primere' trains, all other trains are loaded down to the level that the trains will DRAG at minimum continuous speed over the ruling grade (and if stopped on that grade will need additional power to get the train restarted).