Rotary train car coal dumping - GIF and video

[PJs]

I'm still puzzled about what happens at the couplers that link the car-to-be-tipped with its adjacent, non-tipping car(s). In the first gif, I don't see any car movement that might suggest the cars are being un-coupled prior to tipping.

Are the couplers on these cars mounted such that they can rotate about a horizontal axis to allow the tipping without uncoupling?

I believe the coupler is on a captive yoke shaft that allows it to spin. There are some pics in a google search for "coal dumping train coupling" Here is a link to a model railroad exact replica of an FMC4000. ExactRail HO scale FMC 4000 rotary-dump coal gondola | ModelRailroader.com

The pics not great but the article talks about magnetic coupler and proper height.

One of our techs back in the day took some pictures of the Coal Mountains and the trains feeding from the coal mountains to an eastern coal fired plant. Not a long run...maybe a mile max. Coal was brought in from farther away. The heaps dwarfed the loaders. @¿@