It's a homemade stabilization jack

Thanks to Rivet Master Nuvite-F!
The airforum members have spoken.
The strange device is actually a sort-of homemade stabilization jack and the idea is actually not so bad. Apparently, so says the expert, the older and longer trailers really needed that stabilization.
The image shows the unscrewed jack in half-down position.
Maybe they can be restored/kept. We'll see.  
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