Vintage work crew photos

[Toolmaker51]

What were they pumping or spinning up behind the engine? Maybe getting the turbine spinning?

Performance test, that's a dynamometer.
https://en.wikipedia.org/wiki/Dynamometer

[schuylergrace]

Performance test, that's a dynamometer.
https://en.wikipedia.org/wiki/Dynamometer

No, not the original post, but the follow-up that had video of one of those engines starting and running. They joked about having to get folks from the audience to help with whatever they were cranking/pumping back there. Another thought was that they might have been winding up a flywheel used as a mechanical starter.

[Frank S]

its a pile of rags. But surely there must be other things for 2/3rds of those men standing around watching could be doing.