I'm with Dave Nadler on this; it's pretty easy to sense when
the Antares 20E is in a thermal even with the engine running.
Never flown a FES.
With a bit of practice sensing the thermal in the all-vibro-Solo
powered DG808 was possible too. I never bothered though,
just climb 5000+ feet, switch off and set off searching.

Dave N: Be interesting to know what on earth "plummet
mode" is in the Arcus M?

Dave Walsh