Good question - I'm not sure what actually happened to the two S-72
Rotor System Research Aircraft. They were meant to test a whole bunch
of interchangeable rotor configurations, but never were used in an
actual test program for the X-wing or anything else. I do know they
flew at least them in fixed-wing airplane configuration, but the X-Wing
program itself ran out of money and never flew.

X-50 is indeed going to fly again, hopefully next month. They did some
wind tunnel testing to figure out what went wrong with the software.

HW