Some older military aircraft actually ground one of the 3 phases of 115 vac. Having looked at the circuit diagrams it appears that the 'B' phase output of the inverter (28vdc to 115vac) is grounded, while the 'A' and 'C' phases are sent to the relevant busbars. The only ac loads are very low current flight instruments. There is no 'star' or neutral output from the inverter, just the 3 phases. All of the 3-phase loads are therefore fed from the 'A' and 'C' busbars and a connection to ground provides the 'B' phase.