Dear Austin,
The error “Mach number exceeds 1.0. Equations cannot be evaluated” is an error triggered by the unsteady airfoil aerodynamics (UA) routines of AeroDyn v15. Because the ECD cases involves large inflow skew, I’m curious if the problem with your simulation is more related to problems with the BEMT solution rather than the UA solution e.g. see: AeroDyn v15 convergence issues - #7 by Jason.Jonkman. I suggest that you first see if the solution is reasonable for these cases when UA is disabled (AFAeroMod = 1).
Best regards,