help please
What do you mean?
R-27ERs can only be used when you have a hard radar lock (not IRST) on a plane.
i guess you mean which radar mode will be best for tracking people and firing the ER.
TWS and TWS HDN will be best for finding enemies and getting a lock
To find targets, TWS under 50km or TWS HDN over 50km. With the HDN mode you have far more range but it isn’t good at tracking all aspect targets and it will only reliably pick targets coming to you (hot targets), but as soon as you hard lock, it will be an all aspect PD lock either way if the target is under 50 or 55km IIRC.
TWS HDN might also be useful at shorter ranges when you have too many targets and you just want to see the ones that are coming at you instead of potentially missing them because the radar gets overloaded with stuff.
In a nutshell, TWS is what you should use 95% of the time, and you can essentially forget about the rest because the HDN usefulness is quite niche anyway.