grüss dich , indeed many questions !
switching the condition to Hi idle will just set the idle to roughly 70%ng and any power lever movement will increase power- you just "start" at 70 and not 52 % with the power lever.
regarding beta : they are two abbrevations what beta is . one call it the flat pitch range which is not governor controlled - so the range between flight idle and reverse ( which is again governor controlled) , other call it everything below flight idle ( including reverse)
so when you talk just about the flat pitch range the prop lever is without function excluding pulling fully back to feather.
when talk about beta including reverse where the turbine spools up again, the prop has a function- e.g leaving the prop not full forward will result in a prop spool up to the prop lever setting and not full reverse range.
( e.g a lazy pilot lands with props at 1700rpm and not full forward and than pulls reverse- the engine will do it but the prop spins up to only 1700 )
at beta ( flat pitch ) the turbine speed is fixed at idle so pulling back to alpha will just result in a decrease of prop speed since pitch rises .
at reverse , when the turbine spools up, first the prop rpm rises until reaching full reverse rpm, then reverse pitch rises.
reversing from high idle will result in a lower spool up time and so more rapid reverse reaction.
At which point during engine startup does the oil start to allow changes in Prop Pitch?
a typical startup of a pt6 : condition cutoff, prop forward , lever flight idle ( NOT beta) , engage starter , at min 12% ng condition low idle. igniters start, fuel is open, it should light up. the feathered prop slowly starts spinning, ng rises until stabilized , the prop spins faster and faster until the oil pressure pushes it out from feather to flight idle pitch. advancing power a little will initially only increase ng and prop speed, the pitch is the same until governed prop speed is reached and than pitch is increased to maintain prop speed.
feather from a running engine ONLY from idle speed or you may burst the gearbox due to the massive torque rise. i never recognized a ng drop when feather at idle ( typically at shutdown you first feather, let the prop slow and the cutoff. must say i never looked at this moment at the ng but believe it stays the same )
of course the system is influenced by airspeed- the given prop pitch to maintain prop speed depends on airspeed , engine power is also influenced. e.g setting takeoff power close to redline will result in overtorquing when the aircraft acclerates due to rising engine power from ram air.
hope this helps you, wann gibts das bier für diese tipperei ?
chhers