the really loud screeching at idle is from the bleed band being wide openreducing the air into the combustion chamber so as to not blow the flame out the more power a turbine makes the quieter it gets as all the air is forced thru the engine... some of the sounds you hear docking are there is a large disk brake on the output shaft with often 2 calipers they use a trim pump for brake pressure and can stop the n2 or power turbine to shift when released it sounds like blowing compressed air on a bearing as the blades spin up to speed.....all the blades in a turbine are hollow and have air blowing thru them to cool them thats what a hot start is to big of fire with not enough cooling air inside the blades then they can melt or bend with not good results!
Yes and no
The Bleed band closes at approx 85 percent n1.
Do you know what happens if it closes too late?
Here is the compressor section before balancing
also pictured is a set of Stainless compressor housings.
These were designed for salt water application for the navy.
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