Main Rotor RPM

For MI-8 why we maintain 95%. Why RPM 192 is not considered as 100%. Is there any relation related to sound speed ??? Or its just a company policy??What will happen if the rotor speed crosses sound speed an In which circumstances it may happen??

For MI-8 why we maintain 95%.

Because the flight manual says so.

Why RPM 192 is not considered as 100%.

Only the engineers know for sure.

Is there any relation related to sound speed ???

No.

Or its just a company policy??

It's how the engineers and designers created it.

What will happen if the rotor speed crosses sound speed an In which circumstances it may happen??

The Mi-8 is not capable of flying fast enough for the blade tips to break the sound barrier.

Before you reach any speed where the tips will break the sound barrier, you'll have encountered retreating blade stall.

Generally the majority of heli rotor noise is the TR blade tips breaking the sound barrier.

A good example is the MD500 TR mod that replaces the twin bladed TR with a 4 blader that runs slower - so a lot quieter.

The tail rotor blade tips don't break the sound barrier on any helicopter, not even close.

But the tail rotor noise is a quite a bit higher frequency that is more annoying to humans. So the tail rotor seems loudest close up. But the main rotor is still the main noise producer.