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Old 05-17-2020, 09:36 PM   #1
Kowshik
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Post 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??
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Old 05-18-2020, 11:25 AM   #2
AlphaOneSix
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Quote:
Originally Posted by Kowshik View Post
For MI-8 why we maintain 95%.
Because the flight manual says so.

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Originally Posted by Kowshik View Post
Why RPM 192 is not considered as 100%.
Only the engineers know for sure.

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Originally Posted by Kowshik View Post
Is there any relation related to sound speed ???
No.

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Originally Posted by Kowshik View Post
Or its just a company policy??
It's how the engineers and designers created it.

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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.
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Old 05-19-2020, 11:47 AM   #3
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Before you reach any speed where the tips will break the sound barrier, you'll have encountered retreating blade stall.
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Old 05-19-2020, 11:01 PM   #4
VampireNZ
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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.
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Old 05-20-2020, 08:15 AM   #5
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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.
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