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Well if they are typical quads the prop tips are supersonic.
The CH54 have blades that reflects the wide open unmuffled engine exhaust every time they pass over the fuselage while the hughes HAD a downward exhaust but AFAIK, it is still away from the rotor by a couple foot below the boom
The hughes NOTAR was really quiet because they used exhaust for the tail rotor and it wasn't under the rotor.
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