Ами досега според три форума този звук (от много описван като "buzz saw noise", според мен това го е чувал всеки от нас, но не се е замислял много-много; дори в момента го чувам от един излитащ на мен Airbus!
) е предизвикан от преминаването на върховете на blade-овете в (почти-)свръхзвукова скорост:
airliners.net написа:not sure we need to extend this any further.
just note: the particular sound is named "pure tone" noise, some times oddly called "buzz saw noise".
it characterises a high by-pass ratio turbofan, thus it is coming with all modern engines now to some extent.
it is produced by the fan blades running at relative supersonic airspeed. if there is one frequency emerging only and representing the No. of Blades times Revs, then they call it BPF, the Blade Passing Frequency, if blades group together (totally arbitrary) then a series of frequency emerge; this looks like toothes of a saw on the noise spectrum and sounds like what you folks have heard.
the fan speed varies significantly after take off and the fan mach number changes with altitude and flying speed, thats why this characteristical sound vanishes in climb quite rapidly.
the manufactureres tune the engine ai intakes to absorb most of that sound energy, but like so often in life, they cannot twist the physics totally away.
Лека вечер
Емо