QUOTE(VSA380 @ Jul 1 2006, 03:03 PM) [snapback]91536[/snapback]
Does anyone know why the 757 makes that sort of grunting noise on take-off?
QUOTE(Mcchord_AFB_Airman @ May 24 2006, 12:17 AM) [snapback]85860[/snapback]
As for why the 757 RR engines make that growling buzzsaw sound, I'm no expert on engines but i would say its a combination of the full nacelle type, the shape and density of the fan blades, how much play there is in them, the number of compressor stages, the bypass ratio. The list could go on, the P&W powered versions sound about 90% identical to C-17's(90% engine similarity). Also the tips of the blades are usually going supersonic but since pressure has a direct influence on the speed of sound its not "breaking" the sound barrier even though the tips may be moving at 800mph. The sound is especially influenced by the chord of the blades and how many there are. The more blades there are the more it sounds like a buzzsaw in general, which is why the GE 110/115B and RR A380 Trents are so quite, that and the fan is massive compared to the core, the wide chord blades dont have to turn as fast to get the same thrust. If they had conventional blades they would have a really loud horrible buzzing sound.