Charlie757 wrote:So does this buzzsaw sound disappear in-flight because of external wind noise or because thrust on the aircraft is gradually reduced?
masi1157 wrote:It is not "also" at shaft frequency, it is only at shaft frequency and many many of its harmonics. You can also have a pronounced peak at the blade passing frequency, but that one doesn't disappear at cruise level. It might just get less pronounced.
akiss20 wrote:That’s exactly what I said. “And its harmonics up to blade passing frequency”
masi1157 wrote:akiss20 wrote:That’s exactly what I said. “And its harmonics up to blade passing frequency”
You said "also". Only the shaft frequency and its harmonics are created by supersonic blade tip speed and are perceived as buzzsaw noise. And the harmonics of the shaft frequency reach far beyond the BPF.
akiss20 wrote:[but what is the mechanism of producing energy at higher than BPF from shocks? There probably is one, but either way the acoustic energy of harmonics above BPF is much lower than that at BPF or 1/rev or 2/rev. The 1000th engine order is not of much interest generally.
Farsight wrote:What is fan & N1 shaft imbalance?
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