Figure 1. ERJ (EMB) 145 Aircraft
Figure 2. Rolls-Royce AE 3007 Series Turbofan Engine
Figure 3. Fourier Magnitude, ERJ 145 Climb-out
I recently flew as a passenger in an EMB 145 jet similar to the one shown in Figure 1.
This aircraft has two Rolls-Royce AE 3007 series turbofan engines turbofan engines, as shown in Figure 2.
Here are the rotational speeds for each rotor.
Fan Speed 7903 RPM (132 Hz)
Gas Generator Speed 16013 RPM (267 Hz)
Note that there are several variants of this engine with slightly different rotor speeds.
I made an audio recording from within the aircraft cabin during climb-out, while hearing some distinct sine tones against the background random noise. The audio file is: emb145.wav
A Fourier transform of the sound file is shown in Figure 3. Spectral peaks occur at 133 and 267 Hz, which agree with the specifications for the engines.
Again, this recording was made from inside the cabin. So the fuselage walls would have attenuated some of the engine-generated acoustic energy, particularly at higher frequencies.
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– Tom Irvine