Humming noise of a jet?

Question

Is the characteristic hum of a jet due to 400 Hz power or an undertone of the 24K rpm electric motors?

Answer 1

Noise on aircraft are caused by lots of things that turn or vibrate or even the air steam passing of the fuselage.  However a constant hum is a bit strange.  No two aircraft will sound the same this is why when aircraft are designed they go through a whole series of acoustical and vibration tests to prevent resonate vibrations that can cause damage.

During different phase of taxi, take off to wheels up and flaps retracting you will hear different sounds.  Even having the APU running full time has a different sound depending if a generator is turning on.  The other electrical generators are attached to the engine PTO and can’t be heard in the cabin.

I can assure you aircraft just don’t hum.  However I would like to know what aircraft you are flying on and where you sit to hear the humming sound.  The resonate vibration sometimes is in a different place on the aircraft than where it came from and may sound like a hum to you.

Go to my web site and provide me additional information and I may be able help you more.

Answer 2

here is one for Airbus haters, it is a known fact that Airbus had a problem with their Engine Driven pump (it creates a high pitch sound and can be heard in the cabin) this was first on the A300 that is why the round thing (like a fire ext bottle) on top of the EDP which was place there to dampen the noise (the unit is called dampener). the PW JT9 engine for the 737 also has this called ripple dampener (so that hydraulic fluid) would not be bubbly byut the real reason is noise supression.

Even the A340 has this dampener and when the noise is unbearable and for 3 months problem was still remarked in the log book an Airbus SB was introduced and a 2nd dampener was installed.

So the real noise or humming noise you hear in the engine is always that of the Engine Driven Pump.

SO far Boeing ( GE engine) hasn't encountered anu problems to their EDP cause of no passenger complain.

Answer 3

The only "Humming" i can think of is during a start up when the Generator/Startor, which runs off of 24V, and very high amps depending on the aircarft, that  is trying to spool up the fan blades before they ignite the burners, not a real humming noise,  but more of a very low whoosh sound due to the low rpm and the amount of air being drawn into the engine before iginition.This is the only thing that i can think that doesnt sound like air coming out of the back as a high velocity.  The AC power is only to provide power to the cabin and equipment, the rest of the aircraft usually runs off of 24V DC current .

Answer 4

I have been around lots of turbojet and turbofan engines, and have never heard a "humming" noise from one.  You certainly can't hear the electrical components over the sound of the engine.

A turbojet or turbofan engine makes a "roaring" or "whooshing" sound, which is the result of the high-volume, high-velocity air flow through the compressor and turbine stages and at the lip of the exhaust.  Perhaps you can explain what you mean by a "humming" noise, and your question will make sense.

Answer 5

I think I know what you are talking about...That would be the electric motors.  They are only really noticeable when the engines are off (like when you first board a plane)

Answer 6

You mean the sound of a B757?

Answer 7

Depends on the hums pitch.  Could be the Environmental System, Hydraulic pumps, electrical systems, the beer you drank before you got on the plane.  I just messing with ya on that one.  Where was the aircraft when you heard the noise. Was it flying, heading to the runway or sitting at the gate?  To many variables to answer your question correctly.