Embarrassing Airplane questions!

[johnjoe1]

Sorry for such embarrassing questions...

But when I ride on airplanes- I notice some airplanes make some crazy sounds!
And its totally different from plane to plane- even if they\'re the same make and model.
I\'ve also taken into consideration that I generally am sitting in the same area, too.
I\'ve always wanted to know WHAT is causing some of these sounds.

So, my questions are:

1:
Why do these airplanes make such funny sounds sometimes?


2:
Specifically- what is causing the sound that appears to come from the wings, when taxing to runway/gate. It sounds as if something was trying to extend, and it\'s as far as it could go, and it just keeps cycling- with a screech-like metal sound.


2:
What is causing that repetitious CLUNKING sound that happens beneath the airplane, sometimes, when taxing?

I\'ve noticed it a few times now, and always felt like- when we went flying down the runway it would increase in repetition. But it disappears completely as we fly down the runway! So it\'s obviously not anything to deal with the actual tire system, as it SOUNDS like where it\'s coming from.

3:
Why do some airplanes drive smooth and have no clunks sounds, or screech sounds ever!

Thanks!

 

[nycbusdriver]

Sorry for such embarrassing questions...

But when I ride on airplanes- I notice some airplanes make some crazy sounds!
And its totally different from plane to plane- even if they\'re the same make and model.
I\'ve also taken into consideration that I generally am sitting in the same area, too.
I\'ve always wanted to know WHAT is causing some of these sounds.

So, my questions are:

1:
Why do these airplanes make such funny sounds sometimes?

Airplanes are machines, and often machines make noise. Since airplanes are designed to be as light as possible, yet still strong enough to handle the load, there is little attempt to soundproof some of these extraneous noises which are of an intermittent nature. Soundproofing adds weight, so if the noise is not constant the engineers just decide to let the component be noisy.

2:
Specifically- what is causing the sound that appears to come from the wings, when taxing to runway/gate. It sounds as if something was trying to extend, and it\'s as far as it could go, and it just keeps cycling- with a screech-like metal sound.

Not sure about this one. Screechy sounds very much like electric hydraulic pumps which may be cycling on and off as hydraulic components place a demand on the system. They are very high pitched. You may also be hearing the flaps being extended to the take-off position (but that is not a noise I would term screechy.)

2:
What is causing that repetitious CLUNKING sound that happens beneath the airplane, sometimes, when taxing?

I\'ve noticed it a few times now, and always felt like- when we went flying down the runway it would increase in repetition. But it disappears completely as we fly down the runway! So it\'s obviously not anything to deal with the actual tire system, as it SOUNDS like where it\'s coming from.

This is THE CLASSIC AIRBUS 320 QUESTION! A heard this more than anything else when flying the A320 family of aircraft, and it only comes from people who are sitting over the wing. The further from the wing you are seated, the less you can hear it. The noise is made by hydraulic shuttle valves in the braking system. The brakes are engineered so that the system is always connected to the alternate hydraulic source, however, when the pilot applies brake pedal pressure, the system switches over to the normal hydraulic source, if that source is available. The switching is done by a shuttle valve on each side (one for the left brakes, and one for the right.) They CLUNK loudly when the metal piston inside slams back and forth as the pilot depressed and releases the brake pedals. To my knowledge, only the A320 series of aircraft have this very noticeable noise. You don't hear them once you start down the runway simply because the pilot is (hopefully) not using any brake pedal pressure during the takeoff roll.

3:
Why do some airplanes drive smooth and have no clunks sounds, or screech sounds ever!

Thanks!

They all have their little noises, but some engineers are cleverer than others in hiding them. Also, a lot has to do with where on the airplane you are seated. Even the difference of two or three rows can mean hearing particular noises, or not. If you ever sat in row 1 of an MD-80, you would hardly know you weren't sitting in a library. However, the last row of that same airplane sounds like you've just passed through the gates of hell.