Why is it ......?

Question

Why is it that when you're inside the plane, you can't hear the roar of the engines but when you're on the ground, you can? -- even though the plane is hundreds upon hundreds of feet above you.

Answer 1

I do hear changes in throttle setting when I fly.

Answer 2

Firstly, the aircraft cabins are sound proofed. Secondly, the roar of the engines is generated from the exhaust section, directly behind the units. Since passengers are not seated in these areas, they do not get the full impact of the roar. However, people outside the aircraft are not so fortunate and also the roar has spread out in all directions after leaving the engines.

Answer 3

It all has to do with the speed of sound. Most modern jets travel at about Mach 0.8 which means 80% of the speed of sound. Therefore most of the noise, which by the way comes out of the exhaust of the engine, is behind the jet and cant catch up with it. So its all quiet inside the cabin, thankfully. However, for a stationary observer on the ground doing Mach 0.0, they get hit with the full symphony of jet noise....

Answer 4

The metal and insulation inside the skin of the aircraft help keep out the noise.

Also, the wing blocks some of the noise by having the engine under it.

And the engine produces less noise by having the exhaust below the cabin (exhaust creates the most noise).

If you're on the ground, you have nothing but air to block the noise, and air isn't very good at blocking noise unless you're really far away.

Answer 5

The roar is not emanating from the engines.  The roar is from well behind the engines, where the exhaust streams are braking up in the air.

Answer 6

I wish that people would not post answers in subjects they know nothing about.

The engines sound relatively quiet from inside the airplane because the hull of the airplane is insulated and keeps most of the sound out.  It's as simple as that.

It has nothing to do with Mach numbers and the speed of sound.  Just insulation.  Even the windows are multi-layer, partly for sound insulation reasons.

Also, most of the sound goes down and to the rear, because that is where the exhaust from the engine carries the sound.  Thus if you are in the right place and the wind is right, you can still hear the sound from a jetliner that is fairly high (3,000-5,000) feet.  You cannot hear a jetliner that is flying at 35,000 feet, or even 10,000 feet.

Answer 7

The engines produce sound which you can obviously hear onboard since you are sat right next to them! Do you think you could hear your mother screaming you from 35000ft?

Answer 8

the cabin is padded to prevent the noise being too loud in passenger aircraft. have you ever flown in a military transport? no padding in those hence mega loud engine noise!!!