Why Boeing 777 is so noisy.

On my recent Continental flight to London in a 777, I was very surprised at how quiet the interior of the plane was compared to my domestic flight…not sure what plane that was though, it was just a roar the entire two hour flight.

It was nice not to experience that on my 9 hour flight over the Atlantic, you could’ve heard a pin drop.

On my recent Continental flight to London in a 777, I was very surprised at how quiet the interior of the plane was compared to my domestic flight…not sure what plane that was though, it was just a roar the entire two hour flight.

It was nice not to experience that on my 9 hour flight over the Atlantic, you could’ve heard a pin drop.

“Whilst in Penang a 727 freighter took off – three JT9Ds at full thrust brought back memories as to what noise is!”

I think you might mean JT8D! I have visions of a 727 with three JT9’s on the back. The first tail dragger 727? Mind you, if it did get into the air it would go up quickish!

Chris

“Whilst in Penang a 727 freighter took off – three JT9Ds at full thrust brought back memories as to what noise is!”

I think you might mean JT8D! I have visions of a 727 with three JT9’s on the back. The first tail dragger 727? Mind you, if it did get into the air it would go up quickish!

Chris

Whilst in Penang a 727 freighter took off – three JT9Ds at full thrust brought back memories as to what noise is!

Whilst in Penang a 727 freighter took off – three JT9Ds at full thrust brought back memories as to what noise is!

Talking of noisy aircraft, does anyone recall BAC 1-11’s on a hot summers afternoon with a full payload and having to use de-min water?. Now that WAS noisy!!

Talking of noisy aircraft, does anyone recall BAC 1-11’s on a hot summers afternoon with a full payload and having to use de-min water?. Now that WAS noisy!!

Humans have subjective hearing… not everyone thinks tha same about loudness of a noise. Humans find tonal noise the most annoying… and these occur in short sharp “blasts”… as in… whenever a propeller blade passes through a specific place of air. For instance, if you were stood on top of a propeller engine cowling, you would be most irritated by the noise from the propeller as it pased infront of your face. This can be considered the same for a fan… many blades in a duct, and also turbines.

For low bypass engines, the jet velocity is large, so the noise is large from here. For High bypass engines, there are lower jet velocities so less noise from here… however, high bypass engines have larger fans, so there is more noise from the fan in high bypass than low bypass engines.

If you were on the ground, then you would notice a low bypass engine more than a high bypass engine, this is because the noise from the back end of the engine in a low bypass engine propagates further before it decays to a normal level.

If you were on the ground and a high bypass engine flew overhead, then the sound you would notice mostly comes from the fan. This is the noise which propagates the furthest before decaying to a normal level. And because the fan produces tonal noise, it is this which annoys humas the most.

For the Boeing 777, the fan noise is going to be larger than a lower bypass engine… assuming the same sound absorption within the engine… this is because of the huge fan.

Overall… the high bypass engines throw out less noise than a low bypass engine. This is due to the air velocity being lower at the back end of the engine for a high bypass engine.

Thats my basic input.

Humans have subjective hearing… not everyone thinks tha same about loudness of a noise. Humans find tonal noise the most annoying… and these occur in short sharp “blasts”… as in… whenever a propeller blade passes through a specific place of air. For instance, if you were stood on top of a propeller engine cowling, you would be most irritated by the noise from the propeller as it pased infront of your face. This can be considered the same for a fan… many blades in a duct, and also turbines.

For low bypass engines, the jet velocity is large, so the noise is large from here. For High bypass engines, there are lower jet velocities so less noise from here… however, high bypass engines have larger fans, so there is more noise from the fan in high bypass than low bypass engines.

If you were on the ground, then you would notice a low bypass engine more than a high bypass engine, this is because the noise from the back end of the engine in a low bypass engine propagates further before it decays to a normal level.

If you were on the ground and a high bypass engine flew overhead, then the sound you would notice mostly comes from the fan. This is the noise which propagates the furthest before decaying to a normal level. And because the fan produces tonal noise, it is this which annoys humas the most.

For the Boeing 777, the fan noise is going to be larger than a lower bypass engine… assuming the same sound absorption within the engine… this is because of the huge fan.

Overall… the high bypass engines throw out less noise than a low bypass engine. This is due to the air velocity being lower at the back end of the engine for a high bypass engine.

Thats my basic input.

Having been fortunate enough to experience my first 777 flight from Penang to Singapore last week (yes a 777 for a 52 minute flight!) I can only say how quiet it is on the inside. We were sat on line with the rear edge of the wing and even my wife commented how quiet it was – she isn’t in to aircraft, but was really impressed with the 777 – more so than the Dash 7 where we had to sit rear facing!

In comparison we travelled to KUL on a 747-400 in seats at the rear wing edge and it was very noisy – a combination of engine, wind rush and aircon noises.

Having been fortunate enough to experience my first 777 flight from Penang to Singapore last week (yes a 777 for a 52 minute flight!) I can only say how quiet it is on the inside. We were sat on line with the rear edge of the wing and even my wife commented how quiet it was – she isn’t in to aircraft, but was really impressed with the 777 – more so than the Dash 7 where we had to sit rear facing!

In comparison we travelled to KUL on a 747-400 in seats at the rear wing edge and it was very noisy – a combination of engine, wind rush and aircon noises.

Listen to a DC-9 or a 727 (w/ hushkits no less) take off. Now that’s loud!

Listen to a DC-9 or a 727 (w/ hushkits no less) take off. Now that’s loud!

To save unnecessary wear and tear of the engines, the aircraft computer would calculate a specific power for that particular take off. Consequently, if it were heavy, more power would be needed and if it were light then less power is required. Hence the difference in noise level.
So, during every take off, the-power setting is different. It is never FULL power (most noisy) on every take-off!

To save unnecessary wear and tear of the engines, the aircraft computer would calculate a specific power for that particular take off. Consequently, if it were heavy, more power would be needed and if it were light then less power is required. Hence the difference in noise level.
So, during every take off, the-power setting is different. It is never FULL power (most noisy) on every take-off!

Unf. the 777s are not noisy enough for my liking!!! They are pretty quiet inside and out – I have done a few jump seat rides in them as well as pax rides, and they arev quiet from the inside!

With you there – I don’t think I’ve ridden a quieter widebody except maybe an A340.

What else is better than a widebody throttling up before takeoff? Not much!! 🙂

Sex? Football?

Mike

Unf. the 777s are not noisy enough for my liking!!! They are pretty quiet inside and out – I have done a few jump seat rides in them as well as pax rides, and they arev quiet from the inside!

With you there – I don’t think I’ve ridden a quieter widebody except maybe an A340.

What else is better than a widebody throttling up before takeoff? Not much!! 🙂

Sex? Football?

Mike

Why do we need to know that ‘the B777 is loud because of the big engines’ ??

Why do we need to know that ‘the B777 is loud because of the big engines’ ??