I recently had the opportunity to fly on two separate BA 777, both with GE90 engines (G-VIIO and G-VIIP) and was quite frankly astonished at the noise levels in the cabin on startup, a booming resonance (possibly combustor rumble) that lasted the whole time the engines were spooling up but which thankfully died off when the engine was stabilised at idle.
Anyone know if the Trent 895 powered 777ERs the same?
Rez
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- Gingersnap
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RE: Surprise At GE90 Noise Levels On Startup!
It's been a while since i've been on a GE powered 777, but I do remember it being not all that loud.
As I say though, it has been quite a few years now.
As I say though, it has been quite a few years now.
RE: Surprise At GE90 Noise Levels On Startup!
I've been nearby a FX 777F starting up and also noticed a loud, low rumble on startup that stopped once the engine was spooled up. This was from the exterior.
RE: Surprise At GE90 Noise Levels On Startup!
| Quoting manzoori (Thread starter): a booming resonance (possibly combustor rumble) that lasted the whole time the engines were spooling up but which thankfully died off when the engine was stabilised at idle. |
The "booming resonance" is usually combustor tone (aka combustor rumble), as you noted. It's very engine design specific...some RR's do it, some GE's do it, but not all. It also varies inversely with temperature (it gets louder when it's cold). It goes away once the combuster flows get up to normal operating levels.
With some engine, there's another tone that can be described as a steadily rising howl that goes away...that's the spools spinning up. Combustor tone change volume, but not much in pitch. Spool spin-up stays about constant volume (except when it passes through resonances) but increased in pitch until it "disappears." It doesn't really disappear, it just gets too high pitch to hear.
Tom.
RE: Surprise At GE90 Noise Levels On Startup!
Thanks for your responses guys!
I also wonder if my position in the aircraft contributed to the sound intensity... we were in row 35 so quite near the rear of the aircraft.
I know at RR we put a lot of effort into driving out the combustor rumble tones, I was just a little surprised a relatively modern engine/airframe combination such as the GE90/777 had such an intense and booming resonance to it!
The tones were noted at LGW at around 12ºC and at UVF at around 28ºC.
Cheers!
Rez
I also wonder if my position in the aircraft contributed to the sound intensity... we were in row 35 so quite near the rear of the aircraft.
I know at RR we put a lot of effort into driving out the combustor rumble tones, I was just a little surprised a relatively modern engine/airframe combination such as the GE90/777 had such an intense and booming resonance to it!
The tones were noted at LGW at around 12ºC and at UVF at around 28ºC.
Cheers!
Rez
RE: Surprise At GE90 Noise Levels On Startup!
| Quoting manzoori (Reply 4): I also wonder if my position in the aircraft contributed to the sound intensity... we were in row 35 so quite near the rear of the aircraft. |
It's generally much louder from behind the engine...the gaspath out the front is much longer and more torturous so it doesn't project as well.
| Quoting manzoori (Reply 4): I know at RR we put a lot of effort into driving out the combustor rumble tones, I was just a little surprised a relatively modern engine/airframe combination such as the GE90/777 had such an intense and booming resonance to it! |
The Trent 1000's do it in a big way...you can hear RR 787's start up at Boeing Field from the park just north of the Boeing ramp if you know what you're listening for. It's not particularly disruptive, just very low pitch and distinctive...the 787 has great bass!
Tom.
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- maddogjt8d
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RE: Surprise At GE90 Noise Levels On Startup!
The RR Trent 895 does not have a loud combustor rumble at all. It only whines right before the engine reaches idle. See video examples:
http://www.youtube.com/watch?v=P2J8YsKokWo
http://www.youtube.com/watch?v=x0A2xn7CUps
http://www.youtube.com/watch?v=YmZdlUWOQOQ
http://www.youtube.com/watch?v=P2J8YsKokWo
http://www.youtube.com/watch?v=x0A2xn7CUps
http://www.youtube.com/watch?v=YmZdlUWOQOQ
RE: Surprise At GE90 Noise Levels On Startup!
one of the more distinctive sounds on the airport. can always recognise the sound of a GE90 on start up. other one being the sound off a rolls royce 744 taxi past, always recognisable without being able to see it
RE: Surprise At GE90 Noise Levels On Startup!
I flew on a 77L last night (haven't been on a GE90 equipped aircraft in months) and definitely noticed the loud rumble on start-up. I was sitting just aft of the wings and the noise almost completely blocked out the Service Director talking on the PA.
RE: Surprise At GE90 Noise Levels On Startup!
The CF34's that we have on our 190's have one heck of a low groan during their startup as well. The first time I heard one start up outside my hangar I thought an AA A300 was starting up over at T8...but nope, it was the little E190! I love it when that thing vibrates my bootie when it starts up 
RE: Surprise At GE90 Noise Levels On Startup!
| Quoting B6JFKH81 (Reply 9): The CF34's that we have on our 190's have one heck of a low groan during their startup as well. The first time I heard one start up outside my hangar I thought an AA A300 was starting up over at T8...but nope, it was the little E190! I love it when that thing vibrates my bootie when it starts up |
Now that you mention it, I've been noticing when they start cold, they do make quite a bit of noise (more than a 73G cold start).
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- ThrottleHold
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RE: Surprise At GE90 Noise Levels On Startup!
The noise is caused by "rotor bow". This is due to uneven cooling of the trubine blades after engine shutdown. It was subject to a Boeing information bulletin quite some time ago.
RE: Surprise At GE90 Noise Levels On Startup!
| Quoting ThrottleHold (Reply 11): The noise is caused by "rotor bow". This is due to uneven cooling of the trubine blades after engine shutdown. |
Rotor bow is different than combustor tone. Modern engines have bowed rotor logic in the EEC's to detect and work around it, but combustor tone is a physical property of the combustor and, if an engine has it, it's going to have it until you change the design.
Tom.
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