Thrust
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GE-90 Questions

Mon Dec 05, 2011 5:02 pm

I just figured I'd ask this because quite potentially, with an engine capable of producing 115,000 pounds of thrust, we could potentially build a jet much bigger than the A380. I realize that certain penalties are carried with the GE-90: weight and fuel efficiency being among them. I remember reading somewhere that compared to the Trent 500, the GE-90 burns much more fuel. I'm also slightly curious as to why the GE-90 is so noisy from the perspective of a passenger, yet so quiet on the outside. That's something I've never really understood. Its noise range seems to be narrow, but up close it's deafening, especially at startup and on takeoff.
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Stitch
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RE: GE-90 Questions

Mon Dec 05, 2011 5:59 pm

The "critics consensus" is that the next likely step-change in capacity will be Blended Wing Bodies (BWB) and many of the artist conceptions of such a vehicle show three large high-bypass turbofans in the class of the GE90 / Trent 900 / GP7000.

As to the noise of the GE90, it's pretty loud on the outside at takeoff thrust.   At takeoff power, the blade tips are moving at around Mach 1.2, which is quite high and likely accounts for a not-insignificant amount of noise.

This thread has some good info on the GE90: RPM Of Jet Engines During Take-off (by MerlinIIIB Jun 9 2006 in Tech Ops)
 
Thrust
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RE: GE-90 Questions

Mon Dec 05, 2011 11:53 pm

I was just saying that relative to the average spotter, it's not that loud. For example, it's not anywhere close to as loud as the 747 classics, DC-10s, or L-1011 engines, and not nearly as loud as the turbojets. The sound just doesn't trail behind it. You only really hear it if you're up close to it.
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redflyer
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RE: GE-90 Questions

Tue Dec 06, 2011 12:24 am

Quoting Thrust (Reply 2):
I was just saying that relative to the average spotter, it's not that loud. For example, it's not anywhere close to as loud as the 747 classics, DC-10s, or L-1011 engines, and not nearly as loud as the turbojets. The sound just doesn't trail behind it. You only really hear it if you're up close to it.

Well, those other planes you list do have more engines than the 777, and I believe the 777 is the only plane that uses the GE90, so perhaps that explains the difference in noise levels?
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loggat
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RE: GE-90 Questions

Tue Dec 06, 2011 3:18 am

It would be louder than the older engines except for the technology improvements in noise control. This is done by adjusting the design of the tailcone to mix the core air and the fan air in such a way that the sound frequencies cancel each other out to make the overall noise less. A muffler effect, if you will. This is how it was explained to me in Jet engine school anyway. Someone can feel free to correct me.
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Starlionblue
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RE: GE-90 Questions

Tue Dec 06, 2011 4:10 am

Quoting Stitch (Reply 1):
The "critics consensus" is that the next likely step-change in capacity will be Blended Wing Bodies (BWB) and many of the artist conceptions of such a vehicle show three large high-bypass turbofans in the class of the GE90 / Trent 900 / GP7000.

The reason for the three engines is that the original study was done by McDonnell Douglas.

Then again, three engines is a great number if you don't have deal with pesky tail engine mounting like on the L-1011 or DC-10. One less than four, meaning less complexity, but 2/3 of thrust left in an engine out situation.

Quoting Thrust (Thread starter):
I just figured I'd ask this because quite potentially, with an engine capable of producing 115,000 pounds of thrust, we could potentially build a jet much bigger than the A380.

Sure, it is possible. But as mentioned such a large airliner might well not be a tube with wings. And just because something is possible doesn't mean it makes sense to build.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
tdscanuck
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RE: GE-90 Questions

Tue Dec 06, 2011 5:15 am

Quoting Thrust (Thread starter):
I realize that certain penalties are carried with the GE-90: weight and fuel efficiency being among them.

Until the Trent1000/GeNX came along, I believe the GE90 had the best TSFC in the game. You don't pay a fuel efficiency penalty to use it.

Quoting Thrust (Thread starter):
I remember reading somewhere that compared to the Trent 500, the GE-90 burns much more fuel.

Of course it does, it's significantly larger. That's why you use TSFC, not fuel flow, to compare differently sized engines.

Tom.
 
cobra27
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RE: GE-90 Questions

Tue Dec 06, 2011 9:56 am

Quoting tdscanuck (Reply 6):

Until the Trent1000/GeNX came along, I believe the GE90 had the best TSFC in the game. You don't pay a fuel efficiency penalty to use it.

The A380 engines both RR and GP7200 have around 4 % better SFC

Quoting Thrust (Thread starter):
m. I remember reading somewhere that compared to the Trent 500, the GE-90 burns much more fuel.

Its only normal since it develops almost twice as much thrust.
 
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RE: GE-90 Questions

Tue Dec 06, 2011 2:23 pm

Quoting cobra27 (Reply 7):
Quoting tdscanuck (Reply 6):

Until the Trent1000/GeNX came along, I believe the GE90 had the best TSFC in the game. You don't pay a fuel efficiency penalty to use it.

The A380 engines both RR and GP7200 have around 4 % better SFC

Good data. That still fits with the chronology, since the Trent 900 and GP7200 were developed after the GE90.
Can anyone confirm if, at the time the GE90 was developed, it was the top of the TSFC pile?

Tom.
 
OldAeroGuy
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RE: GE-90 Questions

Tue Dec 06, 2011 2:54 pm

Quoting tdscanuck (Reply 8):
Can anyone confirm if, at the time the GE90 was developed, it was the top of the TSFC pile?

True at the introduction of the GE90. The -115B is slightly worse than the -94B as it has a lower bypass ratio.
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ferpe
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RE: GE-90 Questions

Wed Dec 07, 2011 5:42 pm

This is from an AVNews interview with GEs Brisken from 2006, thus the GEnx data is Boeing target I assume:

In fact, GEnx will achieve a 15.4% cut in SFC over the CF6-80C2B6F, the powerplant of the 767-300ER, Brisken says. GEnx also should have a 6.9% SFC advantage over the GE90-94B, which powers the 777-200ER.

Now the actual cruise TSFC of these engines are closly guarded but I have the following:

PianoX original 2005 description of 788: GEnx/T1000 0.5279 lb/hr/lbf (this should then be the Boeing target TSFC I assume)

There are others floating around internet but they are for other versions of CF6 like:

CF6-80C2B1F 0.605 for the 747

The above should put the GE90-94B around 0.56 lg/hr/lb.


As the TXWB shall be 2% better then the T1000 we can assume this to be somewhere at 0.517
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ferpe
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RE: GE-90 Questions

Thu Dec 08, 2011 3:39 am

Quoting ferpe (Reply 10):
The above should put the GE90-94B around 0.56 lb/hr/lb.

For Thrusts benefit, the way you use such a figure is to multiply it with the cruise thrust in lb and then you get consumption in lb/hr.

Please understand that cruise thrust is VERY different to the 94000 lb that is the engines max take-off rating. In practice an airliner like the 777 need something like 10000-15000 lb per engine to keep M0.84 at typical cruise heights of 40 000 feet, so you end up with a consumption something like 10-20000 lb /hour depending on actual weight of the frame in the instant that you measure fuel burn.
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CX Flyboy
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RE: GE-90 Questions

Thu Dec 08, 2011 4:22 am

The answer from the office is that the GE90, much like the GeNx on the 748 growls during engine start because of 'bowed rotors'.
 
tdscanuck
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RE: GE-90 Questions

Thu Dec 08, 2011 4:40 am

Quoting CX Flyboy (Reply 12):
The answer from the office is that the GE90, much like the GeNx on the 748 growls during engine start because of 'bowed rotors'.

At what point in the start are you talking about? The bowed rotor logic in the EEC, at least on the GEnX, will take out the bow before you accelerate up to idle.

Tom.
 
hal9213
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RE: GE-90 Questions

Thu Dec 08, 2011 12:59 pm

Quoting Thrust (Thread starter):
I'm also slightly curious as to why the GE-90 is so noisy from the perspective of a passenger, yet so quiet on the outside.

I think by pure engine noise, it is the loudest engine I have ever heard. All other older planes (as somebody mentioned) have louder exhaust stream noise, but considering the actual engine -not counting airflow noise-, GE90 is by far the loudest.
Actually, when a 77W flies over you at 5k feet, you can clearly hear the GE90 sound, whereas on many other planes you only hear the "general exhaust stream noise". An exception would also be the typical A320 noise, which again is nacelle airflow noise, and trent engine "vibration noise" which is by far harder to recognise.

Quoting CX Flyboy (Reply 12):
The answer from the office is that the GE90, much like the GeNx on the 748 growls during engine start because of 'bowed rotors'.

Can you elaborate more on the startup growling? I always found that sound very interesting and was wondering, where that (technically) comes from.
 
Thrust
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RE: GE-90 Questions

Sat Dec 17, 2011 8:38 am

Are any engines with more power than the GE-90 being considered at this time? My simple point on this is that four GE-90s open up the possibility for us to possibly develop an aircraft on a scale of incomprehensible size.
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Stitch
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RE: GE-90 Questions

Sat Dec 17, 2011 4:14 pm

Quoting Thrust (Reply 15):
Are any engines with more power than the GE-90 being considered at this time?

Not seriously (as in anything other then computer modeling).
 
tdscanuck
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RE: GE-90 Questions

Sat Dec 17, 2011 4:14 pm

Quoting Thrust (Reply 15):
Are any engines with more power than the GE-90 being considered at this time?

If they are, the OEM's aren't talking about it. I'm not sure there'd be any market for it even if they built one, except maybe stationary power generation.

Quoting Thrust (Reply 15):
My simple point on this is that four GE-90s open up the possibility for us to possibly develop an aircraft on a scale of incomprehensible size.

When you get to that size, engines are not the problem.

Tom.
 
GRZ-AIR
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RE: GE-90 Questions

Sat Dec 17, 2011 9:31 pm

The reason for the loud grumbling of the GE-90 during engine start is due to the large diameter of the moving parts inside. Heat rises, so after a 2hour turn around, the temperature inside the engine is lower at the bottom than at the top. This leads to imbalance which causes vibration/rumbling. As soon as things heat up (after a few seconds), vibration decreases.
As said, this only applies to the starting phase.

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