Brucekn
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GE90-115B taxi thrust

Mon Mar 12, 2018 4:20 am

I did a search on “GE90-115B taxi thrust” and got some hits but didn’t answer my question.

I have just made a round trip from LAX to AKL on NZ, flying in their B77W (NZ 1 / NZ6). I was in “steerage” in the back of the aircraft so engine sound is somewhat limited to the sound of thrust, and less so the sound from the turbines, although the distinct startup resonance was very loud in the aircraft.

I noted that when taxing out to take-off at LAX and AKL, that the aircraft seemed to move effortlessly and didn’t appear to require additional thrust from idle to “un-stick” the aircraft. We appeared to reach what I would call a fast taxi in both instances, once again without any additional thrust beyond idle.

What I’m wondering is if “idle” thrust is able to be set from gross weight, or if there is just one setting for “idle” thrust and it’s sufficient to enable an aircraft with fuel for an 11.5 hour flight (approximately) to taxi? I also noted on landing (presuming considerable fuel weight consumed in flight) that the aircraft didn’t need a lot of braking action- hence I’m wondering if take-off “idle” thrust is higher- and if so, how is it set?

Thanks.
 
Brucekn
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Re: GE90-115B taxi thrust

Mon Mar 12, 2018 4:35 am

Thanks for pointing this post to the correct forum.
 
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EK413
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Re: GE90-115B taxi thrust

Mon Mar 12, 2018 4:38 am

Brucekn wrote:
I did a search on “GE90-115B taxi thrust” and got some hits but didn’t answer my question.

I have just made a round trip from LAX to AKL on NZ, flying in their B77W (NZ 1 / NZ6). I was in “steerage” in the back of the aircraft so engine sound is somewhat limited to the sound of thrust, and less so the sound from the turbines, although the distinct startup resonance was very loud in the aircraft.

I noted that when taxing out to take-off at LAX and AKL, that the aircraft seemed to move effortlessly and didn’t appear to require additional thrust from idle to “un-stick” the aircraft. We appeared to reach what I would call a fast taxi in both instances, once again without any additional thrust beyond idle.

What I’m wondering is if “idle” thrust is able to be set from gross weight, or if there is just one setting for “idle” thrust and it’s sufficient to enable an aircraft with fuel for an 11.5 hour flight (approximately) to taxi? I also noted on landing (presuming considerable fuel weight consumed in flight) that the aircraft didn’t need a lot of braking action- hence I’m wondering if take-off “idle” thrust is higher- and if so, how is it set?

Thanks.


Probably best you ask this question the technical /operations thread?

viewforum.php?f=5

EK413
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Tartarus
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Re: GE90-115B taxi thrust

Mon Mar 12, 2018 4:50 am

Ground idle on the GE90 is about 21% N1. This is usually a sufficient amount of "breakaway" thrust to get it moving under most conditions, as long as there's not an uphill slope or soft tarmac.
At MTOW, I'd usually add a little, up to maybe 26 or 27%, just to get it moving, then reduce to idle again.
Ground idle is the same before takeoff as it is after landing.

Even at ground idle, there's a lot of jet blast out of the back, so it's really important to only use the minimum thrust required.
 
ikramerica
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Re: GE90-115B taxi thrust

Mon Mar 12, 2018 5:20 am

Would you hear the increase from 21-26% as a passenger especially if you went back to 21% quickly?
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767333ER
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Re: GE90-115B taxi thrust

Mon Mar 12, 2018 5:50 am

ikramerica wrote:
Would you hear the increase from 21-26% as a passenger especially if you went back to 21% quickly?

You would be able to hear it as the engine itself goes higher pitched, the cabin air flow probably increases, and the jet blast noise increases depending in where you sit. The GE90is one of those engines though that seems louder at idle than slightly above as it seems to have a very loud groan at idle.
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Brucekn
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Re: GE90-115B taxi thrust

Mon Mar 12, 2018 10:24 pm

Thanks for the replies. What amazed me was the (apparent) lack of braking needed after 11.5 hours of flight, assuming the same idle thrust was used for taxi to take-off and taxi from landing to the gate.
 
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Starlionblue
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Re: GE90-115B taxi thrust

Mon Mar 12, 2018 11:10 pm

Brucekn wrote:
Thanks for the replies. What amazed me was the (apparent) lack of braking needed after 11.5 hours of flight, assuming the same idle thrust was used for taxi to take-off and taxi from landing to the gate.


The slope of the taxiway has a big effect on the need for braking. So that may have been a factor.
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FriscoHeavy
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Re: GE90-115B taxi thrust

Tue Mar 13, 2018 2:43 pm

Brucekn wrote:
Thanks for the replies. What amazed me was the (apparent) lack of braking needed after 11.5 hours of flight, assuming the same idle thrust was used for taxi to take-off and taxi from landing to the gate.



Lack of braking on the runway at touchdown? The fact that it was an 11 1/2 hour flight has nothing to do with that. At the end of a given flight, most aircraft will be rather light.
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FlyHossD
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Re: GE90-115B taxi thrust

Tue Mar 13, 2018 3:13 pm

Starlionblue wrote:
The slope of the taxiway has a big effect on the need for braking. So that may have been a factor.


Beat me to it - thumbs up.

Yes, slope plays a big factor in the thrust needed for taxi as does weight. Also, the type of surface - concrete versus asphalt for example - plays a role, too. On a hot day, asphalt "gives" (think "spongy") more than concrete, so taxiing on concrete takes less thrust.
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TOGA10
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Re: GE90-115B taxi thrust

Tue Mar 13, 2018 3:48 pm

FriscoHeavy wrote:
Brucekn wrote:
Thanks for the replies. What amazed me was the (apparent) lack of braking needed after 11.5 hours of flight, assuming the same idle thrust was used for taxi to take-off and taxi from landing to the gate.



Lack of braking on the runway at touchdown? The fact that it was an 11 1/2 hour flight has nothing to do with that. At the end of a given flight, most aircraft will be rather light.

I think Starlionblue was talking about the taxi in after vacating the runway, as was the OP.
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Brucekn
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Re: GE90-115B taxi thrust

Tue Mar 13, 2018 11:56 pm

TOGA10 wrote:
FriscoHeavy wrote:
Brucekn wrote:
Thanks for the replies. What amazed me was the (apparent) lack of braking needed after 11.5 hours of flight, assuming the same idle thrust was used for taxi to take-off and taxi from landing to the gate.



Lack of braking on the runway at touchdown? The fact that it was an 11 1/2 hour flight has nothing to do with that. At the end of a given flight, most aircraft will be rather light.

I think Starlionblue was talking about the taxi in after vacating the runway, as was the OP.


Yes- thanks, lots of braking at touchdown until evacuating the runway. Arrival airport was AKL (outbound) and LAX (inbound). But I’ve had my question answered- no different thrust settings at idle. Thanks to everyone for their comments.

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