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GE90-115B spool-up response

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In PMDG 777, it takes about 9 seconds from idle thrust to 55% N1 thrust (then push TOGA button) and seems to be slower spool-up response.

In reality,  I feel it takes about 7 seconds from idle thrust to 55% N1 thrust.

Please give me your comment about true engine spool-up response.

Thank you.

Tetsuji Konohira

 

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You can watch spool-up response in the YouTube video "B777 Takeoff RWY 13R".

Start advancing the throttle :  0:39

N1 reaches around 55% N1 :  0:46

It takes approx. 7 seconds from Idle thrust to 55% N1.

Tetsuji Konohira

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That would depend on if the Auto Throttle is being used?

I know in my Airline, some pilots take their time advancing the thrust, while others almost fire wall the damn things.

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I understand that the time to take advancing the thrust from idle to 55% N1 (before pushing TOGA button) depends on pilots. 

So I would like to show you the time difference between "Commanded N1" and "N1 indication".

In the YouTube video "B777 Takeoff RWY 13R",

#1. Start advancing the throttle (by the Captain) :  0:39

#2. Throttle lever position (commanded N1) reaches at approx. 55% : 0:41 (N1 indication still around idle N1)

#3. N1 indication reaches commanded N1 (55%): 0:46

The time difference between #2 and #1 (2 seconds) depends on pilots.

The time difference between #3 and #2 (5 seconds) shows engine response from idle thrust to 55% N1.

 

In PMDG 777,

#1. Start advancing the throttle (by me) :  0:00 (N1 indication at 21.6%)

#2. Throttle lever position (commanded N1) reaches at approx. 55% : 0:02 (N1 indication at approx. 23%)

#3. N1 indication reaches commanded N1 (55%): 0:12

The time difference between #2 and #1 (2 seconds) matches to above YouTube video.

The time difference between #3 and #2 (10 seconds) shows engine response from idle thrust to 55% N1.

As the result, PMDG 777 takes twice the time. (10 sec. vs 5 sec.)

Thank you.

Tetsuji Konohira

  

 

 

 

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Hi,

Your comparison with a video seems to me a little biased if you consider only the spool up time without taking account the atmospheric conditions.
One of the parameters which limits the spool up rate of a jet engine is the pressure ratio at the level of the compressor stages.

So in the case you are explaining, you would need to have the exact same air characteristics than in the video (which includes the atmospheric pressure, temperature, density, humidity...).

PMDG did develop the 777 with real figures and people working in and around the T7 (pilots, flight engineers...) so I would guess that the spool up time is as real as it gets.

In any case, if you have a doubt about the accuracy of the spool up time, PMDG asks to document it with real material. ;-)

If you could get the external conditions in the video, the condition of the engines themselves and reproduce the exact same in the simulator, that would be a good start. 

 

Edit, there is another thread about spool up time but it is on the NGX forum related to the CFM56. However there is a good explanation on how the ambient conditions may affect jet engines performance which also applies to the GE90:

http://www.avsim.com/forums/topic/505618-engine-response-time/?do=findComment&comment=3585578

  • Upvote 2

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21 hours ago, Budbud said:

PMDG asks to document it with real material

Exactly this.

We aren't going to launch an investigation on feelings. The only time we consider stuff like that is if it comes from the Tech Team, whose feelings and intuitions are backed by actual, verified experience, and not a YouTube PhD.

  • Upvote 1

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53 minutes ago, scandinavian13 said:

Exactly this.

We aren't going to launch an investigation on feelings. The only time we consider stuff like that is if it comes from the Tech Team, whose feelings and intuitions are backed by actual, verified experience, and not a YouTube PhD.

Just curious, where does one exactly get a YouTube PhD? You know, for science.

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Hi.

>PMDG asks to document it with real material

>We aren't going to launch an investigation on feelings. The only time we consider stuff like that is if it comes from the Tech Team, whose feelings >and intuitions are backed by actual, verified experience, and not a YouTube PhD.

Since I am not interested in getting a YouTube Phd, so I hope someone will provide you a document with real material.

Thank you.

Tetsuji Konohira

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16 minutes ago, 19dcavscout said:

Just curious, where does one exactly get a YouTube PhD? You know, for science.

haha - I think there are a few YouTube videos that can explain it.

In all seriousness, you can learn a ton of good stuff on YouTube. The problem is that YouTube and aviation doesn't give a clear enough picture for anything other than a cursory bit of data collection, so even the YouTube PhD won't cut it.

...the YouTube PhD isn't meant to be pejorative, either, btw: I learned how to code using a bunch of YouTube videos and a few books.

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