TRENT1000TEN
Topic Author
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Joined: Sun Apr 30, 2017 6:15 pm

C-Series - N1 SYNC on EICAS

Tue Aug 08, 2017 10:54 pm

Watching this video https://www.youtube.com/watch?v=f8UqwKmZAPY, I noticed that on the EICAS there was a "SYNC" annunciation below the engine's N1. Any idea of what purpose this could serve? Engines with TPR/EPR/etc are known to have different N1 readings in order to keep the EPR/TPR/% Thrust the same. What purpose would an N1 SYNC function serve on an engine that uses N1 as its primary?


Thanks :bouncy:

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767333ER
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 12:28 am

Maybe it helps with noise. I know that when two engines are running at different speeds the sounds emitted will be at different pitches and will constantly be going in and out of phase causing an annoying beat of noise.
Been on: 732 733 734 73G 738 752 763 A319 A320 A321 CRJ CR7 CRA/CR9 E145 E175 E190 F28 MD-82 MD-83 C172R C172S P2006T
 
GalaxyFlyer
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 1:14 am

That's it--the engines, both of them, are sync'd on N1
 
Max Q
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 4:18 am

N1 sync is pretty common, we had it on the MD80.

In cruise only you would manually sync the N1's than turn on the sync and it would
(supposedly) keep the fan speed synchronized, some worked, some didn't.


If it did, it made for a far more peaceful rear cabin.
The best contribution to safety is a competent Pilot.
 
TRENT1000TEN
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 4:49 am

GalaxyFlyer wrote:
That's it--the engines, both of them, are sync'd on N1


But doesn't autothrottle/autothrust already sync N1s for N1 engines?
 
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rjsampson
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 5:14 am

Max Q wrote:
N1 sync is pretty common, we had it on the MD80.

In cruise only you would manually sync the N1's than turn on the sync and it would
(supposedly) keep the fan speed synchronized, some worked, some didn't.


If it did, it made for a far more peaceful rear cabin.


...and when it didn’t, it was agonizing for those of us in the very back of the plane. So many memories growing up in the back of DC-9s listening to the “wah-wahs” of out of sync enginges, particularily on climbout.
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
mmo
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 6:16 am

TRENT1000TEN wrote:
GalaxyFlyer wrote:
That's it--the engines, both of them, are sync'd on N1


But doesn't autothrottle/autothrust already sync N1s for N1 engines?



No!
If we weren't all crazy we'd all go insane!
 
AA737-823
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 6:31 am

mmo wrote:
TRENT1000TEN wrote:
GalaxyFlyer wrote:
That's it--the engines, both of them, are sync'd on N1


But doesn't autothrottle/autothrust already sync N1s for N1 engines?



No!


...Then how on Earth does Autothrottle work... Best guess? Throw in some fuel and assume it's making the right fan speed?
 
gloom
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 8:27 am

AA737-823 wrote:
...Then how on Earth does Autothrottle work... Best guess? Throw in some fuel and assume it's making the right fan speed?


Autothrottle is a completely different thing.

N1, fan speed, in perfect world would be the same for both engines. However, the world is nowhere near perfect place. With front fan rotating at a speed, a little bit of difference every here and there (differences - very minimal - to everything from combustion chamber to fan blades, both in terms of mass and geometry) counts. To maintain N1 for both engines, you need to carefully adjust every engine parameters to match that N1.

Back a couple of years ago, it happened quite often to have slightly different parameters - even N1 on takeoff/climb/cruise were quite different, especially with procedure to put two very different engines (one with thousands of hours was matched against new/rehauled one, to reduce chances for emergency stop with both engines).

Cheers,
Adam
 
mmo
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Re: C-Series - N1 SYNC on EICAS

Wed Aug 09, 2017 9:49 am

AA737-823 wrote:

...Then how on Earth does Autothrottle work... Best guess? Throw in some fuel and assume it's making the right fan speed?


If you are asking about an auto-throttle system in a current generation aircraft such as the 777/787, it's a very complicated system.

Quite simply, the FMC monitors several parameters such as airspeed actual/commanded, the instantaneous acceleration, the SAT, current parameters just to name a few. From the difference between the actual IMN/IAS and the commanded value, the FMC will then move the thrust levers to increase/decrease the airspeed. The inputs are very small and the corresponding increase/decrease of speed is not too fast.

The FADEC has nothing to do (directly) with the auto-throttle system. The FADEC provides protection for overspeed, overtemp, over pressure just to name a few. They do not control the inputes to the FADEC, the FMC would do that, assuming the auto-throttle is engaged/active.

You can even stagger the throttles and the system will make the necessary inputs to maintain speed, the thrust levers will stay staggered.
If we weren't all crazy we'd all go insane!
 
Max Q
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Re: C-Series - N1 SYNC on EICAS

Fri Aug 11, 2017 1:50 am

Even on older jets without N1 sync all it took was a little effort from the Pilots to keep the
N1's lined up, unfortunately for some that was too much exertion and the noise in the
back was not pleasant.
The best contribution to safety is a competent Pilot.

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