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skywalker92
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How N1 And N2 Are Calculated?

Thu Jan 21, 2016 11:29 am

How the N1 and N2 (N3 in RR some engines) calculated in a gas turbine engine? Do they accomodate an iquipment like a Tachogenerator? Some one please explain
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Tristarsteve
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RE: How N1 And N2 Are Calculated?

Thu Jan 21, 2016 1:39 pm

On the RR engines, N3 signal comes from a tachogenerator on the gearbox.
The N1 and N2 signal comes from speed sensors. ( Same system on the PT6 engine.)
A sensor gives a pulse every time a target goes past. The target is on on a phonic wheel which is part of the rotating spool, and the sensor is in the compressor housing. there are three sensors for each spool in case one fails as they are buried inside the engine.
Most engines have similar systems
 
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skywalker92
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RE: How N1 And N2 Are Calculated?

Fri Jan 22, 2016 5:08 am

Got it. Thanks a lot
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Horstroad
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RE: How N1 And N2 Are Calculated?

Fri Jan 22, 2016 12:29 pm

For the GE90 N1 and N2 speed signals come from speed sensors, each with three outputs.
The LP and HP shafts each have a wheel with teeth that cause
electromagnetic pulses as they go by the speed sensors.

One N1 speed sensor output goes to channel A of the EEC. The other goes to
channel B. The third speed sensor output goes to the EDIU, AIMS, and AVM
signal conditioner.

Same for the N2 Sensor, except it does not output to the EDIU
 
flyflewflown
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RE: How N1 And N2 Are Calculated?

Wed Jan 27, 2016 9:06 pm

Thanks for explaining how the RPMs are determined. But is that the same as determining N1/2/3?
How is the max actually determined?

Thanks
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Starlionblue
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RE: How N1 And N2 Are Calculated?

Thu Jan 28, 2016 12:03 am

Quoting flyflewflown (Reply 4):

Thanks for explaining how the RPMs are determined. But is that the same as determining N1/2/3?
How is the max actually determined?

The maximum is a nominal "redline" rpm based on design and testing. Basically what you want and expect the spool to do at maximum. N1/2/3 are actual rpm as a percentage of that maximum.

Given that the maximum is not a physical limit but a nominal one, N1/2/3 may in some cases exceed 100%. For example if the engine has been improved or it is found that TOGA thrust can be higher than was expected during design.

A related example are the Space Shuttle Main Engines, which in testing turned out to be able to run at more than 100% thrust. The nominal 100% thrust remained the same, and the actual in service maximum was 107%.
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rwessel
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RE: How N1 And N2 Are Calculated?

Mon Feb 01, 2016 11:14 am

Quoting Starlionblue (Reply 5):
A related example are the Space Shuttle Main Engines, which in testing turned out to be able to run at more than 100% thrust. The nominal 100% thrust remained the same, and the actual in service maximum was 107%.

That's a bit backwards. The 100% number is from the original design. The design was enhanced, but the 100% mark was not moved. The "new" design was supposed to run at 110% as its normal power level, but NASA was never able to get really reliable operation at that power level (RUDs, not just minor failures), and the limit from testing ended up being 107/108%. Late in the program NASA cleared 110% for emergency use.
 
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Starlionblue
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RE: How N1 And N2 Are Calculated?

Tue Feb 02, 2016 12:09 pm

Quoting rwessel (Reply 6):

Quoting Starlionblue (Reply 5):
A related example are the Space Shuttle Main Engines, which in testing turned out to be able to run at more than 100% thrust. The nominal 100% thrust remained the same, and the actual in service maximum was 107%.

That's a bit backwards. The 100% number is from the original design. The design was enhanced, but the 100% mark was not moved. The "new" design was supposed to run at 110% as its normal power level, but NASA was never able to get really reliable operation at that power level (RUDs, not just minor failures), and the limit from testing ended up being 107/108%. Late in the program NASA cleared 110% for emergency use.

Fair point that the design was enhanced and not revealed to be better in testing. But the point is that "100%" was an arbitrary value, not "maximum achievable".
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