Moderators: richierich, ua900, PanAm_DC10, hOMSaR

skywalker92
Topic Author
Posts: 62
Joined: Thu Aug 06, 2015 8:45 am

How N1 And N2 Are Calculated?

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
How They Fly ✈✈

Tristarsteve
Posts: 3670
Joined: Tue Nov 22, 2005 11:04 pm

RE: How N1 And N2 Are Calculated?

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

skywalker92
Topic Author
Posts: 62
Joined: Thu Aug 06, 2015 8:45 am

RE: How N1 And N2 Are Calculated?

Got it. Thanks a lot
How They Fly ✈✈

Posts: 530
Joined: Thu Apr 08, 2010 8:19 pm

RE: How N1 And N2 Are Calculated?

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
Posts: 14
Joined: Thu Jan 21, 2016 9:26 pm

RE: How N1 And N2 Are Calculated?

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
FFF

Starlionblue
Posts: 20092
Joined: Fri Feb 27, 2004 9:54 pm

RE: How N1 And N2 Are Calculated?

 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%.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: How N1 And N2 Are Calculated?

 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.

Starlionblue
Posts: 20092
Joined: Fri Feb 27, 2004 9:54 pm

RE: How N1 And N2 Are Calculated?

 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".
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

Who is online

Users browsing this forum: No registered users and 26 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos