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Robi77

N1 button in B-737-800

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Can anybody tell me what that N1 ( N1 Set ) button on a FSX Boeing 737-800 meansand what the purpose is ?Thanks

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Can anybody tell me what that N1 ( N1 Set ) button on a FSX Boeing 737-800 meansand what the purpose is ?
It's an autothrottle setting. When engaged it tells the A/T to advance to the N1 limit you have set in the FMC (or with a separate N1 setting dial which changes the same value). The limit is marked on the N1 dials on the EICAS display.N1 mode is used during Take-Offs and Go-Arounds, then being set automatically by the TO/GA buttons on the throttles.RegardsPete

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To expand on what Pete has said, the N numbers you see for engines generally refer to the compressor blade stages in an engine, typically being numbered from the front to the back of the engine (so N1 is at the front, N2 is behind it, etc). Different compressor stages are also often mounted concentrically on sleeved shafts with the N1 shaft sleeved over by the N2 shaft etc (depending on how many compressor stages the engine has).The N1 value you see on the instruments refers to the first stage of the compressor (i.e the fan blades you can see from the front of a jet plane) and how fast it is rotating. The actual figure for N1 is a percentage of the maximum rotation it is designed to handle, so if it can rotate at a maximum of 10,000 rpm, then 90 percent N1 is 9,000 rpm. You do occasionally see percentages over 100 percent (meaning the fan is rotating over its normal maximum RPM), and that can be done for either a limited time, or can also be when the engine is re-rated, but the figures in the instrumentation software have not been changed to reflect the new rating of the engine.To make use of the N1 figure, you typically put a value into the FMC which controls the thrust the engine will use. That's the kind of thing Cost Index is about on an FMC, where the engines might only use a certain percentage of the maximum available thrust for economic flight when controlled by the autothrottle, or to extend the aircraft's range or whatever. It is also what you screw around with to make de-rated take-offs, which you might do for reasons of economy, or to adhere to noise abatement regulations, or if the static air temperature is in any way out of the ordinary.Al

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Wish to revive this topic re N1 Set - Auto and Both settings. . In the fsx 737-800 the N1 Set rotary switch is inoperable. Some people I notice have used this switch to allow adjustment of the N1 setting which Ive worked out in reality is done via the FMC. I notice in the ifly version it rotates between Auto and Both when clicking on it but reading the ifly documents it is not clear what the purpose of the Auto setting is vs. selecting Both.. can someone advise.

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I have no idea what the iFly 737 actually models, but 'Auto' means that the N1 bugs get set by the FMC. If you wanted to set the bugs manually, then '1' and '2' means you are individually setting either engine 1 or 2 bugs manually with the knob. 'Both' means you are manually setting the bugs for both 1 and 2 simultaneously with the knob.

 

Not that it matters, but I believe this old topic you've dug up from the grave actually refers to the N1 button on the MCP, not the knobby thing to set the bugs that you are inquiring about.

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thanks.. I am in the midst of making a FIP gauge for the 737-8 incorporating the AP items and I'm including the Auto Brakes and the N1 Set rotary. The available sim variables make it difficult but ifly seems to have done it in their 737s. Question for clarification.. on the real aircraft, in N1 Set-Auto mode, when the N1 button is pressed I take it that activates the FMC calculated N1%. But when 1, 2, or Both options are selected how is the N1 bug actually moved. Is that rotary a double rotary performing both N1 Set and N1 Var functions.

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The knob has two sections, inner and outer, much like the com and nav radio knobs. So you have NI SET, then engines 1, 2 and Both. Next to it you can manually set the Speed Referances, V1, VR, Vref etc, and this sets the bugs on the PFD. Make your selections using the outside knob, then change the numbers using the inside knob

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