Question about "N1"

[cleared4theoption]

I'm posting this here because the main reason for the question is sim-related

In my quest to follow as many real life procedures while flying my CRJ I have a question about Setting and using the N1 in the auto-pilot. I have downloaded a set of real procedures and checklists. The take-off checklist mentions setting the N1 to 70-75%, my auto pilot has a dial for setting the N1 and a button to activate it...what is that all about?

 

[wabower]

N1 is engine fan speed, the big mother you see turning in the front of the nacelle on turbo-fan engines. It pushes the by-pass air that creates most of the low-speed thrust.

I'm posting this here because the main reason for the question is sim-related

In my quest to follow as many real life procedures while flying my CRJ I have a question about Setting and using the N1 in the auto-pilot. I have downloaded a set of real procedures and checklists. The take-off checklist mentions setting the N1 to 70-75%, my auto pilot has a dial for setting the N1 and a button to activate it...what is that all about?

 

[cleared4theoption]

N1 is engine fan speed, the big mother you see turning in the front of the nacelle on turbo-fan engines. It pushes the by-pass air that creates most of the low-speed thrust.

Cool...I guess the bigger question, as it relates to flying the plane, is how does it effect the engine performance at different settings? Do I leave it at 75%...and how is it used in the context of the auto pilot?

 

[taters]

.The take-off checklist mentions setting the N1 to 70-75%, my auto pilot has a dial for setting the N1 and a button to activate it...what is that all about?

This is the N1 target setting for takeoff, it is calculated by the FMS after certain parameters are known such as Gross Weight, temperature, RW length etc.
There is a target setting for Takeoff , Climb and Cruise. The CRJ does not have an autothrottle so you are given targets to follow manually on the EICAS screen so you dont turn the engines into lava.


This 75%ish figure would be in reference to a "Flex" or reduced power setting takeoff. Mostly done to save engine life..., this cant be done on a wet runway, first flight of day, or on some runways.

For the last question....N1 measures % of maximum power which varies with altitude and temp. Basically the higher you go the less air molecules the engine has availible to keep it cool (decreasing air density)so 75%n1 is less actual thrust (& fuel burn) at FL390 then at 3900 ft.

 

[wabower]

Depends on the level of automation in the airplane. Most 500 and 600-series Citations have manual power controls, so N1 settings are used to control power settings, similar to MP settings in HP airplanes or RPM (tach) settings in simple airplanes. Some pilots prefer fuel flow settings rather than N1 settings as a primary reference, but either will work.

Cool...I guess the bigger question, as it relates to flying the plane, is how does it effect the engine performance at different settings? Do I leave it at 75%...and how is it used in the context of the auto pilot?

 

[cleared4theoption]

Cool, thanks for the info!