Why is N1 often at about 37% N1 when flying, but in idle?

Question

Why is N1 often at about 37% N1 when flying, but in idle?

Answer 1

Define N1 and N2, and you will see why..........and here is where you will get briefed on gas turbine engine technology

http://www.picotech.com/applications/gas...

Answer 2

It's usually more than that in flight idle, in the jets I fly.

Answer 3

For the same reason that a propeller RPM doesnt reach 0 at idle.  Airflow moving over it turns the blades a little bit.

They are producing next to no power, just enough to continue running the engine.

Answer 4

If your flying a helicopter, you better hope it's about 90% +/- all the time unless your doing a SEF.

Answer 5

Simply put, there is always going to be some rotation of the engine while airborne. Even if you shut down a turbine engine in flight, you will show some N1 rotation (unless you can stop all of the air from flowing through the engine or it is damaged and seized).

Think of it this way. Why does your car still have RPM's when you are sitting at a stoplight but in idle?

Even in idle, there is still some gas being injected into the engine. The exhaust from that combustion turns the fan (N1), as well as the airflow entering the engine.