731 engine

[jimmyw]

I forget the reason that up in the high flight levels that idle flight N1 is somewhere near 70 - 73 % and down low 20 -30 %.
Also does it matter that the fan turns when the plane is parked for extended periods? I know engine covers do the trick but I've heard some in the know who say there is minimal if any wear on bearings in this free spin in wind scenario.

 

[Hawker800]

Put the covers on. Keeps out stuff thus reduces the chance of FOD.

 

[Fly91]

I forget the reason that up in the high flight levels that idle flight N1 is somewhere near 70 - 73 % and down low 20 -30 %.
Also does it matter that the fan turns when the plane is parked for extended periods? I know engine covers do the trick but I've heard some in the know who say there is minimal if any wear on bearings in this free spin in wind scenario.

I was told the accessory drive still rotates and is not lubricated when the engine is not running, so its bad.

And I don't see why fan blades need to continually be smacking the inward and outward stops for hours and hours. That is wear and tear. Fans b;ades are not supposed to move like that for hours.

 

[LJ45]

I was told the accessory drive still rotates and is not lubricated when the engine is not running, so its bad.

And I don't see why fan blades need to continually be smacking the inward and outward stops for hours and hours. That is wear and tear. Fans b;ades are not supposed to move like that for hours.

You would need a hurricane to turn the N2 and drive the accesories on the ground, you are wrong there!

 

[LJ45]

I forget the reason that up in the high flight levels that idle flight N1 is somewhere near 70 - 73 % and down low 20 -30 %.
Also does it matter that the fan turns when the plane is parked for extended periods? I know engine covers do the trick but I've heard some in the know who say there is minimal if any wear on bearings in this free spin in wind scenario.

A couple of reason they idle higher at flight levels is to prevent flame out and to provide proper bleed air.

 

[Fly91]

You would need a hurricane to turn the N2 and drive the accesories on the ground, you are wrong there!

Yeah, I was told that but didn't know. I wonder what turns from the fan shaft turning. Inside the turbine shaft wouldn't be lubricated either.

 

[LJ45]

there is enough residual oil to not cause a problem in the short term.

 

[TransMach]

QUOTE
I forget the reason that up in the high flight levels that idle flight N1 is somewhere near 70 - 73 % and down low 20 -30 %.
ENDQUOTE

Reason #1 - The computer is programmed to raise the idle speed as altitude increases so that the engine will make minimum spool acceleration required by certification. Turn the computer off at altitude and the engine will slow to min-idle fuel flow.

Reason #2 - Min-idle fuel flow as physically set and will result in a higher idle speed at altitude than at sea level due to the reduced drag of a higher density altitude.

Reason #3 - That's what Garrett wanted to do!

TransMach