Originally Posted by
tdracer
It's not quite that simple. The GE90 does simply motor longer before fuel on, but on the GEnx, max motoring can result in resonance of the shaft which actually makes things worse (and if I wasn't clear earlier, bowed rotor is a bowing of the shaft, not of the discs). On the -1B (787), since it's electric start it's a simple matter to reduce the starter torque to keep the motoring speed down, but on the -2B (747-8) the pneumatic starter air valve is either open/closed, so to keep the motoring speed down they reschedule the stator vanes during the bowed rotor motoring to keep the N2 speed down.
Interesting. Thanks TD.
I assume temperature is a factor in the digital decision making process? I wonder if time since shutdown also plays a role.