A320 V2500 questions
I note that on the V2500-A1 there is a 50 second 'crank' before ignition on start and I understand that this is due to possible rotor bow which the V2500 is apparently prone to.
Is somebody able to explain exactly what rotor bow is and why it happens, why the V2500 is prone to it and how the crank during start helps?
Also, I understand the concept of 'bump' in that it provides approximately 10% extra thrust on top of TOGA, but is anyone able to explain the theory behind how it actually works?
Any other comment on the V2500 vs CFM56 is also welcome!