Originally Posted by
tdracer
Agreed - likely an internal failure caused the case crack. There were a couple events early on with the GEnx-1B (787) where an internal gear failure actually punched a hole in the gearbox (yes, the design was changed to address it).
Planetary gearboxes are commonly used for very high torque applications since it distributes the loads through multiple gears and hence lessens the loads on the individual gears. Planetary gear boxes were common on the early automobiles for that reason - the metallurgy at the time had difficulty making the gears strong enough for a conventional gearbox to last (IIRC the Ford Model T used a planetary gear box). As the metallurgy improved, planetary gearboxes fell out of favor due to their greater complexity and manufacturing costs.
Hoppy - "planetary gear-set" is a rather generic term - commonly used regardless of whether the 'planet' gears are fixed or rotating.
Just curious - is the fan gearbox (regardless of what it's called) readily visible/accessible on the PW1100 series engines? Or is it pretty much covered up and hidden?
There is a difference between calling it a "planetary gear-set" and referring to the star gears as planets.
By doing so the poster is incorrectly describing the way the gearing works as planets orbit the sun gear whereas stars do not.
I only corrected the poster as he incorrectly described the gear system while glibly saying "C'mon guys, it's a straightforward Epicyclic sun & planet gear train".
