Yes, more info on X2 gearbox and rotorhead would be interesting.
Originally Posted by riff_raff
As for Dave Jackson's comment about face gears, NASA spent a huge amount of time and money trying to develop the analysis and manufacturing technology for high performance face gears. Initially they had a lot of promise, but in the end what became apparent is that they had many practical issues that limit their theoretical performance advantages. The main one being sensitivity to mesh displacements under load. Regardless, I believe the Apache block III upgrade includes a face gear in its MRGB.
riff,
Regarding sensitivity to bearing/housing movement: The norm for ground vehicle axle differentials is to use spiral bevel gears for crownwheel and pinions. The spiral allows the line of contact (generally over 3 teeth) to rotate about a point above or below the axle line. This means the differential housing can flex without causing the teeth to spall at the edges. Another side benefit of this is that some worm gear action can be designed in to reduce the ratios a little more, albeit at the cost of efficiency.
Mart