Consider having the X-shaft slide inside one of the pinions to handle expansion. The primary reducer is a separate gear box that is afixed to the middle onf the X-shaft and it moves laterally with expansion of the X-shaft, but by only half the amount. The flexible coupling to the engine will handle the slight misalignment with the engine.

If the stagger can be reduced it will; save weight, align the flight control rods better with the swashplate and probably not be (very) detrimental to blade to blade gap. July 5, 2003 ~ Yes; reduce the stagger to 23" or less depending on how tight the components can be packed.

If the central frame is replaced by cast one, the flange bolts could be at 60º intervals and this will allow for mounting the engine at 60º off horizontal or horizontal (similar to the UniCopter).