Optimized gearbox design - Wind Power Generation and Wind Turbine Design - page 525

It also emphasizes the importance of isolating the gearbox from the parasitic forces
imposed by the turbine on its rotor support.
The volumetric concept facilitates the synthesis of the initial design of gears
rather than using an analytical/iterative approach. It helps to optimise the overall
size and weight of gears by showing the value of using lower ratios in the high
torque low speed stages of high ratio applications, particularly when epicyclic
trains are involved. Ultimately, all stress criteria are subject to arbitrary limits
embodying a string of "factors of ignorance" which tend to be treated as virtual
constants. Ten such factors, with a 5% increase in each, would reduce permissible
load by 40%!