Originally Posted by
JohnDixson
Thanks, Riff-Raff. A previous poster cited an " ultimate " life for the gears at 5000 hours. I assume he meant the fatigue life or Component Replacement Time (CRT ). Can one assume that the gears are exposed to accelerated load testing, multiple samples, a three sigma curve reduction etc?
One fatigue analysis case used to design helicopter transmission components like gears/bearings/etc is based on a composite (cubic mean) of the various speed/load operating conditions and times over a typical mission profile. The 5000 hour number is likely a minimum design requirement at the composite speed/load condition. There are also other fatigue analysis cases considered, such as OEI and max torque, that involve far lower numbers of load cycles.
As for qualification tests performed on an MRGB,
take a look at FAR 27.923.