Lu said:
"It was my contention that the drive shafts were the weakest link and would fail if enough torsion were applied."
Absolutely right. Twist anything hard enough and it will break. (Fudd's axiom, 43rd variation).
Heedm said:
"It is possible that a brake at one end of a shaft that is driven or has rotational kinetic energy from the other end could cause the shaft to fail, but that is only one possibility."
Absolutely right. This is a dynamic situation with several possible outcomes. If I was asked to properly investigate the possibilities, I would need to know:
- what is the deceleration rate of the rotating assembly after the assumed brake failure mode?. .- what inertia is in the rotating mass, including the inertia of the driven accessories(and possible "psuedo-inertia" due to EMF and hydraulic goings-on as the accesories are slowed down)?. .- what are the torsional stiffnesses of all the rotating components involved?
Then it would be simple to predict a time history of omega-dot and omega-double dot and thus torsional loads on the shafts in question, and see if Fudd applies in this case. Well, simple, way back when I had just got out of school and still knew all that stuff.
Lu said:. ."the EH-101 has redundant shafts to cater for a failure of one shaft."
I'll assume that the dual shaft resulted from an FMEA that predicted a single shaft failure due to problems within that one shaft: manufacturing defect, maintenance error, etc. If I understand the connectivity here, the inertia effect of a brake failure could effect both shafts at the same time, and some other mitigation would be required to drive down the RPN (or whatever it's called these days) of this failure to an acceptable level.
Any disgruntled ex-Westlanders out there care to share the details of the FMEA with us? We promise not to tell anybody where the info came from.
[ 15 February 2002: Message edited by: Weight and Balance ]</p>