Originally Posted by
david340r
I puzzled over this strange two way game of rock/paper/scissors some weeks ago, but I've not been able to find anything conclusive as to how it might actually work. However it's possible to imagine a fairly simple mechanical system that would allow it. For example there could be two discs, one attached to the jackscrew and one to the trim wheels, face to face and with several rollers between them and with a spring pressing them together. In one of the discs there would be grooves that were circular segments that varied in depth, so that they got deeper and then shallower and the rollers would normally sit at the deepest point, but any rotation between the discs would make the rollers run up the slope and push the discs apart, but they would soon hit the end of the groove so they couldn't roll any more and then the two discs would be forced to turn together. The moving apart of the discs would push apart a set of clutch plates/dogs disengaging the electric motor drive. I'm sure there are other ways it could be done.
I'll admit I am at a loss as to why several posters insist on trying to redesign or get into nitty gritty details as to friction, clutches, trim wheel load design, etc. It contributes very little to the discussion- especially when it is obvious they dont bother to look for the multi pages-boxes, links of relevant information
So here are a few links for starters which IF time is taken to read and search for further info on the same sites **MAY** help to answer questions or at least provide clues as to where else to look, eventually resulting in part numbers of ' clutches" motors, etc which seem to be the subject of discussion.
https://www.satcom.guru/2019/08/conn...to-action.html
https://www.satcom.guru/2019/05/737-...incidents.html
https://www.satcom.guru/2019/04/stab...and-range.html
https://www.airliners.net/forum/view...?f=5&t=1424319
SEARCH on 737 trim wheel clutch for example
For a clue as to lube issues, etc try the following
https://www.federalregister.gov/docu...-737-airplanes
" We do not agree with the commenter. The intervals and tasks necessary for the lubrication, detailed inspection and overhaul/repair of the HSTA described in Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010, and proposed in this supplemental NPRM, address the unsafe condition of an undetected failure of the ballscrew primary load path and subsequent wear and failure of the secondary load path for affected airplanes. Due to these factors, we have determined that the desired level of inspection will be achieved when performing an HSTA overhaul. We have made no change to the supplemental NPRM in this regard."
" Inspections, Lubrications, Repairs/Overhauls, and Applicable Corrective Actions
(g) At the applicable compliance time and repeat intervals listed in Tables 1 and 2 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010; or Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010; as applicable (depending on airplane configuration): Do the inspections, lubrications, repairs/overhauls, installation(s), and applicable corrective actions, by accomplishing all the applicable actions specified in the Accomplishment Instructions of Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010; or Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010; as applicable; except as provided by paragraphs (g)(1) and (g)(2) of this AD.
https://www.federalregister.gov/d/2011-9410/p-88
https://regulations.justia.com/regul...8/E8-9193.html
" SUMMARY: We propose to adopt a new airworthiness directive (AD) for
certain Boeing Model 737 airplanes. This proposed AD would require
repetitive inspections, lubrications, and repetitive repairs/overhauls
of the ball nut and ballscrew and attachment (Gimbal) fittings for the
trim actuator of the horizontal stabilizer; various installation(s);
and corrective actions if necessary; as applicable. This proposed AD
results from a report of extensive corrosion of a ballscrew used in the
drive mechanism of the horizontal stabilizer trim actuator (HSTA). We
are proposing this AD to prevent an undetected failure of the primary
load path for the ballscrew in the drive mechanism of the HSTA and
subsequent wear and failure of the secondary load path, which could
lead to loss of control of the horizontal stabilizer and consequent
loss of control of the airplane
*****
Note the long up to 25000 hours time for significant rework etc