Originally Posted by
MechEngr
It looks to me that the setscrews index the resolver to the balanced assembly of the vane and the counterweight and that the counterweight is indexed to the vane with a flat on the side of the vane shaft. One can see the flat-bottomed groove in the counterweight that receives the vane shaft. Maybe there was a failure of one or more of the screws that hold the item 45, shaft retainer (?), in place. If so, the resolver would still be attached and the vane would mostly follow the oncoming wind. It seems unlikely as the plane was not exposed to a high g load at the time; I would expect it to fail that way on a hard landing or bumping down the runway during take-off.
While it might be the case that the resolver connection could slip, there isn't any resistance except to angular rate of the vane accelerating the core of the resolver to create loads passing through those set screws. It they were completely loose, the resolver would have no torque to turn it and it would report an unchanging value. Resolvers are small and very easy to turn; those loads are small.
In the case of Lion Air, it's possible the inaccurate resolver was indexed 20 degrees off from where it should have been; it remained exactly that amount through both flights. ET302 saw the resolver reading in accordance with aircraft acceleration just like a plumb bob would follow.
One final thing - the gear attachment is not adjusted to change the calibration of the sensor, the body of the resolver is turned to do that after a rough alignment according to the gear teeth, so the gear could be an interference fit on the resolver shaft and the vane shaft with the setscrew being a belt for suspenders approach. The resolver body is indexed with three cleats.
Suggest take time to read this link - which includes pics and diagrams
https://www.satcom.guru/2019/03/aoa-...-fix.html#more
IMHO- the use of set screw(s) for such an instrument is or should be verboten
D shaped shaft with snapon keeper, splined shaft with d ring keeper or similar should be used for all such assemblies especially counterweight to gear shaft and gear shaft to resolver and arranged that any broken part vane gives a nose down ? result with mechanical limits as to movement or resolver output. Wilbur and orville may have used a few setscrews on their flyer- but that was then ...
Of course if you want to adjust your lionel railroad and engine parts, or your kids toys, even then set screws are now doubtful, since they may be swallowed. Maybe to adjust your clock or doorbell chimes is OK ?