Originally Posted by
bill fly
Hi Walkon,
As I understand you, the stab mechanical parts, forgetting the motor for now, thanks to the recirculating ball nut can not get so frictionally overloaded that they won’t run, even at high aerodynamic loads.
It could even be forced to run in reverse, if no brake is preventing this due to the efficiency of the ball bearings within the nut. Is that right?
Because if this is so, the cause of stabiliser mechanism stalling which may require yo-yo technique could only be an overloaded motor in the electrical case, or lack of trim wheel moment in the mechanical case. .
The principle could even be used, if so designed, to allow an out of position stab to “freewheel” to a near unloaded position if the brake alone could be disengaged.
I have learned something, thanks.
B
Yes- most- but not all ball screw mechanisms can be back driven absent some sort of brake
I'll try to post a jpeg of the boeing 737 NG system and several items to search on which will result in more than most want to know.
The first should get you to a utube video of a jackscrew in operation- note that as it reaches full leading edge up, it sounds like the molor is struggling- and this is with NO airload.
Boeing 737NG horizontal stabilizer jackscrew cycle
boeing_737_ng_horizontal_stabilizer_trim_actuator try search on this term
recirculating ball jackscrew
Ball screw
Roller screw
Cannot post url so try search