Originally Posted by
walkon19
Uhh- not too sure where you get the worm drive screw jack bit - but the 737 series ( and others 767,777, etc - use a double recirculating ball " NUT " on the course threaded screw jack. Which has about a 90 percent efficiency and can therefore be back driven absent a braking system. While the electric motor MIGHT be overloaded at the extreme position (AND) and high speed, it is more likely that the manual (trim wheel- handle system ) is simply unable to produce enough torque absent superman along with the large number of turns required per degree and all by ONE person.
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