Originally Posted by
yoko1
I think this may be an incorrect understanding. The four times reference comes from the maintenance manual, but our FCOM says the force is doubled. I asked our fleet guys who supposedly asked Boeing and the answer was that the pressure delivered to the elevator feel system is approximately four times (increase from 200 psi to 800 psi) but the force actual felt at the control column is approximately doubled to around 40-50 lbs.
This is an interesting question.
1) It appears that the manufacturer's document are not clear about the aircraft actual control forces.
2) In any hydraulic actuator/cylinder, the force is proportional to the fluid pressure acting upon the piston part of the actuator.
For the control force to be only doubled when pressure is actually fourfold, a device must be provided that reduces the force from the actuator to the control column.
As the 737 is a mechanical airplane, such a device - if it exists - should also be a hydro-mechanical unit.
Now what would be the point of increasing hydraulic pressure just to reduce its effect on the control system ?
No doubt some Civil Aviation Agency - and maybe even the FAA - will ask that the actual control forces and torque on the trim wheels be measured before drawing any conclusion as to the plausible scenario of the accidents or the 737 return to service.