2
$\begingroup$

Let's restrict this question to best sellers airliners (A320 and B737). On this aircrafts, the THS is used for pitch trim. The speed requirements may not be has intense as for elevator as it control a longer term action. I excpect the elevator to act quickly (I imagine less than half a second from full up to full down, several degrees per seconds) but what about the THS? Does this speed change depending on the flight phase? (I see no reason, but I may be mistaken) This question is restricted to autotrim function (otherwise, I think the speed of pilots hands may be the limiting factor)

$\endgroup$
  • $\begingroup$ The speed varies depending on which system is operating the trim, e.g. the mach trim might be slower than what the autopilot can trim or the speed trim system that counteres the pitch moments of the flaps but the fastest rate would be manual electric trim. I'd estimate the trim speed to be less than one degree per second because of the way it is actuated, via jack-screw. $\endgroup$ – Jan Apr 21 '19 at 13:52
  • $\begingroup$ @Jan clarified. $\endgroup$ – Manu H Apr 21 '19 at 13:58
5
$\begingroup$

For the A320:

  • Conf 0/1 the rate is 0.3°/s
  • Conf 1+F/2/3/Full the rate is 0.7°/s

I haven't found any difference for A/P vs Manual flight.

In A319, THS freezes in the following situations:

  • The pilot enters a manual trim order.
  • The radio altitude is below 50 ft (100 ft with autopilot engaged).
  • The load factor goes below 0.5 g.
  • The aircraft is under high-speed or high-Mach protection.

In A320, THS freezes in the following situations:

  • The pilot enters a manual trim order.
  • The radio altitude is below 50 ft (100 ft with autopilot engaged).
  • The load factor goes below 0.5 g.

There are further conditions under which THS range is limited, let me know if you would like me to expand.

Source: A320 FCOM DSC-27-20

| improve this answer | |
$\endgroup$
4
$\begingroup$

Using the Boeing 737NG as an example:

When the flaps are up, the pilots' electric trim switches operate at 0.2 units per second (low-speed trim). Otherwise, they operate at 0.4 units per second (high-speed trim.)

With the autopilot engaged, the low & high speeds change to 0.09 & 0.27 units per second, respectively, depending on the flaps setting.

Note: the THS angles are reflected in "Aircraft Nose Up" (ANU) units, which in Boeing's convention, 1 unit ANU = 1 degree deflection. While THS angles can be negative, ANU units are always positive. On the NG, the full range of the THS is 17.1 degrees (from -4.2° nose down to 12.9° nose up), which is mapped to 0 - 17.10 ANU units.

Source: 737NG AMM, HORIZONTAL STABILIZER TRIM CONTROL SYSTEM - ELECTRIC TRIM - FUNCTIONAL DESCRIPTION.

| improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.