8
$\begingroup$

On the a320, can someone explain why this is:

AMM 27-22-00 PB 001
NOTE:The maximum admissible rudder trim limits indicated on the control panel when the aircraft is stabilized in heading with the AP engaged are RH 1 DEG and LH 2.3 DEG.

Why is there a 1.3 difference in deg between LH & RH?

|improve this question
$\endgroup$
5
$\begingroup$

Both engines turn the same way, and the bypass fans exert torque in order to accelerate the air passing through them. The torque needs to be trimmed out using aileron & rudder trim.

|improve this answer
$\endgroup$
  • $\begingroup$ This is really interesting. It seems difficult for the pilot. Why don't the engines turn in opposite directions? $\endgroup$ – Brian Gordon Oct 7 '17 at 6:08
  • 6
    $\begingroup$ @BrianGordon: that would require two mostly different engines. Twice as much spare engines, higher production costs, and so on. Though, many propeller driven aircraft, where the torque plays a bigger role, have counter-rotating engines/propellers. $\endgroup$ – sweber Oct 7 '17 at 6:41
  • 1
    $\begingroup$ Also, it's easier to reverse the direction of a turboprop where you've already got a gearbox before the propeller. Turbofans generally have the fan on the same shaft as the low-pressure compressor and turbine, so you would need to rebuild half the core to change direction. $\endgroup$ – SomeoneSomewhereSupportsMonica Oct 7 '17 at 8:15
  • 1
    $\begingroup$ @BrianGordon it's not really a problem for the pilot when the designers have compensated for it, for example, by allowing more left rudder trim than right. $\endgroup$ – Ben Oct 8 '17 at 1:10

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.