15
$\begingroup$

I know that when manoeuvring on the ground, asymmetric thrust is often used, for example to assist in turns when taxiing.

Are there other circumstances in normal operations which might call for the use of deliberate asymmetric thrust in manoeuvring?

I am specifically not asking about emergency or other abnormal ops, flight testing or auto-throttle operation. I could rephrase the question as "in day-to-day ops of flying an multi-engine commercial jet, is asymmetric thrust ever used to manoeuvre the aircraft when not on the ground?".

$\endgroup$
  • $\begingroup$ I assume that "engine out" does not count as "normal operations". $\endgroup$ – FreeMan Apr 15 '16 at 16:42
  • $\begingroup$ @FreeMan Correct. I'm specifically not asking about emergency or abnormal ops. $\endgroup$ – Simon Apr 15 '16 at 16:48
  • $\begingroup$ Would "Normal Testing Operations" count? $\endgroup$ – SMS von der Tann Apr 15 '16 at 16:52
  • $\begingroup$ @SMSvonderTann No. I am specifically interested in the day to day "just doing my thing" of flying commercial multi-engine jets. Thanks. $\endgroup$ – Simon Apr 15 '16 at 16:54
10
$\begingroup$

This paper from Boeing sheds a light on the subject:

[A]n intentional engine throttle up or down could create a desired yawing moment followed by a desired rolling moment. Using asymmetric thrust to control roll is not precise because of the lag time associated with engine spool-up or spool-down and should be avoided unless no other means of roll control are available.

While the paper is admittedly about righting the plane from an in flight upset, and is therefore based on a disaster scenario, the message still applies to everyday flight: asymetrical thrust is not the preferred method of control, as the delay between adjusting the throttle and the actual thrust change makes it less precise for maneuvering than the main control surfaces.

$\endgroup$
1
$\begingroup$

Asymmetric thrust is sometimes used during strong crosswind takeoffs and landings to provide additional yaw authority for the airplane. A pilot can set a difference in thrust between both engines to alleviate rudder pressure during said operations. This is generally advisable only in steady crosswind conditions as gusts can make the control of the aircraft treacherous.

$\endgroup$

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.