View Full Version : Automatic trim
ben123
22nd May 2003, 21:40
hello everyone, doing some work on automatic pilot systems at college at the moment, I do not have any experiance or information on working on automatic trim systems, so if anyone could could help me with this question I would be very greatful
Q)After engagement of an automatic pilot with automatic trim, when the pitch control is operated the control column will :-
a) move and the trim system will rotate
b) remain stationary and the trim system will rotate
c) move and the trim system will remain stationary
Thankyou for your help
Ben
b)
Trim systems are designed to remove the load from the controls, ie you or the a/p hold the load, and the trim adjusts whatever it adjusts to remove the need to hold a load. It can be a trim tab, moving tailplane or simple bias system.
ben123
23rd May 2003, 00:48
Sorry at college we study typical or general aircraft systems and the questions set are not usually type related, It is quite open to indivual interpretation i suppose. Thankyou for your help.
DrSyn
23rd May 2003, 07:21
If the above 2 answers appear inconclusive, I'm afraid that mine may not appear useful either! However, from 30+ years-worth of several autopilots I will hazard a guess based on my understanding of the question (RTFQ). Ultimately your course guides should give you the answer.
Current autopilots probably cover a development range of over 40 years. Later versions do not have, or refer to, direct "pitch control", as such, as this function is incorportated in the "pitch modes" which control vertical profiles. The trimming laws remain similar however.
I suspect that your question refers to one of the earlier systems (still widely in use) whereby the pitch attitude of the aircraft can be adjusted through a switch or wheel on the A/P panel. In this case, and even if done by "pitch mode" systems, causing a pitch change will result in the control column moving accordingly and the trim system adjusting-out any subsequent resudual force (ie: rotating) - but not relevant to Airbus FBW types!
a) would therefore be the correct answer. Hope this helps.
The answer is a.
(With the notable exception of airbus FBW aircraft) The engagement of the a/p pitch channel will cause the control column to move in response to pitch commands. The automatic trim system will then operate (a better word than rotate) to reduce the standing load on the elevator.
On smaller a/c the trim system will operate a tab which will move so as to reduce to zero the elevator servo current (i.e servo current = out of trim situation, trim operates 'til current = zero, a/c in trim)
On larger a/c the trim system operates the horizontal stab to restore the elevator back to neutral as sensed by position sensors and a neutral shift system.
hope this helps.
P.S. you should have notes that explain this!