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A/T 4-lever-servo-mechanism re engine out

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Member
Registered: Oct 2014
Posts: 341
Question: if all four levers are staggered, with #1 being the highest, #2 second highest, etc... does the trim function align #3 and #4 with #2?

If so, then if it is all a single system, then how can it selectively increase #3 and #4 with #2 without increasing #2 to match #1?

Maybe I mis-understood something...

Point is, does it ignore the idle lever by using whatever mechanism the trim system uses to move only 3 of 4 levers?
« Last edit by United744 on Sun, 14 Jun 2015 14:32:02 +0000. »
Moderator
Registered: May 2009
Posts: 5140
It trims the thrust of an engine only if the difference to the thrust of the second highest lever angle lies within the allowed tolerance. The tolerance values are dynamic, and pretty small. The numbers are mentioned in the Aerowinx manual.

Hardy Heinlin wrote
If I quote myself: "The allowable trim range depends on the current pressure altitude and varies between 1.6 and 2.6% N1 on GE models, respectively 0.03 and 0.05 EPR on the other models."

If the difference to an engine is greater, the respective engine will not be equalized with the second highest thrust.


Cheers,

|-|ardy
Member
Registered: Oct 2014
Posts: 341
Understood.

What I was meaning was whether the trim system is used in the case of moving only 3 of 4 levers (I mean the method of control, not systems logic).

It seems there are at least two methods for moving the thrust levers: AT control via the clutch system that moves all levers, and a second system that trims individual engines (in effect only moving individual thrust levers as necessary)??

I guess the question should be: how does the engine trim system work?
Member
Registered: May 2010
Posts: 843
Quote
I guess the question should be: how does the engine trim system work?


It just tells the Engine Control Computer to add more fuel to the engine until it reaches the thrust required by the FMC (which computes and commands the trimming required).
Member
Registered: Oct 2014
Posts: 341
Ahh OK...
Moderator
Registered: May 2009
Posts: 5140
Thrust equalization is not done by the A/T; i.e. not by lever movements. The EEC just fine-tunes a certain fuel flow valve within the allowed trim range. The command goes directly to the valve, and not via thrust levers.

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