Malam

Alternate Pitch Trim Levers in Normal Mode

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Hello,

I was studying the Flight Control part of the FCOM and I asked myself a question. 

The Alternate Pitch Trim Levers are linked to both STCM via control cables. Therefore, I would assume that the actions on the levers bypass the PFCs and ACEs to be directly transmitted to the STCM. 

In Normal Mode, moving the Pitch Trim Switches on the control wheel sends a signal to the PFCs, which will change the Trim Reference Speed and send the adequate data to the ACEs. The ACEs will then command an elevator deflection, followed by a stabilizer movement to “streamline” the elevator, for it to return to neutral position. 

This elevator deflection is calculated by PFCs. 

The Alternate Pitch Trim Levers being directly linked to the STCMs, I thought that moving the Alternate Pitch Trim Levers in Normal Mode would only move the stabilizer.

Thought it doesn’t appear to be the case. When testing this in the PMDG, while observing the FCTL page, I noticed that in Normal Mode, moving the ALTN Pitch Trim Levers had the same actions than if I had moved the control wheel Pitch Trim Switches: first an elevator motion, then a stabilizer motion to streamline the elevator. 

How is this elevator deflection calculated? In Normal Mode, are the Alternate Pitch Trim Levers linked in any way to the PFCs?

 Maybe I’m considering this with the wrong point of view, if someone could enlighten me I’d be grateful. 

 

Thanks in advance,

Malo

 

 

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1 hour ago, Malam said:

Thought it doesn’t appear to be the case. When testing this in the PMDG, while observing the FCTL page, I noticed that in Normal Mode, moving the ALTN Pitch Trim Levers had the same actions than if I had moved the control wheel Pitch Trim Switches: first an elevator motion, then a stabilizer motion to streamline the elevator. 

Just for the record, are you testing this in flight or on the ground? As the logic of both normal and alt pitch trim switches differ in between modes and from each other differently according to whether ground or flight operation.

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I made all the tests in flight, as on the ground, moving the pitch trim switches on the control wheel or the alternate pitch trim levers would only result in a stabilizer motion.

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I'm not sure of the question, as you noted the FCOM 9.10.3 says the alternate trim levers move the trim reference speed and stabilizer directly in normal mode.  The secondary and direct mode move stab only.

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On 2/14/2019 at 7:59 PM, downscc said:

I'm not sure of the question, as you noted the FCOM 9.10.3 says the alternate trim levers move the trim reference speed and stabilizer directly in normal mode.  The secondary and direct mode move stab only.

Exactly, though in normal mode on the PMDG, when actuating the ALTN Pitch Trim Levers, there's also an elevator deflection. So in Normal Mode, I would assume that the ALTN Pitch Trim Levers send some kind of signal to the PFC to command this elevator deflection.

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