Trim setting

[karmelk 0]

My below mentioned question has obviously in time been raised and answered but which, going back a long time in the Forum, I seem not able to find. I have also tried to read the manuals but there also I cannot find a, for me, plausible answer.

It concerns the actual setting of the trim based on what the FMC calculations. I read somewhere in one of the manuals about Realist Engagement on/off etc. but this also I cannot find.

Please assist and point me in the right direction.

Kind regards

Dirk

[kevinh 409]

The FMC only calculates the takeoff trim position during preflight. All you need to do is set the trim to approximately that value. You won’t be able to set the trim until you have turned on hydraulic pressure in system 2 or 3. 

Realistic engagement relates to the autopilot. With this realism option enabled the aircraft must be properly trimmed before the AP can be engaged. You must manually adjust trim, the FMC does not calculate the required trim position in flight. If the option is disabled the AP will engage regardless of the trim state. This option is set on Page 1 of the SIMULATION menu (found under PMDG SETUP/OPTIONS in the FMC CDU). See page 95 of the Introduction Manual for full details.

 

 

Edited September 2, 2018 by kevinh

[MarkJHarris 128]

Irrespective of any loadsheet trim calculations, all Boeings ASAIK use the FMC computed trim setting. You input the CoG index percentage, and based on this AND the thrust derate setting and flap setting entered, it provides a STAB trim setting to you. Higher thrust gives more nose up moment, larger flap more nose down, etc. On the B737 which I fly for real, a non derated takeoff will require no trim input once you steady at the F/D demands of 15' pitch. a 22K derate with assumed, gives a more gentle takeoff but invariably, you need a quick burst of trim once steady.  It's not an exact science, but remember the tail stabilizer is by far the most powerful control on the aircraft.

[karmelk 0]

Kevinh and Mark, thanks for your input and helped me. But my qustion still remains unswerred and tha is if Reaistic engagement is abled (on) in the FMC where can and must I correct the Trim?

 

Dirk

[kevinh 409]

Dirk,

You must manually trim it, using the stabiliser. I assign the FSX/P3D elevator trim controls to buttons on my joystick, but you can also use the default trim up/down keys to trim.

If you have to apply nose up yoke control input to maintain the pitch angle then trim nose down. Trim nose up if you need to hold a nose down input. Apply small amounts of trim until the pitch angle is stable. It’s not difficult to do with a bit of practice.

[karmelk 0]

Thanks Kevinh, I will try it out

 

Dirk

[Ephedrin 418]

Kevin,

you have somehow confused something 😄

when you have to push the nose down then you need to trim it down too, or you move the stabilizer even more up and have to push even more 🙂 actually exactly vice versa. 

[kevinh 409]

On 9/4/2018 at 3:06 PM, Ephedrin said:

Kevin,

you have somehow confused something 😄

when you have to push the nose down then you need to trim it down too, or you move the stabilizer even more up and have to push even more 🙂 actually exactly vice versa. 

Yes you’re right. Embarrassing or what. 😉 I should have quit when I was ahead before I decided to add that second paragraph.