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rondon9898

Setting stab trim before engine start

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Hi chaps,

For some reason (since the update, though almost certainly coincidentally) I haven't been able to set the stabiliser trim on the new 747 prior to pushback with pre-start items complete and AUX pump on sys 4 running. I can only set the trim once the engines are started.

Can't be a bug as I know PMDG wouldn't make a mistake like that, so it's obviously something I'm doing wrong. By the way, my trim mappings are fine and the trim switches are moving on the control column, they just don't do anything.

Cheers,

 

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I can set the trim after the APU is started and before engine start.

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Yes I used to be able to, now it's not happening. Can't quite work out what I'm doing wrong.

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Trim uses Hydraulics 2 and 3. Are you sure you had the electric (or optionally pneumatic) demand pumps in Auto prior to engine start? After start, your engine hydraulic pumps would have been running (and providing hydraulic power to the #2 and #3 systems)

Also, make sure you're not leaning on your joystick. Normally leaning on the control column in the opposite direction to the trimming action will cause the trim to stop (unless you are using the Alternate trim switches on the thrust quadrant). You may have to adjust your null zones.

Hope this helps

Cheers

JHW

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It may be my null zones then - yes hydraulics are in auto with the auxiliary pump running on system 4. I shall have to test it and come back.

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Like John said, make sure #2 and #3 demand pumps are in Auto, that is the most obvious reason. You cannot trim without them being in Auto. The #4 aux pump is primarily for brakes and nose & body gear steering, but not stab trim.

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You posted the same time I did John Price, so you know how the system works and have them in Auto, disregard my post then, your way ahead of me...

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My trim set-up is always dead on with FMC....so not sure if that is right either since I never had to adjust it. And I thought it is always done thru FMC with Q3....LOL....Can someone teach me how to adjust the trim...and what to use? And how come my trim display always matches exact number in FMC? Doesn't make sense I guess....:blush:

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I always set trim after engine start, it is the first thing I do when checking spoiler, aileron, elevator and rudder control movement.  Timing wise, this generally happens after pushback and I'm on parking brake, and on brake release I start taxi and set flaps.

Alex, full names on all posts in the PMDG forums please.  The FMC never sets trim.  Once A/P is active then trim and control surfaces are controlled by it but not the FMC.  If the trim happens to be the same as the FMC after setting up thrust and takeoff then that is just a coincidence.  Hydraulics are required for trim setting as already mentioned in this thread.

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On the topic of trim settings. IIRC, trim should be set to 6 points after landing, as this is its 'neutral' position. Setting up trim for departure should be done before startup, after HYD DEM PUMPS are in AUTO/AUX position.

Cheers,
 

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23 hours ago, downscc said:

I always set trim after engine start, it is the first thing I do when checking spoiler, aileron, elevator and rudder control movement.  Timing wise, this generally happens after pushback and I'm on parking brake, and on brake release I start taxi and set flaps.

Alex, full names on all posts in the PMDG forums please.  The FMC never sets trim.  Once A/P is active then trim and control surfaces are controlled by it but not the FMC.  If the trim happens to be the same as the FMC after setting up thrust and takeoff then that is just a coincidence.  Hydraulics are required for trim setting as already mentioned in this thread.

Thanks....I understood that Hydraulics are required....but how actually you are adjusting the trim? NGX has a way, 777 does as well, but how you do it on Q3?

Must be coincidence that every of 9 flights I made so far trim was dead on...how, don't know.

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3 minutes ago, rwy23 said:

but how actually you are adjusting the trim?

Elevator trim... same as NGX and 777.  Maybe I don't understand your question. The only difference is there is no tool tips indicating the exact amount, on the 747 you look at the dial and eyeball the setting. Close is good enough.

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6 minutes ago, downscc said:

Elevator trim... same as NGX and 777.  Maybe I don't understand your question. The only difference is there is no tool tips indicating the exact amount, on the 747 you look at the dial and eyeball the setting. Close is good enough.

I guess I am not asking right question, I know where is the dial....but, on NGX you move the trim wheel to set the trim, on 777 you move trim levers to set the trim, but what do you move on Q3 to set the trim.....

Thanks..

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1 minute ago, rwy23 said:

on 777 you move trim levers to set the trim, but what do you move on Q3 to set the trim.....

You're not supposed to move those trim levers on the 777, actually. You're supposed to use the trim toggles on the yoke for both. Set a trim up/down command in the sim joystick/keyboard commands screen.

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1 minute ago, scandinavian13 said:

You're not supposed to move those trim levers on the 777, actually. You're supposed to use the trim toggles on the yoke for both. Set a trim up/down command in the sim joystick/keyboard commands screen.

I have to say I didn't know that....but I knew they are available on yoke (left handle), but why you not suppose to move that? Any difference in set up? Would be good to know...I think I watched your video on YT setting the trim.....

Q3 supposed to be set up on yoke as well I assume, but I think I tried and nothing happen......I did not set buttons for that thru FSUIPC...that might be the option...

 

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1 hour ago, rwy23 said:

I have to say I didn't know that....but I knew they are available on yoke (left handle), but why you not suppose to move that? Any difference in set up? Would be good to know..

For your reading pleasure 777 FCOM 9.20.10 - 9.20.11; the first thing you should have noticed is the levers are labeled "ALTN PITCH TRIM,"  most all aircraft with electric trim are trimmed primarily with the switches on the stick/yoke.

If you are using P3D you don't need FSUIPC for the controller buttons, just assign the buttons directly in P3D controls UI.

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To be honest, I think I read all manuals, but I have to admit that I was concentrated on something else I was searching that I missed that thinking I knew that...but thank you for answer....

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The Altn Switches bypass some of the safety systems on the 747-400 and have a different effect on the autopilot, depending on the autopilot mode. This is why you should normally use the control column trim switches.

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16 hours ago, rwy23 said:

I think I watched your video on YT setting the trim.

I may have been looking down in that area while setting the trim because the indicator is there, but I highly doubt you've seen a video of me working them unless it's one of those videos where I go over every option/button/switch in the plane.

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16 hours ago, rwy23 said:

I did not set buttons for that thru FSUIPC...that might be the option...

Nope. As mentioned, set it up quite literally, in the sim itself using the default sim controls screen.

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1 hour ago, scandinavian13 said:

I may have been looking down in that area while setting the trim because the indicator is there, but I highly doubt you've seen a video of me working them unless it's one of those videos where I go over every option/button/switch in the plane.

Could be not sure....You were showing start from C&D and set-up.....

Thanks Kyle

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14 hours ago, Qavion2 said:

The Altn Switches bypass some of the safety systems on the 747-400 and have a different effect on the autopilot, depending on the autopilot mode. This is why you should normally use the control column trim switches.

John is correct, the control column stab trim switches are Primary and should be used first. The Alternate Trim switches trim at the same rate as the control column switches, have greater forward travel compared with the control column switches, but they react different if an A/P or A/P's are engaged.

In the case of the control column switches, if you trim with a single A/P engaged, the A/P will disconnect. If you are in multiple autopilot mode below 1500 RA on a triple channel ILS approach and trim, nothing happens as the trim is inhibited if you try to trim.

If you trim using the Alternate Switches in single or multiple A/P modes, they will trim and the A/P will sense trim is coming from somewhere other than the A/P, and you will get an Unscheduled Stabilizer Trim message. Alternate also bypasses the control column cutout feature, so for all these reasons, Alternate is just that...Alternate, to be used if the Primary trim system does not trim. 

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