A/P problem with elevator trim

[Petr Bily 0]

Hi,I have PMDG 747X installed on FSX. When I use autopilot using V/S the trim movement goes very, very slow. When I change from +3500 to -3500 it takes very long time. I tried to disable my trim on my ELITE PRO PANEL SE but it did not help. Do you have any suggestion? Can you please tell me what is average time to change for example from level flight to V/S 4000 ft (in FL100 for example full loaded plane) using autopilot?I also have CDU2 from VRInsight installed and FS2Crew Voice.Thank you for your suggestions.Best regards Petr Bily

[downscc 1,327]

A fully loaded 747 won't give you 4000 fpm climb without speed loss. Climb using V/S is a very bad practise, either use VNAV or MCP SPD.

[Petr Bily 0]

Dear Dan,may be I wrongly explained the problem. It is not the question of the speed of the acft but the problem of how fast autopilot set (change) the trim. When I have for example level flight and trim is 5 (just example) and I set V/S +4000 or VNAV should start to climb (there is no difference) the trim should be set to 5,5. But the TRIM is doing..... 5.1 .... 5.2 .....5.1.....5.2......5.3..........5.3............5.4..........5.3........5.4........5.5In my opinion something is fighting with the autopilot. I have the same problem with the throttle. When I set the MCP SPD I can see that the throttle levers are not stabilized but still moving a little up and down and it never finish. I think the problem is my ELITE PANEL PRO SE which is still sending some positions to PMDG and autopilot is changing them. But I think I am not able to switch this off :-(Is here anybody who is using ELITE with PMDG? Or some ideas what to do?Petr

[Paul_Smith 92]

Hi Petr, the 747 is not a Cessna, you do not adjust trim to change rate of climb. Even in a Cessna you do not adjust trim to adjust rate of climb. Pull up your EICAS display to show flight controls, dial in a V/S of 2,500 (+ or -) and watch your FD, EICAS and airspeed. Try and remember that the 747 is an airliner with paying passengers sitting over two hundred feet behind the pilot. 4,000 feet per minute climbs (or descents) will generate an aweful lot of complaints!

[Petr Bily 0]

Hi Paul,A/P on Cessna is using servo motor on TRIM. I am sure with that (I had to order one from US when my old on C-182 was broken). But I have no idea how it works on 747 here you are right ;-). The question is why the trim is moving not only up but up... up...little down... up....up...little down....May be be you are right end everything is correct. But I think that before I install all kind of SW like SerialFP2, FS2Crew Voice, ELITE, etc... the time to start climb from level flight to 4000ftpm was much faster (on A/P of course - by hand it can be very fast) ....Tell me sth. When you use SPD and you open Throttle panel. Are your levers moving or after while stays not moving... My are really still shaking.Petr

[Paul_Smith 92]

You are right about the servo in the cessna, but I am pretty sure it is used by the autopilot to maintain altitude, not to change it. If you want to verify your base installation before installing the extras, just follow the tutorial flight. If everything happens as described, then everything is working correctly. Re the throttles. In SPD mode my throttles move if my speed is not stable. They do not move if my speed is stable. If my speed is not stable and I think it should be, then the first place I look is the weather. FSX weather model is poor, and no amount of ASE or REX is going to improve it much. This shows up with PMDG products more then some others because PMDG use their own autopilot code that behaves the way the real planes do, and real planes are not subject to the wind changes of 50knots and 100 degrees per second that FSX sometime inflicts. If you want weather with PMDG products, you pretty much have to use registered FSUIPC with smoothing enabled.

[Petr Bily 0]

Hi Paul,if you want to change your altitude or FL, you have to maintain the new FL, so the A/P uses TRIM settings. In real Cessna you can see it easily because A/P is turning with your trim wheel. I am sure with that (believe me I have about 200h on it).Back to my problem. I found this. When I start my PMDG 747 without using FS2Crew voice A/P can manage the trim and can hold my FL, react on V/S and also on VNAV. My problem starts when I start to use FS2Crew Voice (exactly like it is in the manual) the B747 does not reflect on TRIM change. Or may be better to say A/P does not want to change trim when it should. Like change of V/S or maintain FL.So just an example...I have FL 100 without autopilot. I set on MCP FL140, click V/S and set +2000. A/P is angaged. But now nothing happens (button V/S is illuminated). The plane starts to go slowly up or down just like no A/P is on. When it goes UP (I can use my yoke for it) I hear at FL 130 beep to say that I am in FL in 1000 ft. It reachs FL140 but goes more and more high. So just it does not react on A/P.When I do it without FS2Crew Voice it works. When I look at TRIM settings (on Thr window) I can see slow change of TRIM as necessary (so to strat climbing TRIM goes UP when it shold descend TRIM goes down and when it reach FL it slowly moves to stabilized position (4.3 - but depends on CG of course).Seems that the problem will be with FS2Crew. I will try to post it in another forum. But if anybody helps me, I will send him big kiss :-)Best regardsPetr