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ISSUE DESCRIPTION
Description of the issue: The 737Max trim on takeoff does not work well. The trim setting in the FMS on takeoff does not lift off the aircraft and requires a lot of pull back on the yoke. The usual trim setting I get is around 4.5 but on takeoff if I leave the yoke, the aircraft dives towards the ground.
FREQUENCY OF ISSUE
How often does this occur for you (Example: Just once, every time on sim load, intermittently)? Every time
REPRODUCTION STEPS
Please list clear steps you took in order to help our test team reproduce the same issue:
Load parameters into the FMS
Trim the aircraft to suggested trim from FMS
Takeoff with correct flap and trim, on lift off leave the yoke
Instead of maintaining a steady climb, the plane starts to dive
YOUR SETTINGS
If the issue still occurs with no mods and add-ons, please continue to report your issue. If not, please move this post to the User Support Hub.
What peripherals are you using: Honeycomb Alpha Yoke
[PC Only] Are you using Developer Mode or have you made any changes to it? Both are same
[PC Only] What GPU (Graphics Card) do you use? AMD
[PC Only] What other relevant PC specs can you share?
MEDIA
Please add a screenshot or video of the issue occurring.
I believe there might be a bigger issue with the trim settings for 737. The FMC will give trim settings to be used for takeoff for different weight/CG but it rarely corresponds to the trim actually required on takeoff. The usual trim required remains about the same and usually well above the recommended value.
The trim is all over the place with this aircraft. Iâve had it so I couldnât lift up off the ground without running the trim switch up and Iâve had it doing wheelies down the runway at 100kts and trying to go into space because the trim was too high. And then in the climb in autopilot (Iâve never made it up to level flight because the performance is so bad an the elevator twitchiness annoys me), the trim wheel is constantly moving up for a while, then down for a while, then up for a while etc and you feel like you are on a boat
I have done further digging into the weight and balance systems on the Boeing 737 and found a significant discrepancy between the EFB and MCDU setups. There are multiple issues so I will address them one by one:
1. Fuel - Fuel values between EFB and MCDU synchronises incorrectly. If you adjust the fuel amount in the MCDU the change is instantly shown correctly in the EFB, however, if you change the fuel amount in the EFB this change will not be shown in the MCDU even though the change does go through and the amount of fuel in the tanks is changed through either method. There is an additional issue in career mode - the aircraft will load wing tanks and central tanks equally, whereas, in the normal 737 operation the wing tanks are filled first and then the central tank is filled.
Cargo - cargo capacities do not correspond between MCDU and EFB, adjusting one or the other does not synchronise the change between the two systems. This creates an MAC discrepancy. Additionally, because currently you are allowed to adjust these values in the MCDU in career mode the EFB does sync to the MCDU, however, fills the cargo forward first and then aft, which sends the CG wildly forward causing unstable flight. The total cargo amount can be much higher in the MCDU (compared to EFB) as it seems to allow you to load cargo to some figure (probably the max takeoff weight as the number can be higher the fewer passengers are entered into the MCDU)
Passenger number is different between MCDU (172) and EFB (168) and the amount of passengers does not synchronise between the two. Again, similar to the cargo loading on the MCDU the PAX amount can put the aircraft into dangerous CG configuration.
Conclusion: the two systems need to coexist, it is possible that currently incorrect trim is caused by some sort of disagreement between the two systems. This is especially dangerous/annoying in career mode, as most EFB inputs are disabled, however, players are free to manipulate the MCDU values which leads to heavy forward CG unless ballast is added. Finally, the player remains unsure as to which CG value to trust for the flight, it is most likely the value provided by the MCDU, as it is the one used to derive the takeoff trim settings, however, for most situations it seems like excessive trim is required upon takeoff, usually when recommended 3.5 by MCDU the actual takeoff trim will be closer to 5.5 which is a severe discrepancy, leading to excessive inputs required by the pilot on the yoke and potential dangerous nose-down behaviour upon takeoff.
Additionally, the issue of "symmetricalâ instead of âsequentialâ fuel loading in career, when the purchase window is used in the menu before flight, I believe, persists for all aircraft as DHC-2 also loads all tanks equally instead of foreâmidâaft which is the sequence to be followed.
Thanks for the invetigation. I think you are on to something. There definitely is a discrpency which is causing the trim to always stay around 4.5 level.
I can confirm. Trim is not working for me. Aircraft nose dived unless I pulled back hard on stick after setting a trim of 4.75.
Note for using EFB. You have to hit âLOAD AIRCRAFT then load instantlyâ in the EFB to sync the EFB settings to the FMC settings. (Fuel, weight, cg etc), but the trim is still wrong or not working as intended I think. I also havenât checked to see what the exact values are that are ported over for fuel/weight/passengers. There is a similar issue with the ATR. Values in FMC often wildly out compared to EFB calculated ones.
