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Brief description of the issue:
787 now has a bug that takes total control of the elevator trim even when not in autopilot. I have no mods or anything else that would get in the way.
This bug is another one that makes it impossible to control the 787. Added in with all the other bugs we experience and I have reported , I now find that actually flying from one airport to another is pretty much not going to happen anymore.
Very frustrating!!!
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Build Version # when you first started experiencing this issue:
1.37.19.0
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what kind of detailed steps do you expect the average end user to give besides the fact that the controls to the Elevator trim have been taken over by the software ,not allowing me to make any adjustments.
Myself ,I am a programmer for over 40 years in C,C++,C# ,lua, XML,XNA,openGL,directX, oh well the list goes on.
I am wondering what kind of bug error report here would you be looking for from us ?
its funny as it responded to the first Nose down , and then the software took over and would not allow me to make any more adjustments. I could take a static picture of the controls, but what is the point of that. they will just show their position at that point in time. They won’t show the software not letting me make the adjustments at all, as that process is dynamic.
After you go through your preflight setup and programming the FMS with weights, fuel, etc…, what takeoff trim numbers are you seeing it calculate for you?
I might mention that i have just spent a few years developing code for the DCS engine ,writing in lua control code for it and learning a new language there for me.
I think this experience might help me diagnose and send in a report on the set of bugs (such as this one) that we are encountering here using the 787 with MSFS.
Well, it has let me adjust that steep trim pitch back after takeoff, and then I seem to lose control and can’t adjust the elevator to trim out for my current TAS . It stopped working. no idea why.
The 78X Working Title Discord server has a lot of experience users, I would also recommend you check there to help debug. If you can confirm a bug after working with them, they log it straight away.
I would also toss out there to check for a trim control bound to a noisy axis or unexpected button/switch/key.
The WT Discord has been silent regarding any issue like this (I spend too much time over there!) so I’m still leaning towards something specific to your setup.
Hmm,I have keyboard buttons and Joystick buttons bound to them. Usually keyboard/Joystick buttons are pretty reliable overall. I will double check them to see if I can discover something.
Operation of the 787 trim is widely misunderstood, but I’ll give a rundown of how it works (IRL and in the sim). The 787 trim is only directly controllable while on the ground or while in direct law (with the FACs off) as the trim surface is moved instead by the fly-by-wire system.
While in the air, pressing the trim switches does not directly move the trim surface. Instead, it changes a value in the fly-by-wire system known as the “trim speed”. The trim speed is the speed (in kts IAS) where the fly-by-wire system is neutral in pitch attitude; in other words, with the hands off the yoke the pitch attitude of the plane will not change.
When the trim speed is above your current airspeed, the fly-by-wire system will command a nose-down force to attempt to accelerate the plane towards the trim speed. Conversely, when the trim speed is below your current airspeed, the fly-by-wire system will command a nose-up force to attempt to slow the plane towards the trim speed. Exactly at the trim speed the fly-by-wire system commands neither a nose up or nose down force.
Pressing the nose-down trim switches (or key binds) increases the set trim speed, and pressing the nose-up trim switches decreases the set trim speed. The trim speed is not displayed on any instrument; instead the pilot should set it by feel just like they would in any other conventional controls airplane, as that is what it is emulating. This type of control law is known as a C*U (pronounced see-star-you) control law, and differs from Airbus control law, which does not have a trim speed term (the U term).
In order to facilitate the forces noted above, the fly-by-wire system will first use elevator for instantaneous response and then will unload the elevator by applying changes to the position of the physical trim surface until little to no elevator is required. In addition, this “elevator first and then unload with trim” strategy to affect pitch change is used for regular pilot commanded yoke changes as well. Therefore, you may see the physical trim surface (indicated on the flight controls synoptic) move in all sorts of ways without being directly commanded via usage of the trim switches.
An example of this is holding the yoke back to command a constant pitch up: the pilot will first see the elevator move to command the instantaneous change but the longer the pilot holds this configuration, the more the trim system will unload the elevator with movement of the trim surface. Eventually, even with the yoke held back you’ll see a return to a more or less neutral elevator with just having a trim change only to affect the commanded input.
This is completely normal and is exactly how the fly-by-wire system affects pitch changes in the real plane as well.
You know , that was awesome. That is pretty much how I thought it might be it working while I was flying it all this time. Now , something weird is affecting that system. Oddly enough last week it was my AUTOTHROTTLE that stopped working. It would not allow me to drop my speed below 285 IAS ever whether it was ON or OFF. To land , I shut off the fuel to one engine and let it die so the speed would drop low enough to land. Now, the AUTOTHROTTLE seems to work fine again. and it’s all in the ELEVATOR system . So weird , this 787 but we LOVE flying it …and with your description of how the Elevator trim works ,no wonder why we love it
Uhh, ok that was actually 10x more detail into how the whole system works than I would have imagined was going on. Now I used to be able to adjust the pitch up and down a bit from that neutral position so the plane would nose up/nose down a bit and stay that way.
But now, All of a sudden the system would take over and set the pitch to something else ,usually pushing the nose up , with no way of me stopping that ,even if autopilot is off. Now ,with the 787 flying like that, well it can’t keep flying like that and so I started up this post.
Are you using trim while you fly manually? Just like a regular controls airplane, you must use trim to maintain altitude with pitch, power, or speed changes. Prior to the plane overhaul in AAU2, the plane had incorrect fly-by-wire which didn’t require trim, and always held your attitude no matter what. This was incorrect and is not how the real aircraft works, nor how the one in the sim works now.
Please see the above; Boeing fly-by-wire does not work like an Airbus, you cannot just point it where you want it, you must continue to use the trim switches to maintain attitude.
I wish the 787 had the trim reference speed on the PFD like you can do with the 777. It really helps to trim on a PC setup where you cannot feel the force on the yoke to help with trimming.
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but we LOVE flying it …and with your description of how the Elevator trim works ,no wonder why we love it 