Still Trim issues with Sp1b

[fro2do 10]

Ok then do an experiment in the 777.

 

Fly  neutral and put the trim speeds up  (apply slight pressure in the oppposite direction ) and while watching the flight controls ECAS page, watch what it does when you release the column.

 

Report back

 

*I get a moderate deflection of the elevators *

I have been following this topic since the beginning and I'm trying to simulate the issue.

When you say fly neutral and put trim speeds up what do you mean? I need speeds

and trim and height numbers...I tried the experiment but what are numbers supposed to be?

I think you mentioned it on a earlier post but can you be more specific on what the outcome should be...So we can try the experiment.

thanks

No 737 and 777 are no different......PMDG737 and PMDG777 yes they behave different on my PC. But they should not.

 

Again it could be my hardware or whatever.

 

 

I suggest you display the trim Ref speed at all times.

 

I am asuming AT is engaged!

This is important because eventually the AT will try to get and keep you at this speed....so eventually you want the FBW trim ref speed right in the middle of that speed bug.

 

(handflying with manual throttle is different because it does not matter where your bug is.....you need to trim for what speed you are actually holding.

If you are a good pilot; actual speed=target speed bug......but since you are alone in there and busy, at times your actaul speed and the target will not be the same and you have to retrim so the FBW trim ref speed is/stays at your ACTUAL speed.....not the speed bug)

 

 

During acceleration from an in trim situation:

keep the FBW ref speed 10-15kt above the actualy speed as the aircraft accelerates.

This way you can pretty much not touch the yoke and fly (keep the pitch you desire) by just repeatedly touching the trim switches. Fly by trimming basically and only here and there help a a bit with they yoke if the nose wants to drop a little.

(Not keeping a continous yoke input helps those trim inputs actaully going to the FBW system as on MY system they dont go there if I holde the yoke)

Not more than 15kt above actual speed as that would cause too much of a nose down tendency.

Not less than 10 kt to prevent blib trim from your inputs going in an unwanted direction (to the actaul speed).

 

Don't sit there and count the knots though....just kinda use the force to estimate that roughly :-)

 

As the actual speed increases you have to keep nodding the trim switch to keep the FBW trim ref speed above the current speed.

When you reach the center of your magenta speed bug you stop trimming.

Since the AT will keep the speed....you are now in trim

 

During clean up after take of you do the same.

Keep the FBW trim ref speed 10-15kt above actual speed.

Again flying with trim basically.

This results in a shallow climb (at 280.000KG take of mass I get for example about +1500fpm this way and a nice acceleration).

 

During deceleration from an in trim situation:

Do the opposite.

Keep the FBW Trim ref speed about 10-15kt below you actual speed while you get slower.

Stop trimming when you reach the center of the speed bug and wait for the AT to catch up.

You are now in trim.

 

 

EDIT: oh....and once you are in trim.....do not touch them trim switches again untill you are again changing speed. So to change pitch to a climb or descend or level off......all you do is point the nose where you want it......steady it......and it will stay there without you having to touch the trim switches at all!!

Now this is what I meant about specifics well done I will try this.

thanks.

[tcas_climb 45]

 

 

IF....IF I have the FBW trim ref speed displayed THEN I can trim it perfectly and THEN the aircraft reacts like the real thing.

 

My head is a little tough sometimes, are you saying that if you have the FBW trim ref speed ON then the aircraft behaves as it should, and if you turn it off the trim starts to behave weird?

 

I have tried the FBW trim ref bug once and noticed that it appears easier but always thought it was caused by a sort of placebo effect, because having it on and knowing what speed you want to trim for you just set it, while with it off and no artifical feel on our yokes, it becomes harder.

[CaptKornDog 282]

For what it's worth, as another data point, with SP1b, I'm still experiencing the issue with trim not being effective unless my controls are centered.  In a climb or descent, as I'm holding some pressure, then trim for a speed change, nothing seems to happen until I center my controls.  For instance, if I'm in a climb, and am around 170 KIAS while holding slight back pressure after my rotation, and gradually accelerate to 250 KIAS while trying to trim to alleviate the force, I have to center my X52 Pro then get a rather abrupt pitch change as the trim suddenly catches up.  I've tried to anticipate this now but it just feels..."awkward and a bit unpredictable" is the best way I can put it, and a good little surprise for those virtual passengers.  I'll try some of the proposed tests here and try to capture the behavior of the blue FBW pipper better as well.  Up until recently, I just assumed I was working the trim system incorrectly, and didn't have the FBW display enabled.

[777simmer 117]

My head is a little tough sometimes, are you saying that if you have the FBW trim ref speed ON then the aircraft behaves as it should, and if you turn it off the trim starts to behave weird?

 

No.

 

What I am saying is, that there are situations/moments where I can not trim by feel.

Some times it does work, some times it does not.

Sometimes I would think I am in trim, only to find out that when I let go of the yoke, my nose goes up or down because I was, in fact, not in trim.

 

The only way I can be absolutely sure that I am in in trim is by displaying the FBW trim ref speed. (cheat mode)

[martin-w 3,235]

For what it's worth, as another data point, with SP1b, I'm still experiencing the issue with trim not being effective unless my controls are centered.  In a climb or descent, as I'm holding some pressure, then trim for a speed change, nothing seems to happen until I center my controls.  For instance, if I'm in a climb, and am around 170 KIAS while holding slight back pressure after my rotation, and gradually accelerate to 250 KIAS while trying to trim to alleviate the force, I have to center my X52 Pro then get a rather abrupt pitch change as the trim suddenly catches up.  I've tried to anticipate this now but it just feels..."awkward and a bit unpredictable" is the best way I can put it, and a good little surprise for those virtual passengers.  I'll try some of the proposed tests here and try to capture the behavior of the blue FBW pipper better as well.  Up until recently, I just assumed I was working the trim system incorrectly, and didn't have the FBW display enabled.

I think you need to submit a support ticket then. Because this is exactly the issue that SP1b was meant to address. [Among others]

 

Behaves well for me. I don't have to centre the controls.

[kevinh 409]

No real world 777 pilot, can tell you when "the system" (whatever you mean by that) of the real 777 is cancelled out, engages, disengages or who knows what else it does and simulates!

 

You would have to be a tech to know what "the system" does and when it does what.

 

You dont need to be a tech to fly the real 777 though.

 

All you need to know is that when you feel a force on the yoke......you have to trim it away.

 

This is the crux of the matter. PMDG have used videos from the aircraft and experience in the simulator to replicate the observed FBW response. This has resulted in a two level simulation (as described in the Intro Manual) where sometimes the FBW is maintaining a set pitch attitude and other times it is responding to trim inputs (what they call fully manual in the Intro Manual). The CDU null zone settings seem to be the switchover point and that may be why some here feel nothing happens if the column is deflected. For others the switch from one "mode" to another works as intended. Generally it appears to work closely to what is expected.

 

C*U control doesn't actually work like this. There is no mode switching between C* (attitude holding with autotrim) and U (speed stability trimming). It all works simultaneously. The difference between current speed and trim reference speed is applied as a proportional offset to the C* control law trim computation, meaning that it is in effect always autotrimming to the trim reference airspeed, not the current one.

 

The only problems I see with SP1b are the occasional lack of response to brief trim inputs (answer, don't make brief inputs outside the "blip" speed range) and the fact you can trim to increase reference speed while pulling the column aft, and vice versa. This should be inhibited and might improve things for some users. Again, the solution would be not to make such contradictory inputs, only trim in the direction you are making a pitch input.

 

It's too easy to overthink this and look for trouble that isn't there. Forget about the trimming issue and use the trim switches intuitively. I find using the FD and A/T helps a great deal.

• Only trim when you change airspeed.
• Apply trim in longish bursts (1 second for every 10 knot total speed change), or blip the trim every 4-5 knots as you accelerate or decelerate.
• When trim feels good when hands free at the new speed, apply a blip trim input (note this is a single input, not a double input) to fine tune the trim.
• If the attitude drifts hands free then regain the required airspeed and adjust trim again, just as you would do with the NGX.

Ok then do an experiment in the 777.

 

Fly  neutral and put the trim speeds up  (apply slight pressure in the oppposite direction ) and while watching the flight controls ECAS page, watch what it does when you release the column.

 

Report back

 

*I get a moderate deflection of the elevators *

I haven't had a chance to try this yet, but this involves flying opposite to how the aircraft is intended to be flown. If you trim to increase speed (nose down), it makes no sense to then apply nose up pitch to maintain speed. I'm not entirely surprised you might have confused the simulation doing so.

[scandinavian13 5,192]

 

 

(cheat mode)

 

▲▲▼▼◄►◄►B A

<START>

 

Did it work?!?

[777simmer 117]

▲▲▼▼◄►◄►B A

<START>

 

Did it work?!?

what??

[Tabs 2,790]

It my be misunderstanding but this is what I have gauged from  flying along with a real pilot.

 

If one pushes the aircraft out of trim using the  trim reference speed and let goes of the column, the boeing 777 will apply elevator accordingly to achieve the trim reference speed set (this is all in manual flight mode with autothrottle engaged).  But if the pilot inputs their own control the system is canceled out and it will only engage again when the control yoke is in the neutral position.

 

Is the above 100% correct?

 

 

Alex

 

This actually is correct *for the internal FBW logic.* In the real aircraft, path/speed following mode is active if there's less than X amount of deflection applied to the column. (I don't remember the specific real world value right now - it's enough for the system to know that it's receiving a deliberate pilot input and should suspend the path/speed mode and respond to the growing "error" term coming from the column position by generating an elevator movement) What does not change during this process in the real aircraft is the artificial feel on the yoke. So yes, the internal mode logic of the FBW is changing between raw input from the pilot and the path/speed hold based on yoke deflection. This is effectively transparent to the pilot though - the force/pressure felt in the controls is continuous. This is what we're trying to simulate in the only way that's really possible without a hyper-realistic force feedback system by requiring your/stick yoke to be deflected more and more to maintain level flight as the airplane gets more and more out of trim.

 

The real system is extremely complicated - there are all kinds of algorithmic generators and processors within the signal path that feed into the final elevator command that goes to the servos. Yes, the C*U control law guides it all and is the primary equation at play, but things are broken up into various modules and many modifications are made to the raw signal coming from the law. The compensations are all different modules, the phugoid generator is its own module, the artificial feel is its own processor, etc. If you didn't have these, the airplane would behave essentially like FLCH in manual flight with the controls neutral - instead of having that "loose" oscillation around the trimmed-for speed when out of trim, the airplane would just pitch directly to the trim airspeed and hold it perfectly just like FLCH pitches to the MCP speed.

 

If you're releasing your controls and there's no response from the path/speed following mode or it takes a long time for it to respond, you've got joystick input still going into the sim somehow that it's reading as pilot input. That's what the control column null zone option in the simulation options is for - increase it. I would set a larger actual null zone on your joystick in the FSX options and/or in the joystick's driver control panel as well.

 

Oh and Kevin - the real airplane actually does allow you to input trim opposite the direction of yoke deflection. We had this tried in the real airplane by someone we trust completely and he confirmed it. The limitation with it is that the stabilizer itself cannot move in this situation - the elevator however can and does. It just won't be offloaded/streamlined until after the yoke deflection is released. This is all modeled in SP1.

[eurowing 13]

do i understand correctly that, if i am trimmed out straight and level, then trim back reducing the trim ref speed let's say by 5 kts, the nose will go up and the airplane will maintain the airspeed equal to the trim ref speed?

 

i hope this is not a dumb question.

[johndrago 4]

f you're releasing your controls and there's no response from the path/speed following mode or it takes a long time for it to respond, you've got joystick input still going into the sim somehow that it's reading as pilot input. That's what the control column null zone option in the simulation options is for - increase it. I would set a larger actual null zone on your joystick in the FSX options and/or in the joystick's driver control panel as well.

 

Hi Ryan,

 

Thanks for the response.  First, let me say that you guys did a FANTASTIC job on this aircraft, and the others as well.  You go the extra mile to make sure that you can come as close to the real thing as is possible on a simulator.

 

Now my question... I'm prepared to be hit for this, however I'm really being serious (friendly), and if it comes across as anything other than that, I apologize in advance.

 

Question:  Since we all are dealing with an OLD simulator (FSX), and the limitations of it, AND the many different types of hardware with null zones, noise, and all the other things that are hindrances to the FBW simulation PMDG has tried to make as close as possible, given the limitations,  has PMDG considered the possibility (don't even know if this is possible) of adding an override option via the PMDG options in the FMC to allow the trim to operate like the 737, meaning NO FBW?  Yeah, I know.... far fetched, no flaming please.

 

I guess what I'm trying to say is that if outside issues such as hardware, software, no force-feedback, etc are already hindering the huge effort you guys made to simulate this feature, but all of these other issues are "ruining" the experience, or not allowing PMDG's hard work to give the experience it's aiming for, is it worth an option to override it?  Kind of like how PMDG's stance was about building a weather radar.  You weren't going to do it unless it could be simulated accurately.   I'm not saying it doesn't work for some people, but from what I've seen, and what others are reporting, it seems as if it's hard to really simulate it within the simulator's confines.

 

Thanks, and I really do appreciate the product.  I can live with it and learn it properly to adapt, I've just been thinking about how to improve this issue so that all can enjoy.

 

John

[777simmer 117]

do i understand correctly that, if i am trimmed out straight and level, then trim back reducing the trim ref speed let's say by 5 kts, the nose will go up and the airplane will maintain the airspeed equal to the trim ref speed?

 

yes.

 

But just like any other conventional airplane it will not just pitch up and maintain that new airspeed. it will undershoot it first and then the nose drops again....then it will overshoot it again and the nose will raise again, etc.

 

After a few of these cycles the aircraft should at some point stabilize at the new trim ref speed. Every conventional aircraft react like this.

 

So in the end you dont want to fly like this.....it takes too long to get stablilized at an airspeed like this.

 

What you do instead is.....put the nose where you want it and then trim away the forces you feel or display the trim ref speed, put the nose where you want it and set the trim ref speed to your new target speed (both are the same but displaying the trim ref speed makes it easier).

[eurowing 13]

i am not using trim like this, it was only an example. i am just trying to understand logic behind the 777 trim.

 

when i set the attitude on final approach and get the trim ref speed to the current speed with a quick trim input, the pitch still changes slightly. not sure about always, but certainly a lot of times. the way i understand it if the trim ref speed is set to the current airspeed then the pitch should be maintained? that is not quite what's happening on my setup. the pitch slowly changes. that is on final approach.

[CaptKornDog 282]

How high have folks seen the control column null zone setting (anyone with an X52 out there maybe)?  I've been trying 10% tonight and haven't seen any discernible difference.  Naturally, it depends on other null zones and a variety of other sensitivity settings but I'm just curious.

[777simmer 117]

he way i understand it if the trim ref speed is set to the current airspeed then the pitch should be maintained?

AT engaged or not engaged?

 

With AT disengaged.....yes!

 

With AT disengaged......No, because the AT is going to try to maintain the magenta bug (target) speed. You should set the trim ref speed to the magenta bug speed.

Ok then do an experiment in the 777.

 

Fly neutral and put the trim speeds up (apply slight pressure in the oppposite direction ) and while watching the flight controls ECAS page, watch what it does when you release the column.

 

Report back

 

*I get a moderate deflection of the elevators *

was that directed at me or Kyle?

This is the crux of the matter. PMDG have used videos from the aircraft and experience in the simulator to replicate the observed FBW response. This has resulted in a two level simulation (as described in the Intro Manual) where sometimes the FBW is maintaining a set pitch attitude and other times it is responding to trim inputs (what they call fully manual in the Intro Manual). The CDU null zone settings seem to be the switchover point and that may be why some here feel nothing happens if the column is deflected. For others the switch from one "mode" to another works as intended. Generally it appears to work closely to what is expected.

 

Thank you for that info.

As I said post 71, I will experiment more with the CDU null zones and the Windows Game Controller nullzone settings.

If you're releasing your controls and there's no response from the path/speed following mode or it takes a long time for it to respond, you've got joystick input still going into the sim somehow that it's reading as pilot input. That's what the control column null zone option in the simulation options is for - increase it. I would set a larger actual null zone on your joystick in the FSX options and/or in the joystick's driver control panel as well.

 

And more valuable info about the nullzone subject.

Thx Ryan.