Handling dynamics with redesigned FBW Sytems

[777simmer 117]

Therein lies one of the problems I'm seeing. If I have any force on the control column whilst trimming, even if the trim reference speed moves 50 kts, nothing happens until the control column is centered, then all the trim change is applied at once and the aircraft aggressively pitches whilst it catches up (if it is a long way out of trim). There is no pitch reaction at all during trimming with the control column deflected and held in a constant position.

 

As a result I'm unable to trim the aircraft by feel, because nothing is happening.

 

I am telling you......you are on to something!

Darn it that I cant try to confirm now.

 

Why dont you put in a ticket and see what PMDG says?!

 

Another problem is the trim is intermittent, and sometimes even runs the opposite direction to that selected!

 

Best regards,

Robin.

Yes I have seen that too!

Sometimes up to three hits of my trim switches wouod not change the trim ref speed at all.

And sometimes out would make a small jump (5kt) in the wrong direction.

 

Null zones don't do anything for me, either.

 

Robin.

Last time I tried I put the Null zone at max (10).

My initial feeling is that it worked better.

Maybe because as you trim, one automatically starts reducing yoke input (to see what happens.....(since we cant feel what happens we have have to see what happens right).....and with nullzone at 10 it could be you reach the point where "all that trim is applied at once) sooner, as in not when centered but while still appliying some force to the yoke. And that could give the illusion of trim inputs working while we are pushing/pulling on the yoke.

 Other than this, the FBW is a marked improvement over the original. B)

 

Yes, but only because now we at least have to trim.

 

I think that I would have been happier if the would have just copied the 737NGX flight model and adapted it slightly to present the bigger mass of the 777!

[cmbaviator 5]

 

 

Last time I tried I put the Null zone at max (10)

 

You mean in the CDU option or FSX ??

 

BTW, is it better to leave nullzone to min on fsx but only chnage the nullzone in the CDU option ?

 

CMB

[Nyxx 6,993]

try setting trim to none repeat /slider to left. You have to keep repeating the command but I have always used trim like this when set to a button.

 

Triming the 777 last night was just like Rob said, just like a 172. I could "feel" the trim on my Warthog stick. Felt great and easy.

[3-2-1-Now 126]

Hi,

 

Some experimentation later (with FBW HIDDEN so no cheating), and it seems that in addition to the control column centering issue where the trim apparently gets applied in full, if you make extreme trim changes (e.g. slow to min speed, trim, then accelerate towards VMO), whilst applying control column pressure and trimming, there is the tiniest change apparent in pressure required, but still the same issue of the full trim change not being applied until the control column is centered.

 

@Rob: Looking forward to reading your analysis. I did send a ticket to PMDG, and they say they forwarded it to the developer, but now I've had a chance to fly it a bit more I think I'm starting to figure out exactly where the issue is in the system.

 

EDIT: Flew an ILS with late go-around (50 ft) and the FBW was in flare mode (note, no FD). Upon selecting gear up, the FBW transitioned to flight mode and the aircraft aggressively pitched up as it instaneously removed the flare program offset. Until that point the climb away was OK, if a bit heavy due to the flare program.

 

Best regards,

Robin.

[martin-w 3,239]

I start to analyse what's going up with trimming. It's interesting which information i get about it. I try to fly stable on 3000ft and that wont work well. If i switch off A/T, then the flight was awesome stable. If you activate the A/T system then you journey begin to start... The flight was not stable. The bird start to descent and then you must trim or control the yoke. You must do this all the time or the bird will descent or climb all the time. I try to let the bird do, it descent to 2800 and try to get stable then begin more with descent i must do something to get it stable and you start to trim

I looked at your video Swen. Does look like the A/T is unstable doesn't it.

Therein lies one of the problems I'm seeing. If I have any force on the control column whilst trimming, even if the trim reference speed moves 50 kts, nothing happens until the control column is centered, then all the trim change is applied at once and the aircraft aggressively pitches whilst it catches up (if it is a long way out of trim). There is no pitch reaction at all during trimming with the control column deflected and held in a constant position.

Robin and Rob... I'm not seeing this at all. Trim is applied whether I'm applying pressure to the control column or not.

[Nyxx 6,993]

Same for me I don't need stick centred I can be pulling back and trimming to ease pressure.

[martin-w 3,239]

So i dont know, but you dont need any response of the bird. It's fly by wire... Is there really a force feedback? Then there must be built in an artificial feel unit something else. Can't believe this....

 

I start to analyse what's going up with trimming. It's interesting which information i get about it. I try to fly stable on 3000ft and that wont work well. If i switch off A/T, then the flight was awesome stable. If you activate the A/T system then you journey begin to start... The flight was not stable. The bird start to descent and then you must trim or control the yoke. You must do this all the time or the bird will descent or climb all the time. I try to let the bird do, it descent to 2800 and try to get stable then begin more with descent i must do something to get it stable and you start to trim again... I have done a video and upload it to youtube:

 

 

What are you thinking? I say, the A/T is not sensitive enough or not precision...

Hi Swen.

 

I've just tested the scenario in your video.

 

That doesn't happen for me at all. I engaged and disengaged the A/T numerous times and all was stable.

 

I can only conclude it's something specific to your system.

[3-2-1-Now 126]

Swen,

 

Looks fine to me? Aircraft is pitching for speed, and the AT is reacting. The AP is then reacting to thrust changes. Looks perfectly normal.

 

Best regards,

Robin.

[Swen 1]

Nice, now i have two different answers.

 

I have taken this video without any weather options. I deactivated it all via FSUIPC. You can see, that without A/T the bird is stable. With A/T not...

 

You tell me thats normal and martin say, he didn't has the problem. So... If you say its normal, yes it is. In normal conditions you have weather and the air is sometimes a littlebit bumpy.. I know this, 'cause i fly sometimes real GA Planes. But there is no weather active and this is happend. If no weather is there, why the engine reduce thrust in flight it i fly stable vertical?

[3-2-1-Now 126]

I watched the video Martin linked. AP is OFF and the FBW will NOT hold altitude. If you started to climb the AT would go to max thrust rating. If you descended, it would go to idle. I don't see anything wrong???

 

Best regards,

Robin.

[Swen 1]

AP is off an A/T is off. And i'm totally stable in the air manually by my own hands with thrust and yoke. But if i engage A/T, then the bird reduce thrust and i start to descent. Slowly but i do. I must correct the bird all the time via yoke. And this without any weather active.

 

Ah, and this test is with 300er. I don't test 200LR at the moment.

[3-2-1-Now 126]

Well that is what starts the whole problem. AT thinks it is very slightly too fast, so reduces thrust very slightly. Speed starts to drop which changes the trim and results in the nose dropping. Aircraft then accelerates, so AT removes a little more thrust. Aircraft pitches up due to now being faster than trimmed. AT sees speed decaying, and adds thrust. Eventually it stabilizes.

 

I'll try it here, but iut is unlikely you will set things exactly as it wants them.

 

Best regards,

Robin.

[whoispankaj 51]

Can somebody explain what is the relation of the null zone to FBW?How does it help to tune? I am trying hard to read and understand the intro manual..somehow it just greases my head and bounces off..

[777simmer 117]

So i dont know, but you dont need any response of the bird. It's fly by wire... Is there really a force feedback? Then there must be built in an artificial feel unit something else. Can't believe this....

 

exactly...That is exactly what is build into the real 777.......an artificial feel unit.

 

It is even called exactly that!

 

When you are in an out of trim condition the artificial feel unit creates a force on the yoke that gives the pilot the feeling that he has to push/pull the yoke to keep the nose pointed where he wants it.

Without this artificial force you would not feel anything when out of trim.

 

When you then apply trim, this artificial feel force is taken away and the yoke stays centered without requiring any continued force.

 

During all this not a single flight control has moved anywhere directly due to your trim input!

Just the force is trimmed away.

 

In the background the FBW trim speed has changed which results in the elevator moving first and then the stabiliser moves so that the elevator and stabiliser are flush again.

[3-2-1-Now 126]

Can somebody explain what is the relation of the null zone to FBW?How does it help to tune? I am trying hard to read and understand the intro manual..somehow it just greases my head and bounces off..

 

I think null zone is the wrong description for it. I have found that setting it to 10% (the maximum) for pitch has helped the trim situation slightly. It's still not there yet, but seems better than before.

 

Best regards,

Robin.