Handling dynamics with redesigned FBW Sytems

[rhanzir 0]

777, If you change air speed you have to trim t7 to new reference speed. No trim required in config changes (flaps, gear, etc.). So, only use trim, when want to change speed.  You don't use trim to slow or accelerate the plane. But if you trim nose down, plane will descend and airspeed will increase and vise versa. 

 

Robert

[Swen 1]

 

Joystick FBW null zone options

Two new global options have been added for tuning the null zone for engagement of the FBW flight path hold mode of the system after release of the controls, both in the pitch and roll axes. These options are intended to simulate the aspect of the real life system whereby the controls must be deflected with a certain amount of force to push the FBW system out of its hands-off path following and speed stability modes and into fully

0.00.169

INTRODUCTION

For Simulator Use Only DO NOT DUPLICATE 18JUL14 SP1

PMDG 777-200LR/F

manual control. During testing it was noted that there was a large variance in how much deflection was needed depending on the specific joystick in use and that often the system would remain in manual control mode even with the joystick released. If you experience the airplane acting as if the speed stability out of trim function never engages to cause the aircraft to pitch to return to reference speed, play around with these settings – your joystick likely needs different values than the defaults.

The options are located at MENU > PMDG SETUP > OPTIONS > SIMULATION on page 2/7 and are labeled CTL COLUMN NULL ZONE and CTL WHEEL NULL ZONE (for pitch and roll respectively).

A note on low weight takeoff trim settings

The 777 (particularly the 200LR) is prone to very nose down takeoff trim settings at low gross weights due to the highly aft (30+%) CG. This is most commonly encountered on short flights with light fuel loads.

FSX’s flight dynamics engine unfortunately has an issue with this type of configuration that will cause the airplane to still feel like it’s out of trim in the nose down direction immediately after takeoff even with the takeoff trim set on the numbers. When the FBW system engages at 100 feet, there can be a noticeable pitch up motion – this is simply the system compensating and correcting for the FSX issue and not any sort of “autotrim” happening. If you find this effect annoying, you can add an extra unit or two of trim to the calculated one at low weights / aft CGs. Even in the real world, anywhere within the green band is acceptable for takeoff, so this isn’t completely out of the realm of realistic anyway.

[hmsdreadnought 12]

Hey people,

 

@777simmer:

Thank you very much for your explanation and advice. I'll do this practices as you said to get the hang of it. Don't worry the FBW Reference Speed I had only activated in the very beginning to get a basic understanding of the FBW mechanism.

Regarding the landing, I'm not a professional but I can say that I don't have the problems with landing. My problem was, that as soon as my controls where centered, the airplane tries to catch the Ref. Speed wich is - as you all explained - perfectly normal. And these corrections cause my V/S to go rapidly down or too much up causing an unstable approach. And this is the point (I think) where I do the mistakes and mess up the landings. But practise makes perfect.

 

@emvaos:

Thanks for your explanation and the comparison with FLCH mode. I understand.

Watched some videos again, these showed that every pilot controls the thrust as well, not relying on the A/T. They sometimes pull and push the yoke, but they control the thrust all the time. Maybe I should set the Autothrust Override mode to always and also work more with thrust. Because when I simply go with the FDs and pitch too my V/S needed for the 3° slope; as soon as the Yoke gets centered, the FBW catches the trim speed 'ruining' my flightpath  ^_^. So I'll will try thrust as well.

 

@Mike:

It's really hard to judge. The elevators and ailerons look 'normal' to me, no overreacting or such. In FSUIPC I set the Slope for both to 0 and the Nullzones as well. In the FMC options I set both FBW nullzones to 2%.

For the buttons I use LINDA.

The drim buttons are set as follows:

On Press: Elevator Trim dnfast / upfast

On Repeat: Elevator Trim dnfast /upfast

 

I'm curious what you guys have set there, maybe I did something wrong with this settings and didn't know it!?

Lets see. Now I'll go learn a bit trimming  .

 

See you later 

 

 

It's probably been said, but make sure you don't have any input at all when your controls are centered.  I was having trouble in my first flights because I was working on a new profile in FSUIPC, and things were not calibrated properly.  The plane comes in like it's on rails for me - much like the 777 simulator I got to fly at the AVSIM conference in Denver.  That plane was so easy to drive even I was able to land it three times without breaking it (once in a 20 knot crosswind) and I'm not a real pilot...

 

Colin Ware

Seattle

[hmsdreadnought 12]

Here is the best resource I've found for learning more about the FBW in the 777:

 

http://www.davi.ws/a...book_Cap_11.pdf 

 

And from that book:

 

 

• An established flight path remains unchanged unless the pilot changes it through a control column

input, or if the airspeed changes and the speed stability function takes effect.

• Trimming is required only for airspeed changes and not for airplane configuration changes.

 

So, the plane pretty much goes where you point it, and when flying by hand, the analogy to level change is the best one out there.

 

Also, in the final stages of flare and landing, the trim will act like trim in any aircraft....

[whoispankaj 51]

I was able to trim the aircraft as was mentioned in the video..and if people are able to trim the aircraft using the cheat..then it leads me to wonder if the definition of a second in our mind varies and hence without the cheat we find ourselves way off..When I first started to trim this aircraft the one second in my mind ticked off in 1/2 sec and I thought I trimmed it for a second..but I found that I was letting it go off early due to the fear of over trimming..but as things started to settle and one second seemed close to one second I found that my trim reference bug was quite close to the commanded speed..and it became easier to trim..just my 2 cents of experience..instead of practicing circuits and landings I just took off to 10000 ft ans started learning to trim it 10knots at a time and that actually helped than trying to do a busy circuit and trying to trim..I am sure it will be tough to get it in trim trying to manage everything..

What I did was for level flight ..trying to sort that out..

[martin-w 3,239]

Well in the video It states so, again its how I understand it, and doing my practice circuits it seemed to do just that along with the V/S increasing/decreasing based on the trim inputs

22 seconds, I should add "Only use the trim switches if you want to change the speed" Trimming is to alleviate any pressure on the yoke and keep the aircraft at a set "profile"

My friend, the above is exactly the same as any aircraft, a 737, a 757 or a basic Cessna. If you want to change the speed, and thus you do change the speed, by adjusting the A/T or manually increasing or reducing thrust... then you trim to relieve the forces on the yoke. Simple as that.

 

It has been stated numerous times, by Rob on the forum [real world 777 pilot] and by beta testers, that you trim the 777 the same as any other aircraft. Boeing desighned the 777 to be familiar to pilots, not something weird and wonderful they have never seen before.

[FlyCathay 18]

https://www.youtube.com/watch?v=kae_wDCGex0

 

can't you click on the ''Watch on YouTube" option in the lower right corner of the video pane? You access this by clicking on the YouTube label there.

 

Found other three videos on the channel for 777 FBW system that are pretty informative.

 

http://youtu.be/-oY4UsM_TkY?list=PL5caETAZRBN6mPhNASIlMg2bkWH2DbtIz

 

http://youtu.be/5QKU0RLa_44?list=PL5caETAZRBN6mPhNASIlMg2bkWH2DbtIz

 

http://youtu.be/141Oj4WAmeI?list=PL5caETAZRBN6mPhNASIlMg2bkWH2DbtIz

[Copper. 78]

My 5 cents worth...

Conditions = no auto pilot, ILS approach, 1 touch and go + 1 full stop (this session), visibility 0.4km (wanted a challenge), no wind/rain, no weather add ons (used FSX user defined weather).

 

Been doing RH circuits off NZAA 05R and for the life of me, can't master the technique for the final approach phase (from ILS intercept to touch down). Applying the Trim Speed Referencing lessons to the dynamic of the final approach phase is challenging, for me at least. I might enable this "cheat" thing. Perhaps it might aid the practice.

 

On the bright side, flew AKL-WLG in the NGX... Nailed it!

 

Brian Nellis.

[cmbaviator 5]

 

My friend, the above is exactly the same as any aircraft, a 737, a 757 or a basic Cessna. If you want to change the speed, and thus you do change the speed, by adjusting the A/T or manually increasing or reducing thrust... then you trim to relieve the forces on the yoke. Simple as that.

 

It has been stated numerous times, by Rob on the forum [real world 777 pilot] and by beta testers, that you trim the 777 the same as any other aircraft. Boeing desighned the 777 to be familiar to pilots, not something weird and wonderful they have never seen before.

 

 

Well when I trim like the NGX, It doesn't work as when I trim after pitch up or down and adjust thrust to maintain the new flight path and speed, the AC will start pitching up or down in order to reach the new trim speed, flight path wise, it's a disaster to maintain

[Werner747 107]

Hahahaha, this thing about the "cheat" - folks I think don't look at the FBW speed indication as a cheat, rather look at it as a wonderful addition to a simulation where we cannot feel the control forces required.  

 

On another note, it is quite interesting reading the responses and difficulties that people are having with the product.   I don't have these issues - I trim and fly it no worries!   That is the pro and the con of our hobby then isn't it?   The different setups and hardware and the different results we all seem to get :-).

 

Kind regards

[martin-w 3,239]

Well when I trim like the NGX, It doesn't work as when I trim after pitch up or down and adjust thrust to maintain the new flight path and speed, the AC will start pitching up or down in order to reach the new trim speed, flight path wise, it's a disaster to maintain

Not sure exactly what you mean.

 

If you are pitching up, and applying thrust to maintain your chosen speed in the climb [A/T off] then no trim should be required, as you haven't changed speed.

 

If you pitch up, and decide to increase or decrease airspeed, then you simply trim out the forces. Adjust trim to suit your new indicated airspeed, just like any aircraft.

 

I'm not saying PMDG's attempt is perfect, some are having issues, it's not as easy as a 737 to trim, and it should be... but technically you should be trimming like you trim any aircraft. Turn on the trim indicator, it makes it much easier.

 

The other thread should interest you...

 

http://forum.avsim.net/topic/447190-how-to-hand-fly-with-cu-law-aircraft/?view=getnewpost

 

 

#

Hahahaha, this thing about the "cheat" - folks I think don't look at the FBW speed indication as a cheat, rather look at it as a wonderful addition to a simulation where we cannot feel the control forces required.

Yes I agree. We have to remember we are sitting behind a PC monitor, not at the controls of the real thing. We don't have the sensory queues you get in the real aircraft. Thus, I have no issue with aids like the FBW trim indicator on the PFD.

[Swen 1]

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...

[cmbaviator 5]

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...

 

 

I've only done one flight since SP1, but I feel like you, the AT doesn't seems responsive enought. During the approach, even with the trim speed close to the AC airspeed and AT ON, when i was pitching up or down to follow the GS accurately, when I released the yoke, the flight path is not well maintained

[3-2-1-Now 126]

PS. The above behaviour occurs when your controls are centred.

 

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.

 

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

 

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

 

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

 

Best regards,

Robin.

[Swen 1]

 

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

Yes i can confirm this. Sometimes happens this but in the time if you trim up and down. Not in one direction.