I have this problem on final approach. Nose is bob up and down. At first I think that AS2012 make some turbulentes, but it's the T7 by itself. If you have bad weather conditions where wind is changing rapid the hole time, the T7 is very very bad to control.

 

Other thing i have problems with Autothrottel yesterday. LNAV and VNAV was activated after takeoff, but the T7 don't speed up in AP mode and hold climb rate. The AP don't push the nose down to give the T7 a chance to accelerate. I must push Alt Hold... So the speed was extrem slow and go slower into the bad range.

 

Anybody happens this too?

 

PS: On final approach, I use only the throttle to get more or less vertical speed like a fighter pilot. The auto trim produce then this effect.

 

The problem started from the altitude above 10000 using LNAV and V/S FPA 1000 and the IAS speed  320.  This is when it starts having the pitch up/down motion.  

 

 

PS: I was using default fsx clear skys weather.

 

Thanks again.

Mo

Hi Martin,

 

You know what, I have that issue now as well.

With first no trim and then too much of it.

I think I needed a bit more flight to see what you mean.

 

 

 

EDIT:

I find the best way to manually fly this aircraft at the moment is by not touching the trim switches (and I am telling you that is not how the real plane works)

 

Thanks Rob, glad you've confirmed my findings.

 

Like Ryan said, it may be that PMDG have misinterpreted the Boeing documentation they have access to. Like you, I try not to touch the trim at all now.

 

I'm looking forward to the findings from your real world flight.

 

 

 

I have this problem on final approach. Nose is bob up and down. At first I think that AS2012 make some turbulentes, but it's the T7 by itself. If you have bad weather conditions where wind is changing rapid the hole time, the T7 is very very bad to control.

Do you have the registered version of FSUIPC?

 

If so, use the wind smoothing function. Also tick the supress turbulence box. Some tick the two boxes next to it as well. Variance and gusts I believe. Works great for fixing the S-Turn issue and erratic behaviour due to sudden wind shifts.

 

 

 

The problem started from the altitude above 10000 using LNAV and V/S FPA 1000 and the IAS speed  320.  This is when it starts having the pitch up/down motion.  

 

 

PS: I was using default fsx clear skys weather.

 

Thanks again.

Mo

I've heard others mention this issue in vertical speed mode. Personally, I've not had this issue yet. But having said that, I don't very often use vertical speed mode, I only use it for small changes in altitude. For big altitude changes I use flight level change or VNAV.

 

Someone else has it here...

 

http://forum.avsim.net/topic/421119-descending-problem/

@Martine-W

 

After few updates of AS2012 you don't need this. 747, Concorde so on are very smooth and don't have this effects.

Okay Swen, no problem.

 

FSUIPC is great for me. Could still be a conflict between the T7 and AS2012. I don't have this issue at all, I'm using REX.

 

Centre of gravity issues can also cause bobbing.

 

Put in a support ticket if you don't get any answers in the forum.

Ryan,

 

Thanks for the update. I can easily imagine how confusing must be to interpret the information available about Boeing's FBW, since there isn't much!! I can't find a better way to get to the root of this than to go do some flying on a 777 Level D Sim, maybe one of your 777 captains on the team can help with that? B)

 

777simmer,

 

Let us know of your findings on the real 777! If not possible, the Sim Check will be great too. I'm too flying it without touching the Trim. I guess until the SP1, it's more System management, and less Hand Flying!

Just out of curiousity, what have you all set the trim repeat slider at in FSX? I belive I´ve read in the intro/tut that the trim change is as slow in the sim as it is in reality. I have my slider set in the middle position and the trim change is pretty far from slow for me. When setting the TO trim I really have to just make quick dabs on the buttons otherwise the change is too great, or rather, the rate of change is too(?) large. This may be the cause of some of the posters saying that they experience no change for a short time and then a rush of change.

Yip, i can confirm this. Did you try to trim the plane via Mouse? Same problem. If i must set trim to 2.50, then it will get to 2.51 then 1.48 then 2.52 and then if you have luck to 2.50. I must click very very short with mouse to get my trim setting.

Hi all gentlemen.

 

First of all, thank yoy very much Ryan for your comments.

 

Last night I did the flight characteristics test proposed in the FCTM, pag. 277 for real 777 pilot training, I want to comment what I think about it.

 

I made the test as follows:

 

Take-off, fully manual, with 17 tons of fuel. Climb to 15000 ft. at 250 kts.

Once in level flight, in trim and at approx. 250 kts, I turned on the autothrottle, speed mode and commanded 250 kts.

Autopilot OFF.

 

I maintain level flight with column only and A/T maintais speed for me. Then, I command the A/T to 320 kts.

 

YES!!, as the FCTM states, as the airplane accelerates to 320 kts, you DO have to exert forward pressure on clumn and/or trim in orther to keep the airplane at constant altitude. I decided just to keep it with the columnonly and no trim, since my joystick is not as strong as the real column ...just to see what happesns.

 

Well, as the airplane keeps accelerating, you feel that more a more forward push is necessary progressively. The aircraft is in fact out of trim at this moment. In the real one, you'd have to be applying trim since the column force must be noticeable, but with my joystick there is no force problems so I do not trim.

 

I continue with forward pressure as the speed nears the 320 kts comanded speed, As the A/T captures a stable 320 kts, while I am exerting forward steady pressure to keep altitude, after a few seconds you feel that now you have to relax progressively the force on column because the nose wants to drop softly, so I gently release the pressure till the point the column reaches neutral and the aircraft is in trim by itself.

 

In deleration, its the same but the on the inverse. I I command A/T to decelerate to 220 kts, you DO need to increase back pressure progresively in order to keep altitude as the airplane decelerates., but one speed stablished at 220 kts, if you gently relax the back pressure o the colum, you see the aircraft has autotrimmed to 220 kts when you let go the colum.

 

I think the FBW is working more or lees ok, and that must be a NOT documented system funtion that when the speed is stable and not accelerating or decelerating, if you're maintaining some constant elevator position, if you have not progressively trimmed manually during the speed increase or decrease (just using your muscles), when the condition is stable, the FBW sees this, and will streamline the stabilizer to your elevator for you, and so, this trims the aircraft automatically

 

 

Cheers.

Cowl, I'm sorry if you think that there is a contradiction between what I and 777simmer are saying. I don't see it as a contradiction, but more a difference of opinion on how true to the "spirit" of the boeing FBW system the PMDG777 simulates. I have done the experiments 777simmer has done in the sim, and he is correct about how the simulation behaves, in that there is almost an auto trimming effect if you continue to apply column pressure as the plane accelerates or decclerates to the desired speed. which is strange because the trim position indicator does not move. I have noticed also that even when the trim button is pressed the trim indicator barely moves and sometimes doesn't move at all.

 

What I am saying is that even though this is NOT TRUE to the aircraft, this is the way FBW is modelled in the FSX simulation platform. To me this makes this difference not so important so far as I would think it very hard to replicate on this scale the control forces you need to exert in real life on the aircraft, and how a true trim system behaves.

 

 Yesterday on a real flight on a 777-300ER I hand flew a departure from an airport in Europe accelarating from flap up speed to 250kts while in the climb, the force I needed to keep the control column down was quite strong, I would compare it to having the CH column pushed in at least 3/4 of travel (and that's understating it). I did this until I grew tired of pushing and and decided to trim. only then did the force needed subside, and I continued to climb to an altitude below 10000ft, at which point I selected the A/P.

 

So as far as I see things, the essence of the way the system should work is simulated, and my tests and yours with the sim prove this, however all of us as flight sim fans should appreciate that the way FSX simulates hand flying, especially of large commercial aircraft, is limited. I'm not saying its poor, just limited.

 

I hope 777simmer agrees, and maybe I was over zealous in expressing my opinion and apologize to him if that was the case, as obviously the modelling is not true to life, even if it is true to the essense that of the aircraft system. I apologize to you also if it caused you confusion.

 

kind regards,

 

K

pilotresponse - great comments on the real aircraft, but as you can clearly see - the real aircraft is NOT auto-trimming whilst the sim is.

 

 

 

I hand flew a departure from an airport in Europe accelarating from flap up speed to 250kts while in the climb, the force I needed to keep the control column down was quite strong, I would compare it to having the CH column pushed in at least 3/4 of travel (and that's understating it). I did this until I grew tired of pushing and and decided to trim.

 

Bingo! In the sim it trims for itself, which is the point we are trying to make. From your comments it appears the real thing definitely does NOT do this.

 

Best regards,

Robin.

FSX has always had the problem of not being able to output us the forces on the control. The solution has always been to limit elevator authority, so as we run out of trim, we must move our controller further, and further, to keep for example, the nose from going up and the plane from gaining altitude. There's a moment when we have reached the full stop of our controller, and we can no longer keep it from gaining altitude. This is the way FSX is showing us that in the real plane, the forces would be too strong right now, and you wouldn't be able to keep holding it. Not ideal, but we have been using this system for years!

 

I don't see why this has to change. All Boeing aircrafts have increasing force needed to mantain the current flight path when the airspeed to up, and the same is true with the B777, so why is PMDG not able to simulate this any longer, if they did it in the 747, 737, etc?

 

Edit: The only difference I would see between the B747 and the B777, and correct me if I'm wrong, is that in the B747, when you trim for a speed, your Yoke will physically move to the position, and keep in that position without any force needed, and in the B777, the aircraft has a Spring that always returns the controller to center position, even as you trim it, so the pilot doesn't have the visual feedback of trimmed position. Is that right? If it it's, maybe this is what caused PMDG to change the way the aircraft is behaving in FSX? Just ideas... I'm sure their team will set this straight in no time!

 Yesterday on a real flight on a 777-300ER I hand flew a departure from an airport in Europe accelarating from flap up speed to 250kts while in the climb, the force I needed to keep the control column down was quite strong, I would compare it to having the CH column pushed in at least 3/4 of travel (and that's understating it). I did this until I grew tired of pushing and and decided to trim. only then did the force needed subside, and I continued to climb to an altitude below 10000ft, at which point I selected the A/P.

 

 

K

Thats exactly what I wanted to do on my flight tomorrow :-)

You beat me to it :-)

 

Good, the confusion is out of the way....now lets see how PMDG feels about it.

 

Thx.

That's exactly the point!

 

And yes i need force, i use a yoke from Saitek. If you have a FFB joystick you don't have a neutral set. The most yokes and joystick go back to middle in neutral position and you need force with your hands to turn forward or back or left or right. This yoke have a neutral position where i dont need force. At this point i know that the plane is stable and well trimmed. If i need force, then i know that my plane is not trimmed well. I need force to push and i need force to pull. If the plane nose comes up, then i need much force via my hardware yoke to push the nose down. I need this force on my yoke! That is the point to use trimming. This is the point where auto trims start to work and you will fight with it!

 

So let me understand:

 

If you reduce throttel and descelerate speed to the new speed, the real 777 will not auto trim at this point right? So then i must trim the plane or force the column or my hardware yoke.

 

If we are on stable speed and stable altitude then FBW will trim automatically a little bit.

 

Right?

On APPROACH, you need not trim for configuration changes, but again you must TRIM for Speed.

(on MANUAL only as on autopilot trimming is automatic)

 

See 777 FCTM Chapter 5 Approach and Missed Approach

page 220 VISUAL APPROACH 

Downwind and base leg:

"Extend landing flaps before turning final. Allow the speed to decrease to the proper final approach speed and TRIM the airplane"

Visual approach - general:

"Once the final approach is established, the airplane configuration remains fixed and only small adjustments to the glide path, approach speed, and TRIM are necessary"

 

Happy landings ! :smile:

 

Guy

 

But on approach, I am having to trim for config changes. In fact I am having to trim just to keep a level approach path. full flaps, gear down, ready to land. I need to keep trimming up then down then up again all fighting the aircraft. This never happened on the 747X or the NGX.

 

And then one gentle tap of the trim and the nose goes flying up or flying down. In the end I am able to make a good landing, sometimes floating a little too much. But there is something either wrong with my system or with the 777. Since I don't have this problem with the 747 or the ngx I'd say it might be a bug.

 

 

Edit: The only difference I would see between the B747 and the B777, and correct me if I'm wrong, is that in the B747, when you trim for a speed, your Yoke will physically move to the position, and keep in that position without any force needed, and in the B777, the aircraft has a Spring that always returns the controller to center position, even as you trim it, so the pilot doesn't have the visual feedback of trimmed position. Is that right? If it it's, maybe this is what caused PMDG to change the way the aircraft is behaving in FSX? Just ideas... I'm sure their team will set this straight in no time!

You are wrong.  747 rudder and wheel trim move the zero force position of the wheel and rudder, but the stabiliser trim does not.  The 747 column has a neutral (zero force) point about 5 deg forward of upright.  It does not move with trim.  If the aircraft is not in trim it will need the pilot to hold the column away from neutral and so hold a force.  The trim moves the stabiliser so that the elevator input can be reduced, ultimately to zero when in trim.

 

The 777 column is exactly the same. It does not have a spring to centre it, it uses a hydraulic force feedback system just like the 747. As in the 747 the neutral position remains the same.  What is different is how the trim operates, as it works through the FBW, not directly on the stabiliser.