Still Trim issues with Sp1b

[777simmer 117]

HI Lucasz

 

I found your post very refreshing. Let me explain - you first admitted to having some problems trimming, but then, as apposed to some other users, you did not proceed to lambast the product, get angry at PMDG etc. Instead you went on to list some thoughtful questions regarding correct procedure. This is what the forums are for / about, in my mind.

 

Tabs has already replied to you with some answers which totally reflect the way I fly the 777, and I am in the camp of those who are not having issues.

 

One of Tabs replies "Nothing is dependent on the MCP window", I feel could lead to some confusion and problems (if you are in AT SPD mode). The second part of that sentence "you should'nt be trimming before changing airspeed" is quite correct - if you do this, particularly if the new airpseed is very different from the one you are currently at, you will immediately introduce instability, and be fighting with the pitch controls (yoke) to get smooth trim and pitch changes.

 

So here are my answers to your questions (reflecting the technique I use, successfully). Maybe in real world piloting of a 777 these techniques are wrong - but they work for me, which may explain why I am not in the camp of those having trim problems (RW 777 pilots who are trying to apply their RW flying technique to the sim seem to be having some issues, which is what they are trying solve via this thread).

 

 

 

If you are using the AT, then yes I do set the new speed I want in the MCP first, before appying any trim. Almost immediatley the plane will start to change pitch in response to the power change the AT command the engines to, in order to get to the new speed. So now you gently start to apply yoke force to mainatin the pitch you want. In the case of this question the example you want is of not changing altitude. So you apply force while the speed changes to keep the VS needle on 0 (or thereabouts - it is sensitive so small progressive inputs on the control are all you need).

 

Now as speed changes, if you are using the fbw marker, it will gradually move away from the current airspeed as the plane changes speed. Now here is the trick - I do not wait for a large deviation to develop between actual airpeed and the fbw marker speed. If you do that you should feel larger and larger control inputs are needed to keep that VS needle where you want it (and at large speed differences - 80-90kts - you will lose elevator authority). You dont want to get near that situation either!

 

So now start putting in small progressive trim changes with the trim swithces, as Tabs suggests, to keep the fbw marker +- in-sync with the changing airspeed. If not using the marker, I keep the VS needle where I want it and can feel the increasing force needed to hold that VS, and so make small, continuous adjustments with the trim switches to trim out the force (this is where some have a problem as they say they cannot feel these forces at all. As Tabs has also mentioned, PMDG cannot duplicate this exactly since the real 777 has a control-force pushback to enhance pilot awareness of the out-of-trim condition, that our sim controls simply do not have).

 

Another tip here is not to trim too far ahead of the current airspeed, keep it there and thereabouts is fine (+-5kts or so). By this I mean if using the fbw marker and slowing down, try not to trim so the fbw marker is too much below the current speed (or if speeding up, fbw marker too much above the current airspeed). If this happens you will get an unwanted pitch change and find you start fighting with the controls (having to instead of pulling back when slowing down, need to introduce some push foward, and then start to pull back again as she gets to, and falls bellow the speed where the fbw marker is). Because its sensitive, if you don't do this with some finesse, you will start porpoising like crazy.

 

 

 

Yes decrease IAS on MCP, but dont just start pushing the trim switches for "X" Secs to get the fbw ref trim speed to the newly selected speed-bug position. As I said in the answer to 1, introduce trim progressively to keep the fbw marker in sync with the current airspeed, until it and airspeed gets to the speed-bug position. At that position, the AT will usually adjust engine thrust (so listen also to what the engines are doing), and use blip trims to keep the fbw marker exactly at the speed-bug position, with fine "nudges" of the control collumn to get the VS needle to stabilse and hold the required VS. Then you can let go and relax!

 

 

 

Absolutely correct! No speed change = no trim change. Just hold back pressure so set the VS at 1000fpm (lets not quibble if it is 1050 or 950), try to get it on the nail if you can (takes practise and fine inputs on the collumn, not yanking it around), hold the backpressure a bit till the engines have stabilsed at the increased thrust they need for the climb, and then let go and climb to your new altitude. You may need to nudge the control collumn occasionally to keep is at say your 1000fpm climb (that is not the plane going out of trim - all planes do this as power changes with air temp, air density, wind changes etc).

 

Some tips I was going to add in a third part post to my series on FBW (for various reasons I am scrapping that post and this post can stand in for it).

 

You are in manual flight mode, so changes to engine thrust limits will have to be handled by you. This means that, if you want to climb at a high rate (say 2500fpm up), you need to allow the engines the power to do this. In AP, VNAV the plane will switch to CLB thrust for a climb, especially at higher altitudes. If you see CRZ ennuciated on the engines page, go to the FMC PERF INIT / THRUST LIM PAGE and LSK the CLB thrust. This will enable the engines to spool up to max allowable climb thrust to handle the higher climb rate (what thrust is need all depends on weight, altitude, winds and air temp). Watch not to set a VS that pushes the needles over the thrust limit (the plane will not allow this), but you will see you have to reduce the climb rate to sensible levels, mainly at higher alts (you will see the AP doing this if not flying manually, and you will also see it occasionally decrease to lower VS to enable airspeed to get back to the MCP value, and then pitch up again once it is at speed). You have to help the plane along like that at times in manual mode.

 

Which brings me to another obvious one. If you are increasing airspeed in a climb, and you want a high rate of climb, you cannot just pitch for a high VS and hope the engines will have the thrust to push up your airpseed while climbing. You have to help it attain the faster climb speed by intially using lower climb rates, and, once the faster speed has been attained, then start to increase VS (pitch) to the max limit the plane will handle and still maintain that speed (all the while progressively trimming as speed changes). Again watch how the AP handles this situation, and copy that when flying manually.

 

 

 

Ah Ha! Again an intelligent question, and others have said dont over-think it - but yes you do need to at least think!

 

Never mind a Cessna, how about a car! You are about to go from a flat section of road down a fairly steep decline (and the VS you want in the airplane is the steepness of the decline coming up). You can go over the lip at 240km per hour, and just hope that on the decline, taking your foot off the gas, and applying the brakes, will slow you down to 200km/hr. Depending on how steep the decline is, you may or may not be able to handle the situation. In a car, safe practise would be so slow down before hitting the decline, maybe shift gears to help the engines to slow the speed, etc. Same with the plane, particularly when coming up to the descent at higher speeds.

 

Slow down first (set the 200kt MCP speed first, let her slow, and trim progressively so the plane is at trim, 200kts). Then push yoke foward till you have your required descent rate on the VS tape, hold the yoke force (no need to trim now), and wait for the engines to complete the spool back. Release the yoke and the plane should be holding the lower speed and VS you want, and in trim (within reasonable descent limits), with only occasional nudges at the controls to keep the VS where you want it.

 

OK, some things to watch for in descent;

 

First, if you were for some reason at CLB thrust limit, set it to CRZ thrust limit with the FMC. This will allow the engines to come back to full idle if they need to, so as to attain the speed / VS combo you want.

 

At certain descent rates, the plane may not be able to slow down to the speed you have set in the MCP. You have some choices then; either pitch up a bit to decrease the -ve VS to help the plane get to that speed OR haul out the spoilers OR accept the higher airspeed if it is only marginally different from what you wanted and you are not busting any speed contraints by allowing this, BUT then trim for that higher speed (progressively set the fbw marker to that increasing descent airspeed / remove the increasing forward yoke pressure you will feel you need in order to maintain the desired VS as speed picks up).

 

One last comment related to it "flys just like a Cessna". Yes and no. A Cessna does not have an AT, and this can really mess one around if you are heavy-handed with the controls. You will find you are hunting around to get the VS you want, and to get trimmed, becuase you are fighting surging engines. Solution; use gentle control inputs (finesse and technique).

 

If you want to really fly it like a Cessna, turn of AT as well. Increases the work load quite a bit! But it is also a lot of fun (and good for flying skills development), and you also have more control over fine setting of pitch and VS via the use of small throttle adjustments. The engine surge problem is certainly eliminated then, but be on your toes with thrust settings! In this mode, "Nothing is dependent on the MCP window", but setting speeds, heading and altitude in the MCP helps to "bug" the desired values for reference, and is good prcatise anyhow in case you want to swich the AT and /or AP back on for any reason.

 

Rob

EDIT:Could you open up a thread somewhere with flying tips so we can continue here with solving some trim problems?!

 

(edited to sound somewhat nicer since the poster already agreed that another thread should be opend for this. thx)

Ok Rob, I feel a bit guily here as I am the one who seems to have started this thread going of-track from a "why is it doing this" to a "how do we fly this as it is, tips thread" Unfortunately while you were seubmmitting your posts, I was compiling and submitted a lengthy reply to Lucasz that has only made this situation worse for

Apology accepted :-)

[geolpilot 88]

 

 

Sure you feel that you need to pull or push on the yoke to keep airplane level.
Everybody FEELS that!
What some do not feel is that when you do trim.....that this feel (yoke push or pull deflection) des not have to be reduced to prevent the airplane from going in the other direction!!
That is where trimming by FEEL comes in.......not the feel of holding the yoke but the FEEL of having hold the yoke LESS when trimming.

 

Rob,

 

We seem to be taking at cross-purposes here, or you are misunderstanding me.

 

What you say above is exactly what I DO feel. A need to initally hold force to hold a set VS / pitch, and then as I trim (only if airspeed is changing!) I feel that I have to hold the yoke LESS and LESS when trimming, so that I can let go, and the plane stays at the VS I wanted, pitches as I wanted and, if I turn on the fbw marker, its at the current, new airspeed.

 

So I am not using merely VS as a proxy for the fbw marker, and guessing at trim. I am also using "feel",  while trimming, to progressively decrease the yoke forces in sync with trimming (and changing airspeed) while holding the VS / pitch I want, until I feel nothing, and can simply let go.

 

Do not know where the guessing comes in here at all. I do feel trimming, honestly!

 

When not changing airspeed, I point the plane where I want it to go, let the engines do their stuff, and when power is stabilised I can let go of the yoke and the plane hppility continues on the new flight path, istill in-trim.

 

Rob

[777simmer 117]

I do want to note that what I observe in the outside view, in the air, with the PMDG is that, while trimming, the amount of elevator deflection reduces, and simultaneously I feel the need to release pressure on the yoke. Until a stage is reached close to being in trim when the elevator deflection is so slight, that I let go of all pressure, and "flick: the stabiliser aligns. So from that observation, the PMDG is trimming, while holding force on the yoke, but using the elevators, not by steadily moving the stabilisers (as you say the real 777 does).

 

That would indicate trimming be feel does work for you, yes.

You will remember I wrote a Lua script to monitor and plot VAS in relation to other variables. I see Simconnect allows one to read a whole lot of variables related to yoke position, pitch rates, G-loads, trim positions, elevator position etc. So I am rather working on that, as it may illuminate things more than just looking at animations. Unfortunately, this will require plotting data on graphs, so I will do that, and people can then have a look at these as see if they spot something.

 

Wow....cool!

[martin-w 3,235]

 

What you say above is exactly what I DO feel. A need to initally hold force to hold a set VS / pitch, and then as I trim (only if airspeed is changing!) I feel that I have to hold the yoke LESS and LESS when trimming, so that I can let go, and the plane stays at the VS I wanted, pitches as I wanted and, if I turn on the fbw marker, its at the current, new airspeed.

 

As I've said many times. It works for quite a few of us.

 

For those it doesn't work for there must be system specific variables at play. It's not purely a PMDG error. There's a variable at play related to "some" users setups, that renders trim only effective when controls neutral.

 

If you remember... Robin, [3-2-1Now] highlighted this previously. PMDG acknowledged he was correct and fixed the issue for SP1b. So clearly, whatever fix PMDG implemented... hasn't worked for some of you.

[777simmer 117]

Rob,

 

We seem to be taking at cross-purposes here, or you are misunderstanding me.

 

What you say above is exactly what I DO feel. A need to initally hold force to hold a set VS / pitch, and then as I trim (only if airspeed is changing!) I feel that I have to hold the yoke LESS and LESS when trimming, so that I can let go, and the plane stays at the VS I wanted, pitches as I wanted and, if I turn on the fbw marker, its at the current, new airspeed.

 

So I am not using merely VS as a proxy for the fbw marker, and guessing at trim. I am also using "feel",  while trimming, to progressively decrease the yoke forces in sync with trimming (and changing airspeed) while holding the VS / pitch I want, until I feel nothing, and can simply let go.

 

Do not know where the guessing comes in here at all. I do feel trimming, honestly!

 

When not changing airspeed, I point the plane where I want it to go, let the engines do their stuff, and when power is stabilised I can let go of the yoke and the plane hppility continues on the new flight path, istill in-trim.

 

Rob

yes, I totally understood the opposite after reading that other post. So disregard those comments on not trimming by feel. You clearly ARE trimming by feel (and you know how to pitch for v/s, lol).

 

thx for staying civil!

However... what I find utterly weird, is that if I fly in trim at lets say 300 knots, and without altering the trim, decelerate right down to 190 knots, all I require to fly straight and level is a very small back pressure on my joystick.Conversely, if I do it the other way round, namely fly in trim at 190 knots, and then without changing trim, accelerate to 300 knots, I require maximum forward movement of my joystick, as far as it will go, and despite this it's still not sufficient and I climb rapidly.I may be wrong, but it seems as if their is a disharmony in regard to trimming. Surely I shouldn't require minimal back pressure when decelerating, but maximum forward pressure when accelerating.

Finally something with the exact same assymetrc results I was seeing. Exactly the same here martin.mI call it oversensitive yoke in one out of trim direction, and verry un-sensitive yoke in the other out of trim direction!

As I've said many times. It works for quite a few of us.

For those it doesn't work for there must be system specific variables at play. It's not purely a PMDG error. There's a variable at play related to "some" users setups, that renders trim only effective when controls neutral.

 

If you remember... Robin, [123go] highlighted this previously. PMDG acknowledged he was correct and fixed the issue for SP1b. So clearly, whatever fix PMDG implemented... hasn't worked for some of you.

yes you are right......I wonder where he is hanging out......could use him here!

 

Martin, I have ordered a new yoke. should be here today or tomorrow

(Saitek Cessna Yoke)

After that we shall see how my system behaves in respect to trim by feel.

[martin-w 3,235]

Asymmetric results yes, but not the trim only effective when centred issue.

 

I feel this out of balance trim must be wrong.  If the real 777 were like that I doubt it would have been certified to fly.

 

I'm sure you will confirm Rob, that the real 777 doesn't behave that way.

[geolpilot 88]

@ Rob Robson and Lucasz

 

I have opened up a new "How to fly FBW" thread, so Lucasz no need for you to do that now.

 

Now if only I could move some of my "how-to" postings out of here over to there. Do not think I can, but maybe a Moderator can do this?

 

Thanks

Rob

[777simmer 117]

By the way guys......do you also have such erratic FBW trim ref speed behavior?

 

If I display it, and try to set for example 210kt exactly, that is realy way too dificult to fine tune here.

 

Try a single short click of the trim switch (I tried both a yoke button as well as Keyboard keys, with the same irratic behavior)

- Sometimes the trim ref speed moves by 1kt, at other times by 2,3, or 4kt at a time

(no I am not talking about blib trim)

- Other times the trim ref speed does not move at all and up to 3-4 clicks of the trim button could be required to make the trim ref speed change.

 

This does not help the "trim by feel" experience ofcourse!

 

You guys seeing the same......or is it all my hardware/system?

[martin-w 3,235]

You guys seeing the same......or is it all my hardware/system?

Have some time, I'll test it now.

[777simmer 117]

I feel this out of balance trim must be wrong.  If the real 777 were like that I doubt it would have been certified to fly.

 

I'm sure you will confirm Rob, that the real 777 doesn't behave that way.

No not at all.

 

I have already PMed with Ryan about that but not much has come back other than "the only way we could simulate the FBW system is by changing elevator authority"

 

He has not confirmed or denied that this should be assymetrical (like you and me have)

or

Symetrical like Kevin has

or

Assymetrical at first and then changing into symetrical as some others again have reported

 

 

And as long as PMDG does not give as info on how the PMDG system should react, we will never know who's system/hardware is behaving as it should :-(

@ Rob Robson and Lucasz

 

I have opened up a new "How to fly FBW" thread, so Lucasz no need for you to do that now.

 

Now if only I could move some of my "how-to" postings out of here over to there. Do not think I can, but maybe a Moderator can do this?

 

Thanks

Rob

thx.

 

Don't worry about moving it......you can still copy and paste stuff so it is in the new thread as well.

[geolpilot 88]

 

 

By the way guys......do you also have such erratic FBW trim ref speed behavior?

 

No can't say I see this. As I have posted before I have my trim repeats set to full right in FSX controls.

 

What I am seeing is that "blip" trim up is erratic. Even within a knot of ref speed, a blip click up and the fbw marker will sometimes head off a few knows below the speed I wanted to fine tune. Blip trip down with a single click "flick" sets the fbw marker exactly at my ref speed, always.

 

Rob

[777simmer 117]

Have some time, I'll test it now.

Cool thx :-)

[martin-w 3,235]

By the way guys......do you also have such erratic FBW trim ref speed behavior?

Yes Rob, I do have this behaviour.

 

Jumps about as you describe. Sometimes about a knot, sometimes 2 or 3 knots.

 

 

 

I have already PMed with Ryan about that but not much has come back other than "the only way we could simulate the FBW system is by changing elevator authority"

Then lets have the changing elevator authority balanced then please.

[777simmer 117]

No can't say I see this. As I have posted before I have my trim repeats set to full right in FSX controls.

 

Rob

So one click on the trim button equals 1kt trim ref speed?

Allways (except during blib)?

[Lucass 3]

@geolpilot

 

many, many thanks for your explanations! Now it's quiet clear to me ... I'll go practice now

 

 

One of Tabs replies "Nothing is dependent on the MCP window", I feel could lead to some confusion and problems (if you are in AT SPD mode). The second part of that sentence "you should'nt be trimming before changing airspeed" is quite correct

 

Yes, of course. It was mine misunderstanding.

 

All the best!

Lukasz