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aceridgey

Still Trim issues with Sp1b

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OK last post for 2night.

 

About flying without the fbw marker or "bubble" as Enrique called it.

 

If flying and using the VS indicator alone as reference, do you not "feel" that, in order to hold a specific VS, you have to hold a certain force on the controls, and hence the need to trim that force out so that the VS indicator stays where you want it to, and you can relax and let go of the control?

 

Can you totally, really not "feel" that you are in trim by virtue of not having to hold any pressure on the yoke/stick when at the VS you want?

 

Just asking for feedback (not control-force feed back, I know one cannot get that)

 

Rob


Robin Harris
 

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Hi friends,

 

I also have problem with trim of this bird and with understanding FBW system (after reading all this thread additionally I have a headache ^_^ -> however above Rob's post quite clears the subject for me...

 

Anyway, I would like to ask you about few things:

 

1. is it necessary to change IAS on MCP before using trim switches? (for example: while flying straight ahead I want to slow down, and don't want to change altitude)

 

2. Let's assume following conditions: flying straight ahead and I want to slow down, and don't want to change altitude - so I: decrease IAS on MCP, push trim switches down for "X" sec. (depends on how much I change speed) and then I HAVE TO push forward control column? - please confirm

 

3. Let's assume situation that I want to change altitude (from FL120 to FL150, with 1000 fpm) and without speed change - so I: only use control column (back pressure until I get 1000 fpm, then release column), without touching trim switches - please confirm

 

4. Let's assume situation that I want to change altitude (from 8000 ft to 5000 ft) and slow down from 240 to 200 kts - what should I do?

 

Thanks for your tolerance and patience (I hope :unsure:  )

 

Lucas


Lukasz Trzaskowski

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Lucas,

I think you (and many others here) are overthinking this and assuming that there's more complexity required from the pilot's perspective than there really is. There's no special procedures you need to do to trim a 777 in manual flight. Nothing is dependent on the MCP speed window and you shouldn't be trimming first before changing airspeed.

 

Here's how it works in the real aircraft - take slowing down from say 300 to 250 knots during a descent at 10,000 feet. I'm assuming manual control of the aircraft here, not on AP or anything where the trimming is done for you. I'm also assuming you are in trim at 300 knots to begin with.

 

- As you level off and bring the thrust back and begin slowing down, the aircraft is still trimmed for 300 knots. This results in a need to continually apply more and more back pressure on the yoke as you slow down. The reason for this is that the airplane is "seeking" the 300 knot speed that you're originally in trim for. It wants to pitch down to return to 300 knots.

 

- The solution is to input nose up trim until you don't feel the need to hold the back pressure anymore. In practice on the real airplane, this is done in little spurts as the speed changes, not by presetting it to your new airspeed (which would actually produce a ton of force in the forward direction in this example) or by waiting until you're at the new airspeed to trim (which would result in a huge back force building up).

 

- There is no FBW speed bug in the real airplane, you just trim until the aircraft generally holds the desired flight path with no pressure needed on the yoke. We've already been over why this is inherently difficult to simulate fully realistically with joysticks or yokes that don't have a dynamic pressure or force feedback system. 

 

I think it's important to understand here that all airplanes (even a Cessna or a Cub or whatever) essentially have a "trim reference speed" too - that FBW marker in our 777 isn't some magical or new concept. When you're in trim in any airplane, you're trimmed for an airspeed and if you deviate from it, you're going to be out of trim and you'll feel that in the controls. That's all this concept is supposed to be in the 777. Yes, there's a bunch of complex internal FBW logic behind how it all actually happens, but that's really not of any concern to the pilot. All you need to know is that it indicates the airspeed the plane "wants" to be at. We put the marker in there to help people understand what the logic is actually doing and to help compensate for the aforementioned issues present with simulating the way the real life yoke dynamic pressure/force feels.


Enter Rob Prest with, again, words of wisdom and sense :-). Glad you're monitoring things also mate.

 

On track to thread.

 

This issue is also very apparent on the takeoff roll (FBW Trim REF speed seems to activate above a certain altitude, is it 50ft/100ft?.) When i take off and accelerate up, I can see and feel the moment the FBW kicks in, as I get a very noticable 'bobble' (a sudden increase or decrease in pitch).

 

Any others finding that (this was in the 200LR today)

 

Alex

 

Yes, and this is very clearly noted in the FBW section of the SP1 supplement in the Intro manual. The FBW activates at 100 feet RA in the real aircraft. The "bobble" you're seeing is due to the FSX issues with far forward nose down trim in the 200 models. (I did actually feel some of this nose down tendency when flying the real simulator at a low GW with trim in the 2-3 region too)


Ryan Maziarz
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In practice on the real airplane, this is done in little spurts as the speed changes, not by presetting it to your new airspeed

 

Not possible with the blip trim Ryan.  Big inputs are required to escape its pull, and then bang, you're over speeding and trimming up to compensate.  Especially bad on approach and/or finals.

 

If this is the final word I am in fear for the new 747.  Are you planning to introduce a trim reference speed with that??

 

God help us.


Richard Wells

 

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Thanks for reply, Ryan, but...

 

[...] Nothing is dependent on the MCP speed window and you shouldn't be trimming first before changing airspeed. [...]

 

I mean set IAS on MCP before using trim switches. Look at this video:

https://www.youtube.com/watch?v=kae_wDCGex0&list=PL5caETAZRBN6mPhNASIlMg2bkWH2DbtIz&index=2

 

...from 4:15 min.

 

* * *

 

Do you mean that when I want to - for example - descent and slow down simultaneously, I should ONLY use trim reference switches?

 


Lukasz Trzaskowski

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Thanks for reply, Ryan, but...

 

 

 

I mean set IAS on MCP before using trim switches. Look at this video:

https://www.youtube.com/watch?v=kae_wDCGex0&list=PL5caETAZRBN6mPhNASIlMg2bkWH2DbtIz&index=2

 

...from 4:15 min.

 

* * *

 

Do you mean that when I want to - for example - descent and slow down simultaneously, I should ONLY use trim reference switches?

That's not how I interpreted it at all.


captainhenrychen-1.jpg


Boeing777_Banner_Pilot.jpg


 


James Bennett

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- There is no FBW speed bug in the real airplane, you just trim until the aircraft generally holds the desired flight path with no pressure needed on the yoke. We've already been over why this is inherently difficult to simulate fully realistically with joysticks or yokes that don't have a dynamic pressure or force feedback system.

 

Hi Ryan,

 

Perhaps you could link to this explanation, because I can't find it anywhere. Can you explain why PMDG chose to progressively reduce elevator authority when out of trim in the 777 when such a fix is not necessary in the 747X or NGX for example? All these aircraft have force feedback systems on the column after all, the 777 is not unique. The reduction in elevator authority is unrealistic and asymmetric. It creates control problems, especially the asymmetry, and adversely changes the pitch handling out of trim.

 

I realise the idea is to make the user apply a larger control input for a given pitching moment and therefore feel a larger force when not in trim but surely a better solution would be to increase the pitch effect of being out of trim? That is how it works in the real aircraft after all. There is no good reason why the 777 should not be trimmable by feel in FSX in exactly the same way the NGX is without artificially reducing elevator authority to enhance joystick/yoke forces.

 

Kevin


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Oh my goodness where is this all going to??

 

We have gone from "it does not trim by feel" to trying to understand how the PMDG FBW is supposed to work, then to asking PMDG to help us understand how the PMDG FBW system works and then to someone digging into the FBW system so deep that he is clearly getting confused by all of it himself and now finally, back to teaching basic flying??

 

 

How are we ever supposed to solve why this darn thing does not fly right (trim by feel) unless we get an answere to the problems at hand rather than tips on how to slow down from 300 to 250kt?!

 

@ Lucas....I am not blaming you for asking the questions you have asked but they clearly indicated you miss a basic understanding of flying and you should be opening up a new thread asking about how to fly the 777 rather than direct this thread in a direction it is not supposed to go.

 

@ Ryan , common now Ryan, you take so much time to answere an easy to answere question, how about helping us with the real problems too then? We have so many unanswered questions.....and in the end you might find the answeres might even help PMDG finetuning the 777.

OK, some seem to imply, based on my Part One post, that I do not know the difference beteeen on the ground behaviour and in-flight behaviour of the FBW. I simply cannot wait to compile my video to show in-flight behaviour doing its thing, given this pre-judgement, so to heck with it, here goes.

........

So now is the time for someone from PMDG to pipe up and say "Rob H, you've nailed it" or " you've got it totally wrong" .

.........

now there is a quick out for many of you who want to discount what I am posting here, right here, right now

 

You gotta stop doing that.

 

The sentiments and being irritated because somebody has a different opinion than you are do not helping anybody.


Rob Robson

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PART TWO. FBW behaviour in the air; what should we expect?

 

I am still waiting for PMDG to answere that.....only they can answere what behavior we should expect in the PMDG777!

 

 

Let me start by saying that you have fast forwarded the discussion a bit.

It was my intention to first establish an understanding of the PMDG FBW system.

And I was waiting for some replies by PMDG to help us with that.

 

Thereafter I would have wanted to tackle the various problems people are having, like trim only applied when yoke neutral, can not trim by feel, erratic trim response, etc.

 

But things are dragging along a bit so maybe your fast fwd is a good thing.

 

 

Next is that I found your long post extremely difficult to grasp.

Either you are way smarter than I am or it was just realy hard to descipher.

The fact that you have not gotten many responses to thas post would indicated the latter.....or that we need to wait longer.....

 

 

I just had 8 hours to ponder over your post and came up with the following:

 

quote1:

"The STABILISER WILL AUTOMATICALLY TRIM WHEN NECESSARY, to OFFLOAD THE ELEVATOR SURFACE and ALLOW IT TO RETURN TO ITS NEUTRAL SURFACE (READ POSITION) WHEN the AIRPLANE IS IN A TRIMMED CONDITION"

 

should read:

The STABILISER WILL AUTOMATICALLY TRIM WHEN NECESSARY, to OFFLOAD THE ELEVATOR SURFACE and ALLOW IT (the elevator) TO RETURN TO ITS NEUTRAL SURFACE (READ POSITION).

The ELEVATOR is now flush with the STAB and the airplane is in a TRIMMED CONDITION"

 

quote 2:

"When the aircaft is at referenced trim speed (TRIMMED CONDITION, part one),

AND IF control column forces are NEUTRAL (TRIMMED CONDITION, part two - if you are still yanking on the control collumn the aircaft is NOT in a TRIMMED CONDITION - it is changing pitch i.e. there is a pitch rate change - low speed, or load factor change - high speed and therefore the C* function is not stable/constant, plus engines are adjusting power accordingly, and UNTIL THIS ALL NULLS OUT the plane is NOT IN A TRIMMED CONDITION!"

 

Yes.

 

Quote 3:

"THEN IF, AND ONLY IF THE AIRPLANE IS IN A TRIMMED CONDITION, will the stabiliser automatically trim to offload the elevator surface (align the stabiliser with the elevator)"

 

 

Eeeeh....the PMDG STAB or the real 777 STAB?

Real 777......No.

The real 777 STAB will not automatically trim AFTER you are in a trimmed condition.....

The STAB moves to BRING you in an in-trim condition!

Aerodynamically you are not in-trim untill the STAB moves to null out the elevator deflection.

 

But maybe you mean; that for the pilot the aircraft already seems in-trim once the elevator has moved to it's new position (because the artificial out of trim force is removed then, and things FEEL in-trim).

And that when that artificial feel force is reduced to zero, the STAB starts moving?

 

My opinion:

It is hard to tell by just looking at the (real) FCTL page when exactly the STAB begins to move. While you are trimming?.....once you stop trimming?.......once artificial feel force is zero and the yoke is neutral?.......once the elevator have reached a precalculated setting as per new FBW trim ref speed?

Maybe artificial feel force is removed as soon as Actual speed = FBW trim ref speed and after that the elevator and STAB just move flush with each other so there is no pitch rate up or down?

it could be anything!

 

Fact:

The only thing I CAN tell you for sure is that in the real aircraft, as you hold the trim switches, the force gets gradually smaller.

not all of a sudden after releasing the yoke.

 

Opinion again:

Maybe my last thought of how trim works is correct. All that seems to happen to me is that you hold the trim switches as long as the artificial feel force is gone, at which point I guess the FBW trim ref speed has moved to match your actual speed. Thereafter the FBW system starts doing its thing with elevator and Stabilizer untill pitch rate is zero.

(I have nothing to offer where you can read about this, but it is what I feel.)

If I remeber correctly, the (real) STAB is moving already while trimming.....and the same can be seen in the PMDG777.

So the real thing is not waiting for anything (in my opinion).

 

 

Nevertheless, you might be moving in the right direction with this!

 

As soon as artificial feel force reaches zero, the pilot would not be pushing/pulling anymore and if I understand you correctly, that is when you think the PMDG (note PMDG.....NOT REAL 777) system assumes an in-trim situation and starts to move the STAB.

 

That would work too I guess (just less conveniant than my theory above because you are then depending on nullzones).

However, that would mean PMDG programmed the trim system wrong!

(Note: the above statement is based on people seeing trim only being applied when the yoke goes through neutral.)

Because artificial feel on the real aircraft is removed gradually. Not all of a sudden!

This gradual reduction of artificial feel is ofcourse what makes trim by feel possible in the first place!

A sudden movement of the STAB (or elevators for that matter) can only result in a trial by error type of trimming. (you trim....you let go.....nope.....you trim you let go...nope....you trim you let go....yippy, in trim)

As we know, instead of artificial feel, PMDG have decided to simulated an out of trim condition by changing elevator authority.

If what you say is true.......that the PMDG first needs to move the STAB and then returns yoke effectiveness to normal.....then that is one step too late!

 

Yoke effectiveness should be gradually shifting back to normal as the trim ref speed approaches your actual speed AND at the same time this should result in an actual aerodynamic pitch change if you were to NOT reduce yoke deflection simultanuously.

Then you can trim by feel!

You would then end up with a neutral yoke and if thereafter the STAB moves flush with elevator without creating a pitch rate, you would not notice a thing (just like in the real thing).

And yes, you would have then discovered why one sometimes can trim by feel and at other times one can not.....I like the theory :-)

(you would only notice it sometimes, because sometimes your yoke will be going through neutral and at other times not)

 

 

quote 3:

It also explains why PMDG have catered for a null zone setting in the FMC setup options. Aware of different hardware specs, and age (pots aging, sensitivity, feeling etc,) they have allowed the user to set a band within which the software FBW can "sense" a neutral force on the controls...

 

Yes null zone makes sence.

 

 

quote 4:

Preferrably Capt. Robert Randazzo, an experienced 777 pilot.

 

I did not know he flies the 777?!

If he did we should have never had a trim problem with the original verion in the first place.

But I am hoping he or Ryan will help us out here just like you are hoping for that.

 

 

quote 5:

"Going by the only Boeing Systems 'authority" I can access for now, FBW is supposed to behave like that in flight, and PMDG have programmed this behaviour of the FBW system absolutely correctly. That is honestly as I see it acting in practise, and this is very clear in outside view."

 

You lost me now......So you changed your mind?

(that is ok.....I am just just asking here)

Before you were saying it was not correct (not like the real thing) that trim was only applied with yoke neutral.

Now you are saying you still see this effect but you think it is correct?

 

I can assure you that artificial feel force reduces to zero while triming gradually.

Not suddenly after you let go of the yoke!

The whole reason you CAN trim by FEEL on the real thing is BECAUSE artificial feel is removed gradually. If it were removed suddenly when you let go of the yoke you trimmed by estimation.....and had to be lucky to be spot on!

For the same reason, yoke effectiveness needs to be shifted back to normal gradually as you are trimming. While the elevators are moving or as you move the Trim Ref speed towards actual speed or something like that.

Not suddenly.

 

I have recalibrated and deleted and reinstalled FSUIPC a few times so who knows what that changed. If I get that behavior (trim applied only when yoke neutral) again I can test for it......otherwise this will be difficult.

For now I have to go by what you see.

And if you say you still see this "no trim effect untill yoke neutral" behavior......I can only say.....that is not right.

 

 

But you still might be on the right path with the other stuff.


Rob Robson

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Hi friends,



I also have problem with trim of this bird and with understanding FBW system

 

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).

 

 

 


1. is it necessary to change IAS on MCP before using trim switches? (for example: while flying straight ahead I want to slow down, and don't want to change altitude)

 

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.

 

 

 


2. Let's assume following conditions: flying straight ahead and I want to slow down, and don't want to change altitude - so I: decrease IAS on MCP, push trim switches down for "X" sec. (depends on how much I change speed) and then I HAVE TO push forward control column? - please confirm

 

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!

 

 

 


3. Let's assume situation that I want to change altitude (from FL120 to FL150, with 1000 fpm) and without speed change - so I: only use control column (back pressure until I get 1000 fpm, then release column), without touching trim switches - please confirm

 

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.

 

 

 


4. Let's assume situation that I want to change altitude (from 8000 ft to 5000 ft) and slow down from 240 to 200 kts - what should I do?

 

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


Robin Harris
 

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OK last post for 2night.

 

If flying and using the VS indicator alone as reference, do you not "feel" that, in order to hold a specific VS, you have to hold a certain force on the controls, and hence the need to trim that force out so that the VS indicator stays where you want it to, and you can relax and let go of the control?

 

eeeeh......must have been getting real late hey?

 

Back to basic flying again :-(

:-(.... because I have explained it before.

EDIT: post 121 here

http://forum.avsim.net/topic/447190-how-to-hand-fly-with-cu-law-aircraft/page-9

 

No you do not have to hold a certain force to hold a certain v/s.

And no, you do not have to trim to establish a certain v/s

All you need to do is point the nose so you get the disired v/s and then you let go. And the nose stays there.

AT will add the thrust required to keep the same speed (IAS).


Rob Robson

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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.

Ans so we have finally come to the reason why some feel they can trim by feel where they actaully do not realize thay can not!

 

You are not trimming by feel you are trimming by guessing!

trial and error!

 

 

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 Robson

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How are we ever supposed to solve why this darn thing does not fly right (trim by feel) unless we get an answere to the problems at hand rather than tips on how to slow down from 300 to 250kt?!

@ Lucas....I am not blaming you for asking the questions you have asked but they clearly indicated you miss a basic understanding of flying and you should be opening up a new thread asking about how to fly the 777 rather than direct this thread in a direction it is not supposed to go.

 

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 you.

 

I agree we need a separate thread for the "how to FBW stuff", so anymore post in that line I will take the initiative to open up a new thread, if not already done.

 

Let me just add that I was spurred on to make these "how to posts" by the fact that a certain user (unfortunately probably a troll) was using this thread to attack PMDG instead of making positive contributions. I was trying to counteract that, as the FBW system is working for me, and supplying some info that uers like that may want to think about (if they care to think about it). Also some users are clearly coming into this thread to find out that kind of information.

 

 

 


You gotta stop doing that.

The sentiments and being irritated

 

Yep, Serves me right for posting when tired and after a bottle of wine! Was also irritated by other factors, so that clearly came across. Sorry.

 

 

 


Quote 3:
"THEN IF, AND ONLY IF THE AIRPLANE IS IN A TRIMMED CONDITION, will the stabiliser automatically trim to offload the elevator surface (align the stabiliser with the elevator)"


Eeeeh....the PMDG STAB or the real 777 STAB?
Real 777......No.
The real 777 STAB will not automatically trim AFTER you are in a trimmed condition.....
The STAB moves to BRING you in an in-trim condition!
Aerodynamically you are not in-trim untill the STAB moves to null out the elevator deflection.

 

Ok, my observations (in outside view while flying) is that the PMDG will only move the stabiliser when the elevator is more or less in line with the stabiliser (a quick flick of the stabiliser is seen as the elevator / control forces come into nuetral)

 

You are saying the real 777 does not do this, so my interpretation of what Bartley meant by "in a triimed condition" is not correct (ie that no control force must be sensed to be coming in from the yoke), for the stabilsers to move and line up with the elevators.

 

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).

 

So maybe thats the difference? The stabs have a huge surface area in comparison to the elevators, so not trimming the stabs until a nuetral force is sensed in the PMDG plane could lead to a big difference in "feeling" out-of-trim conditions.

 

Finally, re my videos; and I am not being sensitive. Some are saying that the animations, both outside of the stabs, elevs, and on the synoptic, may have nothing to do with the problem, and are not necessarily linked to the actual, real workings of the FBW system. I do not concur as I hardly think PMDG would just have these for show without being really linked to what was going on in, and feed-back from, the internal FBW control functions.

 

Be that as it may, lets not argue about that. Time to dig deeper maybe into the numbers to see whats is happening.

 

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.

 

Rob


Robin Harris
 

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I've not paid ultra close attention to this thread, as I don't seem to be having the issues you guys are.

 

 

This issue where you have to centre the yoke/Joystick before the trim applies isn't happening to me. I can trim up or down, whether the controls are centred or not.

 

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.

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