Still Trim issues with Sp1b

[aceridgey 330]

I see that, but how can our two systems react so differently? The only thing that seems different is how the controls signals are input to FSX?

 

Would be interesting to see others comment on it,

 

Alex

[mosteen 111]

Interesting comment regarding null zone above though, could it be that simple?

[adamant365 28]

I definitely had the trim issue prior to SP1b and I can report that it is much better with the latest update. Prior to the patch, I was all over the place, particularly in turns. Although I do have to apply yoke back pressure in turns, otherwise, trimming seems to work much better. I have my main flight controls (rudder, elevator, aileron) mapped in FSX. The only flight controls I have mapped in FSUIPC are the trim switch, throttle, and reversers. I have a 10% "null zone" set in the PMDG menu.

 

Regarding the back pressure in turns...I thought the 777 FBW was supposed to apply the elevator correction automatically in turns. I didn't think pilot elevator input was required in turns to maintain level flight. Am I incorrect?? Because if the FBW is supposed to handle the elevators in turns, that piece definitely isn't working.

[martin-w 3,235]

Trim is very good indeed for me now. Approach and landing was far superior as well.
 

Regarding the back pressure in turns...I thought the 777 FBW was supposed to apply the elevator correction automatically in turns. I didn't think pilot elevator input was required in turns to maintain level flight. Am I incorrect?? Because if the FBW is supposed to handle the elevators in turns, that piece definitely isn't working.

 

No that's not correct. The FBW only alleviates "some" of the back pressure required. The T7 still drops it's nose in turns to a degree.

 

You still have to apply a little back pressure in turns in the T7.

[scandinavian13 5,192]

 

 

Regarding the back pressure in turns...I thought the 777 FBW was supposed to apply the elevator correction automatically in turns. I didn't think pilot elevator input was required in turns to maintain level flight. Am I incorrect?? Because if the FBW is supposed to handle the elevators in turns, that piece definitely isn't working.

 

Incorrect.  The pilot must add back pressure.  This isn't an Airbus...

[BrianW 124]

The PFC’s compensate for turns up to 30 degrees of bank. There should be no need to apply extra yoke back pressure until the bank is greater than that.

Brian

[makdrive 9]

Sp1b is working like a charm. No issues at all.

[tcas_climb 45]

Interesting comment regarding null zone above though, could it be that simple?

It worked for me, it handles lovely now, and now I'm really seeing how the fbw is meant to behave.

 

My hotas warthog has a very tiny spike issue where it fluctuate rapidly between 200 and 280 parameter in the pitch axis forward of center, and it disappears when the stick is dead center and reads 0. Setting the null zone in fsx solves it for me.

[777simmer 117]

The PFC’s compensate for turns up to 30 degrees of bank. There should be no need to apply extra yoke back pressure until the bank is greater than that.

Brian

Correct. But in the real aircraft as well.....you have to kind of guide it along at first. So you turn.......make sure the nose stays where you want it and if not then you help it a little....and then once established in the turn you can pretty much let go.

Only tiny little adjustments are required every now and then to correct for the fact that changing winds etc are still trying to throw you of your path and since this is not an airbus, it will not correct for that.

 

The PMDG mimmicks this quite nicely with SP1b.

 

But....there are two buts.

1) it seems to take a little time for the PMDG777 to get back into its flight path stabilizing mode after an attitude change.

I do not know if my observation is correct but I find that when I make an attitude change that I kind of have to hold it there for a second before slowly letting go of the yoke.

If I let go of the yoke too fast then the nose seems to go back in the direction of its previous state. And because of that it sometimes needs a little more persuasion than I am used to.

I think that path stabiliing mode should kick in a bit quicker.

I assume that is what the FMC nullzone is for ? (I have it at 1%)....but please correct me if I am wrong.

 

2) Not having to hold the nose during a turn only works when you are perfectly in TRIM.

Even if there is only 5kt difference between the FBW trim ref speed and your actual speed the nose will go up or down. (As it should).

And here comes the thing.....even with AT on....one is often flying a few knots fater or slower than where the target speed bug is. This is normal too as the AT is not perfect. So when you turn while the AT is doing a not perfect job (lets say you are at 255kt but you have trimmed for 250kt and your speed bug is also at 250kt) then it will look like STAB turn compensation does not work. But it does....you are just out of trim and need to use the blib trim feature or wait untill the AT has corrected for the speed difference.

 

 

All in all I am getting much better results trimming by feel now.

I had big problems with varying over- and undersensitivity when out of trim. That seems to be gone now.

I would say 90% of the time I can do without feeling the need for displaying the FBW trim ref speed :-)

So definately quite good.

 

But I do also think that sometimes the trim inputs are not actually passed on to the flight model (or STAB) untill you let go of the yoke (neutral).

Again, I do not know if the cause for this is my yoke....the time delay it takes for the PMDG to go back to path stabilizing mode....or incorrect FMC nullzone settings (I have both at 1% now......but still experimenting).

For example, during a descending turn yesterday I thought I was in trim before I entered the turn (FBW trim speed not displayed). But in the turn I just could not keep the nose where I wanted it.....So I trimmed as I felt I had to.....but never got it stabilized. When I then displayed the FBW trim ref speed I saw I was still 15kt out of trim.

I would like to stress that this was not the case for all turns and maneuvers I tried!

Most of the times I trimmed by feel, and then checked where the FBW trim ref speed was, it was spot on :-)

 

I do not know why I could not get the trim right in that turn......but to not have to endlessly fight like that with pitch, I now just keep the FBW trim speed displayed......and with that, things work really well.

:-)

[vpiragibe 1]

For those who test, fly, but do not read the manuals:

 

Reference FCOM, page 9.20.10  from Dec 13, 2010

 

Normal Mode Pitch Control

The PFCs also provide compensation for flap and speedbrake configuration
changes, and turns up to 30° of bank. The PFCs automatically control pitch to
maintain a relatively constant flight path. This eliminates the need for the pilot to
make control column inputs to compensate for these factors. For turns up to 30°
of bank, the pilot does not need to add additional column back pressure to
maintain altitude. For turns of more than 30° of bank, the pilot does need to add
column back pressure.

 

Apparently, not even the Betas are aware of this.

 

However, in straight and level flight, the SP1b is far better then the "triple U" previous version ( untrimmable, unflyiable, unreliable ) .

 

I am waiting the SP1c version already.

 

Vpira

[777simmer 117]

My hotas warthog has a very tiny spike issue where it fluctuate rapidly between 200 and 280 parameter in the pitch axis forward of center, and it disappears when the stick is dead center and reads 0. Setting the null zone in fsx solves it for me.

Good thing you solved the problem.

 

I just wanted to say FSUIPC has a spyke filtering option.

I have never tried it, but maybe that would help too.

 

Anybody know how this function effects PMDG aircraft (positive or negative)?

[martin-w 3,235]

Normal Mode Pitch Control

 

The PFCs automatically control pitch to

maintain a relatively constant flight path. This eliminates the need for the pilot to

make control column inputs to compensate for these factors. For turns up to 30°

of bank, the pilot does not need to add additional column back pressure to

maintain altitude. For turns of more than 30° of bank, the pilot does need to add

column back pressure.

 

 

Apparently, not even the Betas are aware of this.

I believe they were...

 

PMDG have said that during their Level D sim time, and after consultation, it was apparent that some back pressure is still required in a turn, regardless as to what the FCOM says.

[777simmer 117]

For those who test, fly, but do not read the manuals:

 

Reference FCOM, page 9.20.10 from Dec 13, 2010

 

Normal Mode Pitch Control

The PFCs also provide compensation for flap and speedbrake configuration

changes, and turns up to 30° of bank. The PFCs automatically control pitch to

maintain a relatively constant flight path. This eliminates the need for the pilot to

make control column inputs to compensate for these factors. For turns up to 30°

of bank, the pilot does not need to add additional column back pressure to

maintain altitude. For turns of more than 30° of bank, the pilot does need to add

column back pressure.

 

First, I do not see the need for unfriendlyness.

I think PMDG has been trying real hard to get things right and personlly I appriciate they listen to the community as much as they do.

So they desirve a thank you in my opinion....not a slappin.

 

Second, You cant just read a FCTM and say "ok, that is how the things flies.....that is how I will program it".

 

You have to feel it....and that is a problem because even a LEVEL-D sim is not the real thing. The real thing is still nicer and smoother to fly.....believe me.

 

If the FCTM sais "RELATIVE"!

Then that is correct.....the FBW system will hold a relative constant flight path.

Relative means much better than a B737 but not like an airbus in this case.

 

If the FCTM sais "elliminates" then that is not correct.

It does not elliminate the need for pilot input.

Pilot input, albeit small and only here and there, is still required.

What IS elliminated is the CONSTANT need to correct with elevator, during turns etc. You do not need to correct CONSTANTLY like in the 737, but you do need to correct here and there.

 

In the real 777 you do still have to correct here and there during turns.

The real 777 even balloons initially during flap extention believe it or not. (I dont recall what the LEVEL D does).

 

But all in all we are impressively close to the real thing :-)

[scandinavian13 5,192]

 

 

Apparently, not even the Betas are aware of this.

 

No.  We were aware of this, but we're also aware of the fact that, despite what the book may say, physics and the rules of the universe prevail.

 

How many days are in a year?  365, right?

Nope. 365.242.

 

Too abstract?  Go look at performance tables.  You think the plane comes off the ground precisely at the value indicated by the takeoff performance table?  Nope.  Why?  Physics.

 

But the manual says it's so!!!  It must be true!!!

 

Interestingly, and much to the chagrin of the group of people who have a distaste for me here, if the manual were always true, that would mean that I would always be right (part of my job is to be a tech writer, so I write and update manuals).

 

 

 

For someone who relies so heavily on written evidence, and who casts aspersions on those who apparently didn't read it, I find it funny that you didn't read the rule to sign your full, real name on the forum, by the way...

[kevinh 409]

I believe they were...

 

PMDG have said that during their Level D sim time, and after consultation, it was apparent that some back pressure is still required in a turn, regardless as to what the FCOM says.

As Rob says above in post #24, you need to be in good trim and it might need some assistance initially. The point is it shouldn't need continued back pressure in a steady turn up to 30 deg bank. I find if I do it carefully it doesn't. The FCOM is how the FBW is designed to work. As FBW is all software it's not like a mechanical system which might vary according to how it is rigged. It isn't going to fly on rails but it will do as the FCOM says in the right circumstances.

 

This is clearly shown in the ITVV Cathay Pacific 777 flight deck DVD. In that video the Cathay pilot demonstrates a few FBW features in the simulator, including turns. It holds vertical speed zero up to 30 deg bank with no back pressure.

 

 

No. We were aware of this, but we're also aware of the fact that, despite what the book may say, physics and the rules of the universe prevail.

In this case the FBW compensates for the rules of physics for moderate bank angles. That is what it is designed to do. And it does it in the PMDG 777 quite well. I can turn the 777 hands free (i.e. without maintaining back pressure). Can't you?

 

=====================================

 

Back on topic, I had a few problems with the OC and the patch process but SP1b itself is an improvement. Trimming is instinctive. The only problem I have is that short trim inputs don't always move the trim reference speed. You have to press and hold the trim switch before it starts to move. If you try and trim in short bursts nothing seems to happen (unless you are within 5 knots of trim). For normal flying this isn't a problem. If you change bug speed by 30 knots, press and hold the trim for about 3 seconds as you fly the speed change. When at bug speed, if it feels close to trim blip the trim switch to get it exact.