Question about trim on final? 777

[scandinavian13 5,192]

 

 

I am not sure exactly what you are trying to imply with this Kyle?

 

Wasn't really implying anything, really.  Equal weight could be placed in another pilot's assessment, that's all.  Nothing against you, or anyone else, really.

 

I just took issue with the logic of the assertion:

One pilot raises an issue in the forum, and everyone here joins in arms.  Similarly-rated pilots on the tech team check off on it, nobody cares.

 

Like I said.  I'm not taking a shot at you, really.  I've never flown the plane, so I can't say either way.  If you think it's behaving improperly, though, then I'd say you submit a ticket to PMDG and hash it out that way.

[MatthewS 761]

I too have found hand flying final difficult.

 

Could somebody please explain in very simple, plain English "baby language" 

 

1) What the auto-trim is meant to do in real life?

2) What the auto-trim is actually doing in FSX?

Not withstanding this little "issue" above the 777 is an amazing achievement PMDG, congratulations!

[777simmer 117]

I too have found hand flying final difficult.

 

Could somebody please explain in very simple, plain English "baby language" 

 

1) What the auto-trim is meant to do in real life?

2) What the auto-trim is actually doing in FSX?

Not withstanding this little "issue" above the 777 is an amazing achievement PMDG, congratulations!

Many of us have done that.

Just go back through this thread please.

[777simmer 117]

I just took issue with the logic of the assertion:

One pilot raises an issue in the forum, and everyone here joins in arms.  Similarly-rated pilots on the tech team check off on it, nobody cares.

 

But I did not raise the issue.

I did not even have the plane yet when the issue was raised.

I bought it today and confirmed the feelings of others that this is not how the 777 trim works.

 

....and everybody checks off on it....

I dont know what that means (literally)....you mean they gave it their ok and nobody cares?

 

It would be wonderfull if one or more of the tech team pilots would comment here.

I care very much for their opinion and I think the others do to.

Maybe they can tell us that it was the best possible in FSX.

I can accept that.

Maybe they know it is not perfect, but in order to give the plane the feel of an augmented FBW system (which it does have by the way) the trim had to be made different than in real life.

 

There are three threads on this subject.

In one of them Martin said he would wait a little (for my opinion), which he did, and today he said he would put in a support ticket.

[MatthewS 761]

Many of us have done that.

Just go back through this thread please.

 

No simple 1 line explanation, maybe its too complex for that anyway.

 

Is the following correct?

 

Say an aircraft (without auto-trim) is flying at 250kts and the pilot has manually trimmed to maintain altitude (ie 0 fps VS).  If the speed changes to 220 kts the pilot would be required to apply back pressure to stick to increase pitch and maintain 0 fps VS. The pilot could then manually trim the aircraft to maintain this pitch and thus no back pressure is required by the pilot.

 

In the 777 with auto-trim the 777 will automatically trim the aircraft to maintain 0 fps VS rather than the pilot having to manually trim the aircraft using the yoke trim switches?  If the pilot manually overrides the current trim by applying stick pressure then does he press the trim switches in order to tell the 777 to initiate the auto-trim and maintain the current pitch?  Does it matter whether he presses the trim switches up or down?

 

edit:  Is the auto-trim trying to maintain the pitch or the FPA (flight path angle eg 3 degrees) or the VS?   I could see that having it maintain the FPA would be handy because I could be descending at a FPA to hit the runway end markers and no matter how my speed changes (eg as I dial down to Vref + 5) the aircraft would be trimmed to maintain the FPA and thus still hit runway end markers.

[777simmer 117]

No simple 1 line explanation, maybe its too complex for that anyway.

 

Your description of things was is so complex it is almost qute :-)

 

in your FlightsimX folder locate the PMDG/PMDG777X/Flight Manuals folder.

Open the FCTM document on page 1.40

 

read the last line:"The pilot still needs to trim for speed changes......"

 

How is that for a one line explanation?

 

And on the next page you see a table that will remove all speculation as to weather or not those who claim "the aircraft should react to speed changes just like a Cessna" are right or wrong!

 

It says:

CONDITION                        CONVENTIONAL                 777

Airspeed Changes               Pilot counters with column and trim speed

                                            (speed stability)

 

So as they say in Thailand....same same but different.

same same cause it seems to work and feels the same for the pilot as a conventional aircraft.

different because the FBW is calculating all kinds of things in the background that dont matter to the pilot.

 

Now, stop using the word autotrim!

This leads people to believe that the 777 trims away speed changes automatically like an airbus.

And although our PMDG DOES work like that in NORMAL mode at the moment (not in seconday mode which I think behaves better), it is NOT how the real airplane works.

 

And yes, you have to trim in the direction you want the nose to go.

You cant trim up while holding the nose down with the yoke.

 

The book says (on that same page 1.40) the 777 will counter anything that tries to change the pitch attitude or flight path.

read on.....the system minimizes the airplane pitch response to thrust changes...etc etc (not speed changes!)

Minimizes means it does not take everything out completely.

I can assure you that once established on a 3 degrees glideslope (or whatever flight path you are going along) you cant sit there and extend flaps and gear and expect to stay on that GS!

(I am talking about the real 777 here! The PMDG 777 is so stable it actually will stay on the glide slope pretty much)

The system helps you to counteract those influences.....it makes it easier for you to stay on your path......but you still have to work a little bit for your money so to say.

[777simmer 117]

As I mentioned in a simular thread here (I tested both normal and secondary mode)

 

http://forum.avsim.net/topic/419407-hand-flying-tips/page-3#entry2792246

 

I have no more or better/clearer info on the subject, so thats it for me.

I will put in a support ticket as well.

 

One more thread about this topic:

 

http://forum.avsim.net/topic/413705-fly-by-wire-of-the-777-and-its-simulation/page-4

[Mo45 32]

So far I am not really enjoying it at all with the pitching up and down. I am surprised that the beta tester did not pick up this behaviour and I have searched and searched on google and couldn't find the answer. It is nothing to do with the weather also. Just don't understand why I don't get this problem with 737-800NGX PMDG and 747-400 PMDG.

 

Thanks,

Mo

[lbarber 20]

...again...despite the 777 pilots on the tech team...

I have to figure this is a setup issue that is affecting a relatively small percentage of the 777X userbase. Seems to me that there are identifiable problems for a few of us, I don't think everyone is flying around with the same issues that we're talking about here. 

 

Stated another way, my hunch is that the problem is less with PMDG's programming on how the airplane behaves than it is some interaction in some of our FS setups.

 

 

Are other people seeing the yoke jerk around in manual flight?

 

video here:

(way shorter than the last one)

[777simmer 117]

No I have not seen that yet.

 

What is strange is that I did not see the elevator move on your flight control synopsys page.

[martin-w 3,235]

I have to figure this is a setup issue that is affecting a relatively small percentage of the 777X userbase. Seems to me that there are identifiable problems for a few of us, I don't think everyone is flying around with the same issues that we're talking about here. 

 

Stated another way, my hunch is that the problem is less with PMDG's programming on how the airplane behaves than it is some interaction in some of our FS setups.

 

 

Are other people seeing the yoke jerk around in manual flight?

 

video here:

(way shorter than the last one)

 

 

Isn't that the FSUIPC issue? Mentioned before.

 

Wrong setting.

 

Send direct to flight sim calibration, I believe causes issues.

 

Apologies if you've addressed that.

 

Stated another way, my hunch is that the problem is less with PMDG's programming on how the airplane behaves than it is some interaction in some of our FS setups.

 

 

The only thing I can think of for me, is that I use the keyboard to trim. Apart from that, I have a pretty bog standard set-up. Minimum add-on's installed, nothing I can think of that would conflict.

 

I think a lot of people are flying mostly on autopilot, and disconnecting at low altitude. Thus they don't really experience any issues with trimming because they rarely trim.

 

Many are also probably presuming this weird auto trimming with elevator input to be the way to go.

[lbarber 20]

I've tried both FSUIPC setups, doesn't seem to change the problems on my setup.

 

Has anyone else gotten a ticket response from PMDG?

[martin-w 3,235]

I've tried both FSUIPC setups, doesn't seem to change the problems on my setup.

 

Has anyone else gotten a ticket response from PMDG?

I believe quite a few have.

 

PMDG have confirmed that they are investigating the trim issues.

[vanislepilot 2]

+1 here for experiencing your "trim lag/jump" issue #2 Martin.

 

The first thing I do with any aeroplane is learn how to hand fly it. This was the only apparent "issue" I've encountered so far with the aircraft itself.

 

I'll be on approach, decelerating and extending flaps as per the sched and a few clicks of the trim doesn't help out and then it snaps into an overtrim.

 

If it was real world, that would raise the hairs on the back of my neck a bit.

 

Glad it's on the radar now.

[martin-w 3,235]

I'll be on approach, decelerating and extending flaps as per the sched and a few clicks of the trim doesn't help out and then it snaps into an overtrim.

 

 

Glad it's on the radar now.

Yep, that's it Troy exactly.

 

To be honest, this behaviour is more of a concern for me than the [we believe unrealistic] auto-trimming effect with elevator input.

 

I notice PMDG haven't added these issues to the pinned bug issues list yet. Guess they are still investigating.