Question about trim on final? 777

[martin-w 3,235]

I wonder if many are flying mostly on autopilot, and disengaging the autopilot at the last minute, prior to landing. So due to minimal hand flying, probably not as aware of the "suspected" issue as myself and others.

[scandinavian13 5,192]

 

 

So due to minimal hand flying, probably not as aware of the "suspected" issue as myself and others.

 

Would you care to summarize?

...because there's no way I'm going to try to pick through all of that to find some coherent point to bring up to the team.

 

What is your understanding of how it should work?

How is it not meeting this understanding?

[martin-w 3,235]

Would you care to summarize?

...because there's no way I'm going to try to pick through all of that to find some coherent point to bring up to the team.

 

What is your understanding of how it should work?

How is it not meeting this understanding?

 

 

From my understanding, and that of others in this thread, trim in T7 should function as follows....

 

Configuration changes, like flap deployment and increases in thrust, should trim out automatically. They do, so no issues here.

 

Speed changes however, should always require manual trimming by the pilot. The T7 should not auto trim in this circumstance. As speed increases or decreases, trim adjustment should be required just like in any aircraft.

 

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Issue 1. The PMDG T7 seems capable of auto trimming speed changes. As speed increases or decreases and zero vertical speed is maintained as a result of control column input, then by the time the aircraft has stabilised at the new speed the aircraft seems to be magically in trim. This seems wrong and contrary to the documentation.  I don't think anyone is saying this is definitively wrong, just that we can't find anything in the documentation to suggest that this is accurate behaviour. It's also contrary to what was believed to be a capability of the aircraft.

 

Issue 2. If speed changes are manually trimmed, nothing happens until after one second of trim input, [this may be correct behaviour] but when the aircraft does trim it's too much too fast, consequently we find ourselves chasing the trim. A stable hand flown flight path is then difficult.

 

None of us are T7 pilots in real life, so we can only read the documentation and interpret as we see fit. So full apologies to PMDG if we are wrong.

[scandinavian13 5,192]

 

 

The PMDG T7 seems capable of auto trimming speed changes. As speed increases or decreases and zero vertical speed is maintained as a result of control column input, then by the time the aircraft has stabilised at the new speed the aircraft seems to be magically in trim.

 

This is how it is supposed to work.

 

 

 

If speed changes are manually trimmed, nothing happens until after one second of trim input, [this may be correct behaviour] but when the aircraft does trim it's too much too fast, consequently we find ourselves chasing the trim. A stable hand flown flight path is then difficult.

 

I'm unsure on this one, honestly.

 

 

 

Either way, if you really think it's an issue, nobody is stopping you from submitting a ticket.

 

That would be a much more productive use of anyone's time than what has been going on here...

[martin-w 3,235]

This is how it is supposed to work.

 

 

This is what we've been asking. Can you point us to the relevant section in the manuals that mentions this? Or  any real work resources, so we can educate ourselves? I thought I recalled you were unsure of this earlier, so I presume you have found something of interest.

 

 

 

Either way, if you really think it's an issue, nobody is stopping you from submitting a ticket.

 

That would be a much more productive use of anyone's time than what has been going on here...

 

 

That comment wasn't necessary. Nothing untoward has gone ion hear. All have been respectful and careful to point out that any perceived issues may be a result of our ignorance.

 

I absolutely will not submit a ticket and risk wasting PMDG's time, until I'm certain this is indeed an issue, and not how the real aircraft functions. This is precisely why we are discussing this amongst ourselves.

 

On the contrary, it's a very productive use of our time to discuss it hear. By discussing it hear, we seem to have established that one aspect of the issue is as you put it "how it's supposed to work" thus we haven't bothered a no doubt very busy PMDG with unnecessary support tickets.

[scandinavian13 5,192]

 

 

This is what we've been asking. Can you point us to the relevant section in the manuals that mentions this? Or  any real work resources, so we can educate ourselves? I thought I recalled you were unsure of this earlier, so I presume you have found something of interest.

 

FCOM 9.20.10

 

 

 

That comment wasn't necessary. Nothing untoward has gone ion hear. All have been respectful and careful to point out that any perceived issues may be a result of our ignorance.

 

I don't recall ever saying it was untoward or rude.  I simply said it would have been a better use of people's time to simply report it if you feel strongly that it is in error.  Instead there was a lot of back and forth, which, to be bluntly honest, lost me (and probably anyone else trying to make sense of if there is actually an issue here or not - thus my earlier request for a summary).

 

If you read what I actually wrote, you'll see that there were no accusations made:

If you feel strongly there's an error, submit a ticket and get someone working on it, instead of debating it here (where those who would fix it may or may not see it).

I never said you couldn't debate it here if you were unsure, or that debating is wrong (it's me, after all).

 

I wouldn't try to read between the lines of my posts.  You really won't find anything there.  I mean nothing more than the words written on the screen, as you can see in my explanation here.

[lbarber 20]

I put in a support ticket and have been going back and forth with Paul Gollnick on the issues we've been discussing in this thread. He's cleared up a couple of the behaviors we've been seeing.

 

 

1)  Uncommanded Turns would most likely be either the FSX Turbulence effect or a Wind Shift.  You may want to pull up the FLT CTL Synoptic and see if there are any uncommanded inputs occuring for some reason.

2)  It is normal for Backpressure to be required for turns greater than 20 degrees.  This was a hot point of contention with the Boeing Engineers as they wanted the Pitch Control in Turns removed from the AOM since thats not the way it really works.  What it does is help avoid the nose drop in turns but doesn't completely eliminate it.

3)  Trim Response is a little bit sluggish but we tuned it as best as possible in FSX.  I have asked the team to keep looking at this to see if it can be improved.

4)  Reference Speed will be maintained to a point but it is not going to dive the aircraft to maintain Ref Speed.  It will make small corrections to try to maintain Ref Speed under stable flight conditions.

5)   There is some Elevator Pressure alleviation that does occur in the FBW system and that is what you are seeing.  Its not Airbus FBW but is has some trim adjustments.  The pilot should be trimming the aircraft when a control input is being made.

 

 

I think we've established that #2 and #5 are, in fact, correct behaviors for the aircraft. The trim response that I'm seeing WRT #5 seems more aggressive than what he's describing, but again I'm no expert here. I'm still not sure about the trim switch response issues. I need to do some more investigation on that one. I'm also fairly certain that with no weather in FSX I shouldn't be getting uncommanded maneuvers as a result of wind shifts or turbulence, but again, more investigation required.

 

I did try a short flight last night with my FSUIPC settings modified per the instructions on Page 1, things seemed better but I didn't have enough time to objectively test anything.

 

What controllers are you guys using? I have an uneducated hunch that the trim may be inhibited by control spikes.

[martin-w 3,235]

I simply said it would have been a better use of people's time to simply report it if you feel strongly that it is in error.

 

 

"Feel strongly that it's an error," doesn't really apply to me, as I have gone to great pains to point out that I may be misinterpreting, may be ignorant of the real aircraft behaviour, may be in error etc. So, as I say, for me it's a very good use of my time to debate it hear. And you seem to have cleared up one aspect of the issue which is evidence of that.

 

I guess as this is a forum, and we can't see an individuals facial expressions and body language, it's easy to mistake a particular individuals blunt manner for something other than intended. 

I put in a support ticket and have been going back and forth with Paul Gollnick on the issues we've been discussing in this thread. He's cleared up a couple of the behaviors we've been seeing.

 

 

 

I think we've established that #2 and #5 are, in fact, correct behaviors for the aircraft. The trim response that I'm seeing WRT #5 seems more aggressive than what he's describing, but again I'm no expert here. I'm still not sure about the trim switch response issues. I need to do some more investigation on that one. I'm also fairly certain that with no weather in FSX I shouldn't be getting uncommanded maneuvers as a result of wind shifts or turbulence, but again, more investigation required.

 

I did try a short flight last night with my FSUIPC settings modified per the instructions on Page 1, things seemed better but I didn't have enough time to objectively test anything.

 

What controllers are you guys using? I have an uneducated hunch that the trim may be inhibited by control spikes.

 

 

The trim response that I'm seeing WRT #5 seems more aggressive than what he's describing,

 

Yes, I agree, it is aggressive. As I said previously, there's no response at all until the trim is held for one second, and then it trims too fast. I hope they manage to fine tune this.

 

I'm using a joystick. Control spike issue are an interesting theory. I suspect not in my case, but who knows.

[scandinavian13 5,192]

 

 

I guess as this is a forum, and we can't see an individuals facial expressions and body language, it's easy to mistake a particular individuals blunt manner for something other than intended. 

 

Yep.  What is it...70% of communication is in body language?

 

I thought it was amazing how much some people's interpretation of my writing changed after hearing me speak in one of my videos.

[martin-w 3,235]

Yep.  What is it...70% of communication is in body language?

 

I thought it was amazing how much some people's interpretation of my writing changed after hearing me speak in one of my videos.

 

It's just down to writing style, how we express ourselves in words. I write science fiction, so come across as a pretentious git at times. I'm nothing like that in reality, very self deprecating.

[Q_flyer 766]

Personally, I think this has been a great debate... interesting reading the different interpretations and understandings of the T7 FBW implementation.

 

I think Martin's dedication to finding out whether this is an 'issue' or whether we are all in fact dealing with a FBW systems that we know little of yet (aside from assumptions), has been useful and perhaps I am wrong, but it could be the case that a thread like this, could be of use to PMDG, rather than a hinderance or poor use of time.

 

I don't know if any issue exists or not with the PMDG T7s FBW but I do know that I love the hand flying characteristics and I love the 'assistance' from the autotrimming.    As long as you don't fight the trim, the system works beautifully and gracefully to get you stabilized in all phases of flight.

[DescendDescend 25]

777simmer is buying it tomorrow and says he has flown them for 10 years so it will be interesting to get his views.

[scandinavian13 5,192]

...never mind the fact that we had a bunch of 777 pilots on the tech team.

[Alec 370]

I can say I have similar behavior here. It's different from what I read from the manuals, but the manuals almost don't talk about the FBW in detail.

 

My main issue is that it seems the FBW can barely keep up with the airspeed change. If my 777 is trimmed to 170 knots, I remove the A/T, add power, the aircraft starts very very slowly to lift the nose up, and the airspeed goes way up. Shouldn't the FBW pitch immediately up to keep the Trimmed Airspeed of 170 knots?

 

We really need some better documentation on this system than the one that's in the FCOM. I read the whole thing but it didn't explain much.

 

Edit: FCTM!! RTFM

 

FCTM 1.40

 

"Thrust changes no longer need to be countered with a column input. This minimizes pilot work load during accelerations and decelerations. However, for a climb, as thrust is applied, the pitch attitude must be incrteased to begin the climb. For a descent, as thrust is reduced to idle, the pitch attitude must be decreased to begin the descent."

 

This explains the issue I had above

 

But!

 

"The pilot still needs to trim for speed changes. Column forces increase when out of trim to provide the convencional speed error cue"

 

Maybe since we don't have force feedback, PMDG made the aircraft Autotrim, instead of making our joysticks run out of elevator authority eventually?

[DescendDescend 25]

...never mind the fact that we had a bunch of 777 pilots on the tech team.

 

In my experience (and probably PMDG's), strange things happen between testing, release and installation.....