What I understand from that FCOM is that when you use Pitch Trim, the FBW will first move the elevator to get what you asked it, then wth time, it will use the stabilizer, to be able to remove the Elevator deflection, so it's back to neutral again. But it doesn't mean it's AutoTrimming the aircraft. If it is, it's not clearly said in any Boeing Manual. But they have real 777 pilots to assist them, so I also believe it's hard to accept they were going to let such a wrong behavior go unnoticed

 

Hi Alec.

 

And you understood it well. That's corret.

 

When you trim, the system moves the elevators in order to maintain the reference speed you command and then, eventually it adjusts the stabilizer to streamline the elevator...all correct....but that is the actual trimming...is not a "conventional" way to do so, but is trimming.

 

If I move the elevator to a certain angle, either with the column or the trim switch, the moment the system moves the stabilizer to streamline the elevator set by the column or the trim switch, that's the moment when the actual trimming is done.

 

In convertional airplanes, you set your speed with the elevator and manually move the stabilizer after that to trim. When the stabilizer streamlines with the elevator you have set, the aircraft is trimmed and the pressure on the column goes to zero.

 

Here with the 777 it seems that what is actually heppening is that when you move the elevator to set an attitude (though aerodinamically what you're really doing is setting a speed, the one that belongs to that attitude at a particular thurst setting), when this attitude is kept by you with the column and the speed approximates to the one that belongs to that attitude, then the FWB catches it and moves the stabilizer automatically  and trims the aircraft.

 

Regards. 

I get your idea perfectly.

 

The thing that I don't understand is that maybe this 777 pilot didn't want his aircraft to climb, it wanted it only to get back on the glide after a downdraft, or something like that. So after he Pulled the Yoke to bring it back on the Glide, he released the pressure, let it go back to neutral, expecting the aircraft to establish once again on the previous Trimmed AirSpeed, and the aircraft will not do so, because it's now trimmed to the new speed the system interpreted was what he wanted when he did that Yoke Movement.

 

That's what I don't understand, instead of letting the aircraft stability do it's work and get back to the Glide, he would have to make two movements, one for the climb, and another one for reestablish the aircraft on the Glide. Only a 777 pilot will be able to confirm this behavior, but in my mind it goes against what Boeing is saying, that this aircraft is made to behave like a conventional aircraft, this behavior has nothing to do with a conventional aircraft!

 

Maybe the system has a timer, when he detects the pilot has been holding that new Yoke position for some time it assumes it wants to trim the forces to allow it to fly with no input needed? If so, PMDG has already gone more than halfway to making an Airbus (This is Jcomm's Joke! Credit should go to him for this :lol: )!!

Level flight is referenced merely as a base-line, to demonstrate the aircraft is in constant speed, unaccelerated flight when our hands are off the controls.

 

The issue we are all seeing is that the aircraft DOES trim to the new speed (in the case of a pitch-up where the speed bleeds off before the controls are released to neutral), which is contrary to our understanding of the manual.

 

Please do not confuse the thread. It's confusing enough as it is.

 

Best regards,

Robin.

Well pardon me for interrupting.

 

I have just taken the 777 for a manual flight and I have to say the trim and FBW behaved pretty much as the manual says it should. I found no issues with hand flying at all, it handles well.  It's not as nice, or as direct, to hand fly as an Airbus but Boeing have a different philosophy as we know so it may well be a bit "looser".  Things can get a bit confusing if you have the A/T engaged and the commanded speed is not the same speed the FBW has trimmed to, so it's as well to keep these in sync.  I'm not a pilot, let alone a 777 pilot, but I have flown many full flight sims so I have a feel for how things ought to be (generally speaking).  The only issue I found was it seemed to float a little on landing, but as it was my first landing in this sim that's more likely to be my technique. 

 

Personally, and please don't take this the wrong way, I think people are over thinking this because FBW is involved and they are trying to work out how it should behave.  If the FBW doesn't perform exactly as described in the FCOM maybe this is due to a limitation of FSX.  Or maybe the FCOM doesn't describe exactly how the aircraft behaves in every permutation.  For example the FCOM says if you are trimmed and advance the power the aircraft will climb at the trimmed speed.  The first time I tried this I slammed in CLB power and speed increased rapidly before the aircraft pitched up in response.  I trimmed again and increased power more slowly and the sim did exactly what the manual said.

 

The thread title is hand flying tips.  I've now given the thread a tip about speed selection.  If that's not on the subject enough then I don't know what is.  If you think there might be an issue with the FBW report it to PMDG support.  The idea they might not want to be bothered is very strange.

 

 

Maybe the system has a timer, when he detects the pilot has been holding that new Yoke position for some time it assumes it wants to trim the forces to allow it to fly with no input needed?

 

:lol:  :lol:  At least that's how it looks like...

 

 

 

 

Well pardon me for interrupting.

 

Kevin, you don't interrupt anything ^_^ ....and well, I understand what you say, but there is fact here, and it is that the aircraft is showing an auto trimming behaviour, a that's not how the FCOM says it should work. It clearly states that the pilot is required to trim out speed changes manually, just like any other conventional aircraft and in the sim there is no need to do so.

 

There even have been several pilots here that have stated they have meade complete flights without  touching the trim at all, only to set the take off trim....and that's because the aircraft trims herself...

 

Cheers.

This thread has already gone "hot", and even one member has said he has opened a ticket to PMDG

 

I respectfully think that PMDG should say us something about all of this and alleviate us  :wink:

 

If we're wrong and the aircraft behaves correctly, perfert!...we'll all be happy and won't think about this anymore.

 

If we are right and this is some kind of bug, even better....we'll know PMDG is aware of this and will fix it at some time in an update.

 

Cheers.

Hi Rob.

That test somewhat disappointed me even more. May be I'm wrong, but when I was flying in direct mode, it felt just like the same that in normal mode. You can fly form take off to landing without hardly touching the trim switch if you want.

 

Well....I was pleasantly surprised with the Secondary mode.

In my opinion it does better than normal.

 

In Secondary mode a few things dont work (look it up in the systems manual).

One of them is pitch compensation during turns.

 

Try it.

level off, get the plane perfectly trimmed in normal mode (which is easy cause it does that miraculously by itself).

Then fail the Normal mode to secondary mode under CDU Flight control failures.

Dont worry about the checklist for this excersise.

 

still level and trimmed?

Good!

Now put the airplane in 20 degrees of bank without adding any pitch.

Watch how that nose drops slowly and you get -1000fpm real fast!

It does not do that in Normal mode.

 

Well done PMDG :-)

 

 

Open up the flight controls Synoptics pop up page for this next excersise if you can:

 

The next pleasant surprise is that trimming for speed changes is required in secondary mode.

 

Maybe only 70% of what I feel is required in the real plane, but still....you have to trim.

Try it.

Start straight and level in 5000ft or so and with something like 310kt.

Get the airplane trimmed (it takes a little time to get even those last bits of up and down tendencys trimmed away)

Small trim imputs is the way to go when you are getting close to being trimmed.

Just a quick click on the trim for those last corrections is all it takes.

 

Now pull thrust to idle (the nose does not drop as it should, but never mind that).

Notice how during deceleration you have to hold a little bit of backpressure to keep your altitude?

Not much maybe, but that little bit of yoke deflection you have there is definately noticable in the real aircraft!

(on my CH pro yoke it required about 3cm worth of pulling)

And thats what you want to trim away.

I reduced from 310kt to 210kt and needed a good few seconds 4 -5, maybe more but not 10 seconds, to get back in trim at 210kt.

And when I did not trim and let go of the yoke, the nose would slowly drop again and soon I would have -1000ftm.

 

Also note on the flight control synoptics page how the stabiliser is not trimming unless you do so manually. In Normal mode that stab trim value is constantly changing when you give no control wheel input. In secondary mode it is not.

 

This is correct behavior for speed changes and would also be the correct behaviour for the Normal mode.

 

So it can be done!

 

I also tried extending flaps in Secondary mode and saw a little bit of balloning.

Again I felt it was less than I remember, but I admit its been a while since I flew in secondary mode.

(you dont get that on every simcheck either!)

 

So all in all pretty good results in secondary mode.

 

 

I can imagine that many will feel there is not much difference between Normal and Secondary mode.

And that is correct.

The plane is still very flyable.

What makes it so difficult to recreate the differences between those modes I guess is (I have mentioned it before) that we dont FEEL the differences.

No forcefeedback - no feel!

 

I did not try direct mode yet.

That definately is a bit harder to fly, but again you have to feel it to realy notice the difference.

 

 

I dont know if the 737NGX simulates manual reversion (total loss of hydraulics) but I can tell you....that is realy realy realy heavy!

As in muscles are required to roll and change pitch!!

How do you simulate that with no force feedback?

I dont know?

 

The 777 Secondary and Direct mode are still way way easier to fly than 737 manual reversion by the way.

No comparison!

 

Well, good night, enough for one day :-)

Thank you for the report Rob! Have not tried Secondary mode here. Will give it a spin too! 

 

The report of a real 777 pilot makes all the difference here! B)

Kevin, you don't interrupt anything ^_^ ....and well, I understand what you say, but there is fact here, and it is that the aircraft is showing an auto trimming behaviour, a that's not how the FCOM says it should work. It clearly states that the pilot is required to trim out speed changes manually, just like any other conventional aircraft and in the sim there is no need to do so.

 

There even have been several pilots here that have stated they have meade complete flights without touching the trim at all, only to set the take off trim....and that's because the aircraft trims herself...

Thanks, the poster I replied to hinted my first post was unwelcome.

 

Anyway, I didn't see any speed trimming by the system during my flight. But that doesn't mean there shouldn't be any at all. I haven't read the manual thoroughly enough to see if there should be any automatic speed or Mach trim. However perhaps if the sim gets spurious trim inputs maybe that will cause the simulated FBW to reset the speed datum.

 

 

I dont know if the 737NGX simulates manual reversion (total loss of hydraulics) but I can tell you....that is realy realy realy heavy!
As in muscles are required to roll and change pitch!!

 

oooh man...the "nice" NGX manual reversion hehehe....Every time I did it on the TR or now in some checkride, when I step out of the sim I look like being on steroids, arms full of palpitating veins and the white of my eyes in red color  :lol:

 

 

Whit regard to your tests on the 777, yor're absolutely right. I did what you told me plus somo other experiments and yes....in secondary mode, the feeling of the behaviour of the pitch trim is a delight. This feeling is just what I was expecting from the normal mode, apart from the other flight envelope protection, etc....This is definetly the way I think it should behave in normal mode.

 

As a results of my conversations with you, and from my own flight tests, MY "conclussions" are:

 

1: The normal mode does NOT work well. I think is not correctly modelled. It exhibits a sort of "auto trim" mechanism that should no be present. It allows to make a whole flight without ever touching the manual trim and that's not so, as per the FCOM and from you and other real T7 pilots.

 

2: The secondary mode I think is more or less very correctly modelled. As you say, here the pitch trim requeriment for the pilot works like a charm. In this case yes, the airplane DO exhibit a conventional pitch trim behaviour for speed changes. You have to manually trim to relief pressure on the column and fly hands-off. The aircraft won't do it on itself.

 

3: The direct mode, for me, and only in my oppinion, feels like a "copy" of the behaviour of normal mode, with the only difference of not showing stabilizer movement unless you apply manual trim. BUT, though you won't see any automatic stabilizer movements on the flt ctrl page, the aircraft is in fact autotrimming "internally" just like in normal mode.

 

For me, after these conclussions, the thing should be:

 

1: Normal mode: Pitch handling and feeling should be like on secondary mode, but adding the flight envelope protection system and all that stuff.

 

2: Secondary mode: It is well at it is. Nevertheless, any improvement would be welcome.

 

3: Direct mode: If this mode, "internally", has to be a copy of some other mode, it should be a copy of the secondary mode, not the normal mode. In fact, direct mode is almost the same as the secondary mode, with the exception that in this case the PFCs do nothing here. The control surfaces are directly and conventionally comanded by the pilot. No protections at all.

 

These are my thoughts. I'm not going to discuss much more about this issue, because until I hear something about this from PMDG, I think that enough have been said. If they are unaware of this or don't not want to give their point of view about the issue, I respecfully think that keeping writing about this is a waste of time.

 

Having said that, this evening I'll do my last tests on this. All tests I've carried out so far, I've been using a fuel load of approx. 17 tons, in order to resemble and approx "normal arrival" weight because I make a lot of take off an landings, touch a gos, etc. This gives as you know no fuel on the center tanks, and a take off CG location just about 30-31% of the MAC, wich is just a bit backwards and near the neutral point, so the static pitch stability is less, and obviously less powerfull pitching moments.

 

I'm going to do some tests hand flying with heavy weights in order to have the CG forward on the MAC and more static pitch stability to see what happens, and I think with this is done, I'll stop to mess with this issue, at least until a I hear something from the developers.

 

Cheers.

Yes I agree with all that....including the bit of enough said about this.

I will put in a support ticket as well, and then we shall see if anything can be improved for SP1

 

More info, for those who crave it :-) , on the same subject here

 

http://forum.avsim.net/topic/413705-fly-by-wire-of-the-777-and-its-simulation/page-4#entry2793080

 

and here

 

http://forum.avsim.net/topic/418721-question-about-trim-on-final-777/page-4

Well pardon me for interrupting.

 

Sorry, I didn't mean to rude.

 

Best regards,

Robin.

Same here! I opened my PMDG support Ticket, now I'm done testing this FBW like crazy until PMDG has something to say about it. I will continue to have fun with this 777 using AP for the most part of the flight for now.

 

We should soon have some info of this subject I'm sure!

I find this topic interesting.  I had the good fortune to fly the 777 simulator at United's training center in Denver during the Avsim Conference all those years ago.  The plane is amazingly easy to fly - it goes where you point it.  I hope that is represented in this simulation. It should be easier to control than the MD or the 737.

 

Colin Ware

Seattle

Just one more observation from my 2 hours in the 777 sim at United - you used manual trim frequently on approach to keep the needles centered...

 

Colin Ware

Seattle

Sorry, I didn't mean to rude.

 

Best regards,

Robin.

No offence taken Robin. It was late and I was tired.