how to hand fly with C*U law aircraft

[3-2-1-Now 126]

Hi,

 

So the problem appears to be that in the sim, when trimming, it is neither my imagination nor a problem with my specific set up that the aircraft exhibits zero pitch response to trim with the controls deflected.

 

I don't think it is related to lack of simulation of an artificial unit; I think it is simply that the trim is not being applied when the stick is not centered. If that could be fixed, I think it will be a dream to fly.

 

I guess we need to wait for PMDG on this one.

 

Best regards,

Robin.

[CapnOz 111]

I love the new FBW that has been modeled. Nice to have a ' new ' feel to the plane....

[willywonka 36]

Man, Rob should be on the beta team. He knows his FBW

[777simmer 117]

Man, Rob should be on the beta team. He knows his FBW

yeah.....if only he didn't write such yeeeeh long replys confusing the heck out of everyone, lol.

 I don't think it is related to lack of simulation of an artificial unit; I think it is simply that the trim is not being applied when the stick is not centered. If that could be fixed, I think it will be a dream to fly.

  

Yes I guess you are right.

 

I will do one more comparison tomorrow and after that I will put in a support ticket.

 

Enough said here I think.

[777simmer 117]

Oh, one more little thing.

 

About the FBW trim ref speed jumping in the wrong direction at times.

 

When you are in trim, AP off/AT on, at lets say 320kt and then set 250kt on the MCP the magenta speed bug moves down ofcourse.

Thrust reduces and with the FBW trim ref speed displayed you start trimming so that the trim ref speed reduces as well.

I do this in 1-2 second bursts.

 

You are lowering your trim ref speed towards the speedbug right!?

(this thinking results in an incorrect observation of the speedbug jumping in the wrong direction.......wait :-) )

 

At times you might have trimmed just a little too much.

So image you are now at 280kt actual speed, magenta bug still at 250kt and FBW trim ref speed at 276kt and you figure what the heck lets just keep trimming down and set the trim ref speed on top of the magenta bug....your final target anyway right.

 

Well, the blib function then moves the speedbug up to the actual speed rather than down to your magenta bug.

 

So it would look like the FBW speed moves in the wrong direction (it is not going where you WANT it), where in fact it is moving it is moving where it SHOULD (to your actual speed).

 

Not sure if this is everyones problem, but it happened to me at least twice that I thought.......hey wrong direction......ah no disregard, correct direction!

[whoispankaj 51]

Yes its happened to me..but ryan has already mentioned that it will first jump to your current speed if its within 5 knots and then any further application will move it to the intended direction.

[martin-w 3,251]

Hi,

 

So the problem appears to be that in the sim, when trimming, it is neither my imagination nor a problem with my specific set up that the aircraft exhibits zero pitch response to trim with the controls deflected.

 

I don't think it is related to lack of simulation of an artificial unit; I think it is simply that the trim is not being applied when the stick is not centered. If that could be fixed, I think it will be a dream to fly.

 

I guess we need to wait for PMDG on this one.

 

Best regards,

Robin.

 

Except that what you say isn't the case for me or others. Trims fine for me, whether the controls are deflected or not. For some reason, some are experiencing this and not others.

 

It's not perfect for sure, not easy to trim, but as I say, your specific issue I don't have.

[kevinh 409]

Post deleted, I misread the post I was replying to.

[777simmer 117]

The short version and my conclusion after todays and the day before yesterdays flight, is that the 777 FBW system and the trimming system are not something you are going to unraffle by looking at a flight control page.

 

But that is not necesarry either in my opinion.

What I think is important, is that the PMDG simulation is made so that it FEELS like the real thing as much is possible.....even if that means you have to apply some tricks that make the inner working/background coding of the PMDG777 FBW system a little less identical to the real thing.

(but that is just an opinion....where compromises are made is entirely up to PMDG ofcourse)

And that means you should be able to feel forces reduce....or in our case, you should notice your yoke deflection reduce......as you trim for speed.

The fact that PMDG has decided to program the whole FBW system outside of FSX, with compensation for config changes, turns, fall back to seconday and direct mode, etc, might make it impossible to implement this normal trim feeling.

I do not know this as I am not a software programmer.

 

PMDG does say at the end of the intro guide, that the only way they could mimic trim feel was by reducing elevator authority.

Again, I am no programmer so I have no idea what I am talking about here....but it seems to me that if they would just link the FBW trim ref speed directly to an elevator response all would be fine (not 100% realistic, but not noticably different to the user and with correct trim feel).

 

 

Anybody in for a long long story that is interesting but does not really help us much?.....then read on, lol. Otherwise just skip to the last few sentences:

 

I tested the trim system on the real 777 again, this time looking at the FCTL synoptics page every now and then.

On the outbound flight I was PF and on the inbound flight PNF.

On the Inbound flight my Capt was kind enough to join the experiment (anything to understand the aircraft better) and flew manual and out of trim just as I had done on the outbound flight.

Him joining the experiment was quite necessary because after my outbound flight I thought I was going nuts......the aircraft seemed to behave like an airbus all of a sudden, lol.

 

In my opinion you can't really conclude that much about the trim system just by looking at the FCTL page.

The elevator and stabilizer position indications are too course for this.

I guess there is a reason for all that measuring equipment and people on board a 777 flight test ;-)

 

You should browse through the "outbound leg" part rather than sucking up details because the inbound leg report is based on better observations!

I left it in there to paint a better picture of how things feel/seem and how confusing observations can be, making it pretty difficult to recreate something like this.

(so that is a complement to PMDG)

 

Outbound leg:

I did the take off and did not trim during clean up and acceleration.

AT was engaged the whole time, AP was disengaged ofcourse.

Despite not touching the trim, the STAB position on that page changed quite a bit.

From 5.0 during take off roll, to 7.0 while retracting flaps and accelerating, and back to 5.0 once clean and at 250kt.

 

I never touched the trim switches and had to push quite a bit on the yoke to oppose the FBW artificial feel while flying out of trim at 250kt.

 

The yoke was deflected fwd a little bit only (it felt like maybe 2-3cm, an inch) but the force I had to apply was substantial.

I flew like this a little while longer and then started to trim the artificial feel forces away. Strangely I did not see STAB position change during this :-(

 

Then in FL100 we accelerated from 250 to 315kt and again I did not trim.

Artificial force grew substantial again and the yoke was deflected fwd, similar as before.

Again he STAB trim did not change........it stayed at 5.0 units.

After a minute or so like this I started trimming.

First a 1 sec burst....no change in STAB position.

Then a 2 sec burst.....no change in STAB position.

The artificial force I had to oppose to keep the nose from going up was getting less of course and I was getting quite close to feeling no force.

The STAB position did not change untill getting close to a no force condition (almost in trim) but changed only very little. I ended up with 4.5 units of STAB trim.

 

What I find most interesting is that the elevators were not visibly deflected on the FCTL page after reaching 315kt while out of trim (still trimmed for 250kt with STAB at 5.0)

The way I was pushing on the yoke I was expecting to see an elevator down deflection by about at least as much as the width of the pointer is wide. But nothing....or so little that I cant tell!

For a second here, I started to believe that the 777 in fact is in trim all the time and does autotrim for speed and just gives you an out of trim artificial force on the yoke so that you have the feeling of beeing out of trim like in a 737 or 767.

Thankfully the Captains outbound leg showed otherwise, pfew!

 

More confusing stuff!

A few hours later, during descend passing 24000ft to 12000ft I disconnected the AP.

FLCH engaged, idle thrust.

In trim at 280kt I trimmed (out of trim) first in one direction, then in the other while forcing the yoke to maintain a constant pitch and thus 280kt.

Just as during take off, the introduced artificial force I had to overcome (first pulling then pushing) was substantial.

But STAB trim did not go anywhere!!

Elevator deflection.....pffff.....I dont know I could not tell.....looked neutral to me.

So all I did was cause an out of trim artificial force to be generated, and the controls stayed right where they were???

hmmm.....

 

 

Inbound leg:

This time the Capt was flying and we had the FCTL page video-ed during take off and all the way untill at 301kt in 14000ft.

Same conditions, AT engaged, AP off and no trimming.

This time however we did not even trim after flap retraction (250kt). We flew without manually changing the take of trim setting (4.25 units) all the way.

 

The fact that we video-ed the whole thing means I can now look at what is happening as I type this up rather than only glancing at the FCTL page every now and then and then typing from memory.

And the fact that we did not trim for a much larger speed change (175kt after rotation till 301kt) gave us more elevator deflection, one that we could actually see!

(that is why I said, you can just browse throught the outbound leg part a bit because it is not accurate enough to draw any conclusions).

 

Elevator deflection IS in fact minimal!

At the speeds we are flying those huge surfaces really do not need that much to change ptich rate or G-load (the FBW C*U system gives you a pitch rate command at low speeds and a G-load command at higher speeds).

Only during the flight control test on ground do you see the elevator go up and down to the stop.

It is interesting (but not important) to note that the PMDG777 yoke is moving back and forth between max and min in flight which is not so in the real aircraft. (not that I care much or that I think they should change that, it is just an animation and if they wouldn't animate it like they have then people would probably say "hey my yoke is broke").

During the FCTL test on ground you really do see a proportional movement of yoke versus elevator position. (So yoke full fwd = elevator indication full down.)

But once in flight you hardly move the yoke....you feel substantial force.....but the yoke hardly moves. I said before about an inch....lets make that 2 inch just to cover for me not being able to judge that correctly. That is still far off from max/min deflection.

 

Anyway, take off trim was set at 4.25 units.

During rotation the elevator moved up by about as much as the elevator pointer is wide. So not much.....you would think it goes up half way or so, but it really does not.

Not touching the trim switches, positive rate, gear up.....STAB trim was now at 5.0.

(same as on the outbound leg).

Elevators now not deflected (because we are in trim)

Flying runway heading and without further config changes the STAB moved to 4.50 units. That would have been the correction for reduction to CLB thrust!

Elevators still flush.....in trim.....nothing you have to do :-)

Then a left turn (radar heading) and a STAB trim change to 5.5 units.

Nice, turn compensation works as well, :-)

Then acceleration and flap retraction while turning. Again STAB moved automatically during flap retraction and acceleration. This time up to 6.0 units with flaps up.

Passing clean speed (229kt) and accelerating to 250kt, elevator deflection was now slightly downward (I would have expected this during the first leg as well....it probably was).

But elevator deflection is not much....maybe about as much as 1/3 - 1/2 of the width of the white elevator indicator. On video I can see it clearly now.

Then all of a sudden the STAB trim started moving.....5.75...5.50.

What was that?

 

That was some sort of autotrimming!

 

I do not know what that was.....maybe something to do with the C*U changeover from pitch rate commands to G-load commands.....just guessing here!

or

the system does not like a large out of trim situation and starts trimming some of that away while not changing the artificial feel load? (most likely)

or

it trims a little because you are getting close to your target speed.....like an anticipation feature?? (not likely)

 

Elevator down deflection was now even less ofcourse and between 0 and 1/3 of the width of the pointer, but it was still there for sure.

Not all elevator deflection was trimmed away and the force on the yoke was still there as well.

So all still felt B737 like!

 

Passing 5000ft climbing, no more config changes, no more turning, no more changes in STAB position.

10.000ft, accelerating to 301kt while climbing.....for the longest time nothing happened, STAB trim remained at 5.50.

Elevator deflection down was pretty much steady at about 1/3 pointer width

Then again, as we approached 301kt (target speed), this autotrimming....5.25...5.00.

Again I am thinking the same.....does it not like to be too much out of trim?.......does it autotrim in anticipation??

I do not know.

All I know my college is still pushing the yoke, oppossing artificial feel, thinking he is flying a B737, lol.

Elevator position reduced but like before was still there somewhere between 0 and 1//3 of pointer width.

Ok, enough....trimming now.....4.75...4.50...4.25....we ended up with 4.00 units and elevator relaxed (flush), still climbing, passing 14000ft.

 

It makes sence to me that this mini-minimal elevator displacement required only a small STAB position change (5.0 to 4.0) to even it out.

 

By the way, yes, STAB trim moves in 0.25 increments.

 

 

 

Now....disregard all above and untill we have a different feel to trimming (if PMDG decides that is possible) I recommend the use of the FBW trim ref speed indication (cheat mode) to fine tune your trim setting :-)

It works pretty well like that!

 

Happy landings!

[willywonka 36]

Thanks for the report, Rob. Would it be beneficial to send your video to PMDG? Although I think they probably have enough of their own videos.

 

It seems like we'll never really get the right FBW feels at home unless we have a force feedback yoke, because the interaction between the yoke and the plane is quite complex. But this is just a desktop sim, after all. I think PMDG did the best they could given the massive constraints of the desktop computer and FSX.

 

I guess the FBW cheat mark is the best compromise we can get. Might I suggest to PMDG that instead of having it ON or OFF, that there's also an option to show the FBW speed only when the trim switch is pushed, or at least make a hotkey to toggle it on or off. That way you can quickly check the FBW trim yourself, but at other times when you're in trim you won't have to see the "cheat mark." ^_^

[jcomm 5,963]

Superb reading!

[evaamo 549]

That was an interesting read, thank you Rob.

[cmbaviator 5]

Awesome post Rob.

 

After reading, I wanna say A320-A380 FTW, as the C* autotrims for anything, so you don't need  to get confuse with Trim reference speed, artificail feels....

 

 

@ Rob

 

How do you change the flight path while in trim :

 

For instance, lets say that you're in trim for 160 kts speed at a v/S of -500 feets/min, and you want to fly level at 160 kts, do you have to only to increase the thrust ?

 

Because during an ILS approach, wy VS was -900 feets /min and was getting below, so I pitch up until I get -600 fts/min but after releasing the yoke ( AT on), the Ac will slowly pitch down, so I don't know how to maintain a steady flight path Imy vertical speed always go within -900 and - 550 and it's not very stable :(

 

Do you have an advice ?

 

Thnaks

 

CMB

[James Bennett 52]

Struggling to fly this thing. Kyle says to fly it like a cessna, I cannot fly it like this as it seems to wildy pitch up and down and doesn't apply trim until the control column is centered and by then it's maybe over compensated. I also can't tell when I'm meant to be trimming and when it is trimming itself.

[scandinavian13 5,192]

 

 

I also can't tell when I'm meant to be trimming and when it is trimming itself.

 

Question #1: Did you change speed?

Yes?  Trim.

No?  The aircraft has trimmed for you.  Repeat Question #1.