Fly-By-Wire of the 777 and it's simulation

[777simmer 117]

Just a question 777simmer: are you a rated 777 pilot?

Yes.

[Alec 370]

Well, there's this thread, where we're all talking about the 777 FBW, trying to get an idea of how it really works in the real airplane. The FCTM and the FCOM doesn't explain nearly as detailed as we would have liked. It doesn't even mention the C* U law for Pitch control.

 

Your input there, if you're a real 777 pilot, will be very welcome!

 

forum.avsim.net/topic/418721-question-about-trim-on-final-777/?view=getnewpost

[guy 24]

Well, there's this thread, where we're all talking about the 777 FBW, trying to get an idea of how it really works in the real airplane. The FCTM and the FCOM doesn't explain nearly as detailed as we would have liked. It doesn't even mention the C* U law for Pitch control.

 

 

The  C*U LAW is quite well explained in this thread from Pprune:

http://www.pprune.org/tech-log/470643-b777-pitch-control.html

 

If you want to see the REAL COMPLEXITY of that law you can also study the patent definition.  The adress is given in the same thread:

http://www.patentstorm.us/patents/6158695/description.html

 

You can have it as PDF here.

https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US6158695.pdf

 

Good read !  :smile:

 

Guy

[777simmer 117]

Oh boy oh boy.....You guys are right.

This seems wrong (I am being carefull here...more testing to do)

 

VRMM tuturial (everything setup as in tutorial), FSUIPC removed, only a CH yoke and rudder connected (granted, twenty year old analog stuff connected to a digital USB converter).

Using keyboard F1 - F4 for thrust at the moment.

 

AP off, FD off, AT disconnected.

 

I can go in level flight in 5000ft from 300kt down to 180kt (you would not do this in real life cause thats 10kt above yellow bar and way below flaps up maneuvering speed) and back to 300kt again......without ever heaving to touch the trim!

My StB trim automatically changes from 4.1 to 5.4 while slowing down and back to 4.1 when at 300kt again as I am manually maintaining 5000ft.

Yes you do have to compensate with the yoke for the speed change initially (pulling for decelerating and pushing during acceleration) and you COULD trim this away.....but the thing is....if you dont trim it away it gets trimmed away automatically!

 

Now the only problem with this situation is.....and that is why I am now being carefull with saying this is all wrong......In real world flying, this not trimming for airspeed and just holding the yoke to compensate gets quite heavy real quick.

10kt out of trim and you would feel those forces (ok simulated feedback forces) immediately.

So in real life you dont sit there and wait what the aircraft does if you dont manually trim.

You instintively trim away those forces.

 

I have never tried what happens after a while if you dont trim away those forces.

 

I dont think that the FBW system will at some point automatically trim away those forces......but I wont know for sure untill my next rw flight ;-)

 

I must also say....that other than that, the smoothness of the plane, the rate at which it pitches and rolls, that is all extremely well simulated.

The real thing realy does fly like this (other then maybe the trim)

 

I

[cavaricooper 2,615]

Oh boy oh boy.....You guys are right.

This seems wrong (I am being carefull here...more testing to

 

I dont think that the FBW system will at some point automatically trim away those forces......but I wont know for sure untill my next rw flight ;-)

 

 

I

Really? After 10 years of line operation? Ok, I respectfully disagree (without being typed)......

[777simmer 117]

Really? After 10 years of line operation? Ok, I respectfully disagree (without being typed)......

See, that is exactly the kind of crap I have not mentioned I am real world pilot before!!

 

But at some point the discussion on this theme got so deep that I felt like I had to say I am real world pilot. Not for bragging purposes but to let others know I am not making the stuff I write up.

 

Now I dont know if your Avatar means anything, or that it just looks good....but if you have any affiliation to BOEING why dont you give expert opinion?

If you are not some BOEING expert + not typed rated, then I dont know how you could possibly disagree other than for the simple reason of being obnoxious.

 

I am not a test pilot in an empty plane, so I dont sit there and try stuff with 300+ pax behind me!

[martin-w 3,238]

I'm, more interested in when we DO trim for speed. That's the issue I have. No response for one second and then it trims way too much.

 

 

 

Really? After 10 years of line operation? Ok, I respectfully disagree (without being typed)......

 

 

I would say it's quite feasible that if it's not the recommended procedure, and control forces are great, then manual trimming would be the priority. I see why someone would never do this under those circumstances. Why would you?

[DescendDescend 25]

Persevere. I am sure they value everybody's input in order to improve this already excellent aircraft.

 

I wish I had hired one of the BA 777 Level D simulators instead of those darn Airbus things... :mellow:

[martin-w 3,238]

I love Airbus Howard.    :smile2:

[Cowl 11]

Really? After 10 years of line operation? Ok, I respectfully disagree (without being typed)......

 

Really?...don't take me wrong but it's a real world and experienced 777 pilot who's telling this. He's not neither a hobbyist nor an aficionado, but a professional.

 

In spite of being myself also a RW airline pilot, though I have never flown the 777, I'll faithfully listen to and believe what a real 777 pilot has to say about this.

 

Many of us, including me, have noticed this strange behaviour not corresponding with what the actual FCOM is telling about how the 777 FBW system works.

 

Professionally I'm very used to deal with aircrafts FCOMs and other technical documentation. I have throughly studied the 777 FCOM and experimented with the aircraft. I no part of the FCOM I've seen any kind of "auto trimming" feature being mentioned except for configuration (flaps, gear) changes and banking, and only in normal mode. On the contrary, it clearly states that speed changes are to be manually trimmed just like in any conventional aircraft. In fact, this was one of the main objectives of the engineers in the FBW system design, that in speed changes the aircraft should feel just  like a conventional one, requiring the pilot to manually trim in order to relief the pressure on the column, among other things, to take advantage of the past training and experience from her pilots. That is, it was not designed to be just like the Airbus FBW system.

 

Having said all of this, I must say that in spite of, and besides this allegedly "wrong behaviour" issue, the PMDG 777 is simply A W E S O M E, and I'm completely sure that if finally this issue turns out to be and official bug, PMDG will fix it without a doubt. I'm pretty sure that most of us, if not all, think this is by far the best aircraft we've put our hands on in all the at-home computer flight simulation history.

 

Cheers.

[Alec 370]

The  C*U LAW is quite well explained in this thread from Pprune:

http://www.pprune.org/tech-log/470643-b777-pitch-control.html

 

If you want to see the REAL COMPLEXITY of that law you can also study the patent definition.  The adress is given in the same thread:

http://www.patentstorm.us/patents/6158695/description.html

 

You can have it as PDF here.

https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US6158695.pdf

 

Good read !  :smile:

 

Guy

 

Amazing  links! Now I know why Boeing doesn't tell us about it in their manuals! You wouldn't need to be a pilot, but a mathematician to understand the complex law!! But the pprune thread was excellent to explain how this works.

 

I dont think that the FBW system will at some point automatically trim away those forces......but I wont know for sure untill my next rw flight ;-)

 

 

 

We will be expecting your input in this, since PMDG Beta 777 pilots don't seem to visit this forum to give their opinions on these areas of the simulation.

 

 

 

I found it extremely hard to hand fly an aircraft that is not speed stable. It just doesn't make sense for a pilot, specially with this autotrim in place. And I really think there's something wrong with my Pitch Trim configuration, because sometimes I press it for one second and the aircraft will start pitching up, much more than 10 knots, which should about the correct rate as mentioned by real 777 Pilots, and it will almost stall in this condition. Then I start pressing Pitch DOwn Trim and nothing happens. I don't know if it's a controller issue, or what's wrong. I Have deleted my Fsuipc.ini to make sure I'm using only FSX controller interface for no interference with the PMDG simulation.

 

Let's wait to hear more about this subject

[cavaricooper 2,615]

 

 

See, that is exactly the kind of crap I have not mentioned I am real world pilot before!!

But at some point the discussion on this theme got so deep that I felt like I had to say I am real world pilot. Not for bragging purposes but to let others know I am not making the stuff I write up.

Now I dont know if your Avatar means anything, or that it just looks good....but if you have any affiliation to BOEING why dont you give expert opinion?
If you are not some BOEING expert + not typed rated, then I dont know how you could possibly disagree other than for the simple reason of being obnoxious.

I am not a test pilot in an empty plane, so I dont sit there and try stuff with 300+ pax behind me!

 

Dear Rob:

 

My intent was merely to offer a contrasting viewpoint; being obnoxious was not my motive.  As the 777 has been vetted by many type rated pilots, and FBW had multiple revisions prior to release, I believe it to be an accurate depiction.  That said, I have re-read the FCOM and find there may indeed be an argument for a change in speed/trim behavior.  Therefore, as you so succinctly put it, I am perhaps wrong in my initial assumption.  I can tell you that you are in good company, as my wife often believes I am wrong as well- she's just usually a bit less brusque in her approach .

 

The best response to your post would come directly from PMDG, and I should have waited for that.  Mea Culpa.

 

BTW- all my avatar means is that I am fond of Boeings.....

 

Ta!

[martin-w 3,238]

 

 

 

 

 sometimes I press it for one second and the aircraft will start pitching up, much more than 10 knots, which should about the correct rate as mentioned by real 777 Pilots, and it will almost stall in this condition. Then I start pressing Pitch DOwn Trim and nothing happens.

 

 

 

Me too, I've noticed that. Not easy to trim at all. As I've been saying all along.

 

I will probably submit a support ticket at this stage.

[termtek 1]

Me too, I've noticed that. Not easy to trim at all. As I've been saying all along.

 

I will probably submit a support ticket at this stage.

I don't think you need to submit support ticket coz the FBW simulates correctly!

 

Please be aware that 777s system is different to Classic Boeing and Airbus.....

 

Trim for speed means the trim works while speed changed! When you change the conf, gears...target speed you need to trim it!

 

When you on vref with correct conf, you don't need to touch the trim! Or the reference speed will be changed ! To understand the logic, please forget what Airbus does first!

 

Hope this helps,

Frank

 

 

Sent from my iPhone using Tapatalk - now Free

[Flamin_Squirrel 71]

Trim for speed means the trim works while speed changed! When you change the conf, gears...target speed you need to trim it!

 

Nope. Wrong way round.