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PMDG 777 FBW and weird Flight Controls behaviour?

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Hello Everyone,

 

I'm posting there because I have some questions about how the PMDG 777 FBW behave in some conditions that seems a bit weird to me.

I watched the videos of an EVA Air Pilot explaining how the 777 FBW work in a serie of videos about different situations and I noticed the following stuff that don't seem to match what I've seen in his videos on the PMDG 777. (EVA Pilot 777 FBW playlist here:  https://www.youtube.com/playlist?list=PL5caETAZRBN6mPhNASIlMg2bkWH2DbtIz )

_When I'm in level flight, reimmed correctly to the speed I'm flying at, I noticed that the aircraft tend to give some unwanted pitch variation like I'm flying straight and leveled but the plane will make some tiny nose down moves making it struggling to maintain the altitude I'm supposed to fly at.

_Also, during climb or descent, I pull/push the yoke to get the vertical speed I want, then I put the yoke back to neutral, but the VS won't maintain as wanted but will start to fluctuate without other inputs.

_When I want to start a turn from a leveled flight, I just bank the plane let's say to the left, and when I reached the desired bank angle I just put the yoke back to neutral, and for some reason, it seems that the plane can't keep the turn steady and will start descending as soon as I start banking and will fail to maintain the selected altitude.

 

I also noticed some incoherent behavior from the flight controls where the flight controls position does not match what the plane is doing.
_When I bank left and keep my yoke to full left deflection, at some point around 30° of bank, the FBW will stop the roll, in the sim, the roll stop without problem, but the ailerons and spoilers will keep at full deflection, so the plane is  successful at simulating the FBW protection here, but fails at simulating proper flight controls  moves. (for example the default A321 Ailerons goes back to neutral when the FBW stop the bank)
_When I stop all the hydraulics pumps, I notice that the right elevator is deflected fully down, like it would be on the ground with gravity in absence of hyd pressure in the circuit, but during flight, where it can't be deflected that way by gravity due to the aerodynamic pressure on it, and if it was defleccted that way, I couldn't be flying leveled with the right elevator down and the other neutral, this position would most likely lead me straight to the earthand force me to get the other elevator fully deflected to the sky to stay in the air.

 

So here is the list of stuff that I wanted to report, if you want some pics as further explanation, I will find a place to upload them and post them here, maybe someone can tell me if something can be done about that or if it could be fixed in a future update :)

 

Louis Laisement

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Hi, interesting remarks and many thanks for the link to the videos! I'm coincidentally in the process of recording a video analyzing the 777's FBW system, so this will help me a lot.

 

Now, addressing your querries, I see you expect the 777 to fly like something it's not. The FBW on the 777 is designed so that the plane flies pretty much like a conventional airplane from a pilot's point of view. It just enhances the flying qualities of the plane and provides a series of protections, but it does this "back stage". A pilot that's always flown conventional aircraft could hop into the 777, not knowing it's a FBW airplane, and not notice the difference (he will however notice that it's an extraordinarily well-behaved ship). Unlike Airbus, a Boeing pilot doesn't have to learn how to fly again when moving onto the 777.

 

  1. I assume you're flying manually, trimmed for a certain airspeed and want to maintain level flight. Now, how does the aircraft give those "unwanted pitch variations"? Is it through the stab trim, elevators, thrust if you're using A/T?
  2. If you release the pressure on the yoke the aircraft will eventually pitch for the trimmed airspeed (in FSX that's the blue FBW bug on the speedtape). The resulting V/S will vary depending on other parameters, most importantly, thrust. By the way, when you pull/push on the yoke, what you're really controlling is airspeed, not V/S. That is, say you're level flying at 250 knots, in trim and with a certain N1 of say 60%. If you now want to climb, what you should do is increase the thrust, NOT pull on the yoke. Increasing the thrust will make the aircraft climb at 250 knots because it's trimmed for 250 knots. This is what the FLCH mode of the AP does.
  3. That's perfectly normal behavior. If you bank, you'll have to pull on the yoke not to lose altitude and add thrust not to lose airspeed.

Regarding the last 2 points: The pilot's input on the control DOES NOT MATCH the position of the control surfaces, at least in normal law. The pilot's input is sent to a computer called Primary Flight Computer. The PFCs takes a lot of parameters into account, analyzes the pilot's input and generates an "enhanced" signal that's sent to the control surfaces.

  1. That's the bank angle protection in action. The aircraft won't make it easy for you to bank past 35º.
  2. The full down elevator may be compensanted by the stab trim.

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Hello Alpha Floor, thank you for your answer.
Well I know the philosophy behind the 777 FBW so I'm not expecting it to fly like an Airbus, hopefully it doesn't^^, actually I was even surprised by some of the things I discovered in the EVA Air pilot channel. But it doesn't fly exactly like a normal plane, the biggest example of that is the trim for speed (I personnally prefer a normal trim).

To answear your questions, yes I'm flying manually, trimmed correctly for the speed I'm flying at which remains the same during the whole lenght of every scenarios mentionned. For the items I questionned above, I just used my understanding of the videos of the EVA pilot, which seems to show that even if it mimics the "feel" of a normal aircraft, the FBW still does some things that makes it easier to fly. In the video I saw that when trimmed correctly and stuff you won't have some pitch moves and stuff to correct as the FBW will do it by itself. Like with the climb that should stay at the rate I wanted, like I set the attitude to get a 1000fpm, it will stay at 1000fpm even if I release the yoke, that is again from my understanding of the videos. For the turn, it's the same, in the video I saw that the plane does not behave like my little ga plane where I need to pull up to maintain my altitude, it seems that you really have minor inputs to do from times to times to maintain your turn prefectly shaped.

 

 

Regarding the two last points I talked about, you didn't understand what I wanted to talk about (sorry if I'm not 100% clear, I'm French, English is not my native language so I'm doing my best to be as understandable as possible^^)

I know about the bank angle protection, that's exactly what I was talking about, on one side we can see that the plane stopped banking under the action of the FBW, so with action of the control surfaces on the opposite side, but on the 3d plane in FSX/P3D the control surfaces are still deflected according to the yoke position, which does not reflect the true position they should be at with the FBW stopping the turn. I found that a bit disappointing for an addon of that quality and realism to don't have proper movements of the flight controls on the visual model that match what the pilot/FBW/Plane are doing.

Regarding the full down elevator, it can't be compensed by the stab trim as it was not moved and because I tried in Direct Law, nothing changed, only the elevator that dropped. And it couldn't be in that position anyways with the aerodynamic pressure applied on it by the relative wind, it could only be on that position while on the ground.

 

I hope my new post will help you to understand my first one.

Thank you

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But it doesn't fly exactly like a normal plane, the biggest example of that is the trim for speed (I personnally prefer a normal trim).

 

But most conventional aeroplanes are speed-stable (i.e. they will tend to maintain a constant speed when in trim). This is the biggest difference between the Boeing FBW implementation (and conventional direct controls) and the Airbus implementation: the Airbus FBW types are path stable, i.e. they trim for a load factor at the expense of speed. The B777 is designed to trim exactly like a conventional aircraft, it's just the way in which it's programmed via the FBW computers.

 

 

 


, but on the 3d plane in FSX/P3D the control surfaces are still deflected according to the yoke position, which does not reflect the true position they should be at with the FBW stopping the turn. I found that a bit disappointing for an addon of that quality and realism to don't have proper movements of the flight controls on the visual model that match what the pilot/FBW/Plane are doing.

 

My guess would be that this is an FS limitation, but I expect someone with more knowledge of the 777 development process would be able to confirm or deny this. PMDG are good, but at the end of the day they still have to work within the limitations of FSX and I would imagine that the priority was to ensure that the functionality of the systems is correct, even if the indicated positions of the control surfaces are not always precisely as they would be in the real aircraft.

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In my modest opinion, if the 777 was actually designed to trim exactly like a normal aircraft, it would not be a trim for speed, it would just be a button that you use to get a desired attitude, just like in my little ga, or in a 737 or even the 777 in direct law, and I think it may have been better that way to keep the way of flying the same as on other non FBW Boeing such as 747 and 767.

 

As for the FS limitations, I thought about it, but I can see that the default A321 does not have this problem of unmatching visual position to the "virtual" position, that may have been a missed item, It would be really nice if it could be corrected, it would add to the immersion

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In my modest opinion, if the 777 was actually designed to trim exactly like a normal aircraft, it would not be a trim for speed, it would just be a button that you use to get a desired attitude, just like in my little ga, or in a 737 or even the 777 in direct law, and I think it may have been better that way to keep the way of flying the same as on other non FBW Boeing such as 747 and 767.

 

 

But none of the aircraft you talk about trim to maintain a pitch attitude. They are all speed stable. If you trim out the control pressures, the aircraft will settle down at a particular airspeed, not a particular pitch attitude, and if you change the power setting without adjusting the trim, the pitch attitude will change and the airspeed will (after initially fluctuating) settle down at a different value.

 

The A320 series on the other hand is path stable, which is what you are describing: you select an attitude and the aircraft will (more or less, as it's actually maintaining 1g) maintain that attitude if, for instance, you pull off the power, with the result that the aircraft will slow and eventually reach the low speed protections. This is not what a B777, a B747, or a C172 will do: when the aircraft is in trim, if you take your hands off the controls and reduce power the nose will pitch down, you will sink and the airspeed will stay roughly the same (give or take some pitch oscillations in the non-FBW types that are relying purely on aerodynamic stability rather than computers actively controlling the pitch to maintain the trim airspeed).

 

Try it and see!

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I didn't meant that you trim for attitude, sorry again for me not being a native english speaker, I might not always have the right words to explain what I want to say. I know the differences between Airbus and Boeing philosophy, my point here is abouth the differences between the non FBW Boeing and the 777. I don't know how it is called but the 777 trim does not work like the other Boeing or the ga. In ga or classic Boeing your action on the button/wheel will directly move the trim tab or the horizontal stabilizer, in the 777 this is not what's happening during the flight. You don't use the 777 trim the same way you would use the 737 one. But anyways my point here was not to talk about how the 777 FBW trim works, but how the PMDG 777 FBW work compared to the real 777 on the items that I pointed, I perfectly understood what you told me about the trim for speed, unfortunately my vocabulary isn't rich enough to say what I want to say. For me the 777 trim feels less natural than the 737 one, it feels like they wanted to do some FBW but stopped somewhere halfway to keep the old philosophy, it may have been better if their FBW was totally transparent as long as you don't hit the enveloppe protection.

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Hi Louis,

 

I recorded a video on the FBW addressing several points. It will come in handy for the purposes of this thread.

 

 

 


_When I bank left and keep my yoke to full left deflection, at some point around 30° of bank, the FBW will stop the roll, in the sim, the roll stop without problem, but the ailerons and spoilers will keep at full deflection, so the plane is successful at simulating the FBW protection here, but fails at simulating proper flight controls moves. (for example the default A321 Ailerons goes back to neutral when the FBW stop the bank)

 

If you go to 23:25 of my video, you'll see that the aircraft behaves as expected. Now, in the real aircraft the protection creates a force on the control wheel that tries to bring the wheel back to neutral. But if the pilot overcomes this force he will make the plane roll past 35º as you can see in the video. Keep in mind that the input through the wheel doesn't necessarily match the position of the control surfaces since the signal first goes through the PFCs and is altered. In 21:45 you'll see what happens in Direct Law. Also keep in mind that, as you well know, our hardware usually don't come with feedback so you're not feeling the same forces on the yoke as the pilot of the real 777 does.

 

 

 


_When I stop all the hydraulics pumps, I notice that the right elevator is deflected fully down, like it would be on the ground with gravity in absence of hyd pressure in the circuit, but during flight, where it can't be deflected that way by gravity due to the aerodynamic pressure on it, and if it was defleccted that way, I couldn't be flying leveled with the right elevator down and the other neutral, this position would most likely lead me straight to the earthand force me to get the other elevator fully deflected to the sky to stay in the air.

 

 


Regarding the full down elevator, it can't be compensed by the stab trim as it was not moved and because I tried in Direct Law, nothing changed, only the elevator that dropped. And it couldn't be in that position anyways with the aerodynamic pressure applied on it by the relative wind, it could only be on that position while on the ground.

 

 

I didn't fail the hydraulics, I should have done it though, just forgot :'(, but in 46:34 the left elevator is failed and fully down but the right elevator is still working. I don't really understand yet why the failed ACE's will let the elevator hanging, in this case there should still be hydraulic power holding the elevator in place even though there would be no way of controling it, at least it should stay neutral. Maybe the elevator is in fact in a neutral position and it's just the exterior model that's showing it as fully down, I don't know.

 

Another thing I'm not sure of either is what would happen if one elevator alone went full down but the other one was still controllable. I guess an up command from the other elevator together with yaw/roll inputs to correct the moments due to the assymetry would do the trick and the airplane would still be controllable. I don't think it would plunge into the ground. I agree with you however, the elevator wouldn't fall down unless forced so by the actuator. Also, one elevator fully down and the other one neutral will bring the aircraft down most certainly. So this might be an exterior model issue.


 

 


Like with the climb that should stay at the rate I wanted, like I set the attitude to get a 1000fpm, it will stay at 1000fpm even if I release the yoke, that is again from my understanding of the videos

 

The thing is that when you command nose up through the control wheel and then release the force, if there's no change in the trim speed the aircraft will eventually come back to the previously trimmed airspeed. You're not pitching up for a given vertical speed.

 

 

 


For the turn, it's the same, in the video I saw that the plane does not behave like my little ga plane where I need to pull up to maintain my altitude, it seems that you really have minor inputs to do from times to times to maintain your turn prefectly shaped.

 

This really got me, I must be honest. I expected the nose of the plane to drop during the turn.

 

The forum won't let me quote any more...

 

(quote)
In my modest opinion, if the 777 was actually designed to trim exactly like a normal aircraft, it would not be a trim for speed, it would just be a button that you use to get a desired attitude, just like in my little ga, or in a 737 or even the 777 in direct law,
(/quote)

 

I don't agree. In any conventional airplane you trim to relieve the force on the yoke. So first you do a thrust, attitude or configuration change, then you trim until the control force required to keep the aircraft in the desired attitude is zero. This is so both in a Cessna 172 and in a 777.

 

However, unlike a C172, the FBW of the 777 will trim for you when you don't intend to change the speed of the aircraft. The only reason why you would trim would be a speed increase/decrease. Now this doesn't invalid the principle of "trim for zero control force". Say you lower the landing gear and the aircraft trims for you, there's no force required on the yoke the maintain the same path as before, hence no trim required. Say you accelerate from 250 to 280, once you reach 280 you're pushing the yoke forward, in order to release the pressure you'll have to trim nose down like in a conventional plane until the force on the control is zero.

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Hi Alpha Floor, thanks again for answearing,

 

Well I find your videos about the 777 really interresting, the problem I see in it, it's that you analyze what the PMDG 777 FBW does, assuming it's accurate to the real one, which in my opinion seems to be wrong from what I've seen in the EVA Air 777 pilot's channel, that's why I posted this thread, because I found some stuff that seemed to fail to match what the actual aircraft does, I will try to get in touch with some AF 777 pilots friends of my gf to ask them about all the question I have about the 777 FBW system.

 

Again for the bank angle protection, the plane behaves like it should, the problem here is that the control surfaces are not deflected as they should be on the 3D model (matching what the FBW does), and this behavior is in the real life caused by the change in the deflections of the control surfaces.

 

About the elevator, as you thought it's again a problem with the 3D model. It would be like this on the ground as there is no hyd pressure to maintain it (like you can see with planes at the ramp), but it can't be like this during the flight as the aerodynamic pressure from the relative wind would hold it around the neutral position (like when you see the rudder moving with the wind on plane on the ramp without hyd power).

 

For the climb and stuff, why would I have to change my trim setting if my speed does not change? All I said about the plane maintaining 1000 fpm without more pilot inputs where seen in the videos of the EVA pilot.

 

And for the turn, everybody would expect his nose to drop from the turn, that's how any aircraft will do, but the 777 is a FBW aircraft, that's where the difference is, and it is not a fully transparent FBW that does nothing to help you, I think the way it works in the PMDG does not match how the real one performs according to what I've seen.

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Hi Louis, thank you for reading my lengthy posts :)

 

 

 


the problem I see in it, it's that you analyze what the PMDG 777 FBW does, assuming it's accurate to the real one

 

Yes, that's correct. Unfortunately I don't have access to a FFS of the 777 nor to the real aircraft... I assume that PMDG reproduced the aircraft as best as possible for FSX, even more so after SP1 in which they addressed acknowledged FBW issues.

 

 

 


I will try to get in touch with some AF 777 pilots friends of my gf to ask them about all the question I have about the 777 FBW system.

 

Please do so and tell us what you find out! You can show them my video and hear what they think of the PMDG 777 simulation, how accurate it is etc.

 

 

 


and this behavior is in the real life caused by the change in the deflections of the control surfaces.

 

Right, in the end the aircraft ultimately responds to how the control surfaces move, regardless of whether it's a FBW airplane or not. That's just flight mechanics principles which are valid for every plane.

 

 

 


For the climb and stuff, why would I have to change my trim setting if my speed does not change?

 

Correct, I didn't suggest the contrary! The only thing I meant is that when you pitch up or down on the control column you might achieve a certain V/S. Now when you release the control the speed will oscillate from whichever speed there was at control release to the trimmed airspeed. Eventually the aircraft will settle at the trim airspeed and the resulting V/S might not be the initial one from before releasing.

 

 

 


I think the way it works in the PMDG does not match how the real one performs according to what I've seen.

 

I'm beginning to believe the same thing. Will do more tests on how the plane behaves in turns.

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Hi Alpha Floor, thank you for reading my post as well and thank you for answearing them, I find this subject really interresting^^

 

Well PMDG 777 is the furthest we can go in getting touch with a 777 simulation unfortunately with the limitations that comes with this platform. But I still think some good could be done to get it more realistic, if other devs manage to "simulate" Airbus FBW that do everything for the pilot, I guess proper 777 FBW behaviour could be done as it's less complex(these airbus devs even have proper moves from the control surfaces matching what's coming out from the computer, unlike our beloved 777^^). I even heard that in previous verisons, the plane had a closer behaviour to the true one, but they changed it to the bad after following some feedbacks from the youtuber frooglesim which is in no way a 777 type rated pilot(or even a PPL pilot I think). That's why I posted there, because I noticed something that I believe is wrong, so I wanted to report it in the hope that something could be done about it(that's what support is here for anyways^^). I wish I could get my hands on a true 777 sim, I'll see if I can manage to get access the Air France ones in CDG. Also as I'm usually allowed in the cockpit of my long flights to Tokyo, I'll try my best to get the most informations from the pilots, but I think they can just confirm what I'm thinking about our PMDG 777.

 

About what we talked about before with nose in turns and stuff, the explanation is pretty simple, you actually posted it below your video in your sources about the features of the B777 FBW:

• Bank angle protection

• Turn compensation

• Stall and overspeed protection

• Pitch control and stability augmentation

• Thrust asymmetry compensation

 

Now I'd say the ball is in PMDG's side to give us the best we can get out of their product by correcting these "innacuracies" in the FBW and also the ones about the control surfaces position not corresponding to what they should be doing, I might be maniac but that's really important for me, especially for an addon that complex and that expensive

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I scanned over a lot of the posts because they are reeeaalllyyy long. The first and most problematic issue is that this is still fs. In the real airplane, the fbw works along with artificial feel modules which give the pilot a normal out of trim or in trim feel. We dont get that tactile feedback in fs. Fs actually will teach you how to trim incrrectly by trimming for attitude. Most likely because you cant feel what the ajrplane s telling you because we dont habe control forces in fs.

 

Whether youre in a cessna or a jet, you will always be trimming for airspeed. Even if you think your trimming for pitch. We just use the control forces to know if we are in trim or not.

 

The reason we feel these control forces in a real airplane is because we are not at the airspeed we trimmed for. Once we get to the correct speed, we dont feel the forces anymore.

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Hello Louis,

 

that's a very thorough analysis of how the FBW is supposed to work, really an interesting read. Anyway, if you really want to make PMDG of these issues, you should definetely submit a ticket on their support portal. There, you are sure you will get a proper answer, and if the bugs are indeed bugs, they will look into them

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In the real airplane, the fbw works along with artificial feel modules which give the pilot a normal out of trim or in trim feel. We dont get that tactile feedback in fs. Fs actually will teach you how to trim incrrectly by trimming for attitude. Most likely because you cant feel what the ajrplane s telling you because we dont habe control forces in fs

 

Exactly!

 

An FS pilot will trim looking for zero vertical speed mostly. In real life you trim to get zero force on the control. That's the reason why, even though the trim switches on the 777 don't exactly do the same thing as the ones in the 737, they are still used in the very same way.

 

Does the pilot need to apply force on the control to keep the attitude? Yes? Then it's not in trim. Otherwise it's in trim. This is like that in a 777 and in a C172.

 

That's the reason why PMDG thoughtfully included the Trim Reference Speed bug on the speedtape. Great feature for us desktop pilots!

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Exactly!

 

An FS pilot will trim looking for zero vertical speed mostly. In real life you trim to get zero force on the control. That's the reason why, even though the trim switches on the 777 don't exactly do the same thing as the ones in the 737, they are still used in the very same way.

 

Does the pilot need to apply force on the control to keep the attitude? Yes? Then it's not in trim. Otherwise it's in trim. This is like that in a 777 and in a C172.

 

That's the reason why PMDG thoughtfully included the Trim Reference Speed bug on the speedtape. Great feature for us desktop pilots!

the reference bug pmdg included not only helps fly the 77u in the sim, its a really cool way to literally see what trimming any airplane is like. I wish we had these on all airplanes so we can see what resulting aitspeed an airplane will makntain when one re trims it.

 

In essance, say for example, we are flying the 737 and trying to climb at 250 knots. However, we feel that we have to hold an insane amount of back pressure to hold the attitude for the stable 250 knot climb, this means we are actually trimmed for a much higher speed than 250 knots. In this situation, we would just apply nose up trim and then the control forces would be nice and light. Well, the only thing we really did was change the imaginary trim reference speed to lessen the control forces back from the high airspeed we were originally trimmed for back to 250 knots. In this sitation, if we had a trim ref bug, we would have seen this all in action. However, on the 737, we don't have that and the only reference is the control forces we feel.

 

I'm still getting used to it all on the 777 because the process really forces you to think about what you're doing and what your actions are actually requesting of the airplane.

 

Interesting stuff you pointed out earlier!

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the reference bug pmdg included not only helps fly the 77u in the sim, its a really cool way to literally see what trimming any airplane is like. I wish we had these on all airplanes so we can see what resulting aitspeed an airplane will makntain when one re trims it.

 

In essance, say for example, we are flying the 737 and trying to climb at 250 knots. However, we feel that we have to hold an insane amount of back pressure to hold the attitude for the stable 250 knot climb, this means we are actually trimmed for a much higher speed than 250 knots. In this situation, we would just apply nose up trim and then the control forces would be nice and light. Well, the only thing we really did was change the imaginary trim reference speed to lessen the control forces back from the high airspeed we were originally trimmed for back to 250 knots. In this sitation, if we had a trim ref bug, we would have seen this all in action. However, on the 737, we don't have that and the only reference is the control forces we feel.

 

I'm still getting used to it all on the 777 because the process really forces you to think about what you're doing and what your actions are actually requesting of the airplane.

 

Interesting stuff you pointed out earlier!

 

Hi Matthew!

 

It's true that a blue "FBW" bug on the speedtape of the real 777 would be helpful. By the way, they should have labeled it "TRS", as in "Trim Reference Airspeed", but whatever. Now, if Boeing didn't do it I would say it's for 2 reasons:

  1. It's not necessary. No need to add redundant information. What could happen if the plane was perfectly ok just the bug went crazy and indicated a speed that's not correct? Could a pilot potentially lose control of the plane because of that?
  2. Pilot's must not acquire bad flying habits. In this case a bad habit would be trimming based on a bug on an instrument. The correct procedure is trimming to control force annulment. A bug on the speedtape would be screaming to the pilots for them to trim based on the bug.

Regarding implementation of a TRS bug on a conventional plane like the 737 you mention, it wouldn't be possible because the 737 doesn't compensate for configuration changes. Say you're flying at 250 straight and level and in a clean configuration, your stab trim is of value A. Now lower the gear and do what you got to do to keep flying straight and level at 250 knots. Now your stab trim is in position B. Two different positions of the stabilizer for the same airspeed. Now you could say, let's make the TRS bug respond to configuration, acceleration, thrust, attitude and so on, but that would complicate things a lot.

 

Make sure you check out my thread discussing the 777's FBW, there's still some open discussions in there!

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Hi Matthew!

 

It's true that a blue "FBW" bug on the speedtape of the real 777 would be helpful. By the way, they should have labeled it "TRS", as in "Trim Reference Airspeed", but whatever. Now, if Boeing didn't do it I would say it's for 2 reasons:

 

  • It's not necessary. No need to add redundant information. What could happen if the plane was perfectly ok just the bug went crazy and indicated a speed that's not correct? Could a pilot potentially lose control of the plane because of that?
  • Pilot's must not acquire bad flying habits. In this case a bad habit would be trimming based on a bug on an instrument. The correct procedure is trimming to control force annulment. A bug on the speedtape would be screaming to the pilots for them to trim based on the bug.
Regarding implementation of a TRS bug on a conventional plane like the 737 you mention, it wouldn't be possible because the 737 doesn't compensate for configuration changes. Say you're flying at 250 straight and level and in a clean configuration, your stab trim is of value A. Now lower the gear and do what you got to do to keep flying straight and level at 250 knots. Now your stab trim is in position B. Two different positions of the stabilizer for the same airspeed. Now you could say, let's make the TRS bug respond to configuration, acceleration, thrust, attitude and so on, but that would complicate things a lot.

 

Make sure you check out my thread discussing the 777's FBW, there's still some open discussions in there!

oh yeah i agree with you on all counts lol. I was just saying that it woukd be fun to actually see where the plane woukd stabilize after it was trimmed. I guess i only said that becsuse we are trained to trim off control pressure yet a lot of pilots don't truly understand what's going on aerodynamically and the ref bug is a cool way to see in action.

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oh yeah i agree with you on all counts lol. I was just saying that it woukd be fun to actually see where the plane woukd stabilize after it was trimmed. I guess i only said that becsuse we are trained to trim off control pressure yet a lot of pilots don't truly understand what's going on aerodynamically and the ref bug is a cool way to see in action.

 

Oh yes I agree with you! It would definitely be of good help during training, just as an Angel of Attack indicator! (though unlike the TRS "bug", I believe that such an indicator should be legally required on all aircraft)

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oh yeah i agree with you on all counts lol. I was just saying that it woukd be fun to actually see where the plane woukd stabilize after it was trimmed. I guess i only said that becsuse we are trained to trim off control pressure yet a lot of pilots don't truly understand what's going on aerodynamically and the ref bug is a cool way to see in action.

Such a thing would only be possible in a complex computerised aircraft. To calculate the trimmed speed from aircraft configuration, thrust, trim position, etc is not trivial.

 

Pilots don't need to know what's going on aerodynamically to trim the aircraft. Having a trimmed speed indication might be cool from a simmers point of view but is pointless if you can feel the out of trim force. It's just more distracting clutter on the speed tape.

 

I don't find displaying the FBW bug helps me in the least. It's annoying more than anything because most of the time it overlays the speed bug. Instead of trimming by feel you set the FBW bug to current speed. You might just as well have an autotrim button.

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Such a thing would only be possible in a complex computerised aircraft. To calculate the trimmed speed from aircraft configuration, thrust, trim position, etc is not trivial.

 

Pilots don't need to know what's going on aerodynamically to trim the aircraft. Having a trimmed speed indication might be cool from a simmers point of view but is pointless if you can feel the out of trim force. It's just more distracting clutter on the speed tape.

 

I don't find displaying the FBW bug helps me in the least. It's annoying more than anything because most of the time it overlays the speed bug. Instead of trimming by feel you set the FBW bug to current speed. You might just as well have an autotrim button.

 

Hi Kevin, I think exactly the same way. In fact what you're saying here is exactly what I said but with different words (and expressed more briefly). Matt was quoting on my post which resembles your post that I am quoting now.

 

So we could enter an infinite loop with no exit, Matt could answer to you now in the same way that you quoted him and so on.

 

:dance:

 

(just a stupid observation, sorry for the offtopic)

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Hi Kevin, I think exactly the same way. In fact what you're saying here is exactly what I said but with different words (and expressed more briefly). Matt was quoting on my post which resembles your post that I am quoting now.

 

So we could enter an infinite loop with no exit, Matt could answer to you now in the same way that you quoted him and so on.

 

:dance:

 

(just a stupid observation, sorry for the offtopic)

Jaime,

 

There was some overlap with your post but with great respect I certainly wasn't just expressing what you said in different words. I clearly don't agree with you and Matthew that a trim ref speed bug would be useful in pilot training, for example. I also expressed my personal opinion of the 777 FBW bug. How Matthew replies to you (or me) is up to him. If the thread gets repetitive it's up to Kyle to sort it out.

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I clearly don't agree with you and Matthew that a trim ref speed bug would be useful in pilot training

 

But I believe nobody is saying the contrary really. Gotta read between the lines.

 

Yes okay, I said "it would be of good help during training", but what I meant was, it would be of help in understanding what trimming does to an aircraft in an aerodynamic sense.

 

Now the pilot must trim by feel, not by a bug. And he doesn't need this information at all. It just makes the concept more "visual" and understandable. I have an engineering mind and like to understand what's happening in an aerodynamic sense, but that might be just me really.

 

Pilot's don't need to know what Circulation is, or what the Kutta-Joukowski theorem says or anything like that, but it helps.

 

BTW: In German there's a great expression for this: Wir reden alle aneinander vorbei! (roughly saying the same but not understanding each other)

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For what it's worth, I don't see how you are both saying the same thing at all.

 

...and as long as I'm here, I don't see the point of a trim bug in any case where it's possible to feel the control forces.

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But I believe nobody is saying the contrary really.



Yes okay, I said "it would be of good help during training", but what I meant was, it would be of help in understanding what trimming does to an aircraft in an aerodynamic sense.

You agreed it would be useful, I didn't, so we are saying contrary things. I certainly don't agree it would help pilot's understand what timming is in an aerodynamic sense. All it would do is demonstrate that the aircraft is trimmed for a particular speed. That has more to do with stability and control than the aerodynamics of trim. To understand that you need to know about downwash, tailplane incidence and trim tabs amongst other things.

 

Now we really are getting off topic and into an infinite loop (your original concern). You say I said exactly what you did. I've pointed out the difference. You still insist there is none. I disagree. Ad infinitum. To cut this short, can I suggest you don't try and tell other people what they can and can't post? You don't own the posting rights to a particular point of view.


Edit, I see Kyle agrees with me that we aren't saying the same thing.

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I'm sorry Kevin, I won't continue going on with this and it wasn't my intention to upset you.

 

Also may I add I'm not native in English. This causes me some trouble sometimes. I believe if we were talking about these things in a bar over a beer we would all get along pretty well. The problems of written communication...

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