PMDG 777 FBW and weird Flight Controls behaviour?

[Alpha Floor 237]

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!

[ahsmatt7 1,199]

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.

[Alpha Floor 237]

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)

[kevinh 409]

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.

[Alpha Floor 237]

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.

 

 

(just a stupid observation, sorry for the offtopic)

[kevinh 409]

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.

 

 

(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.

[Alpha Floor 237]

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)

[scandinavian13 5,192]

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.

[kevinh 409]

 

 

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.

[Alpha Floor 237]

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...

[skelsey 765]

 

 

...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.

 

I may be missing something because I don't have the 777, and so I don't know in practice how it feels.

 

However, most of us are able to trim every other FSX aircraft without being able to feel the control forces (more strictly -- without having dynamic feel -- even with a bog-standard yoke or stick, we still feel out-of-trim control forces by sheer virtue of the fact that we have to apply a force to the controls in order to maintain the speed/flight path we desire) and without the assistance of a trim bug. Given that the fundamental principles of trimming still apply to the T7 (i.e. having to maintain a pull force? Run in some nose-up trim, and vice-versa) even if the mechanism by which the aeroplane achieves the demand is slightly different, I'm not really sure what the benefit of the bug is even in the T7, but I appreciate that some people do seem to find it useful.

[Alpha Floor 237]

I'm not really sure what the benefit of the bug is even in the T7

 

While PMDG could tell you the real reason, "my" take is, they did it to "teach" FS-pilots that they only need to trim for speed changes in an attempt to make the FBW-logic of the 777 clear.

 

But as you say, there's no real reason to have the function enabled. I have a jerky old controller and do enable it, like to have. Kevin for instance does not. The choice is yours...

[ahsmatt7 1,199]

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.

I think you missed ny point. I also, in my opinion, from countless hours of dual given, having a trim bug to make it easier to understand whats going on would be of some importance for a brand new pilot. A ton of pilots will never fully grasp what is going on when they trim the airplane. All they knkw is, conttol force. Thats fine!! Thats exactly what trim is used for. Im not aeguing that at all. However, when someone says that they trim for attitude or cant figure out why they are always out of trim, its obviois they truly dont understand whats going on aerodynamically.

 

 

At the end kf the day, i never ever said having a trim bug is a necessity or that pilot training is going downhill without it. Ihonestly feel that its not needed. However, I did say it woukd be cool and fun to see trimming in action when it comes to aerodynamic forces.

 

When I explain trim to someone, I use the trim. Ugh reference and they immediately understand it and can actually apply the concept much better than others who have only ever ever heard trim to relieve pressure.

 

I think trim bugs on a conventional airplane is useless and not needed. I do feel though it's a fun, cool and very easy way to teach what is going on when we trim an airplane to a brand new student.

[kevinh 409]

I think you missed ny point. I also, in my opinion, from countless hours of dual given, having a trim bug to make it easier to understand whats going on would be of some importance for a brand new pilot. A ton of pilots will never fully grasp what is going on when they trim the airplane. All they knkw is, conttol force. Thats fine!! Thats exactly what trim is used for. Im not aeguing that at all. However, when someone says that they trim for attitude or cant figure out why they are always out of trim, its obviois they truly dont understand whats going on aerodynamically.

 

 

At the end kf the day, i never ever said having a trim bug is a necessity or that pilot training is going downhill without it. Ihonestly feel that its not needed. However, I did say it woukd be cool and fun to see trimming in action when it comes to aerodynamic forces.

 

When I explain trim to someone, I use the trim. Ugh reference and they immediately understand it and can actually apply the concept much better than others who have only ever ever heard trim to relieve pressure.

 

I think trim bugs on a conventional airplane is useless and not needed. I do feel though it's a fun, cool and very easy way to teach what is going on when we trim an airplane to a brand new student.

I didn't miss your point, nor did I say any of the other things you imply. I just don't agree that a PMDG style trim speed bug can teach pilots about the aerodynamics of trim.

 

You say it would be a cool and fun thing but clearly only in theory since you also agree such a trim bug has no place in a conventional aeroplane. You could of course manually set a speed bug on the ASI when in trim and then demonstrate that if you return to that speed the aircraft returns to being in trim.

[icaruss 18]

I didn't miss your point, nor did I say any of the other things you imply. I just don't agree that a PMDG style trim speed bug can teach pilots about the aerodynamics of trim.

You say it would be a cool and fun thing but clearly only in theory since you also agree such a trim bug has no place in a conventional aeroplane. You could of course manually set a speed bug on the ASI when in trim and then demonstrate that if you return to that speed the aircraft returns to being in trim.

I'm not sure if I would like it or not. I'd have to see the implementation of this bug in the real aircraft. It sounds to me like a different application of the trim system, which might or not might work.