Announcement

Collapse
No announcement yet.

As sloppy as it gets without crashing...

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #61
    It isn't easy to quickly see a trim runaway, but then, they don't happen that often!

    There is a trim indicator on the Boeing so you can see the trim position, and you could see the trim moving on that - but you'd only look at it if you needed to.

    Both Airbus and Boeing have been happy to do away with the moving trim wheel, and have been for years.

    And wouldn't it help have an obvious feedback of trim movement to increase the awareness of for example deteriorating speed in VS, ALT or GS AP modes?
    Possibly. It would be interesting to see if there were more of these event types in aircraft without a moving stab wheel compared to those with, but it would seem a little overkill to have a moving stab wheel in an aircraft that you don't trim!

    Comment


    • #62
      Originally posted by MCM View Post
      Both Airbus and Boeing have been happy to do away with the moving trim wheel
      I am not, for what it's worth (i.e. e little less than nothing)

      it would seem a little overkill to have a moving stab wheel in an aircraft that you don't trim!
      You mean the Airbus? Because AFAIK you still trim the 777 and the 787.

      --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
      --- Defend what you say with arguments, not by imposing your credentials ---

      Comment


      • #63
        You do trim the 777 and 787, although it is not in the same way that you trim a conventional aircraft like the 747 or 767.

        The trim switches set a trim speed, and the flight control computers do their own thing with the stab to keep themselves happy at that speed. You aren't directly controlling the stab trim. So I guess in one sense you are trimming, but in another, you are not.

        My understanding is that if you had a stab trim wheel on a 777, in manual flight you would find it moving even without you touching the trim switches. I'd find that a bit disconcerting I think!

        Comment


        • #64
          Originally posted by MCM View Post
          Possibly. It would be interesting to see if there were more of these event types in aircraft without a moving stab wheel compared to those with, but it would seem a little overkill to have a moving stab wheel in an aircraft that you don't trim!
          Well, the A320/330/340 has a trim wheel mainly for ground takeoff setting and as a mechanical and direct law backup in flight. That's your primary SA for trim status I'm told, the second being the numerical indication on the SD FLT/CTRL page.

          The A380 and A350 have a pitch trim indication on the PDF in direct law. I have no idea what that looks like but perhaps it is the same graphical indication that you see on the ground for takeoff setting.

          I read that the A350 has a hat switch but I cannot find any confirmation on that. Perhaps it is an option.

          Comment


          • #65
            Originally posted by MCM View Post
            You do trim the 777 and 787, although it is not in the same way that you trim a conventional aircraft like the 747 or 767.

            The trim switches set a trim speed, and the flight control computers do their own thing with the stab to keep themselves happy at that speed. You aren't directly controlling the stab trim. So I guess in one sense you are trimming, but in another, you are not.
            Right, but in a sense, it's quite similar to the conventional planes.
            While you don't "set 189kts with the trim" you do "trim for 180kts".
            In fact, in a conventional plane you trim for a given AoA, but as long as there are no weight, CG, configuration or big thrust changes (where the thrust line passes far from the CG) that's equivalent to trim for a speed.

            The 777 and 787, in normal law, will compensate for these changes so as to keep the "trim speed" constant, so for example you don't have to re-trim when you extend the flaps or lower the gear.

            My understanding is that if you had a stab trim wheel on a 777, in manual flight you would find it moving even without you touching the trim switches. I'd find that a bit disconcerting I think!
            That fits my understandig too. But I don't find it so disconcerting.

            For example, you are established in ILS and extend the flaps from 15 to 25. The trim will move to account for the change in config and keep the same trim speed.

            Now, am I talking of the 777 in manual flight, the 737 in AP, or the 737 in manual flight (where the pilot is trimming himself)?

            I would see this as pretty consistent.

            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
            --- Defend what you say with arguments, not by imposing your credentials ---

            Comment


            • #66
              Thats a good point Evan, I hadn't considered if the ones in the 320/330/340 move around much. I guess they do! Its probably a little different in an Airbus where you are expecting the aircraft to be moving the trim by itself (as you are not doing it), compared to a Boeing where you are both manually trimming and having the aircraft trim itself in manual flight.

              Gabriel, yes, it is similar to conventional aircraft, but it isn't the same. The point being that it will move independently from your manual trimming. I've never flown in that cockpit configuration so I don't know. Just like anything, I imagine you would get used to it!

              I've never flown an aircraft with a big spinning trim wheel - just with trim switches and a trim position display, so I probably don't know any different - but I've never heard a 737 pilot move to the 767 or 744 and complain about the lack of trim wheels.

              In the brave new world we have a number of instances of being removed from directly knowing what a flight control is doing - just something we have to get used to, and to be aware of.

              Comment


              • #67
                Originally posted by MCM View Post
                I've never flown in that cockpit configuration so I don't know. Just like anything, I imagine you would get used to it!
                You were born in a 767 or what?

                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                --- Defend what you say with arguments, not by imposing your credentials ---

                Comment


                • #68
                  Originally posted by MCM View Post
                  In the brave new world we have a number of instances of being removed from directly knowing what a flight control is doing - just something we have to get used to, and to be aware of.
                  I think the pitch trim wheel on the A320/330/340 was a concession to those uncomfortable with the new technology who demanded both a means of flying mechanically and an historically intuitive means of determining pitch trim status. It is quite odd there, a bit of antiquity in the cockpit of the future, but it serves both purposes and was possibly instrumental in winning the approval of concerned regulators.

                  The wheel is marked in alternating black and white stripes, which makes it more visually obvious when it is in motion. Getting back to what we were discussing (the potential danger of a silent, automated pitch trim that suddenly is lost and requires manual adjustment in very stressful abnormal attitude scenarios) the wheel is right there in plain view next to the thrust levers and, in a tight spot where commanding forward stick is not giving you what you expect, you don't have to read the settings, you can just quickly move the wheel into the green band until you get out of that mess and then trim it by the scale.

                  Airbus, in evolving its cockpit-commonality principal, finally dropped the mechanical pitch trim when it introduced the EHA/EBHA solution for the A380/350 that relies entirely on electrical power if hydraulics are lost. We have arrived at the point in technological evolution where regulators can be convinced that a total loss of hydraulics and all electrical power is virtually impossible in flight. That took a lot of adjustment in our faith in technology. But gone is the large and obvious mechanical wheel to let you know 'what it's doing now', replaced by an indication (in rare cases of direct law reversion) on the PFD.

                  I've noticed that the later 767 and 757's dropped the trim levers and moved to the pedestal switches. The 747 dropped the levers for the switches after the -300. Strange that the 777 brought them back (maybe for the same fear-of-FBW issue). It seems even the levers are considered vintage these days. Only the 737 continues to use the wheels. I wonder is the 737-Max will finally embrace the future...

                  Comment


                  • #69
                    Originally posted by MCM View Post

                    My understanding is that if you had a stab trim wheel on a 777, in manual flight you would find it moving even without you touching the trim switches. I'd find that a bit disconcerting I think!
                    That's what happens in the 'Bus, and I don't find it disconcerting at all.

                    Comment


                    • #70
                      Originally posted by ATLcrew View Post
                      That's what happens in the 'Bus, and I don't find it disconcerting at all.
                      I guess a yoke or throttles moving on their own in response to a control system could be disconcerting too...

                      ...or not.
                      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                      Comment


                      • #71
                        Originally posted by MCM View Post
                        Airbus Golden Rule


                        How many accidents/incidents have we had now where the 'Dual Input' alert is screaming away in the background and no-one notices/acknowledges it? Time for Airbus to go away and have another serious think about the issue, because it keeps cropping up time and time again. Remember - pilot overload = loss of hearing.
                        It must be simple enough to program force feedback into the side sticks when a conflicting input is made. Which would be a 100% clear indication.

                        Comment


                        • #72
                          Originally posted by Quench View Post
                          It must be simple enough to program force feedback into the side sticks when a conflicting input is made. Which would be a 100% clear indication.
                          It's not just a matter of program but also of hardware. Current Airbus' sidstick are simply spring-loaded joystick with no means of generating any feedback beyond the displacement itself and the passive force proportional to it due to the spring. In other words, the current Airbus' sidesticks are physically incapable way for the plane to actively tell the pilot anything at all. If you move the sidestick one inch back from its neutral point you will have the same displacement (of course: one inch) and the same force regardless of whether you did that with the plane happily flying in normal cruise, with the plane overspeeding, with the plane stalling, with the plane fully powered off in the hangar, or while playing with a spare sidestick in the maintenance warehouse.

                          --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                          --- Defend what you say with arguments, not by imposing your credentials ---

                          Comment


                          • #73
                            Originally posted by Gabriel View Post
                            It's not just a matter of program but also of hardware. Current Airbus' sidstick are simply spring-loaded joystick with no means of generating any feedback beyond the displacement itself and the passive force proportional to it due to the spring.
                            Not exactly accurate: the sidesticks do create a breakout force resistance in autopilot mode. Such technology exists to create force-feedback in a hand-controller. That's not the problem. The problem is that this would sort of defeat the point of using them in the first place. If you want pilots to deal with trim feedback manually you should stick with the yoke. If you want the aircraft to relieve you of that task you use a sidestick. With a FBW yoke, you are given the illusion of flying the plane traditionally. With a sidestick you are telling the plane where you want it to go and letting it fly 'traditionally' (except in direct law, where you also have to trim and be very alert about your basic parameters).

                            On the issue of dual inputs, as I said before, you could use electromagnets to 'lock' the non-priority-side stick or use robotics to link them but then you are adding complexity and opportunity for failure into the means of control. I think it is much safer and easier to fix the pilot screening process.

                            Comment


                            • #74
                              Originally posted by Evan View Post
                              It seems even the levers are considered vintage these days. Only the 737 continues to use the wheels.
                              FYI, in the other universe, the new Tupolev 204SM retains the trim wheels. The sidestick Sukkoi Superjet has only the pedestal switches.

                              Comment


                              • #75
                                Originally posted by Gabriel View Post
                                I am not, for what it's worth (i.e. e little less than nothing)



                                You mean the Airbus? Because AFAIK you still trim the 777 and the 787.
                                For what this is worth (probably f*ck all) whenever trimming in flight simulator or wondering about where the trim is set, I always look at the TRIM INDICATOR.

                                I imagine it's not that difficult in the aforementioned aircraft. The wheel only tells you it's moving, not where it's set.

                                Comment

                                Working...
                                X