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Any Chance tp fix 747 steering bug?

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    Any Chance tp fix 747 steering bug?

    It is documented that is many cases when steering > 20 KTS on the ground (with idle power), the 747 will quickly accelerate to 80 kts violently causing major controllability issues. This comes into play after landing when trying to exit a high speed taxiway at even 21 KTS. Iamnot sure of the max taxi speed of the 747 on high speed exits - but any chance PMDG can fix this bug?
    Paul Gugliotta

    #2
    Paul, I've never had a problem taking a high speed turn off at 40 kts. GS. You didn't mention your configuration, e.g., FD off, A/T disconnected, etc. What is on the FMA when this happens?
    Dan Downs KCRP
    i7-10700K 32GB 3600MHz 2080Ti

    Comment


      #3
      Paul, I'm assuming you're using a tiller to make that turn because I only ever recall people having that issue when they tried to use the tiller. Somebody said, and hopefully Brian can chime in here, that if you're trying to make a high-speed exit, you can use the rudder pedals to do it since the nose gear turns up to 7 degrees with the rudder pedals.
      Captain Kevin

      Kevin Yang

      Comment


      • DDowns
        DDowns commented
        Editing a comment
        Always use rudder pedal steering for high speed exists. The tiller is not a good choice above 18 kts for several reasons, including P3D changes steering laws above that speed. RSR talked about this when we first introduced the tiller steering options.

      • thibodba57
        thibodba57 commented
        Editing a comment
        Using the pedals works well enough. But it requires a lot of rudder input to make a high-speed exit. But I would argue in the 74 you really don't want to be exitting at to high a speed. That's a lot of energy to dissipate due to weight. By the time your making the initial turn I find you are usually going slow enough and it's shallow enough an angle you can aid it with a tiny bit of pressure on the tiller if need be. As I pointed out awhile back. As much throw as your have in the tiller (150-160 degrees for 70 degrees of travel). It's still pretty sensitive.

      #4
      Paul,

      Just to be on the same page.
      Which 747 airplane model exactly, I'm wondering if this was a saved situation which it might have possibly a corrupt file (during saving). When you mention that is documented can you direct us to those specific situations, please? That will help a lot in narrowing down the issue. On my end, I can't duplicate your issue, either way, to be noted that I don't dismiss what you are experiencing.

      In the real world, we can exit the rwy on high-speed exit taxiways up to 60 KTS, but this is not the issue here.

      You mentioned power to idle and then quickly accelerating to 80 Kts, what happens after 80, is still at idle?

      It has nothing to do with FD off, A/T disconnected or any FMA in this case especially when the engines are verified and conformed at idle.

      Yes, if you have a/t arm switch on and by accident, you hit TOGA that would be something else. That happened many times and many airlines have a/t arm switch to arm position before t.o. and not during taxi and they turn it off after landing checklist.

      Anyhow, help us with more details, please.
      Vlad Tepes

      Comment


        #5
        The B744/-8 nosewheel steering tiller should be used to steer the aircraft on the ground at normal taxi speeds. Turning off a runway onto a high speed taxiway is usually easily accomplished using the rudder pedals only until the G/S is < approx 20 Kts.

        Without getting into too much technical detail, PMDG have modelled the aircraft’s Rudder Fine Steering behaviour as well as Body Gear Steering. Paul’s issue might therefore be caused by a combination of incorrect use and/or setup of his nosewheel steering and the action of the Body Gear Steering kicking in.
        Michael Codd

        Comment


          #6
          Well. I know Kevin has seen this also. It happens on P3dV5.2 any PMDG 747 when taxing >20 Kts and using the tiller. Even if I am at 21KTS and attempt to use the tiller for a turn, the plane accelerates at a rapid pace - even though at idle. Using the rudders I can turn > 20 kts. I simply know NOT to use the tiller greater than 20 Kts, but there is no mercy at 1 kt over the magic 20 kt limit. Definitely a BUG as a plane can't go from 20 kts to 80 kts in 1 sec at idle power!!!

          Paul Gugliotta

          Comment


          • DDowns
            DDowns commented
            Editing a comment
            As I wrote earlier, the tiller is only good below 18 kts. P3D changes ground steering behavior above that and there is nothing PMDG can do about it. This was acknowledged last year when tiller steering was released in an update.

          #7
          Excellent points, but the issue to concentrate on is just why is " the 747 will quickly accelerate to 80 kts violently" in this case?
          Let's try to figure out what is triggering that issue.
          If he doesn't provide exactly at what speed is noticing the problem, specific aircraft, and if it was a default PMDG saved position or possibly a personal saved situation that might be corrupted we can't come to a sound explanation.
          After we get the info some of us might try to duplicate it on their PC and eventually exchange information.
          Vlad Tepes

          Comment


            #8
            Originally posted by Vlad Tepes View Post
            Excellent points, but the issue to concentrate on is just why is " the 747 will quickly accelerate to 80 kts violently" in this case?
            Let's try to figure out what is triggering that issue.
            If he doesn't provide exactly at what speed is noticing the problem, specific aircraft, and if it was a default PMDG saved position or possibly a personal saved situation that might be corrupted we can't come to a sound explanation.
            After we get the info some of us might try to duplicate it on their PC and eventually exchange information.
            There is a known bug in P3D, or at least there used to be, where the way lateral acceleration was modeled had an odd quirk that under certain conditions the aircraft would take off like a frisbee. I really don't know if this is related to what Paul experienced but it is odd that the aircraft accelerated to 80 kts and not any faster without an input other than tiller steering above 18 kts. This is not anything I've ever experienced in all the testing hours I have in beta or in use since then. The more I think about it, which hasn't been very much, he apparently observed an acceleration straight ahead, no lateral acceleration. So back to my original question: what's on the FMA?
            Dan Downs KCRP
            i7-10700K 32GB 3600MHz 2080Ti

            Comment


              #9
              Perhaps it might be a bug with P3D, I don't know and I never experienced that issue.
              FMA is no concern in this case based on his statement, the airplane is already on the ground with idle power after landing while exiting the rwy not accelerating straight ahead.
              "This comes into play after landing when trying to exit a high-speed taxiway".
              Something else is going on here and unfortunately, without any detailed information, we all just speculate.
              Vlad Tepes

              Comment


                #10
                Vlad, hopefully this clears up any confusion.

                https://clips.twitch.tv/AverageProductiveJaguarSSSsss
                https://clips.twitch.tv/RelentlessAm...irdSuperVinlin

                Also seen this with the 777.

                https://clips.twitch.tv/StrangeResou...cpqRS8G3B9tDfN
                https://clips.twitch.tv/CleanInnocen...VVmWtj-GiK48MH
                Captain Kevin

                Kevin Yang

                Comment


                #11
                @Captain Kevin,

                I noticed from all the videos that it looks like there is some kind of a spike of a max brake application, the airplane initially neals down followed by an immediate turn (either direction), and then that spike goes away. Like a momentary brake lock. Is it my impression?
                Vlad Tepes

                Comment


                  #12
                  All I am saying is Kevin and me are one of your most experienced pilots with high end systems and see the same bug. We do know how to work around it, but sometimes it causes a crash. No physics can explain sudden acceleration while turning at 21 kts. Is there a setting we have wrong? But the steering works perfectly when. Not using the tiller > 20 kts. No I have Fsuipc but don’t use it currently as all my peripherals work great.

                  I use a joystick as a tiller. I ordered the cat3design tiller. I doubt it would make a difference, but I’ll let you all know how the tiller works out. It is coming from Australia and probably sit in a LA port for months
                  Last edited by Paulyg123; 13Jan2022, 03:43.
                  Paul Gugliotta

                  Comment


                    #13
                    Originally posted by Paulyg123 View Post
                    All I am saying is Kevin and me are one of your most experienced pilots with high end systems and see the same bug. We do know how to work around it, but sometimes it causes a crash. No physics can explain sudden acceleration while turning at 21 kts. Is there a setting we have wrong? But the steering works perfectly when. Not using the tiller > 20 kts. No I have Fsuipc but don’t use it currently as all my peripherals work great.

                    I use a joystick as a tiller. I ordered the cat3design tiller. I doubt it would make a difference, but I’ll let you all know how the tiller works out. It is coming from Australia and probably sit in a LA port for months
                    Paul,

                    Dan answer here "https://forum.pmdg.com/forum/main-forum/general-discussion-news-and-announcements/pmdg-747-queen-of-the-skies-ii-forum/157509-any-chance-tp-fix-747-steering-bug?p=157537#post157537" is the exact answer of what you see.
                    Chris Makris (Olympic260)
                    PMDG Technical Support
                    http://www.pmdg.com

                    Comment


                      #14
                      Originally posted by cmakris View Post

                      Paul,

                      Dan answer here "https://forum.pmdg.com/forum/main-forum/general-discussion-news-and-announcements/pmdg-747-queen-of-the-skies-ii-forum/157509-any-chance-tp-fix-747-steering-bug?p=157537#post157537" is the exact answer of what you see.
                      I never saw this behaviour with the original ground handling in either FSX or P3D. I've only ever experienced it with the new ground handling. It may well be a P3D bug but the effect happens more readily with the new model. It could be that the limit is more easily exceeded. It feels to me that as soon as the tyre slip angle exceeds the skid limit you start to get a large and increasing forward ground reaction which accelerates you rapidly to flying speed. It's as if the sign of the friction force is inverted or some additional friction force in the model is suddenly removed leaving a net forward force.

                      The acceleration can be triggered in the low speed range where the PMDG model is active. Of course you should never cause a skid at low speed but its easy to misjudge your ground speed. Such a skid should not trigger rapid acceleration like this.

                      Comment


                        #15
                        Originally posted by Vlad Tepes View Post
                        I noticed from all the videos that it looks like there is some kind of a spike of a max brake application, the airplane initially neals down followed by an immediate turn (either direction), and then that spike goes away. Like a momentary brake lock. Is it my impression?
                        Negative, that brake application you're seeing is me slamming down the brakes when I realize I need to slow down a hell of a lot more to attempt to make that turn. Whether that should actually be done is an entirely different story (and probably shouldn't be). As for FSUIPC, I do use FSUIPC for my throttle quadrant. The rest of my flight controls are mapped via P3D. Part of the problem is I'm using the Logitech Extreme 3D Pro as the tiller, and the rudder axis doesn't have that much travel to begin with, so it doesn't take much to oversteer it.
                        Originally posted by Paulyg123 View Post
                        I use a joystick as a tiller. I ordered the cat3design tiller. I doubt it would make a difference, but I’ll let you all know how the tiller works out. It is coming from Australia and probably sit in a LA port for months
                        Paul, I don't think you'll be waiting that long, as it would be shipped via air to Los Angeles. I ordered it just a few hours after it became available, it's already at my house as of two days ago. That's considering the original estimate was for the 17th. I'll try it out once I get home next week and see what happens. Using the Logitech Extreme 3D Pro isn't necessarily ideal given the limited travel it has. With the new tiller, I think trying to make small turns should be easier.
                        Captain Kevin

                        Kevin Yang

                        Comment


                          #16
                          Kevin:
                          Do you ever do pick ups from LA port? It must be a zoo over there, but it must be a great time to be a trucker now. If you are there, kick a few containers for me and find my tiller? I may need a hint or 2 on how to set then up properly.
                          Paul Gugliotta

                          Comment


                            #17
                            Originally posted by Paulyg123 View Post
                            Do you ever do pick ups from LA port? It must be a zoo over there, but it must be a great time to be a trucker now. If you are there, kick a few containers for me and find my tiller? I may need a hint or 2 on how to set then up properly.
                            We only pull reefers. We don't do containers. In any event, I'm not going to be in California anytime soon anyway since I'm scheduled to be home next week. Once I get home, I'll be able to set up the tiller.
                            Captain Kevin

                            Kevin Yang

                            Comment


                              #18
                              Originally posted by Paulyg123 View Post
                              I use a joystick as a tiller. I ordered the cat3design tiller. I doubt it would make a difference, but I’ll let you all know how the tiller works out. It is coming from Australia and probably sit in a LA port for months
                              Paul, just tested the new tiller out, and as I suspected, it made a significant difference. Yes, the issue with the plane gaining speed is still there, but from the testing I have done, it only starts to do this when I have the tiller cranked more than 45 degrees over. And if you're going that fast, you really shouldn't need to crank the tiller over that much in the first place, so it's definitely a significant improvement. With the Logitech Extreme 3D Pro, the rudder axis only has maybe 15 degrees of travel in each direction, so it wouldn't take much to turn it enough to where the plane would lose it. With the new tiller having almost 90 degrees of travel in each direction, 45 degrees is about halfway, so you have a lot more room to work with before the plane loses it.

                              I'll add the disclaimer that I'm not scheduled to be home right now.
                              Captain Kevin

                              Kevin Yang

                              Comment

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