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Aircraft spinning with full tiller

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    Aircraft spinning with full tiller

    Hi everyone!

    Since the last NGXu update I've done very few flights, but today I've noticed something that has never happened before.

    After landing, I tried to vacate at a high-speed exit, while going at about 40kts. Since I reacted slightly too late, I gave full left tiller, and the aircraft initiated a turn. But a couple of seconds later, it started spinning around on itself and it stopped after one complete revolution. I thought it was because of the "high" speed, but during the taxi in, I had the same while applying full tiller at 25kts.

    I was using a default panel state, and an independent joystick/throttle axis for the tiller. I do have FSUIPC, but being the freeware version, no flight control or axis is linked to it.

    Has anyone experienced this, especially after the last update?
    Giovanni D. Tarar
    FAA CPL+IR Single & Multiengine Land
    I love flying when I'm in a bad mood

    #2
    Just to clarify, do you mean something like this?

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

    Kevin Yang

    Comment


      #3
      Something very similar. The only difference is that in my case the spinning was progressive. So the aircraft started turning from the tiller input, and the turn got progressively faster and faster at the point of spinning on itself. All in a matter of 5/10 seconds.
      Giovanni D. Tarar
      FAA CPL+IR Single & Multiengine Land
      I love flying when I'm in a bad mood

      Comment


        #4
        From what I was told here, you don't want to be using the tiller at speeds higher than 20 knots. If you're taking really tight turns, you don't want to be going more than 10 knots. I still have a bit of getting used to with this one.
        Captain Kevin

        Kevin Yang

        Comment


          #5
          Oh I gotta teach myself how to slow down in turns as well! 😁

          But since it was the first time it happened, and it was shortly after the update I guessed it could be something within the update. I'll try to use less tiller (no more than a half) if between 10 and 20kts.
          I've also done another flight recently and I was extra careful not to use the tiller above 20kts, and this time full tiller didn't spin the aircraft. I assume it was the high speed.

          Another thing is probably worth mentioning, is that the tiller mode I'm using is Raw Input, instead of Rate-Based. This could make the nosewheel deflect fully even at higher speed, hence spinning the aircraft. My knowledge here is pretty limited, but I think that if set to Rate-Based even a full tiller won't deflect the nosewheel at higher-than-20kts speeds.
          Giovanni D. Tarar
          FAA CPL+IR Single & Multiengine Land
          I love flying when I'm in a bad mood

          Comment


            #6
            The clips I posted above was the first time I even operated the 747 with the new ground handling, so it definitely takes time to get used to.
            Captain Kevin

            Kevin Yang

            Comment


            • CBT_Phoenix
              CBT_Phoenix commented
              Editing a comment
              I absolutely agree. Especially cause I'm used to steering an aircraft with pedals, and I don't have any rudder pedals for my setup, so this makes it even harder to get used to it.

            #7
            Looks like an oversteer....
            Well, I've got race driving license but that only help a little more understand what wheels will do at and beyond it's limit...
            And for a 70 ton tricycle....I don't think I know well what well happen outside it's envelope... And I don't think it could be well simulated with P3D....
            ZHU Hai
            B737 Ground instructor

            Comment


              #8
              Originally posted by AngelofAttack View Post
              Looks like an oversteer....
              Well, I've got race driving license but that only help a little more understand what wheels will do at and beyond it's limit...
              And for a 70 ton tricycle....I don't think I know well what well happen outside it's envelope... And I don't think it could be well simulated with P3D....
              Agree, physics is definitely not well simulated in P3D, so I assume that going full tiller at high ground speeds would have some arguable results. It won't spin the aircraft for sure, but probably it'll make it tip on his wing...
              It just looked weird how immediate was that even at 25kts. The aircraft literally accelerated on the turn so fast that it looked almost like something was pushing him to spin. I guess it's just P3D doing weird stuff when he doesn't know how to properly simulate the forces acting on the aircraft.
              Giovanni D. Tarar
              FAA CPL+IR Single & Multiengine Land
              I love flying when I'm in a bad mood

              Comment


                #9
                As the nose wheel only load about 10% of all weight, I think a high input at high speed, beyond the rubber's maximum slip angle, will make a understeer and the aircraft will barely turn, it's like a wing stall in some sence.
                The only way I could image an airliner going into oversteer is when braking hard to near or into the skid of main wheel, thus the mainwheel could not provide side grip to keep it in line, and more percent of load is transfered to the nose thus it can turn harder than ever.
                ZHU Hai
                B737 Ground instructor

                Comment


                  #10
                  Originally posted by Captain Kevin View Post
                  From what I was told here, you don't want to be using the tiller at speeds higher than 20 knots. If you're taking really tight turns, you don't want to be going more than 10 knots. I still have a bit of getting used to with this one.
                  wrong. Many of my pilot friends who fly for an american based airline uses tiller from GS 59 and below. GS 60+ will break it. Ive also had this happen, and or the speed accelerates without thrust added and will go up to 250KTS. the only time i dont have this is when im below GS10 and or differential braking in turns above GS 10. definitely something rsrandazzo will have to look into the coding about.
                  Alex Kulak
                  PMDG Studier and flyer

                  Comment


                    #11
                    Originally posted by Swaluver88 View Post

                    wrong. Many of my pilot friends who fly for an american based airline uses tiller from GS 59 and below. GS 60+ will break it. Ive also had this happen, and or the speed accelerates without thrust added and will go up to 250KTS. the only time i dont have this is when im below GS10 and or differential braking in turns above GS 10. definitely something rsrandazzo will have to look into the coding about.
                    Well that's something new. Between GS 25 and 59 do you know if full tiller is being used, or can be used? When below 25kts no issue is encountered, but above that speed I've noticed that a full tiller input will make the aircraft spin on itself.

                    Also, as Zhu said above, the result of a full tiller at high speed will make the nosewheel understeer, hence not providing any turning force.
                    Giovanni D. Tarar
                    FAA CPL+IR Single & Multiengine Land
                    I love flying when I'm in a bad mood

                    Comment


                    • Swaluver88
                      Swaluver88 commented
                      Editing a comment
                      I'll ask them but considering theyll make 180 degree turns onto a taxiway from Rwy. Yeah it's like the code is reading the opposite or disagreeing and triggering an opposite effect

                    #12
                    Originally posted by Swaluver88 View Post

                    wrong. Many of my pilot friends who fly for an american based airline uses tiller from GS 59 and below. GS 60+ will break it. Ive also had this happen, and or the speed accelerates without thrust added and will go up to 250KTS. the only time i dont have this is when im below GS10 and or differential braking in turns above GS 10. definitely something rsrandazzo will have to look into the coding about.
                    RSR has explained that when lateral g-forces exceed a specific limit, I think it was 0.62 g, then you have entered the realm of unrealistic control input and the PMDG code simply hands the ground steering over to the simulator default code. Imagine the lateral g forces at a quick 90 deg turn, say 25 kts results in 0.80 g which means your 200 lb body is being pressed against the arm rests by 160 lb lateral force. You don't want to try.

                    He has also discussed a feature within P3D that he has complained to LM about but it remains. Where excessive manhandling of the nose gear will introduce a frisbee effect and send the aircraft spinning. PMDG has attempted to mitigate this but only up to a point.

                    At GS below 45 kts one might take the high speed turnoff but you should be using the pedals until below 25 kts. I keep my 90 deg turns below 15 kt in the 737 and 10 kt in the 747.
                    Dan Downs KCRP
                    i7-10700K 32GB 3600MHz 3080Ti

                    Comment


                      #13
                      Originally posted by DDowns View Post

                      RSR has explained that when lateral g-forces exceed a specific limit, I think it was 0.62 g, then you have entered the realm of unrealistic control input and the PMDG code simply hands the ground steering over to the simulator default code. Imagine the lateral g forces at a quick 90 deg turn, say 25 kts results in 0.80 g which means your 200 lb body is being pressed against the arm rests by 160 lb lateral force. You don't want to try.

                      He has also discussed a feature within P3D that he has complained to LM about but it remains. Where excessive manhandling of the nose gear will introduce a frisbee effect and send the aircraft spinning. PMDG has attempted to mitigate this but only up to a point.

                      At GS below 45 kts one might take the high speed turnoff but you should be using the pedals until below 25 kts. I keep my 90 deg turns below 15 kt in the 737 and 10 kt in the 747.
                      Still at 15kts I get the spinning effect. Let's see if lockheed fixes it in 5.1
                      Alex Kulak
                      PMDG Studier and flyer

                      Comment


                        #14
                        Originally posted by Swaluver88 View Post

                        Still at 15kts I get the spinning effect. Let's see if lockheed fixes it in 5.1
                        Full tiller at 15 kts??? That is unrealistic. Full tiller might be use to make a slow sharp turn out of a hard stand but you're not going to apply full tiller above maybe 5 kts. Those 180's on a runway are not done at anything above 10 kts.
                        Dan Downs KCRP
                        i7-10700K 32GB 3600MHz 3080Ti

                        Comment


                          #15
                          Originally posted by DDowns View Post

                          Full tiller at 15 kts??? That is unrealistic. Full tiller might be use to make a slow sharp turn out of a hard stand but you're not going to apply full tiller above maybe 5 kts. Those 180's on a runway are not done at anything above 10 kts.
                          Not full tiller I'm talking about what rsr was venting about to them
                          Alex Kulak
                          PMDG Studier and flyer

                          Comment


                          • DDowns
                            DDowns commented
                            Editing a comment
                            Ah yes.... sorry I misunderstood. Just keep those lateral g forces reasonable and this problem will not happen.

                          #16
                          Originally posted by Swaluver88 View Post
                          wrong. Many of my pilot friends who fly for an american based airline uses tiller from GS 59 and below. GS 60+ will break it. Ive also had this happen, and or the speed accelerates without thrust added and will go up to 250KTS. the only time i dont have this is when im below GS10 and or differential braking in turns above GS 10. definitely something rsrandazzo will have to look into the coding about.
                          I'm just telling you what was relayed to me, so if that's wrong, you'll have to take it up with them.

                          https://forum.pmdg.com/forum/main-fo...4552#post64552
                          https://forum.pmdg.com/forum/main-fo...1395#post71395
                          Captain Kevin

                          Kevin Yang

                          Comment


                            #17
                            Unfortunately this is still a Sim so there are no proprioceptive cues which in real life will tell you right away that you’re going to fast. Lateral loads mean nothing in the Sim as a user, probably needed when writing the code however.

                            As stated above for now until is fixed and as a good technique, 90 deg turns less than 10 kt and straightaways not faster than 30 kt should work ok.
                            Rafael Cordoves

                            Comment


                              #18
                              Originally posted by Swaluver88 View Post
                              wrong. Many of my pilot friends who fly for an american based airline uses tiller from GS 59 and below. GS 60+ will break it. Ive also had this happen, and or the speed accelerates without thrust added and will go up to 250KTS. the only time i dont have this is when im below GS10 and or differential braking in turns above GS 10. definitely something rsrandazzo will have to look into the coding about.
                              Who's driving these aeroplanes? Lewis Hamilton? 😁

                              I can't speak to the 737, but I would be quite surprised if Boeing's guidance was much different to the B747:

                              Originally posted by FCTM
                              ...at speeds greater than 20 knots use caution when using the nose wheel steering tiller to avoid overcontrolling the nose wheels. When approaching a turn, speed should be slowed to an appropriate speed for conditions. On a dry surface, for turn angles greater than those typically required for high speed runway turnoffs, use approximately 10 knots.
                              I guess you might be able to get away with using the tiller at higher speeds if you are exceptionally careful and smooth and use minimal input, and I can only assume that is what your friends are referring when they refer to using the tiller at such high speeds. But if you start yanking it about sharply then you are going to at best injure somebody in the back and at worst break something. Certainly anything like full tiller at 40 or even 25 kt is well beyond the realms of what is sensible. One only need imagine what sort of ride/level of control one would expect in your normal road car if you were to suddenly crank in maximum steering whilst travelling at 30 to 50 mph to extrapolate what sort of response would be likely in a 130ft-long, 70 tonne airliner on stilts.

                              Aeroplanes are not well designed for ground movement and they are typically ungainly and quite fragile in this environment so need to be treated with care -- not to mention the fact that 150ft behind you the pax/cabin crew in the aft galley etc are at significant risk from violent manoeuvring which will be magnified at greater distances from the centre of rotation and the myriad of hazards that may be encountered on the ground! Smooth and progressive input is required -- smoothly and slowly wind on tiller pressure, hold it and then smoothly unwind it back to neutral as you come out of the turn (don't just release it and let it snap back which is what I see a lot of simmers do!). The ground speed readout is very useful as it can be difficult to judge speed in the aircraft and Boeing recommend referring to it when taxiing.

                              As I mentioned in the B747 thread, I am not suggesting that the spinning, acceleration etc from the PMDG model when putting in large deflections at high speeds is accurate but it's only really an issue if you start trying to drive a 737 around like it's an F1 car...
                              Simon Kelsey

                              Comment


                                #19
                                Originally posted by Icaruss View Post
                                Unfortunately this is still a Sim so there are no proprioceptive cues which in real life will tell you right away that you’re going to fast. Lateral loads mean nothing in the Sim as a user, probably needed when writing the code however.

                                As stated above for now until is fixed and as a good technique, 90 deg turns less than 10 kt and straightaways not faster than 30 kt should work ok.
                                Rafael, there is nothing unfortunate about it because it can be just as difficult to judge your taxi speed from a real flight deck; especially if it is in an aircraft as big and as high off the ground as a B744/-8 or an A380. Boeing were so concerned about this issue when they were starting to develop the original B747 that they constructed a cockpit on top of a vehicle so that the test pilots could get used to taxying around at that height.

                                Perhaps we should all give PMDG a lot of credit for striving to replicate their aircraft's taxying behaviour so that it matches as closely as possible that of the real aircraft? Boeing and Honeywell, as well as PMDG, all provide a G/S readout on their Nav displays to show the pilots what their taxy speed is and, just as happens in a full-sized aircraft or simulator, we need to use it and adhere to the recommended taxy speeds. Provided you always refer to your G/S readout when approaching a turn and don't enter it taxying too fast then you will be less likey to encounter any serious problems when using P3D. But if anyone expects a PC simulated aircraft to behave itself when the tiller is being used at taxy speeds approaching 60 Kts G/S (as Alex alleges his pilot friends do) then they are living in cloud cuckoo land. It should never be necessary to use the tiller at those high taxy speeds in any real passenger aircraft that I know of and it is likely to invite trouble; even if the pilot is called Lewis Hamilton or is used to flying military jets! It is certainly not necessary in aircraft like the B744/-8 because they are fitted with rudder fine steering.
                                Michael Codd

                                Comment


                                  #20
                                  Originally posted by Michael Codd View Post

                                  Rafael, there is nothing unfortunate about it because it can be just as difficult to judge your taxi speed from a real flight deck; especially if it is in an aircraft as big and as high off the ground as a B744/-8 or an A380. Boeing were so concerned about this issue when they were starting to develop the original B747 that they constructed a cockpit on top of a vehicle so that the test pilots could get used to taxying around at that height.

                                  Perhaps we should all give PMDG a lot of credit for striving to replicate their aircraft's taxying behaviour so that it matches as closely as possible that of the real aircraft? Boeing and Honeywell, as well as PMDG, all provide a G/S readout on their Nav displays to show the pilots what their taxy speed is and, just as happens in a full-sized aircraft or simulator, we need to use it and adhere to the recommended taxy speeds. Provided you always refer to your G/S readout when approaching a turn and don't enter it taxying too fast then you will be less likey to encounter any serious problems when using P3D. But if anyone expects a PC simulated aircraft to behave itself when the tiller is being used at taxy speeds approaching 60 Kts G/S (as Alex alleges his pilot friends do) then they are living in cloud cuckoo land. It should never be necessary to use the tiller at those high taxy speeds in any real passenger aircraft that I know of and it is likely to invite trouble; even if the pilot is called Lewis Hamilton or is used to flying military jets! It is certainly not necessary in aircraft like the B744/-8 because they are fitted with rudder fine steering.
                                  Not sure where you see I’m critic of PMDG on this issue. In the contrary, very impressed they looked into this so deeply. The “unfortunate” part that I stated was due to any simulator in general where a lot of cues are missing like seat of your pants, motion parallax, etc.

                                  I’m a test pilot myself of both military and commercial aircraft I have a pretty good idea how OEM test pilots come up with taxi speeds on aircrafts such as the 747.

                                  I just stated the obvious, simulators are real good. Good enough to be qualify pilots, but there will always be limitations.
                                  Rafael Cordoves

                                  Comment


                                  • Michael Codd
                                    Michael Codd commented
                                    Editing a comment
                                    I agree with you regarding full size simulators. They are very good but they can never reproduce with 100% accuracy the same feeling and sensations of flying in the real aircraft that a pilot has.

                                  #21
                                  I'm honestly impressed by the complexity involved in something as simple (for an airplane) as the ground steering.

                                  I've never given a full nosewheel deflection on a real PA28 above 20kts, but I witnessed it as a passenger and it was not pleasant. It felt like the aircraft was about to tip over.
                                  I assume the same can be applied to a 737, and it's pretty accurate in the NGXu with the new steering system.

                                  Dan talked about a frisbee effect, and that describes pretty accurately what I experienced recently. And the speed from which it went from turning to spinning, looks like the way the turn was being handled changed mid-way through.

                                  From what I've read above, my guesses are that replicating my maneuver in a real aircraft, would result in an understeer, making the nosewheel deflect, but not having any turning action on the aircraft. PMDG did a wonderful job with the new steering system, so I'm wondering why this is not simulated. Perhaps for a sim's limitation? Or to avoid having a huge impact on performances on the ground, where usually fps are notorious to drop significantly?

                                  But I can say that from my point of view, is not safe to fully deflect any aircraft's nosewheel above 10kts, especially if accelerating. Not only for the lateral forces and understeer, but also for the sideload being applied to the main wheels, hence potentially damaging the wheels and the struts.
                                  Giovanni D. Tarar
                                  FAA CPL+IR Single & Multiengine Land
                                  I love flying when I'm in a bad mood

                                  Comment

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