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Comparing taxi physics to a flight deck video

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    Comparing taxi physics to a flight deck video

    One aspect of the current state of the NGXu's taxiing physics is that you pretty much can't turn above 10 knots. Watching this flight deck vid and seeing them easily exit the runway between 20-14 knots, I tested it myself at Aerosoft EDDK, following the groundspeeds in the video. It was simply impossible to make the exit in the NGXu at the same speeds, using the default raw input tiller mode. On its face, it seems like the new taxi physics need work before they get ported to the 747/777, but I'm curious to know what PMDG/the real-world NG pilot's here think.

    https://youtu.be/uLX7KKUalHc?t=523

    Alex Pugh

    #2
    Originally posted by AirBadger View Post
    One aspect of the current state of the NGXu's taxiing physics is that you pretty much can't turn above 10 knots. Watching this flight deck vid and seeing them easily exit the runway between 20-14 knots, I tested it myself at Aerosoft EDDK, following the groundspeeds in the video. It was simply impossible to make the exit in the NGXu at the same speeds, using the default raw input tiller mode. On its face, it seems like the new taxi physics need work before they get ported to the 747/777, but I'm curious to know what PMDG/the real-world NG pilot's here think.

    https://youtu.be/uLX7KKUalHc?t=523
    Go to nose wheel over it, I've turned the NGXu below 5kts with no power, small little pushes in the rudder works best for me instead of slamming it all the way down. However that's what works for me.


    Also how do you get the feeling of turning an actual plane through a video vs actually turning one and then comparing it?

    Also there could be a little bit more improvement to taxing the NGXu, need to get in a CAE 737 simulator and test it out
    Alex Kulak
    PMDG Studier and flyer
    Ramp Agent

    Comment


      #3
      Last time I tried to use the tiller to steer a 737-200, it felt like I was about to flip the simulator on its side. Unfortunately, I don't remember how fast I was going, but I don't think it was that fast, given that I was already stopped on the runway initially.
      Captain Kevin

      Kevin Yang

      Comment


        #4
        If Southwest can taxi this thing with a limit of 45 knots then it's clearly not designed right! Just sayin.....
        Herb Barrett-King

        Comment


          #5
          Originally posted by WN737 View Post
          If Southwest can taxi this thing with a limit of 45 knots then it's clearly not designed right! Just sayin.....
          Ah yes... "Southwest style" taxi LOL
          Serge Saakov - KPVD
          my YouTube page

          Comment


            #6
            If my memory is right, It's been told here in the forums by real 73 pilots, that the tiller is not used over 20 Knots, they use the rudder to steer. Please prove me wrong if it's not the case. If this is the case then the steering and taxi physics are very well modeled. I got used very quickly taxiing the NGXu with a separate steering tiller controller and setting steering feel "using rate based".
            Last edited by 737NG4EVER; 21Jan2020, 00:23.
            Sergio Naiberg

            Comment


              #7
              I'm honestly confused with all the issues folks are having with the new taxi physics. Sure, it took a bit to get used to but once I relearned the technique, I prefer it. I feel like it wanders less in a straight line so I can spend longer with my head in the cockpit without worrying that I'll look up to find I've drifted into the active. Making a sharp turn from slow or stationary does require some finesse on the power. Too much power and as the turn radius tightens, the rate of turn will increase to an unacceptable level. It just requires more control touch now.

              Since you are sitting at a desk instead of an actual aircraft, you can't feel the movement of the aircraft so that adds to the difficulty of controlling your cartoon airplane. I flew OH-58s in the Army and have difficulty hovering a helicopter in P3D on full realism for the same reason. Can't feel the airplane. You need small control inputs and use your periphery to help judge movement and speed.
              Travis D. Perkins
              i7 9700k 5.0ghz, RTX2080, 32GB 40000mhz, AOC Agon 35"

              Comment


                #8
                Here's the NGXu while making the same turn at the same speed as in the video I posted. https://streamable.com/dknx0 Not a perfect match, but I did my best to match the speeds and the point at which they started turning. As you can see, at 14 knots, it goes off into the grass, while in the video, they have no issues.
                Alex Pugh

                Comment


                  #9
                  Originally posted by WN737 View Post
                  If Southwest can taxi this thing with a limit of 45 knots then it's clearly not designed right! Just sayin.....
                  If SWA manages to keep the damn thing on the pavement all the way to the gate, then reality itself has been altered. Just sayin.

                  Comment


                    #10
                    I'll add some points I've mentioned before in previous threads on the issue. These come from real experience in the airplane and from the Boeing Flight Crew Training Manual

                    Any turn greater than a high speed runway turnoff, 30 degrees or more, should be at approximately 10 knots in dry conditions. You risk scrubbing the nose wheel causing premature tire wear. You can wear the tires out really quickly. You'll get a wicked nose wheel shimmy due to the imbalance. You can do higher speeds with wider turns. You get a feel for it with experience. Really depends on whether you have a good profit share program 😛

                    Normal Taxi speed is 20 knots. 30 knots in straight sections, but you risk over controlling the nosewheel.

                    In the NGXu, I don't find too much of an issue if I stick to the above. The tiller is more direct and depends on your joystick resistance. In the real thing there is resistance due to the hydraulics and it's much easier to finesse. Without a hydraulic system controlling an actual nosewheel, and real world forces acting on you and the aircraft, its never going to feel right. Level D sims taxi like crap too.

                    Some advantages with the new taxi physics are that you can finally do single engine taxi. Disadvantages, are that there is a noticeable change in steering at certain speeds, and you can turn the airplane indefinitely with a minimum radius turn with idle thrust. From what I understand are due to limitations with P3D and a work around of its crappy physics.
                    Last edited by MeatServo; 21Jan2020, 04:57.
                    ATPL - Class I Instructor - Seaplane - B737 - BE1900D

                    Comment


                      #11
                      It‘s important to keep in mind that our „tiller“ is mostly a Z axis of a joystick that has a moving angle of about 15-20 degrees each side if not less. A 737 tiller moves a lot more. Also it would be interesting to know the actual resolution of that joystick axis. If it jumps in increments of 500/16384 or more then it‘s rather a hardware issue than a bad ground steering. „Cheap“ pc flight hardware like my old sidewinder joystick did that, expensive hardware like a thrustmaster hotas warthog or the MFG rudder pedals have a much higher resolution. Using that I have absolutely no issues taxiing the 737 properly and smoothly.
                      i7-6700k, GTX 1080TI, 32GB DDR4 RAM @1600MHz, 4k

                      Comment


                        #12
                        It should have quite some stronger steering ability between 10 and 20kt. I can not make quite a lot of turns we usually take at more than 10kt at my homebase.
                        Greetings,
                        Emanuel Hagen

                        Comment


                        • DDowns
                          DDowns commented
                          Editing a comment
                          I'll tap on a brake (differential braking) when the tiller needs assist in a turn above 10 kt but for the most part my turns are always < 12 kts. The Chancellor needs differential braking too so this is all very familiar.

                        #13
                        Taxi issue is fine? It's feels more 'intuitive' and you have to pay more attention.
                        Last edited by VBHB; 21Jan2020, 10:54.
                        Peter Walsh.

                        Comment


                          #14
                          Originally posted by VBHB View Post
                          Taxi issue is fine? It's feels more 'intuitive' and you have to pay more attention.
                          For the record, I didn't start this thread because I'm having issues taxiing. I've gotten used to the new physics and the quirks. I know to take turns at 10 knots. I know rudder can be used at 20+ knots to keep a straight line. The question now becomes, "Is this accurate?" That's why I posted this flight deck video and then recreated the scenario in the sim. As Emanual states, it might need some tuning to strengthen steering ability from 10-20kt.

                          It should have quite some stronger steering ability between 10 and 20kt. I can not make quite a lot of turns we usually take at more than 10kt at my homebase.
                          Alex Pugh

                          Comment


                            #15
                            Originally posted by MeatServo View Post
                            I'll add some points I've mentioned before in previous threads on the issue. These come from real experience in the airplane and from the Boeing Flight Crew Training Manual

                            Any turn greater than a high speed runway turnoff, 30 degrees or more, should be at approximately 10 knots in dry conditions. You risk scrubbing the nose wheel causing premature tire wear. You can wear the tires out really quickly. You'll get a wicked nose wheel shimmy due to the imbalance. You can do higher speeds with wider turns. You get a feel for it with experience. Really depends on whether you have a good profit share program 😛

                            Normal Taxi speed is 20 knots. 30 knots in straight sections, but you risk over controlling the nosewheel.

                            In the NGXu, I don't find too much of an issue if I stick to the above. The tiller is more direct and depends on your joystick resistance. In the real thing there is resistance due to the hydraulics and it's much easier to finesse. Without a hydraulic system controlling an actual nosewheel, and real world forces acting on you and the aircraft, its never going to feel right. Level D sims taxi like crap too.

                            Some advantages with the new taxi physics are that you can finally do single engine taxi. Disadvantages, are that there is a noticeable change in steering at certain speeds, and you can turn the airplane indefinitely with a minimum radius turn with idle thrust. From what I understand are due to limitations with P3D and a work around of its crappy physics.
                            What do you mean about new physics? Are you talking about fs2020 or is PMDG updating something and you’re on the BETA?
                            Jordan Collins

                            Comment


                            • MeatServo
                              MeatServo commented
                              Editing a comment
                              From what I understand PMDG has tried to work around the flawed P3D ground physics hence the new behavior. Its explained in the intro.

                            #16
                            Taking the FCTM in "context" the 10 kt limit is for legal purposes.
                            Numerous Boeing docs have legal overtones with regard to operating "techniques".
                            Just read the fuel imbalance checklist in the 777/787 to see that in action..lol.
                            Unlike an Airbus which has a exponential steering system making fine adjustments very easy and over controlling difficult the Boeing direct system is a pain to taxi with in comparison.
                            Using rudder above 15-20 kts to avoid over controlling is pretty common however its still pretty easy to use the tiller you just need to be fine and gentle. Its not that it wont react and skid it simply is to reactive making for a jerky ride down the line. You can easily steer the aircraft with the tiller at 25-30kts you just need to be smooth it responds fine without issue.
                            There is NO ISSUE with skidding nosewheels and to say the aircraft will skid at greater than 10kts is simply incorrect unless you simply gave it full tiller in one direction or the other which would be the grossest case of mishandling ever seen.
                            You can steer aircraft off at high speed exits using rudder at up to 60kts so saying it wont steer is simply wrong.
                            Nice steady turns yes but your also braking which applies more load to a nosewheel as well.
                            Starting new myths about aviation that aircraft can't be steered etc, tires will slide out and you will lose control are baseless in reality and day to day aircraft operations.
                            Wide turns on taxiways in any narrow body or widebody can be safely taken at up to 20kts without scrubbing or skidding or damaging nosewheels its all related to the tightness of corner vs speed not whether your using a tiller or pedals.
                            In wet conditions the thing which causes skidding etc is being on painted lines ie tight turns on thresholds doing 90 and 180's to line up at greater than 5 kts will cause shuddering as the nosewheel slips on the painted surface.
                            I have never experienced a nosewheel skid or slide in the wet in normal ops on standard taxiways in normal conditions ie non contaminated.
                            Regarding taxi speed aircraft fitted with carbon brakes which is a massive number these days are "recommended" to continue to 30kts then brake back to 10 and so on and so forth in that cycle. This is to minimize brake wear as carbon brakes wear per application so continually slowing down to 15-20 etc wears brakes far more quickly than one application from 30 back to 10Kts.


                            Darren Howie

                            Comment


                            • Swaluver88
                              Swaluver88 commented
                              Editing a comment
                              Just gonna put this out there. It must not be a pain to southwest pilots... theyll come flying into the gate before I can blink my eyes marshalling them in. N1 @45%

                            • MeatServo
                              MeatServo commented
                              Editing a comment
                              This is true, on the other end of the spectrum we had 777 drivers drop down to the 737 taking corners too fast and going through nosewheel tires like butter. The FCTM 10kt guidance is primarily for premature tire wear not controlibility.

                              Much of it depends on the balance sheet. If in our operation the company makes more money getting to the gate quicker without compromising safety, and if that means burning through a few extra nose wheels in a year that we get an amazing deal on, taxiing faster could be worth it.
                              Last edited by MeatServo; 22Jan2020, 16:37.

                            #17
                            It just looks ridiculous wen on the outside view even at 10 knots the aircraft just slides like a rally car
                            Duarte Vieira

                            Comment


                              #18
                              Originally posted by dehowie View Post
                              In wet conditions the thing which causes skidding etc is being on painted lines ie tight turns on thresholds doing 90 and 180's to line up at greater than 5 kts will cause shuddering as the nosewheel slips on the painted surface.
                              Don't get me started on that. I slip on painted lines all the time when they're wet, and that's just from WALKING on them.
                              Captain Kevin

                              Kevin Yang

                              Comment


                                #19
                                Maybe he has used right toe brakes. I can recall a Delta flight from Detroit to Toronto operated with an CRJ (700?). After landing the pilot told us he has lost control over the nose gear. He was steering the plane carefully with a combination of individually controlled engine thrust and toe brakes. It worked out very well. (I he hadn’t told us...)
                                Josef Kolb

                                PMDG B737-600 to -900/747-400/747-8/777-200LR/777-300ER

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