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Autobrake effectiveness

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    Autobrake effectiveness

    Hello,

    Upgrading from the legacy NGX to the new NGXu, I've noticed that on my setup the autobrake effectiveness is much stronger on the NGXu. I'm not sure if this is a peculiarity inherent only with my installation or if something is perhaps amiss with the new flight dynamics. In any event, what I've noticed is that the NGXu is stopping in about half the distance calculated on the EFB OPT. For instance, if I enter the runway, winds, temp, runway condition, etc. in the OPT at an autobrake setting of 2, I might get a calculation of around 6100ft required for landing. However, when I use autobrake 2 under the conditions calculated, my NGXu stopping distance is about 3000ft or around half of the OPT calculated value. Curiously, the old legacy NGX actually performs very close to calculated values under the same flight conditions.

    Has anyone else noticed this behavior with the NGXu? Thanks!

    -Aaron Cumberland

    #2
    The OPT calculation does NOT credit reversers, and contant 15% addtion to actually distance.
    When using normal reverser, AB1 and 2 normally would even not pressue up because reverser alone could provide more deceleration than needed.
    ZHU Hai
    B737 Ground instructor

    Comment


      #3
      I noticed something similar, it feels quite strong to me as well. Will do some research and discuss with the developers.
      Greetings,
      Emanuel Hagen

      Comment


        #4
        Originally posted by AngelofAttack View Post
        The OPT calculation does NOT credit reversers, and contant 15% addtion to actually distance.
        When using normal reverser, AB1 and 2 normally would even not pressue up because reverser alone could provide more deceleration than needed.
        Hello. I normally use only idle reverse, and I tested the stopping distance on the NGXu with no reverser at all. To the best of my knowledge, the autobrake system on Boeing aircraft provide a rate of deceleration rather than a constant specified braking strength. The autobrake system polls the deceleration rate from the IRS and modulates brake pressure to adhere to the autobrake selected setting. If thrust reverse is used, the autobrake system 'senses' the additional deceleration additive and eases up on the braking to maintain a constant rate of deceleration. However, on an uncontaminated runway, use of reverse thrust should not affect actual stopping distance; rather, just the amount of braking pressure required. Someone please correct me if I'm wrong on this understanding.

        -Aaron Cumberland

        Comment


          #5
          Originally posted by Emi View Post
          I noticed something similar, it feels quite strong to me as well. Will do some research and discuss with the developers.
          Thanks very much! I'm actually relieved someone else notices this.

          -Aaron Cumberland
          Last edited by Aaron Cumberland; 05Dec2019, 17:02.

          Comment


            #6
            If you don't use reverse thrust then the performance will closely match the expected values. The problem is that the simulator platform has an unrealistic simulation of reverse thrust in that it maintains a constant effect regardless of speed as opposed to reality where it is only effective at high speeds. We ran into this is the QOTSII beta, where the improved ground friction model was first introduced. We spent a week plotting the landing distances and deceleration rates and comparing to Boeing engineering data and the autobrakes worked very close to perfect but that reverse thrust really buggered the results.

            Most realistic results can be achieved if you remove reverse thrust below 90 kts... realistically it would be below 60 kts but this is were the simulator platform has low fidelity.
            Dan Downs KCRP

            Comment


              #7
              Originally posted by DDowns View Post
              If you don't use reverse thrust then the performance will closely match the expected values. The problem is that the simulator platform has an unrealistic simulation of reverse thrust in that it maintains a constant effect regardless of speed as opposed to reality where it is only effective at high speeds. We ran into this is the QOTSII beta, where the improved ground friction model was first introduced. We spent a week plotting the landing distances and deceleration rates and comparing to Boeing engineering data and the autobrakes worked very close to perfect but that reverse thrust really buggered the results.

              Most realistic results can be achieved if you remove reverse thrust below 90 kts... realistically it would be below 60 kts but this is were the simulator platform has low fidelity.
              Hi Dan. I fully understand platform limitations factoring in. I'm actually seeing autobrake effect to be almost twice what it should be though, even with no reverse thrust activated. And for the reason you mentioned, I rarely use anything but idle reverse with PMDG aircraft. Maybe 2020 will finally nix that bug once and for all.

              -Aaron Cumberland

              Comment


                #8
                Originally posted by Aaron Cumberland View Post

                Hi Dan. I fully understand platform limitations factoring in. I'm actually seeing autobrake effect to be almost twice what it should be though, even with no reverse thrust activated. And for the reason you mentioned, I rarely use anything but idle reverse with PMDG aircraft. Maybe 2020 will finally nix that bug once and for all.

                -Aaron Cumberland
                To be sure, I didn't go through the same exercise with the NGXu that was done with the 747... ran out of time. If there can be some documentation in the form of measured deceleration in the sim verses what the tables provide then that belongs on a support ticket. Emanuel has taken an interest and since he is type rated Captain on the tech team, I'm sure supporting documentation would be helpful.
                Dan Downs KCRP

                Comment


                  #9
                  I didn't see it mentioned, but landing distances also include a 1500’ air distance. Basically from the fence, flare to touchdown.
                  ATPL - Class I Instructor - Seaplane - B737 - BE1900D

                  Comment


                    #10
                    I just noticed, with 738WSPF, The PMDG EFB given landing distance is much less than what my company's OPT on EFB would give.
                    Then I double check it with manual calculation by QRH table, the difference between me and OPT is less than 100m, but about 400m more than PMDG's EFB give. not even what 15% could cover, it feels like if PMDG didn't count flare distance?
                    The actially runway I used, even with a slightly long flare I feel , is another 500m less.
                    I'll send a ticket with more details.
                    ZHU Hai
                    B737 Ground instructor

                    Comment


                      #11
                      Originally posted by AngelofAttack View Post
                      I just noticed, with 738WSPF, The PMDG EFB given landing distance is much less than what my company's OPT on EFB would give.
                      Then I double check it with manual calculation by QRH table, the difference between me and OPT is less than 100m, but about 400m more than PMDG's EFB give. not even what 15% could cover, it feels like if PMDG didn't count flare distance?
                      The actially runway I used, even with a slightly long flare I feel , is another 500m less.
                      I'll send a ticket with more details.
                      The EFB calculations are made according to the available charts/tables) from Boeing manuals. your company OPT can have additional tables included.
                      Chris Makris (Olympic260)
                      PMDG Technical Support
                      http://www.pmdg.com

                      Comment


                        #12
                        Originally posted by cmakris View Post

                        The EFB calculations are made according to the available charts/tables) from Boeing manuals. your company OPT can have additional tables included.
                        I see, It seem the data available form Boeing to you is more limited than I would thought?
                        But one of the biggst problem is the EFB says "Landing Distance Reuired" but it shows the distance without 15% addition, which means it's the "Actual Landing Distance".
                        And the aircraft managed to stop with only about 80% of that non-factored distance in my particular case ....
                        ZHU Hai
                        B737 Ground instructor

                        Comment


                          #13
                          Originally posted by AngelofAttack View Post

                          I see, It seem the data available form Boeing to you is more limited than I would thought?
                          But one of the biggst problem is the EFB says "Landing Distance Reuired" but it shows the distance without 15% addition, which means it's the "Actual Landing Distance".
                          And the aircraft managed to stop with only about 80% of that non-factored distance in my particular case ....
                          For the last I understand that you mean the actual stooping distance is not the same as the EFB calculates correct?
                          Chris Makris (Olympic260)
                          PMDG Technical Support
                          http://www.pmdg.com

                          Comment


                            #14
                            Originally posted by cmakris View Post

                            For the last I understand that you mean the actual stooping distance is not the same as the EFB calculates correct?
                            I'll rather refer the distacne I made in PMDG's bird as SLD (sim landing distance) for clarify, All xLD is from 50ft height to full stop

                            The EFB's result is same as what PMDG's QRH would provide, and the QRH says "Actual (unfactored) distances are shown." Thus it's ALD, but the text in EFB says it's "Landing Distance Required" means RLD, the RLD = ALD+15%, this is the 1st problem.

                            In our QRH and EFB, it says "All reference distances and adjustments shown have been increased by 15%.", Thus RLD. This two set of data isn't that much differ if all converted into same standard.

                            The 2nd problem is, the SLD I did, as this single datapoint at least, is about 82% of the ALD from PMDG's EFB or PMDG's QRH.

                            It's just my guess, but maybe someone in your team use the QRH data as RLD rather than ALD to put in EFB and adjust the SLD?
                            Last edited by AngelofAttack; 27Dec2019, 03:22.
                            ZHU Hai
                            B737 Ground instructor

                            Comment


                              #15
                              Originally posted by AngelofAttack View Post
                              I'll rather refer the distacne I made in PMDG's bird as SLD (sim landing distance) for clarify, All xLD is from 50ft height to full stop

                              The EFB's result is same as what PMDG's QRH would provide, and the QRH says "Actual (unfactored) distances are shown." Thus it's ALD, but the text in EFB says it's "Landing Distance Required" means RLD, the RLD = ALD+15%, this is the 1st problem.

                              In our QRH and EFB, it says "All reference distances and adjustments shown have been increased by 15%.", Thus RLD. This two set of data isn't that much differ if all converted into same standard.

                              The 2nd problem is, the SLD I did, as this single datapoint at least, is about 82% of the ALD from PMDG's EFB or PMDG's QRH.

                              It's just my guess, but maybe someone in your team use the QRH data as RLD rather than ALD to put in EFB and adjust the SLD?
                              Understood now.

                              Sicne these are different systems they were worked from different teams. will notify them to inestigate
                              Chris Makris (Olympic260)
                              PMDG Technical Support
                              http://www.pmdg.com

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