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NGXu VNAV not realistic

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    NGXu VNAV not realistic

    Morning!

    I´m guessing this topic has probably been answered but I haven't been able to find anything specific.

    Is it a known bug that the VNAV is very slow to capture a speed set using Speed Intervene? Also the plane doesn't seem to like to descend any more than 4600ft/min even in V/S?

    Answers much appreciated!

    Jangaloo H


    #2
    VNAV is very bugy... but IRL the aircraft is also very slippery to slow down or descend over 2500fpm, let alone 4600
    ZHU Hai
    B737 Ground instructor

    Comment


    • jangaloo
      jangaloo commented
      Editing a comment
      Thanks for your reply - hopefully that gets fixed as its certainly nowhere near how it works IRL and the NGX has it modelled much better. Have just switched from the NGX to the NGXu and it seems some things work better with the NGX than the NGXu....IRL With VNAV engaged and speed intervene(the speed window open) the aircraft should speed up, ie the VS increases to capture the speed set...Nothing to do with VS mode.

    #3
    I usually prefer LVL CHG over VNAV SPD for exactly this reason: It is slower to capture speeds and slower to respond overall. Probably Boeings attempt to improve pax comfort.
    Regarding descend rates: It'll go 5° Nose Down, that's it. The resulting V/S is what you'll get.
    Only in V/S it will go as far as 10° Nose Down, but believe me: You don't want to do that!

    Comment


    • DDowns
      DDowns commented
      Editing a comment
      The B736 with a high CI such as used for business, will exceed that 5 deg ND quite easily. I usually change the econ descent speed to something like 290 to keep deck angle reasonable. But, this is only in the B736. The B737/8 not so much.

    • Emi
      Emi commented
      Editing a comment
      Is that in the NGXu or in the real one? Limits above are from the real one, which as far as I am aware have also been implemented into the NGXu.

    • DDowns
      DDowns commented
      Editing a comment
      To be honest Emanuel, I don't trust my memory. Perhaps 5 deg ND in the B736 with CI 85 is what I was seeing and I may have interpreted it as a steep angle. I do recall always changing descent speed to 290 to decrease the angle.

    #4
    Originally posted by Emi View Post
    I usually prefer LVL CHG over VNAV SPD for exactly this reason: It is slower to capture speeds and slower to respond overall. Probably Boeings attempt to improve pax comfort.
    Regarding descend rates: It'll go 5° Nose Down, that's it. The resulting V/S is what you'll get.
    Only in V/S it will go as far as 10° Nose Down, but believe me: You don't want to do that!
    Once you learn how lvl chg works its amazing. 😍😍
    Alex Kulak
    PMDG Studier and flyer

    Comment


      #5
      Originally posted by Emi View Post
      I usually prefer LVL CHG over VNAV SPD for exactly this reason: It is slower to capture speeds and slower to respond overall. Probably Boeings attempt to improve pax comfort.
      Regarding descend rates: It'll go 5° Nose Down, that's it. The resulting V/S is what you'll get.
      Only in V/S it will go as far as 10° Nose Down, but believe me: You don't want to do that!
      So it's simulating the real one correctly then and it's not buggy?
      Niklas Graefe
      Prepar3D v5.2 | 737/777 | i9 9900K 5 GHz | Corsair 32 GB | RTX 3090 24 GB | W10 | HP Reverb G2

      Comment


      • jangaloo
        jangaloo commented
        Editing a comment
        No its not simulated correctly. IRL its alot more responsive. As ZHU said it is buggy..

      #6
      Originally posted by threegreen View Post

      So it's simulating the real one correctly then and it's not buggy?
      I haven't flown the NGXu in a while now so I don't want to give any definitive statement on this right now.
      From what I *remember* (and it's been a while) it was quite alright, however once you pitched it down to something in the negative I believe to remember that the V/S you'd get from the NGXu was less than the real one. I recall a chat with an FDE Dev who said if this was changed you'd break other stuff so this would be a compromise. But as said, it's been a while....

      Comment


        #7
        VNAV on the 747 is not correct, I presume it is not as good as it can be on the other Boeings, yet.
        It is on the development list of PMDG, but first LNAV is in upgrade to the beta team (which will also find its way to the other types), and then a certain bird for MSFS, and… Well, you get the idea, there is a line.
        René Moelaert EHLE

        Comment


          #8
          Originally posted by Fleng200 View Post
          VNAV on the 747 is not correct, I presume it is not as good as it can be on the other Boeings, yet.
          It is on the development list of PMDG, ....
          That would be great, has that been announced anywhere ?

          kind regards
          Manolo Ruiz Carrió

          Comment


            #9
            From what I recall, both VNAV SPD and LVL CHG are far more effective in the NGXu at changing airspeeds than in the real airplane. Sometimes ATC wants us to fly a specific speed during descents in busy airpaces. This is often due to traffic sequence so if they want a speed, you need to give it to them NOW. So you hit SPD INTV or go LVL CHG and the real airplane takes its time. It's not rare that we prefer to go V/S -300 and use speed brakes. Then, once the airplane reaches the ATC requested speed, we go back to VNAV or LVL CHG. As EMI said, the airplane may be looking after passenger confort in ways that are sometimes not ideal depending on what the situation requires (ATC, weather, etc).

            Note that in "Common VNAV" equipped airplanes (unlike the variation of "Basic VNAV" that the NGXu has), pressing SPD INTV when the airplane is on VNAV PTH will not change the mode to VNAV SPD. It'll just open the speed window and the airplane will remain in VNAV PTH. This takes some time to get used to by the pilots and it requires some vigilance as well, as using LVL CHG over VNAV SPD has some associated threats, as LVL CHG will not respect altitude constraints that some of your waypoints along a SID, STAR or IAP may have.

            So, long story short is that LVL CHG and VNAV SPD in the NGXu changes speeds more quickly than the real airplane and the atmosphere in P3D is just too damn ideal. But worry not. The autopilot in a multi million dollar full flight simulator also changes speeds more effectively than the real airplane floating in the real atmosphere.
            Last edited by Aeromar; 29Nov2021, 11:25.
            Omar Josef
            737 FO
            757/767 rated
            Spain

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