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  6. Possible engine performance bug when reducing RPM in cruise

Possible engine performance bug when reducing RPM in cruise

Scheduled Pinned Locked Moved TBM 850
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  • E Offline
    E Offline
    Eseem
    wrote on last edited by
    #1

    First, let me just say that v1.1 was a great update, really love the revised beta range and aerodynamics, and the artificial BETA light is much appreciated.

    I'm currently cruising along at FL290, and was reducing the RPM from climb to a more comfortable 1800rpm as the manual states you may do so without impact to performance (i.e. on page Page 5.11.12A, the asterisk) to any green band value as long as you don't exceed the TQ limit.

    With RPM at 2000 and 103%TQ, I get only approx. 10-15kts shy of the corresponding listed TAS from the performance table. Pull back to 1800 though, the torque rises as expected, but the TAS and IAS plummets which they shouldn't do. This is my first flight in 1.1, so I'm note sure whether this is reproducible yet.

    Not a massive issue, but it'd be nice if a lower RPM could be used without performance impact in the future. For now, I'll just lower the MSFS volume ;)

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    • E Offline
      E Offline
      Eseem
      wrote on last edited by
      #2

      Screenshots showing the two states:

      https://i.imgur.com/HkAE9wY.png

      https://i.imgur.com/OYYz56R.png

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      • R Offline
        R Offline
        rbringh
        wrote on last edited by rbringh
        #3

        Agree but that is just from talking to my neighbor the King Air pilot. I fooled with the engine.cfg file for weeks and had the same result. They are probably having a time with this engine having the 850 mode. Only way to increase TAS is increase throttle.

        Most documents I read on constant speed turbo props is HP=RPM x Torque.
        Increase Torque with steady NG should equal increase in speed.
        Increase NG should increase torque = increase speed.

        I am assuming the decrease in RPM is being done by increasing prop pitch which increase air flow and torque.

        Other Turbo props I have act like this but they don't have dual limitations that is caused by 850 mode. Maybe it's a issue in the turbo prop model from Asobo.

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        • Black SquareB Offline
          Black SquareB Offline
          Black Square
          Black Square Developer
          wrote on last edited by
          #4

          This is something that has always bothered me about MSFS's propeller simulation, as it does not jive with my experience flying variable pitch propeller airplanes. I hoped it would get better with the CFD propeller dynamics added a few sim updates a while ago, but it didn't. I'm not aware of any parameter that has an effect on this, but if there is one, please let me know so I can make the adjustment in all of my aircraft.

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          • E Offline
            E Offline
            Eseem
            wrote on last edited by
            #5

            Thanks for acknowledging, sadly I don't have any dev skills at all so I wouldn't know where to even begin.

            Cheers

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            • R Offline
              R Offline
              rbringh
              wrote on last edited by rbringh
              #6

              Black Square, ask Asobo for a thrust_scaler/torque table. Well thrust_scaler/prop rpm table might be better.

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