Very strange behavior v 0.1.1



  • @Martyn I seem to be losing fuel flow at high MP. It will just keep dropping unless I back the MP down then it will slowly rise again. Also the MP that I can display on hardware is not matching the gauge. At sea level it was fine but at 8000 the gauge which was as 40 at SL had dropped to around 36. Raising this to 40.5 showed 43.84 on hardware. Display is reading ENG MANIFOLD PRESSURE:1 value Overboost light seems to be coming on at 41 MP on the gauge, but hardware is showing 44.22

    I checked this against 0.1.0 and I do see a similar behavior in an overboost condition about the decreasing fuel flow so I assume this is by design and a consequence of OB, but the gauge and hardware MP match.

    In this picture the hardware is displaying 43.94 MP

    https://drive.google.com/file/d/1G0lU5CvsnsHv7XLj2tvpudg4BoR66Axw/view?usp=sharing


  • JF Staff

    We're using custom code to get around limitations of the MSFS turbocharger and manifold pressure behaviour, and that results in a mismatch compared to the default manifold pressure variable.

    Are you able to use an LVar instead to drive your hardware?



  • @Martyn I understand that. Thing is If the MP on the gauge is above 36-37 the fuel flow is slowly decreasing till the engine shuts off Comparing to 0.1.0 I can get the same behavior, but not until the MP is 42-43 and the OB light is. In the picture you can see max rpm, MP 41, but fuel flow has dropped to 11.



  • @weptburrito I'm having the same issue. Engine loses power, fuel flow as I fly. Mp is still good but fuel flow goes down and exhaust temp goes down as I fly. Tried turning fuel pumps on for fuel pressure and yes, I am leaning fuel mixture as I ascend. Already crashed one plane because of this, I'm looking for a new mechanic.....



  • @Daytona125 can confirm I have it too.

    Also the EGT works strangely, at some mixture values the needle shows all the way left (zero?) with engine still running and most of the time the white needle shows more than the redline needle, which shouldn't happen.



  • @Skyhigh747 The "redline needle" is just a reference marker that you can adjust by turning the center knob on the gauge... The actual REDLINE is permanently marked on the gauge at 1650 degrees. Also, when the EGT is below 1200 degrees the needle will remain at the far left of the gauge.



  • @RetiredMan93231 said in Very strange behavior v 0.1.1:

    @Skyhigh747 The "redline needle" is just a reference marker that you can adjust by turning the center knob on the gauge... The actual REDLINE is permanently marked on the gauge at 1650 degrees. Also, when the EGT is below 1200 degrees the needle will remain at the far left of the gauge.

    Ah thanks for clearing that up! I am used to the III where I never seen the Redline exceeded



  • The turbo is much better than Carenado's recent Seneca... On that you can open the throttles at idle and get max boost before the engine has even started to rev up... which is impossible. No turbo lag at all lol.



  • I experienced the same issue today. After some period of climb my EGT needle will suddenly be full left and fuel flow begins decreasing along with RPM even with both levers full forward. It slowly continues dropping off until the engine stops producing any power. Restarted the flight and tried again and experience the same exact issue after about the same amount of flight time.



  • @CZemer17 @weptburrito @Skyhigh747
    There are a couple problems with piston engine modelling in MSFS that have been carried over from FSX and before. JF's custom engine modelling does not go so far as to resolve this issue.

    The problem is that fuel flow in the sim is proportional to power. Therefore, you always can find max power by leaning to peak fuel flow. That's backwards of course because the mixture should actually be setting the fuel flow (proportional to throttle position). The other bug is that turbocharged engines in FS must still be leaned with altitude in order to maintain power. In practice, what you have to do is just keep leaning to peak fuel flow during your climb to prevent the power loss. There's no way to simulate proper use of the mixture control in MSFS without going to the level of, for example, an A2A aircraft.



  • Ok lets try this another way as I never said anything about mixture or how well it is or isn't modeled.

    Try this for yourself also

    First pic, level off right after takeoff at 1500 ft. AP on. Running full steam, MP 40, RPM 2575 , speed settling around 155. Mixture reduced to peak. FF about 18. I am also displaying these values on my radio panel.

    Screenshot (327).jpg

    Second pic, I slewed up to 7500. Only adjusted mixture back to peak. Note the drop in MP and throttle is at same position. I could be wrong but isn't supposed to stay in a turbo at least up to critical altitude? And this doesn't happen in 0.1.0. Now, according to the numbers on my panel, my MP is still 40

    Screenshot (328).jpg

    Now in the 3rd picture, I've increased the MP back to 40 on the gauge. Initially FF was just over 20. But after 5m 13s it has dropped to 15 and will continue to drop till I lose power. MP displayed on my panel is show almost 43

    Screenshot (329).jpg



  • @weptburrito, JF has acknowledged that there is currently a problem with the turbocharger performance in this aircraft, which you have documented very well, and they are actively working on a solution... But, I should point out that the real world performance of the turbocharger in this aircraft is a little different than what you might be expecting... The standard turbocharger in this aircraft uses a "fixed waste gate" instead of a "variable waste gate", which means the turbocharger produces a constant fixed manifold boost pressure, regardless of altitude. As your altitude increases the turbocharger does not automatically increase the boost pressure to compensate for the reducing outside ISA pressure, as in some other aircraft with variable waste gate turbochargers. So, in this aircraft it is normal operation to require continuous readjustment of the throttle as you climb to maintain a constant MP setting. The max MP setting (41) can only be maintained up to the critical altitude (12,000 ft MSL).



  • @RetiredMan93231 said in Very strange behavior v 0.1.1:

    As your altitude increases the turbocharger does not automatically increase the boost pressure to compensate for the reducing outside ISA pressure, as in some other aircraft with variable waste gate turbochargers. So, in this aircraft it is normal operation to require continuous readjustment of the throttle as you climb to maintain a constant MP setting. The max MP setting (41) can only be maintained up to the critical altitude (12,000 ft MSL).

    Ah see I did not know that!!! I only know in that regard it was different than 0.1.0 which behaved like I expected, holding MP up to critical altitude. Learn something new everyday!



  • There's is a sim-wide oddity with mixture settings. If you stray too far outside the the acceptable mixture range, rather than the engine running rough and then trying to quit, the engine will just slowly develop less power. As it does so, it will show decreased fuel flows. Try leaning the mixture and you might find that you actually start seeing a fuel flow rise due to this odd behavior. Unless JF implements their own fuel system/engine management in the aircraft we will see this behavior due to the default issues with the sim.



  • @Daytona125 @weptburrito

    Just reporting this exact behavior which is happening all of a sudden the last few days. Saw this thread and the other “Erroneous fuel flow” thread and was wondering why you guys were having a problem. BAM! Flying along, enjoying a beautiful S Cal afternoon in this beautiful bird, and I start losing power, notice the fuel flow dropping and have to crash land. Did another flight, same thing. Yesterday afternoon tried another flight, no issue at all! Perfect flight. All happy with myself that it worked, I go up today, 😡, you guessed it, power loss, fuel flow tanking but luckily got to my arrival. This issue seems to show itself 45-55 minutes into a flight, and I do lean as I gain altitude. This issue makes the plane pretty much unplayable for me. Right? I mean 45 minutes into a flight and the engine just stops performing in a 15-20 minute slow motion exercise.



  • @ChivasRx For a quick and dirty hack, in the engines.cfg file of each turbo

    \justflight-aircraft-pa28-turboarrow\SimObjects\Airplanes\JF_PA28_TurboArrow_III\engines.cfg
    

    just a little ways down is "detonation_onset=41" change it to 45. This should make do until JF can get it properly sorted out.



  • @weptburrito

    Really appreciate that little nugget! Will check it out tomorrow. Just finished a short 45 minute flight without incident. Lately I might have been running the engine slightly higher at 38-39MP, 23-24 RPM. Backed it down to 36/22 this time.

    Thanks again!