Mixture Behavior



  • I'm trying to understand better how the fuel injection system works in the Turbo Arrow III and IV. When I was reading the Just Flight manual yesterday, I came across this quote on page 15:

    "The induction system incorporates a fuel injector. The injector is based on the principle of differential pressure, which balances air pressure against fuel pressure. The regulated fuel pressure established by the servo valve when applied across a fuel control makes the fuel flow proportional to air flow."

    It sounds like the fuel injection system is designed to modulate fuel flow depending on the amount of air entering the intake manifold. That would make sense, because for any given setting of the mixture knob, the fuel:air mixture should stay constant no matter the throttle setting. The part that confuses me is: if the system is based on pressure, why would it be necessary to lean the mixture during climb in a turbocharged aircraft as long as the pilot periodically adjusts manifold pressure to keep it steady?



  • I tested the mixture behavior in the newest 0.2.0 version of the Turbo Arrow III today. If I leave the mixture at full rich during the climb, I notice a drop in fuel flow beginning somewhere near 6000 ft. By 9500 ft, the fuel flow drops significantly with every 1000 ft of additional altitude. I decided to lean the mixture for maximum fuel flow during the climb to maintain proper climb power. I haven't seen anything in the Turbo Arrow POH that suggests leaning during the climb, so I'm guessing this is an artifact of the mixture logic in MSFS.



  • It's a bug Marc.



  • I really wish this could be fixed. Sort of brakes the immersion for me when the engine doesn’t behave as it should IRL.



  • Thanks for the feedback. I suspected this was a bug in the underlying MSFS mixture logic, because I've seen similar behavior in other turbocharged planes. I've created a bug report on the MSFS forum.

    https://forums.flightsimulator.com/t/inaccurate-mixture-behavior-on-turbocharged-piston-engines/411095



  • Check my post in this thread:

    https://community.justflight.com/topic/2360/v0-2-1-throttle/7

    It's a nuisance, but for now there arrears to be no way around it unfortunately.