Dopster198 131 Posted January 25, 2022 Share Posted January 25, 2022 I usually put the fuel booster switch (aft and fwd) on when starting the engines, leave them in that position the whole flight, and turn them off at engine shut down. As far as I understand that's correct procedure. But my question is, are these switches actually operative in the sim? I can happily start my engines with either or both of them in the 'off' position, or switch them off during the flight without any apparent ill effects. Am I missing something? Link to comment Share on other sites More sharing options...
Aerosoft Aerosoft Team [Inactive Account] 51558 Posted January 25, 2022 Aerosoft Share Posted January 25, 2022 Now I am not behind my system now, but as far as I remember from the diagram there are multiple pumps. That's a good thing because with the tank in the fuselage and the engines on the wings they can't be fed by gravity like they are for example in the A320. Also keep in mind that none of our aircraft simulate these non standard procedures. Link to comment Share on other sites More sharing options...
Finn 873 Posted January 25, 2022 Share Posted January 25, 2022 The Twin Otter has two low pressure pumps for each Tank (FWD & AFT). FWD Boost pump 1 & 2 AFT Boost pump 1 & 2. Only pump 1 OR 2 for each Tank normally runs, the other will be on standby, should the other fail. Additionally each Engine has it´s own high pressure fuel pump. Here is how these pumps operate in the real Twin Otter: Each Boost pump has a caution light. Each light is energized by a pressure switch in the delivery line of the corresponding boost pump if the fuel pressure downstrean of the pump falls below 2 Psi. In normal operation the pressure from the No. 1 boost pump in each tank actuates the No.1 pressureswitch, which extinguishes the No.1 Boost pressure caution light. It also renders the No.2 boost pump and the No. 2 boost pressure caution light inoperative. Should the No.1 boost pump fail, and thus the No.1 fuel pressure switch activates (No. 1 Boost pressure caution light will illuminate) due to low fuel pressure, this will turn on the No.2 boost pump automatically. Should this not happen automatically it can be done by switching the STBY BOOST PUMP EMER switch from NORM to Up position. Boost pump 1 FWD is powered by the Left DC bus and feeds the Right engine Boost pump 2 FWD is powered by the Right DC bus and feeds the Right engine Boost pump 1 AFT is powered by the Left DC bus and feeds the Left engine Boost pump 2 AFT is powered by the Right DC bus and feeds the Left engine Also... Boost pump 2 (FWD/AFT) will only activate if Boost pump 1 (FWD/AFT) fails, or the STBY BOOST PUMP EMER switch is in the up position, or the Boost pump switch is set to TEST (springloaded). The Engines though can run on their High pressure fuel pump alone i.e none of the low pressure fuel pumps runs, but it is not allowed. At least one low pressure fuel pump must run per Tank, and this only up to 8000 ft. It has been reported that the Engines has been able to run without the low pressure pumps up to 16.000 ft. So it isn´t unrealistic if the Engines keep running without the low pressure pumps running below 16.000 ft. But above 16.000 the engines will quit. The altitude is only approximatly, and depends on air pressure, temperature etc.. Link to comment Share on other sites More sharing options...
Dopster198 131 Posted January 25, 2022 Author Share Posted January 25, 2022 So condensing all this for my layman brain: the engines can in fact start and continue running with both Boost pumps off, because standby pumps take over? @Mathijs Koki understand the limitations of the simulation and what Aerosoft have chosen to model and not model, and I’m perfectly fine with that. But in this instance, it’s about where you draw that line - even the default MSFS aircraft will not run without their fuel supply turned on. (ignoring the above standby pump thing for a second). Link to comment Share on other sites More sharing options...
Dopster198 131 Posted January 25, 2022 Author Share Posted January 25, 2022 Actually, ignore me, I think I understand better now. I was conflating the overhead red fuel levers (which control the actual fuel supply) and the fuel boost pumps (which pump the fuel around) Feel free to close this topic Link to comment Share on other sites More sharing options...
Aerosoft Aerosoft Team [Inactive Account] 51558 Posted January 27, 2022 Aerosoft Share Posted January 27, 2022 Because we believe this topic has been answered we have closed it. If you have any more questions feel free to open a new topic. Link to comment Share on other sites More sharing options...
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