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Guest chrut

FSMC Fuel logic B744 FSX

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Guest chrut

Good day!So I was reading the PMDG 747 manual and came across the airplane limitations pages. Here I was reading about fuel distribution and logic. Whenever the tanks are all full, all fuel pumps switches should be on - so far so good. But here is where I run into a problem (p. 7 Specifications and Limitations):"When Flaps Extended: FSMCs close crossfeed valves 2 & 3. Override pumps fuel engines 1 & 4, main tank pumps fuel engines 2 & 3. When Flaps Retracted: FSMCs open crossfeed valves 2 & 3. Override pumps in center tank fuel all engines."So when I select takeoff flaps (20 in my case) and they are in transit, crossfeed valves 2 & 3 remain open, center tank still feeds all engines (this could be accurately modeled, as there says nothing about FSMC closing/opening crossfeed valves when they are in transit). After the takeoff flaps are in place (20) the FSMC closes crossfeed valves 2 & 3 correctly, but the centertank isn't letting the override pumps feed the engies instead. The center fuel pumps, when switched off, goes inactive and only then let override pumps activate. When center tank pump is turned on again, override pumps goes inactive. It should also be noted that when flaps setting 1 and 5 is selected, the FSMC does nothing (crossvalves open and center tank still feeds all engines).Pictures below:I've just started to taxi after pushback and selected take off flaps earlier than I would, just to show you that when the flaps are in transit, the FSMC doesn't do anythingTakeoff flaps 20 are in place, crossfeed valves 2 & 3 are closed automatically but the center tank remains activeHere I de-select flaps, just to show what happend when flaps are in transit From the overhead panel, I've switched off center fuel pumps and only then the override pumps correctly becomes activeWhen center fuel pump switches are turned on, the same tank is feeding all engines, override pumps go inactive

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Hi, I think there is a typo in the limitations chapter (should read center pumps, not override center pumps).Take a look at page 46 (Aircraft Systems):See your 2nd and last picture: The FSMCs will close crossfeed valves 2and 3 when takeoff flap settings aredetected on the ground. The center wingtank will provide fuel to engines 1 and 4,while engines 2 and 3 will receive fuel fromtheir respective main tank. In thisconfiguration, the override/jettison pumps fortanks 2 and 3 will be inhibited fromoperating. When flaps are retracted, the FSMCsautomatically re-open crossfeed valves 2and 3, and the center tank will now providefuel to all four engines.Jan-Paul

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Guest chrut
Hi, I think there is a typo in the limitations chapter (should read center pumps, not override center pumps). Take a look at page 46 (Aircraft Systems):See you 2nd and last picture: The FSMCs will close crossfeed valves 2and 3 when takeoff flap settings aredetected on the ground. The center wingtank will provide fuel to engines 1 and 4,while engines 2 and 3 will receive fuel fromtheir respective main tank. In thisconfiguration, the override/jettison pumps fortanks 2 and 3 will be inhibited fromoperating. When flaps are retracted, the FSMCsautomatically re-open crossfeed valves 2and 3, and the center tank will now providefuel to all four engines.Jan-Paul
Most excellent, thanks! But what about when they are in transit? Normal?

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Guest chrut

Never mind, thanks to Paul I got this sorted out. Thanks!

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