Fuel Tank Pressurization

[Guest jase439]

Are the fuel tanks pressurized in this simulation? Page 74 reads:At high altitudes the fuel tanks are pressurised, thus facilitating fuel pumping and preventing fuel boiling, to a maximum of between 1.2 and 1.5 psi. This increasing differential pressurenecessary to maintain a minimum absolute tank pressure with increasing altitude.However, the fuel tank pressure is always reported to be 0.0 PSI regardless of altitude.J

[Guest Phoenix_7]

not possibleJohn PSS SUPPORTsupport@phoenix-simulation.co.ukhttp://www.avsim.com/pss/phoenix.jpg

[Guest jase439]

Not possible or not implemented? It does seem you *could* emulate this behavior.Speaking of fuel, I was sailing along at M2.0 last night, and my #4 tank went dry. My primary x-fers (5, 6, 7, and 8) were also empty at that point, with fuel flowing into the mains from Tank 11 (via 5 and 7). At the moment my #4 tank went dry - as if a magic wand had been waved - my primary x-fer tanks were instantly filled to the brim with fuel w/ no fuel drop from any other tank. The O/FULL lights illuminated for all the x-fer tanks. While the auto-refuel was 'compassionate', it threw my C/G steeply forward and I was unable to maintain M2.0 from that point. Are the tanks meant to "auto-refill" like that? I had my cross bleeds open, so I was expecting #4 to start drawing fuel from the other mains. The refill was very unexpected.J

[Guest Phoenix_7]

fuel transfer should go as followsduring takeoff climbtanks 5 and 7 reducetanks 6 and 8 should be shutCG moves forwardset transfer to rearwardfuel moves form 9 to 5 and 7climb continues to M = 2.00when 9 is dry set pumps offtank 10 reduces into 5 and 7when 10 dry set pumps offas 5 and 7 low press onset trans 5A-5 and 7A-7 onfuel goes from 5A,7A to 5 and 7as 5 and 7 go dryset 6 and 8 LH and RH pumps to onset 5 and 7 pumps to offwhen 6 and 8 go dryset pumps to offfuel is now provided directly from 1-4 to enginesJohn PSS SUPPORTsupport@phoenix-simulation.co.ukhttp://www.avsim.com/pss/phoenix.jpg

[Guest jase439]

The VFE was enabled at the time. Doesn't the VFE manage x-fer of the fuel?

[Guest Phoenix_7]

yesJohn PSS SUPPORTsupport@phoenix-simulation.co.ukhttp://www.avsim.com/pss/phoenix.jpg

[Guest jase439]

BTW, I don't mean "refill" in the standard fuel x-fer sense - I mean the tanks instantly went from 0 KG to 7,000+ KG's each, throwing the CG from far AFT to far FWD. A bad place to be at 2.0M and 60,000' ;-)

[Guest Phoenix_7]

only time I've heard of that was with 'unlimited' fuel checked??John PSS SUPPORTsupport@phoenix-simulation.co.ukhttp://www.avsim.com/pss/phoenix.jpg

[Guest jase439]

I'll see if I can repro. I don't ever run with unlimited fuel, but will double check that to make sure I didn't fat finger something in the realism dialog. From what I could see, there was a fuel imbalance on the #4 tank - it was running lower than the others for whatever reasons. When it ran dry, that was when all of the x-fer tanks went instantly full. The fuel panel was displayed at the time as I was curious what *would* happen when #4 ran dry. It almost appeared like the fuel gauges were resetting themselves to a default state.Normally, with a x-fer you would see a slow steady increase in 1 or more tanks and a slow steady decrease in another. This was as though I had invoked some magic "add fuel" cheat key ;-)J

[Guest jase439]

I can drive this bug now. Looks like a numeric overflow/underflow condition. I can provide repro steps if y'all are interested in investigating further.

[Guest jase439]

It appears that the AUX tank is mysteriously populated with some incredibly large value when one of the corresponding mains go dry. In this test, I emptied all but a little fuel in the mains, and some in Tank 11. I then let the #2 engine run dry. In this particular test, I intentionally turned off the pumps on tank 11, and closed the inlet valves going into the transfer tanks so fuel would not flow out of Tank 11 (I would have left Tank 11 empty for this test, but I was at altitude, and having no fuel in Tank 11 empty caused me all kinds of C/G badness). The crossbleeds valves on all the mains were open. I believe the latter point is an important step in reproducing this bug.It appears that the fuel quantity display actually went negative before all hell broke loose. I went to the FS fuel dialog after this happened and the Left Aux tank had gone from 0% to 51194%, yielding a net fuel weight of 21,039,504 lbs (~9.56 million kilos).That's alot of fuel - even for the concorde.If I were a bettin' man, I would venture to guess that the fuel remaining gauges do not properly account for crossbleed fuel usage and when an engine is being fed from another tank via the cross bleeds, it incorrectly decrements fuel from the tank that is empty causing some negative fuel remaining value to be generated (or insanely large positive value) which in turn causes FS to explode.Just a theory you might want to roll by Alex. I will create a scenario/situation "just" prior to the bug occurring and e-mail it to you.J

[Guest Phoenix_7]

J,I will try and reproduce this and send your report to Alex and EugeneThanksJohn PSS SUPPORTsupport@phoenix-simulation.co.ukhttp://www.avsim.com/pss/phoenix.jpg

[Guest Phoenix_7]

J,I found the followingif all crossfeeds openwhen tank 2 goes dry you get the refuel to 100%if all crossfeeds closedtank 2 goes dryengine stopsno refuelopen crossfeedsall ok, no refuelreport sent to AlexJohn PSS SUPPORTsupport@phoenix-simulation.co.ukhttp://www.avsim.com/pss/phoenix.jpg

[Guest jase439]

Yes. That is exactly what I observe on this end also. Thanks for the follow up.J