Below 2000lbs fuel + negative G's = flameout?
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IIRC, AB depletes fuel from the reserve tanks faster than the pumps can feed it from the rest of the fuel system. Flameout can occur if the reserve tanks are not near full : with neg Gs, fuel will flow away from the feeder and flameout occurs, as you feed air instead of fuel.
Check again in your scenario, but put the fuel quantity selector switch (near the HSI) to RSVR. If the Aft and Fwd needles are not near 480, that’s your explanation
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Chirschn posted a link to screenshot on post#5:
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Well, the fuel QTY switch is on NORM and not RSVR, so I cant really tell if my theory is correct
I cant tell if those 500 fwd lbs and 1500 aft lbs are in the wings or in the reserve tanks
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Well, the fuel QTY switch is on NORM and not RSVR, so I cant really tell if my theory is correct
I cant tell if those 500 fwd lbs and 1500 aft lbs are in the wings or in the reserve tanks
Indeed
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This is because you are failing to understand the system in full and you are giving a scenario not even covered under what you referenced. That quote is talking about just normal engine running not full AB operation. Even with normal conditions the system cannot maintain full fuel flow in full AB forever. There are two ways that the engine is fed through the res tanks. One is bolted to the floor and thus negative Gs impact or remove it’s ability to feed the engine. You doing that while asking for max fuel flow of course you are going to flame out.
This situation is also not one you are going to be duplicating in real life scenarios. The goal of the BMS team is to make a simulation that behaves as close to real as they can. This is just making it more realistic to how the real deal would behave.
The AB doesn’t matter only the G’s do. I just tested it again. Fuel Flow Rate at idle 800 and I managed to cause a flameout again at just below 2000lbs. I only wrote about the AB to remove the excess fuel faster to get below the 2000 mark. I’ll do more testing tomorrow but in the meantime maybe you can answer these two questions: are the RSVR tanks supposed to be the last tanks to be drained or not? What’s the significance of the 2000 lbs mark?
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Well, the fuel QTY switch is on NORM and not RSVR, so I cant really tell if my theory is correct
I cant tell if those 500 fwd lbs and 1500 aft lbs are in the wings or in the reserve tanks
Cruz
Check my last commit , I had issues with AI and flame out though I checked that fueflowrates are correct and RSVR should never empty …
So considering the report of the OP I suggest to have a deeper look
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Well, the fuel QTY switch is on NORM and not RSVR, so I cant really tell if my theory is correct
I cant tell if those 500 fwd lbs and 1500 aft lbs are in the wings or in the reserve tanks
I’m not sure I follow? The fuel qty selector is on Norm in the picture above. The first picture I posted showed another screenshot with the RSVR tanks both at 500lbs. You can load up the AAR mission for more detail.
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Cruz
Check my last commit , I had issues with AI and flame out though I checked that fueflowrates are correct and RSVR should never empty …
So considering the report of the OP I suggest to have a deeper look
I can have a deeper look indeed
I’m not sure I follow? The fuel qty selector is on Norm in the picture above. The first picture I posted showed another screenshot with the RSVR tanks both at 500lbs. You can load up the AAR mission for more detail.
There are 2 fuel switches : the ENG FEED switc, on the left panel. And the FUEL QTY switch near the HSI that you showed on the picture above.
ENG FEED should stay in NORM to ensure fuel feeds from both the aft and fwd reserve tanks.
FUEL QTY has no impact on the fuel system, only on the fuel quantity display. I asked for you to put it on RSVR so we can check what the reserve tanks level actually is, since its the only one that matters there I didnt find your pic with it on RSVR and both needles at 480 lbs. I just tested, and I can trigger a flameout with both reserves at around 480 lbs, which should not be possible indeed So a deeper look will be had
EDIT : ok, found your pic, and I have the same.
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I can have a deeper look indeed
There are 2 fuel switches : the ENG FEED switc, on the left panel. And the FUEL QTY switch near the HSI that you showed on the picture above.
ENG FEED should stay in NORM to ensure fuel feeds from both the aft and fwd reserve tanks.
FUEL QTY has no impact on the fuel system, only on the fuel quantity display. I asked for you to put it on RSVR so we can check what the reserve tanks level actually is, since its the only one that matters there I didnt find your pic with it on RSVR and both needles at 480 lbs. I just tested, and I can trigger a flameout with both reserves at around 480 lbs, which should not be possible indeed So a deeper look will be had
EDIT : ok, found your pic, and I have the same.
Oh okay! Sorry if I caused any confusion
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So I checked. This is a peculiarity of the D model, I believe
Essentially, in normal conditions, the engine is fed equally from the FWD and AFT circuit. However, the D model has around 1000lbs less in the FWD circuit compared to the AFT circuit, because of that pesky backseat.
The result is that in a low fuel situation (like around 2000 lbs), the FWD reserve is not full anymore, when the AFT full reserve is still full and has 1000 lbs more in the main AFT tank to back it up.
As a result, in neg Gs, what happens in the code now is that the FWD tanks being not full and with neg Gs, the FWD pump ingests air (because fuel is displaced to the top of the tank) and that causes a flameout.
So the code works as intended, but to be extra sure, I’m asking a specialist to see if our modeling of the situation when only one of the 2 pumps ingests air is correct.
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The AB doesn’t matter only the G’s do. I just tested it again. Fuel Flow Rate at idle 800 and I managed to cause a flameout again at just below 2000lbs. I only wrote about the AB to remove the excess fuel faster to get below the 2000 mark.
OK just a language issue then as the way it was written sounded like you were doing this test at 2k fuel in AB which is just a little crazy. As long as the engine feed knob is in normal this shouldn’t be a thing. The two fuel pumps in the reservoir tanks will easily keep the engine running at 800 PPH regardless of inverted or negative G…
I’ll do more testing tomorrow but in the meantime maybe you can answer these two questions: are the RSVR tanks supposed to be the last tanks to be drained or not? What’s the significance of the 2000 lbs mark?
Yes the reservoir tanks are the last to empty. L3crusader covers the significance of 2k fuel is and this would be BMS only. The real deal won’t do that at your stated 800 PPH if the engine feed knob is in normal. If it is in the off position it would certainly flame out but that wouldn’t be limited to 2k fuel but at any fuel quantity remaining.
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So I checked. This is a peculiarity of the D model, I believe
Essentially, in normal conditions, the engine is fed equally from the FWD and AFT circuit. However, the D model has around 1000lbs less in the FWD circuit compared to the AFT circuit, because of that pesky backseat.
The result is that in a low fuel situation (like around 2000 lbs), the FWD reserve is not full anymore, when the AFT full reserve is still full and has 1000 lbs more in the main AFT tank to back it up.
As a result, in neg Gs, what happens in the code now is that the FWD tanks being not full and with neg Gs, the FWD pump ingests air (because fuel is displaced to the top of the tank) and that causes a flameout.
So the code works as intended, but to be extra sure, I’m asking a specialist to see if our modeling of the situation when only one of the 2 pumps ingests air is correct.
First of all thank you for digging into the code that quickly Just my luck that I ended up testing something related to the fuel systems while flying the F-16D model which seems to have that quirk IRL too but seriously the level of detail is just mind blowing! You guys rock!
Since I couldn’t sleep I also went ahead and created my own test mission with the F-16CM Block 50 (the plane I flew that made me investigate flameouts in the first place) and the Block 52 just to be sure. It seems to be working correctly with those two. No flameout above 1000lbs! I must’ve dropped below the threshold in my campaign mission without realizing (I was concentrating on getting back to the tanker during a turn) and then in order to investigate the issue ended up with the D model… at least I’ve learned a lot about the fuel systems!
Thank you all for helping out!
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Ditto on the level of detail and effort that went into these features…
I asked for this in the last iff thread, a bit tongue in cheek, not thinking it would happen.
4.34 has blown me away, and I’ve barely started to dig into it!
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4.34 has blown me away, and I’ve barely started to dig into it!
Indeed. This is a very good time to be a BMS pilot.
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As a result, in neg Gs, what happens in the code now is that the FWD tanks being not full and with neg Gs, the FWD pump ingests air (because fuel is displaced to the top of the tank) and that causes a flameout.
So the code works as intended, but to be extra sure, I’m asking a specialist to see if our modeling of the situation when only one of the 2 pumps ingests air is correct.
So I did ask, and that wasnt actually correct. If one of the pump ingests air, the volume of air actually fed will be negligible compared to the other pump’s fuel output.
Correction is easy enough
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How about on engine side? I seem to recall that there are negative G limitations on the oil sumps for some engines/variants - is that also included/already in there?
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if I remember corectly if inverted more than 30s HYS/OIL may lights up. But no real engine limitation. Is not implemented in game.
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That’s at least start…thanks.
One would think that if you continued with the OIL lights up for some time that you might eventually get a bearing failure…and/or engine fire. Something maybe worth looking into for the future?
I like the fuel management thing…that’s cool!
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One would think that if you continued with the OIL lights up for some time that you might eventually get a bearing failure…and/or engine fire. Something maybe worth looking into for the future?
Already asked … No idea if it will/could be done.
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Another failure to understand how the res tanks feed. If you go to engine feed off and go inverted or negative G you are removing most, if not all, of the systems ability to feed the engines. That you should be able to duplicate at any fuel load and would be the normal response to an abnormal input.
Or from BMS1F-16CM-1 Page 123 in reference to the engine feed knob.
“With the knob in OFF none of the pumps work and fuel transfer occurs only via gravity and siphoning action. During heavy manoeuvring or negative G the engine may flame out.”
And a failure tot Read the post correctly. But thanks for the use of more words to say the same thing