Fuel Imbalance Question
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The TE TR433_02_Navigation starts with this fuel gauge
After reading the dash-1 on p118, I got to ask: What is the imbalance that it’s showing and what are you supposed to do to fix it? -
I believe what this is telling you is that you have too much fuel in the forward set of internal tanks; i.e. - you are nose heavy, which is a bad situation to be in for landing.
What I do (and I’ll bet it’s not strictly Dash 1 procedure) is to turn the Engine Feed knob to burn from the appropriate tank set (fwd or aft) until the imbalance is resolved or lessened. Once resolved, I place the knob back to NORM.
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I believe what this is telling you is that you have too much fuel in the forward set of internal tanks; i.e. - you are nose heavy, which is a bad situation to be in for landing.
What I do (and I’ll bet it’s not strictly Dash 1 procedure) is to turn the Engine Feed knob to burn from the appropriate tank set (fwd or aft) until the imbalance is resolved or lessened. Once resolved, I place the knob back to NORM.
It is, actually. Way to go! The only steps you are missing are to test the pointers and to assess whether a fuel leak exists, and whether trapped fuel in externals exists.
@jc1:
The TE TR433_02_Navigation starts with this fuel gauge
After reading the dash-1 on p118, I got to ask: What is the imbalance that it’s showing and what are you supposed to do to fix it?Pretty much what Stevie said. The F-16 has several fuel tanks, and its center of mass moves around a bit during flight. As the position of the CoM affects the handling characteristics of an aircraft significantly, several systems are in place to manage the levels of fuel in these tanks, so as to prevent the center of mass moving too far outside a certain limit. These systems work by labeling each tank as being either a forward tank, or an aft tank, and trying to keep the total weight forward and the total weight aft fairly similar to each other.
Normally, fuel is pumped from both sets of tanks simultaneously, using a suction feed called the Fuel Flow Proportioner, which is augmented by fuel pumps. This keeps the fuel level in both sets of tanks about the same, because the fuel is fed evenly from both sets of tanks. Under normal conditions, a fuel imbalance simply doesnt happen. In the real jet, its most common to happen if fuel becomes trapped in an external tank and stops feeding correctly. In BMS, I dont think Ive ever had a fuel imbalance situation.
If the CoM moves too far aft (a fuel imbalance exists and the aft tanks are much heavier than the forward tanks), fuel is automatically pumped into the forward tanks. If the CoM moves too far forward, there is not an automatic system to correct it. In both cases, the pilot should identify the issue, and assess whether the imbalance is due to faulty pointers showing incorrect positions on the fuel gauge, or due to trapped fuel in external tanks, due to a fuel leak, or due to a fault with the FFP or another part of the fuel system. In all cases, the pilot should attempt to correct the imbalance before landing, and should attempt to limit AoA to less than 15 in the case of an aft imbalance.
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Too little fuel forward, too much fuel aft. Turn the feed knob to rear to drink from the aft tanks.
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Too little fuel forward, too much fuel aft. Turn the feed knob to rear to drink from the aft tanks.
Wait a minute. This is just the opposite of what Stevie and Blu3wolf said.
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Think of it this way - it you burn from the front only the needle will fall and cover the red - thus, too much fuel in the forward tanks.
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Think of it this way - it you burn from the front only the needle will fall and cover the red - thus, too much fuel in the forward tanks.
Makes sense to me, but what about Frederf?
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…methinks he will land nose first.
Yes he would. I just took the flight, with the feed knob forward, not aft. The imbalance corrected.
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Answered my own question by testing two TEs with a B and a D model and both gauges looked fine. That would make Stevie/Blu3wolf correct and Frederf backwards.
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@jc1:
Yes he would. I just took the flight, with the feed knob forward, not aft. The imbalance corrected.
If you have the feed knob in normal from the start then barring a very strange setup (one wing tank load versus two) then the aircraft maintains it’s own fuel CG.
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@jc1:
Makes sense to me, but what about Frederf?
That’s a D-model gauge yes? The aft tank should exceed the forward for in-limits CG. The needles being at the same place suggests excessive forward fuel and excessive positive stability.
C-model gauge is the other way around.
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That’s a D-model gauge yes? The aft tank should exceed the forward for in-limits CG. The needles being at the same place suggests excessive forward fuel and excessive positive stability.
C-model gauge is the other way around.
Frederf check again with 4.33. With 4.32 that would have looked fine but they fixed the B/D model gauges in 4.33 so they show in balance like they should on two seaters. Both the ground ops (B model) or the AAR (D model) TEs show it being good now.
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If you have the feed knob in normal from the start then barring a very strange setup (one wing tank load versus two) then the aircraft maintains it’s own fuel CG.
…huh. I wonder if that is modeled in BMS? I would suspect it is. I have to suspect, as I have not once tried an assymetric loadout with the wing tanks before.
There is also the potential for trapped fuel in a wing tank causing fuel to flow into only one wing, which would also cause an imbalance, but Ive not ever seen that happen in BMS.
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…huh. I wonder if that is modeled in BMS? I would suspect it is. I have to suspect, as I have not once tried an assymetric loadout with the wing tanks before.
There is also the potential for trapped fuel in a wing tank causing fuel to flow into only one wing, which would also cause an imbalance, but Ive not ever seen that happen in BMS.
It is. I have flown this way a few times. Just select wing first and the single tank drained just fine. It is an odd way to configure a jet I will give you that.
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please do your homework about fuelsystem before spreading wrong info to the Op
Fwd /Aft unbalance means you have a right / left imbalance and thus need to trim roll inbalance.
Gc longitudinal evolution is of course modelled as well but is not related with Fwd / aft unbalance.
shame the fuel article is no more available, someone should put it back solwhere
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Given that its FR and AL, it would depend on how much fuel you have left, as to whether the effect will be a net pitching moment, or a net rolling moment.
If no fuel remains in the wing tanks (internal and external) then it would seem highly unlikely that a roll trim will be required.
As far as homework… my source is a -1. If Im spreading wrong info here… perhaps there is some disconnect between the dash and the simulator?
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Given that its FR and AL, it would depend on how much fuel you have left, as to whether the effect will be a net pitching moment, or a net rolling moment.
If no fuel remains in the wing tanks (internal and external) then it would seem highly unlikely that a roll trim will be required.
As far as homework… my source is a -1. If Im spreading wrong info here… perhaps there is some disconnect between the dash and the simulator?
you are right but that means you and me need to be more precise for everyone.
as long as fuel is in wings or ext wing tank, aft / fwd will act on Roll inbalance and gc long, then when empty GC longitudinal only.
but lets be clear, flcs handles automatically the longitudinal imbalance whereas pilot must trim in roll.
in consequenve Fwd / Aft inbalance for the pilot has only an effect on roll triming.
i included in the fuel article the evolution of GC long during a typical mission…. (ext tanks are for example splitedd in 3 tanks each…)
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from the TE builder perspective, here is what happened
- there is no way currently to start TE in the air with less fuel load than full
- the TE uses script to dump fuel
- the fuel imbalance is not meant on purpose but inevitable due to the dump fuel scripts.
- Bug report was filled in on the issue
- I knew this would raise a few question from the usual suspect (who all chimed in in this discussion so far ) but it was decided low priority. Which makes sense since the F-16 is not supposed to be able to dump fuel anyway
The fuel article explained it well, but so does the BMSdash1 p118
Since the left and right side empty first into the fuselage any kind of imbalance happening soon after takeoff will probably induce a shift of the CG to the left or to the right, inducing a roll which can be neutralized with the aileron trim in the exact same way an asymmetrical loadout is compensated.
That roll will be noticed before the external wing tanks are empty and if you succeed in overcoming the temptation to check the possibility of joystick drift, you will probably realise something is wrong with your load. Since your weapons haven’t been dropped yet you should think about a potential fuel imbalance problem.
Furthermore as said above, when one of the wing tanks starts to empty you might get a TRP FUEL warning signalling that some fuel is trapped in the other external tank. That is your second clue.
If you need a third clue you should consider playing PS3 games The second type of imbalance will happen when the wing tanks are empty (both external and internal) and concerns only the internal fuselage tanks. If they empty into the FFP unevenly the difference in weight will induce a shift of the CG forward or backward.
That imbalance is much harder to detect by simply flying the aircraft and may induce serious problems in some envelopes of the flight model: the aircraft becomes more prone to departure of controlled flight under certain AOA.
The only way to detect such a condition early is to check the needles on the fuel quantity gauges as often as possible. As long as you don’t see the red portion of the needles there is no fuel imbalance problem. The red portion of the needles becomes visible when the difference between the two needles is more than 600 lbs.As far as homework… my source is a -1. If Im spreading wrong info here… perhaps there is some disconnect between the dash and the simulator?
In the course of writing manuals I learned that reading docs often not enough. Very often actually tetsing in the game provide much better answers
the left/right trim at imbalance if I remember right is quite left unexplained precisely in the real dash1Red Dog
Reality if for ppl who can't handle simulation -
Indeed, but trim is not really the issue there. Trimming out the roll moment is a ‘nice to have thing’, whereas keeping the CoM within the limits is a ‘must have thing’. FLCS will trim for 1G, but the trim isnt the issue being addressed. The ability to maintain control of the aircraft without a departure is what is being addressed.
I wasn’t even thinking about trim with my post. The focus was meant to be on keeping the CoM forward of the aft limit.
