Low Fuel Warning System

antz · by **antz** » 06 Jun 2013, 12:35

Hi,

Iwould like to know in C model why do the fwd fuel low come on at 400 lbs & the aft fuel low come on at 250lbs where in D model the fwd fuel low come on at 250lbs & the aft fuel low come on at 400 lbs.

fiskerwad · by **fiskerwad** » 06 Jun 2013, 19:49

antz wrote:Hi,

Iwould like to know in C model why do the fwd fuel low come on at 400 lbs & the aft fuel low come on at 250lbs where in D model the fwd fuel low come on at 250lbs & the aft fuel low come on at 400 lbs.

I think it has something to do with center of gravitas or something?
fisk

exfltsafety · by **exfltsafety** » 06 Jun 2013, 19:57

I think the difference is a result of the smaller F-1 fuel tank in the two-seater. Because of that the single-seater has more fuel in its forward tank system than its aft tank system and the two-seater has more fuel in its aft tank system than its forward tank system. Having the settings as they are means that both versions will be at about the same total fuel level of 400 pounds when the second low light comes on.

mor10 · by **mor10** » 07 Jun 2013, 02:59

The A model have a 2000lbs tank behind the cockpit while the B has no tank there, hence 2000lbs less fuel. I guess this is similar for the C and D models.

exfltsafety · by **exfltsafety** » 07 Jun 2013, 14:20

lamoey wrote:The A model have a 2000lbs tank behind the cockpit while the B has no tank there, hence 2000lbs less fuel. I guess this is similar for the C and D models.

The B and D have a tank behind their cockpits; it's smaller than the one behind the A and C cockpits.

f16fuelguy · by **f16fuelguy** » 09 Jun 2013, 02:56

in the C model in the FWD reservoir there are 2 fuel pumps one mounted on top of the tank and one on the bottom, and the AFT Res tank only one pump mounted on the bottom of the tank.
In the D model it is switched, so that is why the low level light is different.
the low level light comes on when the reservoir fuel level drops down, it dose not matter how much fuel is in the rest of the aircraft

exfltsafety · by **exfltsafety** » 09 Jun 2013, 14:10

The upper fuel boost pump's purpose is to support negative g flight. It was put in the reservoir tank that is normally the last tank to empty (forward res for single seater and aft res for two seater). The differing placement of the upper fuel boost pump and the differing fuel low caution lights are both a result of the smaller F-1 tank in the two seater.

guardbaby · by **guardbaby** » 12 Jun 2013, 15:25

The 5-2 has a good "Fuel Sequence, Pounds Expended and Fuel Differential" chart which shows you the tank totals and fuel burn sequence of between the single/double seat aircraft.

duvshack · by **duvshack** » 13 Feb 2018, 07:05

antz wrote:Hi,

Iwould like to know in C model why do the fwd fuel low come on at 400 lbs & the aft fuel low come on at 250lbs where in D model the fwd fuel low come on at 250lbs & the aft fuel low come on at 400 lbs.

The C model fuel system has a larger FWD fuel system; thus the low fuel coming on at 400 lbs FWD and 250 AFT.

The D model fuel system has a larger AFT system; thus the low fuel coming on at 400 lbs AFT and 250 FWD.

As mentioned previously, the #3 B/P changes from FWD (C) to AFT (D) Res (follows the larger of the two systems, which would be the absolute last few hundred pounds of fuel if it were to run that low.