Typical Fast Jet Fuel system?
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Typical Fast Jet Fuel system?
A quick question for some jet drivers - Considering the rapid roll rates, hard turns with rapid reversals, ultra high rate climbs and descents, inverted flight and the range of "g" onsets involved in flying modern fast jets, can anyone describe a typical fast jet fuel system for me. Is it similar to standard airline transport type fuel systems but with higher pressure pumps etc etc or is it a totally different system of plumbing, baffles and pumps etc.
Just curious how the wet stuff safely manages to get through to the engines under such a dynamic and violent environment.
cheers
Vic
Just curious how the wet stuff safely manages to get through to the engines under such a dynamic and violent environment.
cheers
Vic
It's totally different, there are interconnected tanks in all sorts of places with lots of interconnecting spaghetti, solenoid valves and a computer or two. Don't even try and imagine it.
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Typically, each engine's fuel tank group has a collector box with a fuel boost pump. This box contains captive fuel, sufficient for x seconds of negative g manoeuvres, aerobatics etc.
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The fuel systems will generally have a series of transfer pumps, which will pump the fuel from the tanks, into a collector group, for example on Tornado there is one collector tank for the front group which feeds the left engine, and two smaller collector tanks for the rear group which feeds the right engine.
The collector tanks will then contain boost pumps to feed to the engine driven pumps, which really crank up the pressure. Most if not all modern aircraft will have double ended boost pumps, so that the fuel can be drawn from either end during inverted flight/negative g. Prior to this many older aircraft had a fuel accumulator to compensate instead, which stored a limited amount of fuel under pressure to feed the engines during negative g.
The Jaguar was designed around the transition period of accumulators to double ended pumps, so was initially designed to have both D.E. pumps AND fuel accumulators. In service however, the accumulators were never fitted, as they were found to be unnecessary, despite the fact that they still appear in the fuel system diagrams!
The collector tanks will then contain boost pumps to feed to the engine driven pumps, which really crank up the pressure. Most if not all modern aircraft will have double ended boost pumps, so that the fuel can be drawn from either end during inverted flight/negative g. Prior to this many older aircraft had a fuel accumulator to compensate instead, which stored a limited amount of fuel under pressure to feed the engines during negative g.
The Jaguar was designed around the transition period of accumulators to double ended pumps, so was initially designed to have both D.E. pumps AND fuel accumulators. In service however, the accumulators were never fitted, as they were found to be unnecessary, despite the fact that they still appear in the fuel system diagrams!
AC Fuel System
The AC fuel system is there primarily to transfer fuel to the engine(s) yet maintain the balance of the ac. The typical engine fuel pressure may be around 3000-3500 psi however, the ac systems are often low pressure 40-50 psi therefore ac pipes are high bore low weight aluminium and ecu pipework is high strength stainless steel. Nevertheless the ac system must cope with rapid changes in flow requirements, in and out of reheat, as well as extremely rapid changes of attitude and g loading. To that end your backing or booster pumps will supply far in excess of your max requirement and be returned to tank, sometimes via a cooling matrix to remove some heat from elsewhere in the engine, oil or fuel immediately before being burnt.
Accumulators were superseded by DE booster pumps. However if they fail, providing there is fuel being transferred into the collector tanks most Engine Driven Fuel Pumps will drag the fuel out. Fuel is usually transferred from other groups by dc electrical pumps submersed in the fuel. Fuel tanks are now almost exclusively integral and sealed whereas they were previously bag tanks. Most fuel managment/transfer is carried out automatically to maintain trim and balance.
One additional thing not often found on large aircraft, Fat Albert being the one exception I am aware of is the use of external fuel tanks. Usually the fuel is transferred up once there is sufficient space inside the fuselage, this can be either by pressurising the tank using engine bleed air and the pressure forces the fuel through a stack pipe or using dc pumps again. All other things; filters, pressure raising valves, non return valves, and low and high level sensing devices will be common.
All dead easy really.
Slopjockey
Accumulators were superseded by DE booster pumps. However if they fail, providing there is fuel being transferred into the collector tanks most Engine Driven Fuel Pumps will drag the fuel out. Fuel is usually transferred from other groups by dc electrical pumps submersed in the fuel. Fuel tanks are now almost exclusively integral and sealed whereas they were previously bag tanks. Most fuel managment/transfer is carried out automatically to maintain trim and balance.
One additional thing not often found on large aircraft, Fat Albert being the one exception I am aware of is the use of external fuel tanks. Usually the fuel is transferred up once there is sufficient space inside the fuselage, this can be either by pressurising the tank using engine bleed air and the pressure forces the fuel through a stack pipe or using dc pumps again. All other things; filters, pressure raising valves, non return valves, and low and high level sensing devices will be common.
All dead easy really.
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Pretty much exactly as I had previously said then Slops
Apart from your comment on typical system pressures.
Tornado's AC Booster pumps in the front and rear collectors operate at 4-5 bar. The Engine Driven Pump (FSP) raises this pressure to 14 bar. This is the dry engines system pressure, 213 psi. The reheat system obviously requires more pressure, hence the Vapour Core Pumps in the reheat fuel control unit, however, this is still nowhere near the 3000 - 3500psi you describe.
The hydraulic systems on a Tornado operate at around 3500psi, or 240 bar. The fuel system certainly does not.
I don't know if you are referring to large aircraft when you describe this type of system, but I find it hard to believe, not to mention inefficient, if there are fuel systems operating at 3000 psi.
Apart from your comment on typical system pressures.
Tornado's AC Booster pumps in the front and rear collectors operate at 4-5 bar. The Engine Driven Pump (FSP) raises this pressure to 14 bar. This is the dry engines system pressure, 213 psi. The reheat system obviously requires more pressure, hence the Vapour Core Pumps in the reheat fuel control unit, however, this is still nowhere near the 3000 - 3500psi you describe.
The hydraulic systems on a Tornado operate at around 3500psi, or 240 bar. The fuel system certainly does not.
I don't know if you are referring to large aircraft when you describe this type of system, but I find it hard to believe, not to mention inefficient, if there are fuel systems operating at 3000 psi.
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Thanks
And here I was, content with the concept of it being made of spaghetti.....
Thanks guys. It amazes me that that fuel, being as heavy as it is can still get through to the engines at exactly the rate with the huge changes in fuel flow from throttle slams and clicking in and out of burner the turning and rolling. Fadec probably helps at the terminal end of the fuel's journey too. It must work just fine, mid dogfight would not be the time to have to remember to turn on the fuel pump, switch over tanks with some lever on the floor, count to five and turn the pump back off.
Thanks for the replies.
cheers
Vic.
Thanks guys. It amazes me that that fuel, being as heavy as it is can still get through to the engines at exactly the rate with the huge changes in fuel flow from throttle slams and clicking in and out of burner the turning and rolling. Fadec probably helps at the terminal end of the fuel's journey too. It must work just fine, mid dogfight would not be the time to have to remember to turn on the fuel pump, switch over tanks with some lever on the floor, count to five and turn the pump back off.
Thanks for the replies.
cheers
Vic.
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Alberts Hyds work at 3000 (ish) psi ish however on the mighty J the fuel booster pumps work at 15 to 24 (ish) psi. I know we don't go upside down, look very exciting or pull loads of "G" but a fuel system working at 3000 psi
all spelling mistakes are "df" alcohol induced
all spelling mistakes are "df" alcohol induced
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Vic,
As you might have guessed from all these answers mate, it is pretty automatic.
Not in the same way as you describe though. The fuel systems as a whole will operate the same way if we were cruising at 1g for the whole trip, or if we were busy throwing ourselves aound the North Sea at 7g (
)
The systems are designed as such, that under all situations and operating conditions, they operate in the same way.
In Tornado for example
Tanks feed from Fin, FR groups, O, UWings, Wings (Not before 3250kg L Peacock before you start
) Wings, Main Group.
This in it's self ensures that all C of G limits are contained.
Sorry to bore you all again
Speke,
Imagine how large and solid those fuel pumps would have had to have been to consistantly produce 1400 psi (95.2 bar)
And we\'re talking over 40 years now!
Even in the combustion chamber, we\'re talking about pressures that are at their maximum 160psi, So why on earth would you need a 3340 psi differential at the injectors?
You wouldn\'t would you?
Sorry to be pedantic
3 Years as a JT apprentice A/P made me this argumentative
As you might have guessed from all these answers mate, it is pretty automatic.
Not in the same way as you describe though. The fuel systems as a whole will operate the same way if we were cruising at 1g for the whole trip, or if we were busy throwing ourselves aound the North Sea at 7g (
) The systems are designed as such, that under all situations and operating conditions, they operate in the same way.
In Tornado for example
Tanks feed from Fin, FR groups, O, UWings, Wings (Not before 3250kg L Peacock before you start
) Wings, Main Group.This in it's self ensures that all C of G limits are contained.
Sorry to bore you all again
Speke,
Imagine how large and solid those fuel pumps would have had to have been to consistantly produce 1400 psi (95.2 bar)
And we\'re talking over 40 years now!
Even in the combustion chamber, we\'re talking about pressures that are at their maximum 160psi, So why on earth would you need a 3340 psi differential at the injectors?
You wouldn\'t would you?
Sorry to be pedantic
3 Years as a JT apprentice A/P made me this argumentative
Last edited by The Rocket; 30th Aug 2005 at 00:00.
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Lo w pressure pumps on Albert operate at 15-24 psi. High pressure pumps (dump pumps, Aux and Ext tank fwd pumps) operate at 28-40 psi.
Methinks somebody confused fuel pumps with hyd pumps, since circa 3,000 psi is a fairly standard hyd pressure (2900-3200psi on Albert).
16B
Methinks somebody confused fuel pumps with hyd pumps, since circa 3,000 psi is a fairly standard hyd pressure (2900-3200psi on Albert).
16B
I think we are all getting confused here by different pressures.
V2, 'jet' engines burn stuff like paraffin - it is not flammable at room temp like petrol and you have to squeeze it at very high pressure through small orifices in the combustion chamber so that it atomises and then it will burn. That bit, from the high pressure (HP) fuel pump to the combustion chamber will work any way up at whatever g.
What I think you're after is how it gets from the tanks to the engine. In many of the manoeuvres you mention, the aircraft is still experiencing positive g - even upside down, like looping in a roller coaster. Even the other manoeuvres, if flown in balance, will not slosh the fuel around as much as in a race car. The problem comes with negative g. In aircraft likely to get thrown around, the tanks are compartmentalised. The tank which fuel is finally drawn from is called the collector tank. That is (usually) kept full by transfer from the other tank sections - this can be by gravity, pressure or by pumps. If the collector tank stays full then fuel can be pumped to the engine at any attitude. The collector contents could fall if transfer fails from the other sections - this could be due to loss of transfer pressure or even the fuel quantity becoming low (ie less than collector tank volume) - in this case the drill would be to avoid negative g so that fuel can still be drawn from the bottom of the collector tank. Even then, some systems have double entry pumps in the collector tank so that if the fuel is at the bottom (positive g) the bottom feed takes the fuel, if the fuel is at the top of the tank (negative g) the top end feeds. Also prolonged negative g may affect fuel transfer to the collector tank and this can be why some aircraft have negative g time limits (as well as other considerations like engine oil).
V2, 'jet' engines burn stuff like paraffin - it is not flammable at room temp like petrol and you have to squeeze it at very high pressure through small orifices in the combustion chamber so that it atomises and then it will burn. That bit, from the high pressure (HP) fuel pump to the combustion chamber will work any way up at whatever g.
What I think you're after is how it gets from the tanks to the engine. In many of the manoeuvres you mention, the aircraft is still experiencing positive g - even upside down, like looping in a roller coaster. Even the other manoeuvres, if flown in balance, will not slosh the fuel around as much as in a race car. The problem comes with negative g. In aircraft likely to get thrown around, the tanks are compartmentalised. The tank which fuel is finally drawn from is called the collector tank. That is (usually) kept full by transfer from the other tank sections - this can be by gravity, pressure or by pumps. If the collector tank stays full then fuel can be pumped to the engine at any attitude. The collector contents could fall if transfer fails from the other sections - this could be due to loss of transfer pressure or even the fuel quantity becoming low (ie less than collector tank volume) - in this case the drill would be to avoid negative g so that fuel can still be drawn from the bottom of the collector tank. Even then, some systems have double entry pumps in the collector tank so that if the fuel is at the bottom (positive g) the bottom feed takes the fuel, if the fuel is at the top of the tank (negative g) the top end feeds. Also prolonged negative g may affect fuel transfer to the collector tank and this can be why some aircraft have negative g time limits (as well as other considerations like engine oil).
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In my helicopter - we have a bucket in the back and the crewman pours it into the float chamber when it gets a bit low - at least I think that's how it works!
When he drops the funnel he makes an awful mess!
When he drops the funnel he makes an awful mess!
