Falcon 900EX EASy / Falcon 900LX
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It follows that the total heat generated by a tankfull of 0.79 S.G. fuel is only 97.5% of that of the same tankfull of 0.81 S.G. fuel. Engine performance is unaffected; fuel may well be metered by volume but the lower the S.G. the more volume the FADEC demands to achieve the required thrust (2.5% more, using this example) and that reduces range by an equivalent amount.
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Except that your fuel goes into the nozzles at a constant temperature ( heat exchanger ) negating the "effect" of temperature.
This is why it does not matter much, and everyone is "creating" fuel by the end of cruise.
This is why it does not matter much, and everyone is "creating" fuel by the end of cruise.
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You cannot escape the fact that the calorific value of fuel is directly proportional to its mass, not its volume. A pound of fuel generates n units of heat (thrust) regardless of its S.G. and temperature but the volume of that pound varies with both these factors.
It follows that the total heat generated by a tankfull of 0.79 S.G. fuel is only 97.5% of that of the same tankfull of 0.81 S.G. fuel. Engine performance is unaffected; fuel may well be metered by volume but the lower the S.G. the more volume the FADEC demands to achieve the required thrust (2.5% more, using this example) and that reduces range by an equivalent amount.
It follows that the total heat generated by a tankfull of 0.79 S.G. fuel is only 97.5% of that of the same tankfull of 0.81 S.G. fuel. Engine performance is unaffected; fuel may well be metered by volume but the lower the S.G. the more volume the FADEC demands to achieve the required thrust (2.5% more, using this example) and that reduces range by an equivalent amount.
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The temperature of the fuel at the nozzle is totally irrelevant: the calorific value of a pound of fuel at 100C at the nozzle is exactly the same as it is at -10C in the tank. It is the temperature of the fuel at delivery to the tank that is important.
The volume of a unit mass of fuel changes by about 0.1% per 1C temperature change. A 1,000 litre tank will hold 800kg of 0.80 S.G. fuel at 15C. Because of expansion the same tank would hold only 784kg of fuel if it were delivered at 35C - so a range reduction of 2%. Conversely, 816kg of could be loaded if the delivery temperature was -5C giving an increase in range of 2%.
Now combine this with the discussion in my previous post - a tankfull of 0.79 S.G. fuel delivered at 30C will give 4.5% less range than that tankfull of 0.81 S.G. fuel delivered at 10C.
The 'creation' of fuel in flight is down to inadequacies in the fuel measuring system.
Lastly, be it a Gulfstream or a Falcon, it is a certification requirement that fuel expansion up to 2% (equivalent to heating it by 20C after delivery) will be accommodated by tank design.
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Not to mention the quality of the crude used to produce the fuel and the refining process. Irrespective of delivery temperature, the SG of a Jet A delivered in east asia will NEVER get even close to the one delivered in Canada for instance...
That's why my ORIGINAL question was about what quantity the Falcon 900 operators could expect normally...
That's why my ORIGINAL question was about what quantity the Falcon 900 operators could expect normally...
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Sorry Lelac, I can't help you there. It is some 15 years since I flew a 900 and apart from that it was a cracking aircraft to fly I don't remember much about the detail. My contribution was merely to address the notion that a full tank of fuel would 'get you there' regardless of other factors.
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Quantity goes to the float switches when full, then you will have the above answer that will go into computations to tell you that you will be heavier in winter and lighter in summer. And one guy telling you that he flies 4650 AIR MILES with its bird....
Dassault planes are flying like the book if they are flown like the book says.
QUALITY of fuel is far more important than its temperature, and (except when bags or pax were SUPER heavy, and not weighted) I flew the 2000, the 900 and the GLEX with their numbers on OFP, even if leaving the ground with 1000 to 2000 less than indicated required, upon arrival, numbers are matching.
But i do agree with everything written above... in a perfect world of entropy and exergy..
Dassault planes are flying like the book if they are flown like the book says.
QUALITY of fuel is far more important than its temperature, and (except when bags or pax were SUPER heavy, and not weighted) I flew the 2000, the 900 and the GLEX with their numbers on OFP, even if leaving the ground with 1000 to 2000 less than indicated required, upon arrival, numbers are matching.
But i do agree with everything written above... in a perfect world of entropy and exergy..
