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Guest Ian_K

PSS-Vulcan Fuel Consumption

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Has anyone had any luck in correcting the very high fuel consumption with this aircraft. Some have done tests that show a range of only around 1200nm being possible. I can concur with this having at cruise recorded 37,000lb/hr at mach 0.84 alt 40,000ft 86-89% thrust.Can any one help with where I should start if it's not already been done. I am a complete newbie to editng cfg files in this - so be gentle with any explanations.Brian.

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Hello Captain,FAQ 42:Does anyone know if, in FS200?, there is a way to adjust the fuel burn in jet aircraft? Hello,yes we do. Other than adjusting the throttle, do you mean the specific fuel consumption (SFC). The default is 0.5 h-1 which is multiplied by the fuel_flow_scalar in the .cfg file. Concorde is a bit different with reheat etc.You may have a fuel prediction from a Flight Planner, Flight Manual or a description included with the model. All of these will be wrong unless the model is well designed and you take into account all-up take-off weight, head winds, reserves etc.What can go wrong:MS screwed up with a constant value of the specific fuel flow. It is the airframe type default value multiplied by the fuel_flow_scaler in aircraft.cfg. In a car you have miles per gallon. In jets you have lbs of fuel burnt per hour per engine per lb of thrust being generated at any time. This is the SFC.In a long flight most of the fuel will be burnt in cruise so you want the cruise sfc. Most engine manufacturers specify this at M0.8 and FL350 and this is listed in Janes All the Worlds Aircraft until recently. Take off SFC can be twice as high.The designer may have screwed up by using a bad choice for the fuel_flow_scalar value. The only thing is to change this and to fly in the best flight profile which is defined in terms of MN and FL with changes made at specific values of remaining aircraft weight. There are Boeing manuals freely available for many types but the 777 is not one of them yet.Ian

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Thanks for the info.Which way do I adjust the Scalar do I increas it to increase fuel flow or the other way around?Will changing this figure have an effect on any other flight characteristics. i.e thrust Rgds,Captain B

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Double the scaler to double the fuel flow and half the range. Thrust is not effected.Ian

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>Hello Captain,>FAQ 42:>>Does anyone know if, in FS200?, there is a way to adjust the>fuel burn in jet aircraft? >>Hello,>yes we do. Other than adjusting the throttle, do you mean the>specific fuel consumption (SFC). The default is 0.5 h-1 which>is multiplied by the fuel_flow_scalar in the .cfg file.>Concorde is a bit different with reheat etc.>... In jets you have lbs of fuel burnt per hour per engine>per lb of thrust being generated at any time. This is the>SFC.>In a long flight most of the fuel will be burnt in cruise so>you want the cruise sfc. Most engine manufacturers specify>this at M0.8 and FL350 and this is listed in Janes All the>Worlds Aircraft until recently. >>Take off SFC can be twice as high. No. Static and low Mach (initial climb) SFC is lower, not higher. You know that. ;) I think that's how MS figured the default 0.50 lb per lb/hr. 0.40 to 0.50 is typical for STATIC SFC. Often, only Static SFC is given for a turbine. However, SFC always increases as speed increases. Best (lowest) is about 0.55 lb per lb/hr, but a JT8D runs more like 0.84 in cruise. While old turbojets run about 1.l in cruise. So, fuel_flow_scalar should be between 1.1 to 2.2 to get correct cruise PPH. Assuming appropriate drags are set.>The designer may have screwed up by using a bad choice for the>fuel_flow_scalar value. More typically hasn't changed from the default. Leaving the excessively low 0.50 lb per pph default. ;) Maybe making up by setting excessive drags. Of course, that screws up other things.>MN and FL with changes made at specific values of remaining>aircraft weight. There are Boeing manuals freely available for>many types but the 777 is not one of them yet.>Ian The 777 uses modern turbines, SFC in cruise would be the same as for the 747-400: 0.560. With correct (low) drags, PPH, range, etc would come out fine.Ron

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I shall remove the offending line.SFC is useful for piston a/c but like a lot else got transfered to jets irrespective of whether it was a good idea or not.The SFC of normally aspirated pistons is about 0.55 /h/bhp but many (smaller) jets run at about 1000 lb of fuel/h when idle so SFC varies a lot with throttle and a little with air temperature.A more useful term would be the ratio of fuel flow MINUS idle fuel flow to net thrust. This is sensibly a constant so FF = FF_idle + the_new_coef* net thrust.In most of the jets I analyse I get these straight lines and when corrected to non-dimensional values they merge into a single line.Now why did Bruce Artwick not do that for jets so MS could steal it (err buy in a mutualy agreed contract) for MSFS.The other term I was eluding to was the Exhaust Gas Temp (EGT) would be better called the Jet Pipe Temp (JPT) as it is in British practice.Ian

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