Cruise Altitude Fuel Burn at Various Gross Weights

[Guest]

Hi,Does anyone have information/opinion on whether FS2002 adequately accounts for gross weight when calculating fuel burn? In running a flight using a 737-200 from SJC to LAX, I get the following:115,000 lb t/o weight: 4935 lbs used73,000 lb t/o wt: 4554 lbs usedBoth flights used a 35,000 ft cruise altitude @ .76M.It seems to me that the difference should be greater. Is there anything in the aircraft.cfg file I could adjust to fix this, or does it even need fixing?Thank you,Kurt

[michal 44]

I am not sure. But unless you are an air/engine file expert if you fix this something else may get screwed in the process. If it bothers you enough I would rather use some well known add-ons that have all these elements right from start. Michael J.

[Guest GabrielR]

Trying to answer the question: Coudnt agree more with the response, I use also the default, I'm not an expert, but taking a look at some of the figures, and the data from the manufacturers (I spent one week doing that with the 744 and the 734) I can guess that this fuel burn is not completely accurate. I am not trying to put anybody down, I think that MS did a great job, given the circumstances, and you can get an "average" fuel consumption that is close to reality. If you have the time, and given the fact that in the sim you can have ideal conditions, try to have your own figures of fuel usage for every phase of the flight. if you dont have the time, there are some people that have done this and have nice data (check out the pilot's assistant in the partners section in AVSIM) Michal, which add ons do you think are closer to reality? I woul die to try them.

[michal 44]

Heard of 767PIC ?? - probably the most "famous" example. Also DF737 by Dreamfleet. There may be others I didn't use however. All above are payware, but then how about Bill Grabowski's ERJ-145 - freeware. Heard good things about Falcon 50 - another probably outstanding freeware.Michael J.

[Guest]

It doesn't seem like it would be a problem with FS, itself, but with the model I'm trying to use. I suppose if I can't solve it I could always adjust the fuel scalar depending on the payload.Thanks,Kurt

[Guest Ron Freimuth]

>Does anyone have information/opinion on whether FS2002 >adequately accounts for gross weight when calculating fuel >burn? It can, but only if the AIR file is accurately modeled. I aim for +-3% in PPH at a given FL, speed, and weight. At the LRC (Long Range Cruise) Mach, real AC range should be within 1% of the maximum range (which would occur at some lower Mach number). At higher than LRC Mach range should decrease, rather rapidy at the highest normal cruise speed. Best range at a given weight requires the FL to be appropriate. At lower or higher FL's range will decrease. Perhaps by 4% if one is 2000 ft higher or lower than optimum for the current weight. > In running a flight using a 737-200 from SJC to LAX, >I get the following: >>115,000 lb t/o weight: 4935 lbs used >73,000 lb t/o wt: 4554 lbs used >>Both flights used a 35,000 ft cruise altitude @ .76M. >It seems to me that the difference should be greater. Is >there anything in the aircraft.cfg file I could adjust to >fix this, or does it even need fixing? >Thank you, >Kurt The ratio of fuel used for the two weights doesn't look that far off. But, I don't have my 737-300/400 data handy. Seems the -300 should burn something in the range of 4200 to 5300 pph at Mach 0.745, FL 350. Depending one TO weight. So, what I remember is a higher ratio than what you show. But, your flight isn't that far, so climb and descent have a significant effect. Typically, FS AIR files set Induced drag at LRC and higher speeds as to low as weight and/or altitude increases. If Induced Drag were zero, weight would have no effect on drag and thus PPH. Further, range will increase, rather than decrease at Mach numbers higher than the appropriate LRC speed. TBL 401 in an AIR file affects how much lift and Induced Drag decrease at significant Mach numbers. Generally above Mach 0.60. Rather than peak at values higher than 1.25 or so, it should peak at about 1.22 at about 0.02 Mach number below LRC value, then drop rapidly. The default jet AIR files only drop rapidy at Mach 0.80 or 1.00. They only roughly approximate the appropriate curve for a given AC. TBL 403, "Mach Drag" typically increases too much at Mach 0.80 and beyond. I've been setting it to less than "5" at Mach 0.80 now that I've learned more. "Drag - Zero Lift" in REC 1101 typically comes out below "40" if one can adjust Specific Fuel Consumption to an appropriate value. This is done in FS2K2 in aircraft.cfg. The default SFC is 0.50 in FS2K and FS2K2. That is way too low. 0.80 is more appropriate for 1960's turbines, such as in the 707. Perhaps 0.62 for a 737-300/400. SFC = 0.50 * fuel_flow_scalar. The later term can be be set in aircraft.cfg to increase SFC to a more appropriate value, but only when the drags in the AIR file are realistically low. Otherwise one can adjust that value in aircraft.cfg to get an approprate PPH at one specific flight condition. Or, to get appropriate total fuel use on one's typical trips. Assuming much more time is spent in cruise than climb (longer flights). Ron

[Guest]

Thanks for your explanation. This is quite a bit more difficult than I was hoping it would be... I did get the Fuel Scalar set pretty well, but it turned out to be only for that particular flight and payload. After that I did the two SJC-LAX flights and had the feeling there wasn't enough spread in the fuel use. I'll work at it more with your comments in mind.Thank you,Kurt