FSbuild's fuel prediction is off

[Ralgh 43]

I am using FSBuild for all my flight sim planning. I have done the majority of my flying in the LDS 767 and FSBuild gets the fuel right on. I also have the PSS Airbus 320 and it also gets the fuel right. So far out of three flights in the 747 it has always been way short. I did the math on the last two flights (about 5 hours each)and I burned 123% and 115% of the fuel it planned. Are you guys that use FSBuild using anything different for your fuel planning? Is there more accurate performace data available for FSBuild? I am using Active Sky for the winds so that shouldn't be the problem.

[VHOJT 167]

Hi thereDo you have the PMDG 747 profile from the fsbuild website?If so, maybe increase the fuel bias a little in the aircraft file in the Fsbuild folder.

[Guest Tom C.]

Are you using it for the passenger or freighter model?If, as above, you have the correct profile from FS Build the passenger model should be spot on.The F model should be heavier on fuel usage due to the extra weight so you'll have to add to the figures for your flight. I try to add 10/15000 kgs extra than what the program gives me.

[Ralgh 43]

>Hi there>>Do you have the PMDG 747 profile from the fsbuild website?>>If so, maybe increase the fuel bias a little in the aircraft>file in the Fsbuild folder.I didn't even thing to look there. I just got it. I am eager to get a flight planned and flown now but I have to go out for a while. It always seems like I have to leave right when I want to fly most. Funny how that happens. Thanks for the help.

[VHOJT 167]

No worries. Let us know how it goes!

[Ralgh 43]

well it looked like it was going better but at the end of the LAX-HNL flight I was still way short of the planned fuel. This time it burned about 13,000lbs too much fuel. That was 111% of planned fuel. I did do two flight plans, one with the PMDG 747 numbers and the other with the default FSBuild numbers and there was a 10,000lb difference, the PMDG numbers being the higher.I have it flying a flight back to LAX with no winds just to take that variable out of it but right off the bat it was showing arriving at LAX with 10,000lbs less than planned and that number got worse through the climb.One thing that occured to me was that maybe the cost index might be causeing the problem. I am using 60. I will have to look in the documentation to see what PMDG recommends.

[ronzie 21]

On the 737s the fuel at destination sometimes generates a warning during the climb. At cruise where cruise efficiency fuel burn occurs it should go away. Look at your destination on the PROG page after cruise stabilizes, and while I would not count on it there is a fuel reduction during descent.This is documented.The FSBuild aircraft profiles are text so you can edit in your own figures based on the PMDG performance documentation and save that file under a discreet name to try. I believe there is separate FSB documentation in one of its folders that describes the file fields and syntax.In the FSB aircraft tab when planning are you setting the fields in minutes for TAXI, EXTRA, HOLD, ALTERNATED, etc., so that extra fuel is included in the NAV LOG total fuel calculation? Make sure in that tab you also put in the correct weight. You can also put in the average wind component ("-" is headwind in that field).On the 737NG performance pages you can enter your average cruise wind aloft speed/direction, ground and aloft air temp, and after the route is entered before you depart the FMC should tell you forecast fuel at destination so there should be no need to take off without enough fuel. I assume the 747 FMC is similar. Don't forget to fill in the fuel (EXTRA) field which is the amount you wish remaining at destination so the FMC forecast will take that into account.

[Ralgh 43]

I've been planning with FSBuild for the LDS 767 for several months now and I do it like you said with the TAXI, HOLD, etc. fuel. I fly a real 737-800 and have ridden jumpseat on way more 757s and 767s than I care to remember. All the FMSs seem to work very similar. To be honest I have done little reading about the 747 FMS but it seems very similar to the other Boeings.I am just wondering if the PMDG 747 is burning more fuel than the real one or are the planning numbers too low, or maybe I am just doing something wrong or maybe my installation is doing unique. That's a lot of ors. I am currently flying from Los Angeles to Sydney. I know both Qantas and United use 747-400s on that route. It is looking questionable if it will make it right now. I just topped off the fuel at the end of the runway which is about 10,000lbs more than the planned fuel.One thing I have seem consistently is that the FMS fuel at destination number stedilly decreases during every flight. Just for reference I have the LDS 767, PSS Airbus Pro, PMDG 747-400, and PMDG 737 NG/800/900. I haven't done much with the 737 but it did match some real life flight plans I used and the others match the FSBuild fuel number pretty close. It just seems like my 747 is burning more fuel than FSBuild and the FMS are thinking it will. Oh one last thought. I can't imgine this is the problem but I am using the Rolls Royce version but I believe they all actuall use the CF6 performance numbers as does FSBuild.

[Farlis 2,280]

>Oh one last thought. I can't imgine this is the problem but I>am using the Rolls Royce version but I believe they all>actuall use the CF6 performance numbers as does FSBuild.Depends. If you have the Freighter version installed the performance models for the engines are different.Karsten

[michal 44]

Did you compare FSBuild fuel prediction numbers with the ones calculated manually according to the manual? Folks usually report that hand-calculated numbers give good accuracy. There is also this fuel planning tool for 744 by Felice Valente. I would do some cross checking.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

[ronzie 21]

"One thing I have seem consistently is that the FMS fuel at destination number stedilly decreases during every flight."This seems like decreased efficiency due to:Ground speed less than expected due to actual headwinds aloft.Fuel burn higher than anticipated expected for cost index/N1/cruise performance. This seems like an incorrectly interpreted FMC parameter not matching actual flight performance. This would not have anything to do with FSBuild (which I shut down anyway after planning). Is the displayed N1 at the values stated for the various stages of the flight? I'd look at that, the TAS, OAT, GS in flight compared to the preflight entered values.

[Ralgh 43]

The thing is it happens every flight. The winds whouldn't be that off every time. If that were the case I should be up on fuel sometimes too. I just finished my flight to Sydney from LAX and it took about 14.5 hours. The FSBuild planned burn was 340,594lbs. The actual burn was 382,300lbs. I went into the tables in the manual and figuring coservatively I came up with 342,000lbs for that amount of time (which should account for the winds). That is prety close to the FSBuild numbers.What I was trying to say about the FMS numbers changing is that the performance numbers FSBuild and the FMS are using are not matching the actual performance of the plane. The do seem to match each other. It's like I'm flynig with the doors open or something. I guess the bottom line is that on average I am burning 113% of the planned numbers so I will just add that amount to my planned numbers and I shouldn't run out. It makes that L.A. Sydney flight marginal but I can't see myself doing that much.Just so you know where I am comming from I have done 30+ flights of varying length on the LDS 767 using FSBuild. The behavior of the FMS numbers and fuel burn are the same as their behavior in the 737 I fly for a living so I am familiar with the way things can change enroute.

[ronzie 21]

Just to be clear I was not criticizing your technique or skills. I was just suggesting matching the parameters off of the EICAS and ND with those read off of the FMC to insure the panel is performing correctly and in VNAV the FMC is correctly controlling the aircraft and there is no error on pitch and thrust control especially during cruise.I think I read on the 747 the APU sucks quite a bit of fuel. I know being a single PF with no PM it is easy to miss shutting it down.I'd also suggest you go into spot view to see if anything is hanging out causing excess drag (per your suggestion).If you have an FSUIPC before 3.53 it also caused a bug with reporting the wind broken down components to the FMC -- some kind of incorrect trig calcs was in there for a short time. The FMC wind component displayed did not match the breakdown from that on the ND wind vector displayed. That would affect your other models, however.So far no one else is reporting this fuel burn discreapancy but it would be interesting to see if it shows up elsewhere.Since I don't do the 747 but restrict myself to medium/short legs on the 737 because of available sim time, I can't try it myself.

[Ralgh 43]

Well this was just one flight but the results were encouraging. I calculated fuel numbers from the PMDG documentation and came up with, for a four hour flight at 360, at burn of about 88,000lbs. I figured the correction for landing above the 475,000lb weight they use (my weight 543,500lbs). I came up with 26,320lbs. That seemed like a lot but I figured it in. I also calculated the burn in FSBild and it came up with 82,102lbs. The one main thing I changed about the flight is I didn't use the FMS generated ECON numbers. I manually entered the ones in the PMDG performance data. Then I flew. The fuel numbers in the FMS actually rose as I flew (never happend before)but only by a reasonable amount. When I landed I checked the burn for the flight and it was 81,900lbs. Almost exactly what FSBuild said. This was done not using Radar Contact so I probably saved a few pounds with not being vectored around but that is still within reason. The ECON numbers it usually gave me at a cost index of 60 were climb around 330Kts/.84, cruise at .84 and I can't remember the descent but those probably aren't significant with the low fuel flow for that part of the flight.I also checked the N1 and FF numbers during cruise. The manual said 91.5 N1/22,0000lbs/hr and I saw 94.0 N1/22,000lbs/hr+-. I slowed briefly to check the .84 numbers and the fuel flow was about the same and a bit slower cruise. I did notice on my LA-Sydney flight a lot of the decrease happened in the climb but I guess using that .76 mach cruise is pretty important too. I will do a bunch more flights like this to make sure this wasn't a fluke but I like what I see so far.Oh yeah and the APU was off for all of the flghts.

[ronzie 21]

Sounds like you are on your way.According to the docs I have including Mike Ray's 700 sim book, I believe it was stated that it is not unusual to get a low fuel warning (the burn calc, not the level) during climbout until cruise is reached. I would assume this relates to the readout on the PROG page.I really need to refresh my FMC/OPS discipline but I just can't get my sim sessions close enough for things to "burn in".If you (without bothering to lift off) try different cost indexes, how do the ECON numbers stack up for the recommended cruise and burn.Finally, what do you select on the N1 performance page.I've seen in an article the plotting of performance curves and trying to get an intersect that gets a decent travel time with an efficient burn. I'm glad that the FMC supposed to get it right.As an aside, when you are real-world flying the 737s, what variant are you using at what cost index, just out of curiosity.Thanks.