Sign in to follow this  
Arnaud

weird fuel burnoff on a 6.10 hour long flt

Recommended Posts

Hey All,Today for the first time I was badly surprised with the 744F fuel burn on an RJAA-PANC cargo flight.I held a real flight plan, on which the average winds was 20 knots tail wind, and average altitude temperature.I matched everyhting as on the flight plan, zero fuel weight plus the ramp fuel gave me the exact same MTOW as on the flightplan. In a word,everything set ok.At the begining of the flight, the FMC prediction PROG page gave me a fuel over destination way lower than what was on the flightplan. I didnt use real weather, just the default westbound 25knots winds, which gave me the same average winds as on the flightplan.The FMC was right, once landed, I could only but notice that more than 9 000 kgs of fuel were 'missing'.The flight time was exactly the same (6.10 for 6.10).The fuel left at cut-off was 8.300kgs, when I should have read at least 4.000 more. What could cause such a greater burn off?Everything during the flight macthed the flight plan, although I could notice waypoint after waypoint loosing more and more fuel (I mean, compared to the technical flight plan, the gap went bigger and bigger)Anyone ever noticed weird fuel burn on such short flights?A delta of 2.000 kgs on a 6 hours flight is okay, that's what the reserve are set for, but more than 4.000kgs without any hold not anything seems a bit too much IMO.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

I'd set the cost index to 100, but as the flightplan I had was at mach.85, the whole cruise was manually set to M.85 in VNAV.So I dont believe the cost index value did impact there.About the OAT during cruise, the FS default weather provided temperatures around -54 C, and the temperatures in the flightplan werent much colder, they were even sometime warmer -like -48 C- or less.

Share this post


Link to post
Share on other sites

Well,Actually the flightplan I used is actually a flight plan for a 744ERF,with CF6-80C2B5F engines, and a brand new one, with a CCM at -1.90, this might explain a little bit the huge difference in the fuel burnoff.But I'd rahter thought that 744ERF would have had a bigger burnoff fuel than the PMDGs instead, hence my doubts.

Share this post


Link to post
Share on other sites

My experience is that the FMC's fuel calculation will be correct, that is with one gigantic "IF." The weather it encounters in MSFS's simulated atmospheric environment matches the weather dynamics it has programmed into its computer.For instance, a wind at 25/270 won't be a direct tail wind if the flight plan transits latitudes. If the FMC's burn calculation is to be relied on, then the wind at every waypoint must be manually entered during the pre-flight. (Sure hope AS6 will interface with PMDG's FMCs like it does with FSBuild. I want forecast winds LSK-able for preflight and LSK-updatable during flight. 1000 foot intervals would be great, thanks. Why not dream a bit!)I've given up attempting to duplicate real world flights in MSFS

Share this post


Link to post
Share on other sites

Thank you Sam,Interesting post. However, it is the most part of the fun, I think, totry to macth the reality, and very likely the first reason why I like the PMDG products so much, at the same time.My wondering has nothing to do with FMC actually, it's just related to an exagerated fuel burn off on a 6 hours long flight.(my mistake, I shouldnt even have mentionned the FMC inputs)To be more exact, the FMC was terrribly accurate on that flight, it predicted from the begining that I was going to burn more fuel than I thought.The fuel boarded, the remaining fuel at cut-off: a huge difference (over 4.000 kgs) with what I had on the real flightplan.I will hopefully do an 8 hours long flight today, with a real flight plan as well, ans see what happens.EDIT: Well, I havent been precise enough since the begining of that thread. It's actually NOT the first flight I do with a real flight plan. Generally, the thing with FS and PMDG pretty much match the real flight plan (more or less 2.000 kgs difference and couple of minutes) on longer flights.So the question was: is there anything that could explain the fuel burn making such a jump?

Share this post


Link to post
Share on other sites

I compared the burn numbers between the PMDG airplane and a real world flight. This was not a projected flight plan. It was a real number set from what really occurred as the real flight was flown. I had fuel and winds, waypoint by waypoint from the real world FLIGHT. I plugged it all into the PMDG FMC and the difference was ~1000 lbs from a 250K burn. Now, this I can only guess . . . because MSFS simply will not duplicate the environment accurately enough. I believe that if I actually flew the airplane in the conditions that the real airplane encountered, my burn would have been as the FMC forecast.If during my simulated flight, the burn was not as predicted, I would assume that MSFS was inputting weather that was different from my original projection. This is my guess about what happened here. The MSFS enviroment you were flying in did not match the flight plan's winds. You can tell what

Share this post


Link to post
Share on other sites

Sam,:-) I know well about the winds indicator on the ND! But, even better, the tail wind component indicated on the FMC PROG 2 page (where you can aslo read the SAT btw).Again, I followed that flight from departure block till arrival block, writing down waypoint after waypoint, as you say, the encountered weather (winds and temp) besides the flight plan datas.Even with all the interpolations and corrections you might do, I should not have landed with more than 8.000 lbs less than scheduled.On a real flight plan, you have an 'average' wind value, which is a sum of all the winds expected on the route at given flight levels.On the flight plan I had that average wind was +20 (20 knots tail wind), and all along the flight in FS the average tail wind was indeed 20 knots, all along the route (checking that in the FMC rather than on the ND).Same for the temperatures.So all this doesnt answer my question as to why I found such a huge gap between the flightplan and the actual flight in FS.You claim that you hardly excess ~1.000 lbs on a 250K flt? ...mmmm, sounds good.I usually get ~4.000 lbs, not 9.000 lbs as on that bloody RJAA-PANC, that's the reason why I am a bit alarmed.EDIT: Oh, thought I might perhaps specify I'm in RL a flight dispatcher for a major european company with lots of 744s, both pax and cargos, and that I prepare and check those real flight plans daily, so I know a little bit what a flight plan is and how important the winds and temp are ;-) From this, I also know from 744 pilots that they hardly encounter such huge difference when nothing special happens on the flight, given that the weather enroute forecasts are more and more accurate, which had lead the companies, years ago, to reduce the route reserve for fuel savings (from 5% to 3% for most of them).In the case of my RJAA-PANC flight, I had burned the whole 5% route reserve plus the final reserve, I couldnt even land the alernate fuel (which was Fairbanks). In real life I would have had troubles with local authorities in case of a control.

Share this post


Link to post
Share on other sites

How about engine selection? Those old ratty Pratts, if they aren't leaking, check the oil level. During a preflight, we make SURE there's a puddle under them. GE's the boss! For fun, just load the flight plan into the FMC and see what you get for projected burn. No flying. Now swap engine selection. Did burn change? We had a thread on that a bit back but I was too lazy to check it out. You're elected. Try it out. Now maybe you can tell us. I understood the Average wind factor was calculated on the basis of the legs page wind inputs. Again, I'm a bit lazy today, but can you tell me? Can I enter an average wind component and have the FMC use that for fuel burn calculations? If this is so, the only way this burn would be linear (leg by leg) is if the flight plan maintained a single heading for the entire trip. Of course IRL, this never happens. During a normal flight (that would transit various headings during the course of a flight), the following would happen: IF the FMC was working off a single average winds number, the FMC would be predicting too much fuel burn during downwind component legs and too little during up wind component legs. It would average out OK in the end, but would leave all sorts of burn errors in route. On the other hand, maybe that PROG page winds number is the average winds the airplane encountered during the flight. If this is the case, then the FP said +20, the airplane actually saw +20. However, if this number is actual winds, what did the FMC use for initial flight planning. I

Share this post


Link to post
Share on other sites

>fuel burn on an RJAA-PANC cargo flight.>>I held a real flight plan, on which the average winds was 20>knots tail wind, and average altitude temperature.....>westbound 25knots winds, which gave me the same average winds>as on the flightplan.Something doesn't add up here. If you flew from Tokyo to Anchorage and the average "real" tailwind was 20 kts then this was clearly an "eastbound" wind. But then you said that you set up the "westbound" 25 kts wind in FS. Your westbound 25 kts wind would be a headwind, not a tailwind on your RJAA-PANC trip.Also setting up an "average" 20 kts wind (tail- or head-) manually in FS by using fixed heading is prone to serious error when flying between Tokyo and PANC due to the fact that heading on this route will vary due to proximity to the Pole. Another place for possible error is approximation of the "average" wind - this is far from trivial calculation in cases where wind direction is at sharp angles to the route.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

Share this post


Link to post
Share on other sites

>Something doesn't add up here. If you flew from Tokyo to>Anchorage and the average "real" tailwind was 20 kts then this>was clearly an "eastbound" wind. But then you said that you>set up the "westbound" 25 kts wind in FS. Your westbound 25>kts wind would be a headwind, not a tailwind on your RJAA-PANC>trip.That's what I was thinking as well when it was first posted. I thought maybe I was just going crazy.

Share this post


Link to post
Share on other sites

Hi Sam,You bet I've had already reloaded that RJAA-PANC flight just to see what the FMC predicted. It predicts always the same fuel burn, as I said, the PMDG FMC is very (now)accurate: what it predicts is actually what is left over destination, once the flight had been completed.I tired both with winds input in the LEGS/DATA pages, and without, only make a slight difference.No, the PROG 2 tail/head/cross winds factor indicator are actual winds, not average. I dont think the 744 gives that kind of information(of no interest for the pilot), only a flight plan does, in order to define the required fuel.Other than that, I loaded an PANC-EBBR flight last night, with a real flight plan as well...and although I havent completed the flight, the FMC gave me a fuel over destination again way smaller than what my real flightplan said there should be.I am now off to check what the differences between 744F and 744ERF are, most likely in there lie the difference between my flightplans and the PMDG birds.Since I bought the 744F, I've always been surprised to see that PMDG 747 cargo max zero fuel weight is 288.100 Kgs, when the 744ERF's mzfw the company I work for is only 277.100 Kgs.The 744pax didnt give me such gap between my flightplans and the PMDG thing. Maybe something got screwed in the meanwhile with the cargos?

Share this post


Link to post
Share on other sites

Michael and Mike,Ouch, for one moment I also thought I had gone mad. The first post I made was done late in the night, or early in the morning, after that famous flight, so I was a bit tired and confused.Of course I meant I was flying eastbound.Now what is really weird: I didnt input any kind of winds in FS, I just let the default athmosphere with its winds and temp, which are indeed usually (according the latitude) 25 knots eastbound winds and standard temperatures.What really bugs me now about that flight, is that I recall for sure I was having tail wind (shown on the ND as well as the FMC), that is for sure.I did had eastbound winds all along the route indeed (like 265/25 for instance) Thanks for pointing my typo.Regards,

Share this post


Link to post
Share on other sites

> How about engine selection? Those old ratty Pratts, if they>aren't leaking, check the oil level. During a preflight, we>make SURE there's a puddle under them. GE's the boss! >>For fun, just load the flight plan into the FMC and see what>you get for projected burn. No flying. Now swap engine>selection. Did burn change? We had a thread on that a bit back>but I was too lazy to check it out. You're elected. Try it>out. >>Now maybe you can tell us. I understood the Average wind>factor was calculated on the basis of the legs page wind>inputs. Again, I'm a bit lazy today, but can you tell me? Can>I enter an average wind component and have the FMC use that>for fuel burn calculations? >>If this is so, the only way this burn would be linear (leg by>leg) is if the flight plan maintained a single heading for the>entire trip. Of course IRL, this never happens. During a>normal flight (that would transit various headings during the>course of a flight), the following would happen: >>IF the FMC was working off a single average winds number, the>FMC would be predicting too much fuel burn during downwind>component legs and too little during up wind component legs.>It would average out OK in the end, but would leave all sorts>of burn errors in route. >>On the other hand, maybe that PROG page winds number is the>average winds the airplane encountered during the flight. If>this is the case, then the FP said +20, the airplane actually>saw +20. However, if this number is actual winds, what did the>FMC use for initial flight planning. I

Share this post


Link to post
Share on other sites

hello guys,just read on stevens va forum that pmdg is burning more fuel than predicted by fmc and real flightplans and ps1 aircraft ...so from my experience and feedback you need to bias +20% to get the fuel in need by air file and fs 2004 weather ...maybe some other users can report heresee youphil

Share this post


Link to post
Share on other sites

I can only report that a real 744 pilot ('Janov' - you may find his report in the old forum) did exhaustive tests of the long-range fuel consumption in this simulation and he reported that it was highly accurate as compared to real life figures. The only area where he noticed higher fuel burn was when taxiing but this is due to a well known problem - runway friction coefficient.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

Share this post


Link to post
Share on other sites

>I can only report that a real 744 pilot ('Janov' - you may>find his report in the old forum) did exhaustive tests of the>long-range fuel consumption in this simulation and he reported>that it was highly accurate as compared to real life figures.>The only area where he noticed higher fuel burn was when>taxiing but this is due to a well known problem - runway>friction coefficient.>>Michael J.>http://www.precisionmanuals.com/images/for...argo_hauler.gif>http://sales.hifisim.com/pub-download/asv6-banner-beta.jpgMichael,do you have the direct link or something to read with ???!!! i canot see or read the exforumsee you

Share this post


Link to post
Share on other sites

>I can only report that a real 744 pilot ('Janov' - you may>find his report in the old forum) did exhaustive tests of the>long-range fuel consumption in this simulation and he reported>that it was highly accurate as compared to real life figures.>The only area where he noticed higher fuel burn was when>taxiing but this is due to a well known problem - runway>friction coefficient.>>Michael J.>http://www.precisionmanuals.com/images/for...argo_hauler.gif>http://sales.hifisim.com/pub-download/asv6-banner-beta.jpgMichael,the only report i found was eddf to vomm with interruption to varna in bulgaria not the best way to check long flight ....please pm me i ll give all datas for a SAA 202 kjfk fajs and you ll report us what you found using the weather given by the flight plan and of course fuel results ...truly yoursphil

Share this post


Link to post
Share on other sites

>the only report i found was eddf to vomm with interruption to>varna in bulgaria not the best way to check long flight ....That's the one. If he found only a 0.1 ton discrepancy during a 2-3 hr flight that's pretty darn good.Another point - if you try to measure accuracy of a fuel burn - forget about any weather products. Fly with default weather, standard atmosphere and compare against table values. Trying to reproduce real weather in FS is a futile proposition which is bound to inject huge errors.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

Share this post


Link to post
Share on other sites

Michael,Janov, of whom I remember well indeed, did test the 744 pax version.I find myself the 744 pax very accurate compared to real 744 flightplans.Here I am talking about the 744F - 744F, Michael.

Share this post


Link to post
Share on other sites

>>the only report i found was eddf to vomm with interruption>to>>varna in bulgaria not the best way to check long flight ....>>That's the one. If he found only a 0.1 ton discrepancy during>a 2-3 hr flight that's pretty darn good.>>Another point - if you try to measure accuracy of a fuel burn>- forget about any weather products. Fly with default weather,>standard atmosphere and compare against table values. Trying>to reproduce real weather in FS is a futile proposition which>is bound to inject huge errors.>>Michael J.>http://www.precisionmanuals.com/images/for...argo_hauler.gif>http://sales.hifisim.com/pub-download/asv6-banner-beta.jpgMichael,for a so huge aircraft flying two to three hours to check long range ability is not the best way to do on my own opinion of course ....now trying to check a 13 or 15 hours flight is a better way and the one i used when i beta tested some aircrafts including 777 and 747 classics and -400 but that s another stories ....about weather if you have the weather from the flight plan and create on winds side you have a good comparaison i asked someone to do the follow up from lhr to lax with the datas posted by steve to see the results as some users posted some huge surprising fuel missing with long haul ...but again we have to double checks the pax and cargo version to see where is the trouble ...from my models (boeing datas) the cargo is burning a little less fuel but due too his less speed at better range .... so it seems the both are burning similar fuel in real ops but not with pmdg air ...so everybody want to check is welcomeyou choose the flight and i give infos on fuelsee youphil

Share this post


Link to post
Share on other sites

If we can find a way to get FS9 to duplicate those winds accurately enough to allow a meaningful test flight, that'd be the boss! So far, I don't think it's possible. Even AS6 only inputs winds 6000 foot intervals.To test fly with any kind of comparative credibility, the winds must be perfectly duplicated in the FS9 environment. Otherwise, an actual flight in FS9 for fuel burn comparisons is an irrelevant exercise for this comparative purpose. Any test flight -long or short- will not be able to 'prove out' the model's fuel burn vs real life.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this