B747 & B74F performance vs. the manual

[Ivan Kovacevic 0]

Hello,Ever since the latest update for the FS9, I've noticed a small difference in the performance of the 744, fuel wise. I used to do flights like Heathrow to Seattle and achieve great precision in terms of the fuel (difference of less than 3000kg over the estimate). Unfortunately, with the new update (where the engine data was supposedly revised), even though I'm real happy with the new spool-up times, the fuel consumption seems to disagree with the manual.I haven't changed the method I use for fuel planning, but I've now started getting to my destination with over 10 tonnes more fuel than what I anticipated. I'm just wondering if there will be an update to the manuals or anything like that, that would allow for more precise fuel calculations again. Regards,Ivan Kovacevic

[JSACKS 0]

That is an interesting observation. I've not flown long hauls for ages. But if true, that is a significant deviation in terms of fuel flow accuracy.I'd be interested in any replies mesself.Jonathan

[DLP084 5]

I am also interested on this topic. Jan-Paul

[Guest hansense]

I purchased the PMDG 747-400 to MS Flight Sim 2004 in 2005 and I have flown it regularly ever since. First please let me congratulate PMDG on a truly excellent and realistic Boeing 747-400 addon to Flight Simulator. It is a real pleasure to fly. The details are magnificent etc. etc. In my eyes the best simulator on the market. I am flying PMDG 744 with the latest patch installed. I really enjoy the realism aspect of the product and therefore I have noticed that the fuel burn of the simulator is a little too high. The primary thing when flying long haul flights in the simulator is to be within real life limits and it is my experience from using your simulator that certain very long flights are not possible in PMDG due to excessive fuel burn even though all parameters are correct. For instance flights such as Chicago to Hong Kong are not possible in your Simulator despite they are just within the limits of a real 747-400. Let me give you an example. Based on a true flight plan from 4 May 2005 from Chicago to Hong Kong I have made an identical flight plan in PMDG. Furthermore I have keyed in winds according to the flight plan in the FMS. The real flight plan states the total trip fuel burn to be 159,700 kgs whereas PMDG estimates 164,310 kgs. That is a deviation of 2.88% which reduces the remaining fuel to below "normal" minimum fuel of 24,000 lbs / 10,700 kgs. Please see below. lbs/kgs 0,453592 Fuel according to Fuel according to Deviation flight plan lbs/kgs PMDG FMC kgs KORD 380100 172410 172410 0 0% 5490N 325000 147417 147300 117 0% 6594N 286200 129818 129200 618 0% 75N17 244500 110903 109900 1003 1% ORVIT 208900 94755 93600 1155 1% SUKIN 163400 74117 72600 1517 2% RUKAN 136300 61825 59600 2225 4% SULOK 102200 46357 43300 3057 7% WXI 63400 28758 25500 3258 13% LIG 42000 19051 15800 3251 21% WYN 34400 15604 12400 3204 26% VHHH 28000 12701 8100 4601 57% Trip Fuel 352100 159710 164310 Deviation in pct. 2,88% 4601/159710 Real flight 7029 nm PMDG 6980 nm On the real flight plan burn out of that particular 744 doing the route in question is already 2.5% (climb and in cruiise) so the actual fuel burn deviation is 5.38% over book values. If no winds are keyed in trip fuel is 159,000 kgs but the flying time is also 30 minutes shorter. According to the manual page 2 - 8 this is also higher than the book value. Parameters:The flying time in my example is identical to the real flight plan within 4 minutes and the distance is around 45 nm shorter in PMDG. Zero Fuel Weight (ZFWT) is 214,200 kgs and the fuel load is the same 172,410 kgs. Cost index used is 50 as in the real flight plan. I have also done the flight real life at 223,000 kgs with a flying time of 15.07 hrs. It is a great shame that there is such a discrepancy as that is the real fun part of flying the simulator when you are really battling with the limits of the performance of the 747-400 as in real life. Especially on the following routes ORD-HKG, LAX/SFO-HKG (winter) and LAX-MEL. With a ZFWT of around 223,000 kgs the ORD-HKG is not possible to do in PMDG (around 10,000 kgs higher fuel burn and 15 hours flying time) but it is actually just possible according to real flight plans under the same conditions (winds, altitudes, ZFWT, fuel, cost index etc.). (It is my general impression that the the fuel burn of PSS' 747-400-simulator is more accurate and closer to real life. I can forward the flight plan to PMDG that I am using in case PMDG want to look more into this "problem". There are roughly 45 waypoints and I have the wind matrix for each way point. I can see from the credits that the number of highly qualified people, pilots etc. that has been involved in this product is high so I trust that every effort has been made to make the PMDG 744 as realistic as possible. Especially because of that I am writing to you either to find out if there is a discrepancy/error or if I should be doing anything wrong. 1)Therefore I would like to hear if PMDG is aware of this discrepancy and are you able to correct it? (It said on the home page that the fuel burn was with a couple of percent of real figures. However, more than 5% is not good) 2)Are the fuel burn data you are using in PMDG based on very early production aircraft (bearing in mind that there is also slight difference between PW, GE and RR-powered aircraft) ? 3)Could it be my setup (PMDG 744, Load manager or ????) that is not working correctly in some way?(could it be that the there is an error in transfering the ZFWT to MS FS so perhaps it is using a much higher ZFWT figure and consequently higher fuel burn) 4)How much does the actual wind conditions affect the FMS (Progress page) compared to what has been keyed in as estimated wind conditions? For how many nautical miles does the FMS assume that the current wind and temperature conditions will prevail over the estimated winds? I hope that PMDG will be able to respond to this. I think PMDG 744 is a fantastic and realistic simulator and I would really appreciate if PMDG is able to identify the discrepancy or in case that there is an error is able to correct it. I look forward to hearing whether other people have experienced similar problems and what there experience is. RdgsClaus

[JSACKS 0]

Interesting post. 2.88% doesn't sound like much but on the other hand it amounts to about 11,000 lbs of fuel in The Queen which is enough to fly around another 250nm at light weights.In the meantime, I guess I would make favorable (even if unrealistic) changes to the wind in the sim so you can complete such a flight. Jonathan

[G-CIVA 62]

Bump,Some very interesting observations.BestSteve Bellhttp://online.vatsimindicators.net/1020636/523.png

[Ivan Kovacevic 0]

When I originally started this topic, I was comparing what the PMDG supplied manual said compared to what the PMDG model performed in the Sim. I find it completely useless to ever compare 'performance' of the real plane (and it's manuals) with FS planes and their performance. Of course, I wouldn't be too happy to see the 80$ addon completely out of sync with reality, but whether it takes 107 or 110 tonnes - I really don't care. There are so many factors that contribute to this (temperature, pressure, climb profile (econ, high speed, high angle) traffic situation and many many more) that it's really hard to actually compare the two.I do, however, like to have the supplied manual for the addon saying what the addon really does. Unlike some other addon manufacturers that shall not be named, who put in the manual that the takeoff EPR is 1.95 and the minimal N1 is 101%, but when you sit in the plane, even with throttles full forward you can't achieve anything over 1.8....that's just pointless. Regards,Ivan Kovacevic

[JSACKS 0]

Good points, Ivan. Jonathan

[emvaos 13]

Nothing changed performance wise for the latest patch. The FMS libraries continue to predict fuel burn within 20 lbs/hr. Winds aloft and ISA deviation are the major factor for any differences you might see. Furthermore we are talking sub 5% differences over a very very long route on a base sim (MSFS) that features a single aerodynamic body (yikes). Took a few miracles to get the 744 at this extreme accuracy. A difference of 2.88% compared to some flight plan by some company is more than acceptable. FYI : In modern days fuel burn / flight planning software used by major operators advanced from type specific to registration specific. To such detail where after very flight fuel burn data are uploaded to the software database for each registration for next flight predictions. No 744 burns exactly the same fuel with another, within this small margin. We are talking almost 20 year old planes in many cases.As an ending note I am very happy that PMDG users go that far into disecting every aspect of the model (splitting the atom). As an active simmer I wish other vendors benefited too from these observations instead of the usual over the top hype so that I don't have to redo perforance after I buy this or that product :)===================================== E M V Precision Manuals Development Group www.precisionmanuals.com=====================================

[Ivan Kovacevic 0]

Well, something had to have changed - because I as I mentioned before, I used to be within 1-3 tonnes of the planned estimate, now even if I'm taking a bit LESS than what the manual says (not taking the normal contigency) I am still a good 10 tonnes over the estimated fuel.

[phil747fan 14]

Ivan,a 3% increasing in fuel burn is nothing in a real fleet ... i ve seen a +15% for a 747 from the books and that s was with real ops not in simulator ...!!!so now you have to think about it when planning.see youPhil

[JSACKS 0]

So maybe bottom line is no worries on this item? Like Ivan I am also looking at "textbook" accuracy, but perhaps it don't exist because of atmospheric and other diffs that change with every flight?Jonathan

[Guest hansense]

Guys, Interesting and very thoughtful comments. I appreciate that there are so many variables and parameters that affects the performance. As mentioned temperate, winds, pressure, angles etc. affect performance and what we are discussing here is "only" a five percent deviation over book values. (Please note that in my example the 747-400 in question already had a fuel burn out of 2.5%)However, the five percent deviation means that it is not possible to do one of the most challenging routes flown by the 747-400 today - the Chicago to Hong Kong flight. This flight is on the limit of what a 747-400 can do today and therefore just as exciting to fly in the simulator - also because of very low temperatures (affecting fuel temperature) and altitude restrictions in Russia and China etc. I have flown many flighs on the PSS 747-400 (more than 1,200 hours combined between PSS and PMDG) and it is my experience that the fuel consumption is MUCH more accurate in PSS (Much in this context is around 5%). Why is that? I trust that the PMDG is using the same (Boeing text book) manual/fuel flow per weight matrix. This should give a pretty exact fuel burn? I am not a programmer and I have no understanding of the (probably) very complicated programming needed to make the PMDG-simulator. Well, coming back to Ivan's point: "what the PMDG supplied manual said compared to what the PMDG model performed in the Sim".If taking the flight I have used as an example. According to the manual based on ZFWT of 214.114 kgs and an optimum flight level of FL390 a 15.00 hours flight should consume around 155.800, the FMC calculates this to around 159.710 (cost index 50) and the actual simulator flight used another 8.400 kgs. (realistic winds and temperatures were downloaded and ofcourse they will not be like the real winds and temperatures due to the limitations of the flight simulator and weather generator program - in this case FS_Meteo).So it seems to me that there is discrepancy between the manual and to the performance in the sim. Is it wrong to assume that we can expect the PMDG-model to be performing pretty close to the book figure? The flight simulator doesn't have to perform exactly like a real 747-400 but it is my humble experience that the fuel flow is generally too high in the PMDG. The cool thing about flying in a simulator is to simulate a real flight which 1)means building the flight plan according to actual jet ways, winds aloft, choosing the right fuel consumption as it varies with Zero Fuel Weight etc. etc. 2)Fly the actual flight with realistic weather (FS Meteo etc.) and then do the tactical managing of the fuel flow during the flight. Apart from enjoying the actual flying some of the excitement is lost if the simulator is not performing within a reasonable margin fuel wise. I have around 30 real flights plans with full set of parameters (routes, winds, temperature etc.) and none of those flights I have been able to perform within a reasonable fuel deviation - i.e. less than 5 percent! Why is that?I appreciate that there are some parameters that will affect such flights which makes it impossible to say here that the PMDG could be burning way too much (five percent) over book values. That is why I am raising my hand again and asking whether there are some things that we are doing wrong which could contribute to a higher fuel burn? It could be that the weather generator program exagerates temperature, transfering ZFWT from the load planner to FS, pitch angle during cruise, trim etc. etc. I am therefore very interested to hear other simmers experience on the fuel burn in PMDG as it is my humble experience that the fuel flow is too high. To the PMDG-crew. Please don't see this as criticism in any way but rather my ambition to get the simulator to be as real as it gets. RgdsClaus--The fuel burn table above looks like a mess so I have copied it in again. lbs/kgs 0,453592 Fuel according to Fuel according to Deviation flight plan lbs/kgs PMDG FMC kgs KORD 380100 172410 172410 0 0% 5490N 325000 147417 147300 117 0% 6594N 286200 129818 129200 618 0% 75N17 244500 110903 109900 1003 1% ORVIT 208900 94755 93600 1155 1% SUKIN 163400 74117 72600 1517 2% RUKAN 136300 61825 59600 2225 4% SULOK 102200 46357 43300 3057 7% WXI 63400 28758 25500 3258 13% LIG 42000 19051 15800 3251 21% WYN 34400 15604 12400 3204 26% VHHH 28000 12701 8100 4601 57% Trip Fuel 352100 159710 164310 Deviation in pct. 2,88% 4601/159710 Fuel according to flight plan is already affected by a 2.5% burn out over the book values. Real flight 7029 nm PMDG 6980 nm

[phil747fan 14]

Claus,you ll never be able to repeat a real flight done or planned especially under FS environment !!!.even with the computer it happens that we ll never encounter what it was expected to happens ...let s say we re supposed to have a tail wind of 40 knots but during the flight we have a headwind of 20 knots not the same story at all and it happens ... and that s why it s still to the crew to check fuel burn and hopefully we still have a 5% reserve so in fact maybe you ll have to dig more and more inside the planning factor.i ve made a lot of flights under PMDG for FS9 not FSX maybe not the same enveloppe and fuel burn but what i can say it s most of the time the fuel burn is around 5% more than predicted means in fact before doing anything that the PMDG hull is burning 5% more than the books and we saw it everyday in real ops ...!!!! so nothing you cannot deal.let s take C-GAGM fin 342 with PW 4056 engines at one moment it burned 9 % more than books do you think at ops we stopped using it and writing Boeing about this ? : no, we adapted and follow the burn of this specific hull ...consider it that way.the numbers you find after that so long flight is margin and the fuel price is not a factor here lol ...maybe if you want to save fuel you can think about RIF or reclearance in flight ...have a nice mondayPhil

[Guest hansense]

Phil, Thank you for your comments which are very interesting - especially the part about C-GAGM. You must have lots of great experience which us wanne-be pilots would love to hear more about. I appreciate your views and I am fully aware that each individual 747-frame has a different fuel consumption which varies over the course of its life (going up and down depending on maintenance, performance improvement programmes, leaking fuselage/more drag etc. etc.). But you are actually touching my point and that is that the PMDG should be closer to the book values as it restricts some flights to be flown - such as the ORD-HKG flight(?). The exciting part of flight simming in my view is to manage the fuel during the flight and to keep within the limits of the fuel plan and - tactically decide whether the destination can be reached due to different winds than forecasted or a fuel stop will be needed en-route. I spend a lot of time on the flight plan prior to a flight as well as deciding the actual fuel flow which would depend on MZFT and as your experience with FS9 tells you - there seems to be about 5% increase in fuel flow. Well, if that is fact then I just need to add 5% to the fuel flow that the manual is showing. However, it just restricts us from performing certain flights which are being flown everyday and I just think that is a shame as I want to do shorter flights as well as those flights that really pushes the limits of the 747-400 (e.g. LAX/SFO-HKG (winter) and LAX-MEL/SYD or ORD-HKG).(It could be a great thing if the simulator would allow various fuel burn out on a random basis as that would add more realism to the simulator). RgdsClaus