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Guest Andalouse

confused....

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Guest Andalouse

I'm sorry i have to bring it up again. But i was searching the forum for the question for a 747-400f fuel planner! I knew this question came up a hundred times. So that isn't my question.The thing is you always get the answer from pmdg. The FMC is the best fuel planner there is. I agree with that but...and here is the question.How come they say the FMC is a good fuel planner but you can't enter the winds. the reaction also is you have to enter the winds in the legs page. Then when i read the manual i come up with this"this function is currently not modeled in the 747-400"Am I missing something or is the FMC not the best fuel planner there is. Because when i'm flying long haul flights over the ocean the time can be 1hour wrong and the fuel up to 15.000kg for a 9 hour flight from ellx to kjfk (one that i did yesterday).can anyone help me? I have this question for a while now....thanks

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Guest Andalouse

thanks for the answer...but i'm not looking for a fuel planner because i know by now there is none for the freighter.And i'm certainly not saying the FMC is not a good fuel planner. I use it all the time. I just want to know wether i can input the wind or not to let the FMC calculate the fuel very precisely?thanks in advance.

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Hi Nick,first of all - to my understanding - the FMC is NOT a fuel planner but an instrument in FSSim and RW to watch the fuel performance of the flight by waypoint to next waypoint and the fuel at destination.Second, you CAN enter the wind data into the FMC on the legs page/rte data.Third - the mentionned flight planning tool calculates only the TOTAL fuel for the trip, which might be correct ( I never used this or the PMDG manual way of calculating the trip fuel . . .) I built my own flight planning tool ( based on Excel ) - I devide the total distance in 15 more or less even parts ( just the CRZ phase ) and add climb and descend time and fuel. Then I let Active Sky calculate the winds for this route and calculate windcorrection and component for each part of the trip and based on the inflight weight calculate the fuel for each portion of the flight which gives me a average fuel-flow for the trip.So far I reach my destination with this formula within plus/minus 1 % of the calculated value.After having logged approx. 1500 hrs on the PMDG 737/747 - I am retired so I have plenty of time . . . - I was disappointed about the FMC estimates which I got after levelling off at my first flight level. They were ALWAYS much too low - sometimes I received an "INSUFFICIENT FUEL" message - so I started to keep records of those RTE/DATA values of the FMC.I give you a few examples of my last flights :All flights ex Berlin / EDDT/TXLFMC Estm. recorded ex RTA/DTA page after level off at initial FLall step climbs accdg. to FMC ( but I found out that step clbs give better fuelperformance if initiated at MAX minus 10 instead of OPT plus 10 )I recorded all waypoints of my flight plan, but here I will only give the avg. FFI found out that with a lower cost-index the FMC calculation will be closer to actual !All weights in K lbs1.NOV 17KSFO TOW 832,0 W/C -4 C/I 150 M.865 FMC CRZ time 596 mins / act 591 minsFMC est fuel at dest 26,6 (insuff fuel msg !) - act fuel at dest 45,3FMC est. avg FF 24948 lbs/hrACT avg FF 23308 or minus 6,6 %2.NOV 22KSFO TOW 863,0 W/C -36 C/I 150 M.865 FMC CRZ time 618 mins / act 619 minsFMC est fuel at dest 35,8 - act fuel at dest 56,7FMC est avg FF 25276 lbs/hrACT avg FF 23794 or minus 5,9 %3.NOV 25KLAX TOW 831,2 W/C -9 C/I 150 M.865 FMC CRZ time 611 mins / act 637 mins ( wrong winds - another story !! )FMC est fuel at dest 30,6 (insuff fuel msg !)- act fuel at dest 44,5FMC est avg FF 24826 lbs/hrACT avg FF 23450 or minus 5,5 %4.DEC 22KLAS TOW 807,8 W/C -30 C/I ZERO = 0 M.83 FMC CRZ time 659 mins / act 652 minsFMC est fuel at dest 39,0 - act fuel at dest 49,7FMC est avg FF 23436 lbs/hrACT avg FF 23050 or minus 1,6 % !! lowest possbl. cost-index !!There are several incorrect values in the FMC - first of all the last entry in the FMC rte/dta shows for the last waypoint next to touchdown of chosen runway ( mostly the inner marker) about 2500 lbs fuel more than the value for the runway - in actual this value is never more than 1000 lbs !! ) - another 1500 lbs of fuel for which the fuel at dest differs !The calculation of the FMC should be rather simple :The FMC "knows" the weight of the aircraft, on basis of the cost index it knows the mach number and speed ( at standart temperature !) and it has the winds forecasted between each waypoint and should calulate on this standart basis ( weight, speed, time between waypoints and standart fuel-flow )But it calculates steady with the present speed - in these days the temps at high altitudes might drop quite a bit and thereby the TAS also drops considerably ( but only in a specific area, not for the whole trip !! ) In other words the TAS might be calculated at 485 but will drop between 30W and 40W due to very low temps to 475,and the FMC will take this (low) TAS for the whole trip - despite the fact that near LAX the temp might be well over standart!@ allPlease let me know if there are any mistakes in my assumptions ...


Karl-Heinz Wichmann - EDDI/THF "Tempelhof"

"The mother of all airports" - Sir Norman Foster

Now CLOSED - its a shame !

747400.jpg

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Guest Andalouse

thanks for that explenation....I know that the FMC is not a fuel planner but you can use it as one!If you can enter the winds in the RTE/DATA page. Can someone give me a screenshot and some explation from how to do so. I tried everything in long flights but i never managed to put the enroute winds into the FMC. I searched the manual, the forum and FMC But i failed to do so!Can anyone help me please to have a better flight planning! All the rest i managed to do but with this i fail everytime. For short flights that isn't a problem but on the long flights with 100+ kts headwind it can be!

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Hi Nick,go to the legs page and you'll find on the bottom a link to rte/dta - hit this and insert the wind in the scratchpad like 250/35 and then transfer to the waypoint on the right side ...that's allif you use the first waypoint ( not within the climb phase - a/c must in level flight already - I mean the waypoint you want to enter the wind must be in level flight ) the wind entered will be used for all waypoints - so there you can enter an average wind for the whole trip - just try it - you cannot destroy the plane ... or your PC


Karl-Heinz Wichmann - EDDI/THF "Tempelhof"

"The mother of all airports" - Sir Norman Foster

Now CLOSED - its a shame !

747400.jpg

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Guest Andalouse

It finally worked to put the winds in. So thank you very much.Is it normal that when you put the winds in on the ground they disappear again once airborn. I don't when they dissappereadagain but they did. So i have to enter them again once in cruize. I had time to spare but i also have to put them in on the ground to check the fuel!But thanx again. A new world is opening!

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The PMDG has a bit of a bug whereby if you change the DEP/ARR procedures in the DEP/ARR page, the enroute winds are erased and must be re-entered. Manually inserting waypoints seems not to cause this to happent though.


Rudy Fidao

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Karl-Yes- you clearly are a retired guy with lots of extra time. ;-) Good to see you aren't letting the mind go dull!You asked if there are any mistakes in your assumptions- so i'll point out one:"The calculation of the FMC should be rather simple :"We have about 9,000 pages of documentation on this little computational monster that would seem to indicate otherwise!!! :-)Admittedly- the fuel prediction method we have chosen to use is less robust than the actual FMC. There are many reasons for this- not the least of which we do not have all of the internal facilities required in order to feed corrected data to the computation.To do this REALLY precisely- we need to develop a way to import current wind data as if it were coming in by ACARS- and we need to dynamically break the route into directional segments and produce individual calculations for each segment based on predicted wind and temperature at transversal altitude. This would result in the most optimal results.So- while it may appear "simple" it can actually become quite complex- especially on longer routes as a result of the continual computation flow. In the actual FMC this is done with data tables but i bet you can guess how much luck we'd have getting access to those- and constructing them ourselves would really not be a valuable use of our development time. We have some ideas for this process- which really must include the importation of live wind data along the route- but I do not see this process taking place for the 400/400F in the near future as it is a protocol set we haven't yet succesfully implemented with this FMC code basis.It is on the agenda for the future, however!All of that being said- this FMC does quite well at the purpose for which it is designed. A correctly calculated fuel plan is not likely to trigger an INSUFFICIENT FUEL warning EXCEPT in some instances during the climb at extremely high fuel consumption rates. (As mentioned in the manuals/tutorials: If you get an insufficient fuel warning during the climb- you can eliminate the nuisance by adjusting the RESERVE figure lower... then upon completion of the initial climb reset it to your desired number....)The other point here is that the FMC is NOT a fuel PLANNING tool as the other poster here has suggested. The fuel planning tables in the manual are your best bet for fuel planning. The FMC is a monitoring tool...Glad you are using the 400 to enjoy retirment, Karl! When the NGX arrives check this process again and see if you think we improved it. ;-) (Actually- I believe the MD11 is already improved also...)


Robert S. Randazzo coolcap.gif

PLEASE NOTE THAT PMDG HAS DEPARTED AVSIM

You can find us at:  http://forum.pmdg.com

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Oh, the boss himself ...Hi Robert,perhaps my message came not across the right way - the FMC is already calculating with complex and a big amount of figures !What I mean is that the FUEL-FLOW ( and not the total amount of fuel used ) is different in the actual process of flight from what the FMC is calculating shortly after levelling off at initial flight level.The difference is about MINUS 5,5 % at higher cost-index and around MINUS 2 % at c/i zero - I don't understand the reason for this - by simple I meant that the two calculations should be identical.On a recent trip from EDDT-KLAX the FMC EST was 24826 lbs/hr, my calculation called for 23756 lbs/hr and ACT FF was 23450 lbs/hr ! Why the difference ? It is logical if the flight time is significally shorter, the TOTAL fuel used should be less, but why is the FF so much less in actual flight ?btw .: I will NOT switch to FSX so fast ( in fact I got it for christmas ...) - not the right PC available ...


Karl-Heinz Wichmann - EDDI/THF "Tempelhof"

"The mother of all airports" - Sir Norman Foster

Now CLOSED - its a shame !

747400.jpg

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