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MCDU vs. TPC Take off parameter

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Hallo, irgendwie mach' ich was falsch oder der FLusi!? May be I'm doing something wrong Data: A340-300in MCDU ZFW: 390 Block 140 APT: EDDS Dep.: Rwy 07 in TPC Vers. 1.6Rwy 9500 ft at 2500ft elev; 0 headwind; dry; Flaps 1; Grossw: 530000; 5 degree; No IceTPC calculates with Throttle ToGa: V1 125 VR 141 V2 151MCDU calculates Perf. page (Mouse right click) TO V1 166 VR 173 V2 173??mfghk.hans kurscheidt

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It's just my opinion but I would trust the MCDU figures as I have always found them to be fairly accurate compared to real world tables from Airbus fight deck manuals. I have one or two issues with programs like TPC and tomaflex where a few errors have crept in (tomaflex has got the flex temps completely wrong for example). It would be very interesting to know the calculations that go into TPC's figures but it would need someone to reverse engineer it somehow. Rob Elliott, EGPE InvernessPSS Airbus Support andAirbus Fleet Training Captain, British Airways Virtual airbus@speedbirdonline.co.ukhttp://www.speedbirdonline.co.uk/airbus.htmlhttp://www.bavirtual.co.uk

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Thank's 4 the quick answer,do you have a table for the 340-300 runway calculation ??Rgdshk.Never mind,found them already Txhk.

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As far as I know the author of TPC is a real Aibus pilot and I think that we can trust his calculations. Anyway, I do it.ciao, Ren

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The V Speeds might be OK although without knowledge of how each parameter is affecting the result it is impossible to say - I like to know how these things are calculated :) But what is wrong is the flex which is usually calculated at 67, whatever the other parameters are. That doesn't seem right to me and in fact is definitely wrong for the PSS Airbuses anyway due to the error in PSS programming for the thrust related to the different flex temp figures. For the PSS Airbuses you need to be entering a minus figure and I have previously given figures for the approx N1% for each flex temp here on the forum. TPC is a good idea and I would love to know the basis for its calculations, but personally I don't use it.Rob Elliott, EGPE InvernessPSS Airbus Support andAirbus Fleet Training Captain, British Airways Virtual airbus@speedbirdonline.co.ukhttp://www.speedbirdonline.co.uk/airbus.htmlhttp://www.bavirtual.co.uk

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Hi guys,I didn't want to drag anybody in a dispute about tools, I just wanted a clear view on what's right. I'm running out of rwy, when the bird is full.I investigated further..Some nice fellow has put the PSS 340-300 performance tables into this forum. w/ config 1+F, Press alt. 2000ft, ref temp & pressure; Outside Temp 20 deg; Rwy dry & length 3250 m; the MTOW is 254 Tons (metric) IAS(Kt) V1/r/2=138/151/160. That looks OK.Checking it out w/ MCDU and TPC, TPC is ~10Kt too low, MCDU is ~ 10Kt too high, the truth seems to be in the middle. Wherby MCDU seems not to distinguish between Vr/V2@PSS of course I would like to know, why the MCDU calculates as it does and !! are there values in some config file you can tune ??!!?? Does the MCDU recognise selected Rwy settings in the FLightplan. It looks to me doubtful if the info and other info like outside temp. are considered (e.g. there is no place to enter outside temp for TO). Hence I believe the thing 'assumes' some generic stuff values?? where are they ??given that I enter the values from the Perf. Tables as V1/Vr/V2,??? how is the link between the flight characteristics and the way MCDU calculates or V1/Vr/V2 values are entered. In other words, even if I enter the right table values into Vx, how will the bird fly, does the MCDU calculate these higher values, because the flight characteristics programmed NEED these speeds ??Yours Truelyhans kurscheidt

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Hi there, can't edit my previous mail, hence a new replyI still investigated further:The MCDU does NOT recognise any flight plan settings.the MCDU does NOT recognise Fuel on B. for V1/Vr/V2 calculations!!Test: Go straight to Init pg.2, do NOT enter any F-plan on pg1; enter ZFW and do NOT enter any fuel value. Go to PERF and presse right mouse over V1/Vr/V2 and the values are there, independent from F-plan and Fuel/block (because they are empty).Just a quick check, if somebody could feedback to me:If I enter 390 into ZFW, and NOTHING else I get V 163/173/173; same for you ?? A340-300That shows of course a nice bug, that your take off speed is independent if you have 100Kg or 100000Kg fuel on board.@PSS, that still leaves me with the questions from my previous mail, please answer:how to modif values, if possiblehow the bird (sim) flies (what values are considered); to be precise: at some point, you have a TOW, temp, an Altitude, Speed, Pressure, location etc. Which one of these and when are these values considered for flight behavior? only airborn, always, during run up ?Especially, which parameter exactly do you consider for flight characteristics? If the MCDU is the only place to tell the bird how heavy it is ZFW + Block = TOW and you consider only ZFW for Vx, what do you consider for flight characteristics ? ZFW or TOW ???Rgdshk.

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Dears,it's really confusing, but the source of the problem are possible inconsistencies between the - actual load & fuel as of the payload editor- the MCDU data and the way it uses it- the data the Flusi uses to let the bird fly.There is no forced consistency or plausi check on values between these.I tried to sort my mind, this may help all who want to do it right.Please consider FS9 Payload and Fuel editor figures as following:ZFW 352 (285+67); Fuel 100%/100%/100% = 246.5 That gives a fully loaded bird with a gross weight of 599 (all x1000 lbs)enter the aircraft. The ECAM shows GW: xxgo to INIT page 2 of MCDU: enter ZFW 352 NOTHING more!You'll find:ECAM display has changed to GW: 599MCDU TOW is still undefinedGo to MCDU PERF. Rightclick V1/Vr/V2 you'll find the values and also F:174 S208 and O 277 are calculated, although you have no yet entered any Block value.Conclusion:The ECAM display uses the ZFW from the MCDU and the Fuel value from the FS9 load editor and calculates the right Gross Weigth. (GW) This GW is then used by the MCDU to calculate Vspeeds and F/S/O speeds, regardless if any or whatever value is in the BLOCK of MCDU Init pg.2You can enter whatever you want as Block, only the MCDU TOW changes, all other values remain the same. So the Fuel Value of the load editor is the master figure and the MCDU block value is only to calculate the MCDU TOW, but w/out effect on the bird's flight characteristics.This does not apply for the payload. If you change the ZFW in the MCDU, the GW and everything else (speeds) changes. That means the ZFW in the MCDU is the master figure and NOT the payload editor figure. Exactly the other way around as with the fuel!Insn't it nice .. :-jumpy So now you can endup with inconsistent figures, if you enter a different Block value, as you have previously allowed for fuel in the fuel paylod editor.That still gives you the right GW, but wrong TOW. What does that mean, apparently not very much. I did a few test flights to check the speed/climb profiles with extreme wrong TOW, and the bird behaved absolutely the same, hence the TOW seems to be ignored for any flight profile and only the ECAM GW figure seems to be valid. However with the wrong Block value, it does initially mis-calculate the transition points, e.g. when you'll supposed to reach FL 100.The MCDU Flight Plan Fob at Destination is calculated right (even if Block is extremely wrong), but Landing Weight remains wrong. It seems that the MCDU TOW is only used to calculate the LW for later.The ECAM Fuel display shows always the right quantities independent from Block.I would still be interested to hear from PSS, how the MCDU calculates the Vspeeds and if that be influenced. The take off characteristics cannot be the same in Mexico City during Summer and in Hamburg during Winter.Regardshans kurscheidt

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There's rather a lot to take in here so you won't get an instant answer. But one thing you should be aware of is that the calculations in the MCDU are hard-coded and PSS support people don't have access to the code. So I can't give you any detail about the logic within the calculations. I wish I could as these sort of mathematical things I love to get to grips with. Rob Elliott, EGPE InvernessPSS Airbus Support andAirbus Fleet Training Captain, British Airways Virtual airbus@speedbirdonline.co.ukhttp://www.speedbirdonline.co.uk/airbus.htmlhttp://www.bavirtual.co.uk

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Yes, I know, it's heavy, but thinking about it on Sunday evening, over a glas of Red, I found some logic in it, when you look at it from a real world perspective.In a real world, there is no Load/Fuel Editor. The bird 'knows' how much fuel it has on board through it's measurement system. What it doesn't know, how much payload it has. Hence as soon as the pilot has entered the ZFW, it takes it's own Fuel weight and it has the GW.There is no consistency problem so far.I can also understand that the pilot should have some 'freedom', how much fuel he wants to 'declare' for Nav purposes (Block), rather than taking it hard from the FoB.Of course, PSS could do nothing about the payload/Fuel editor, because it forms part of FS9. The conclusion might be allowed that the payload part of the editor is meaningless.Regarding the MCDU Vspeeds, it seems to be a curtesy of the programmers, to make it easy for beginners to get some values, rather than searching large tables, they don't usually have. I suppose this feature does also not exist in reality. Real pilots must do the real table/chart work. So, if one wants to do it right, forget about the mouse right click and go into the tables. I hope the bird appreciates it and knows the right values to follow :-)The remaining issue is that this should be described better somewhere rather than leaving the innocent user with all that confusing possible inconsistencies and behavior.Rgdshk.

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Hello Hans,--snip--So, if one wants to do it right, forget about the mouse right click and go into the tables--snap--I completely agree with you! But - only few of us have the chance to own these tables! Nor do I and that's the reason why I have to use TPC. At the moment there is no chance for me to check either the MCDU nor the TPC values. It's my feeling (and the belief in the TPC author's knowledge) which says that TPC is closer to reality.Kind regardsRen

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Dear Rene,you seem to be quite passionated about TPC.There are in this forum A340 performance tables to download under the topic"FYI: How to get real N1% Flex settings"For me, the MCDU as TPC as others are tools to help Flight Simmers to do things right and at lesser effort, or to compensate for usually unavailable info. However, I think we all agree that in principle all these tables and tools should produce the same (+-10%) values.As a matter of fact they do NOT !I might be permitted to believe that the tables derived from 'official' EADS documentation are closest to reality. You may give it a trial yourself, but I think I found out that MCDU and TPC produce significantly different values as the tables suggest.For your own conclusion.Rgdshk.

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Hello Hans,passionated - not really. But the TCP values seem (to me!) a bit more realistic than the PSS ones.As I told you, I have no tables at all. 340 tables don't really help cause I fly an A330. But I have to admit that I don't pay so much attention on these TO values. TPC is good enough for me and that's it. I can bear the difference to reality.ciao, Ren

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