barramundilure

PFPX Fly Precisely and PMDG ZFW differences

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Hi Everyone just changed over to the fly precisely templates for flight planning in PFPX and while doing my first flight with them flight encountered a problem.  The B738W was heavily loaded in planning and actually exceeded the ZFW in the PMDG aircraft by about 700kg in the sim.

I assume we cant change the ZFW in the aircraft but was wondering if others had found this issue as well and what they did about it?  The templates have a number of engine options available ie CFM56-7B24, CFM56-7B26, CFM56-7B27 - what should i be using?

 

Many thanks

Tim Carter

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16 hours ago, barramundilure said:

I assume we cant change the ZFW in the aircraft

Correct, you have to change the DOW and MZFW, MGW, MTOW and MLW in PFPX to match the aircraft you are flying.  Since no two aircraft are exactly the same this is not unrealistic.  The engine for the variant you are flying is shown in the FMS ID page, and can be found in the FCOM.  The 737-800/900 are 26k lb thrust rated engines.

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Hi,

You can find these values in the aircraft.cfg.

Since these values are in pounds in the file, I usely set them in pound in pfpx then switch to kg once the values are set.

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12 hours ago, barramundilure said:

Hi Dan

Any idea where i would find these exact figures to insert?

As Romain said, most are in the aircraft.cfg.  There are a few I derive from the FMS, for example max fuel is whatever number  you see with 100% fuel load and maximum cargo is whatever you see in the cargo bays with 100% payload.  Nothing complicated.

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Personally, I wouldn't obsess about these weights, provided you are using a profile with the appropriate engine rating etc. 

MZFW, MTOW etc are very often purely paper limits - pay Boeing some more money and you'll get a new piece of paper with a higher limit (and to be honest if you really want it and pay Boeing enough money they will probably even find a way to certify your aircraft for a weight above the 'structural' limit -- might require some additional inspections/maintenance regime etc but almost certainly doable). Airlines quite often 'write down' the weights as landing and navigation charges are based on MTOW - there is no difference between the airframes, engines etc. 

As long as the weights you are using are for a B737NG you will be absolutely fine.

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On ‎11‎/‎24‎/‎2017 at 6:31 PM, barramundilure said:

I assume we cant change the ZFW

Sure you can.  I have converted my -700/-800 to BCFs.  To get the weight as planned for the flight, go to the FMC, FS ACTION/ PAYLOAD / SET MAX which should be 120.5.  Then adjust the FWD CARGO/AFT CARGO numbers until you have reached the desired ZFW. 

blaustern

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DO NOT modify the aircraft.cfg or ANY other config files.

If you do, and the plane does weird stuff, note that you were warned.

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1 minute ago, scandinavian13 said:

DO NOT modify the aircraft.cfg or ANY other config files.

If you do, and the plane does weird stuff, note that you were warned.

Precisely -- I should perhaps clarify my reply above that there is no need to change anything in the cfg files, or to obsess about matching PFPX to the precise values in the cfg files in relation to MZFW, MTOW, MLW etc etc.

As long as you are using a profile appropriate to the aircraft model, the ZFW you set in the aircraft matches the ZFW you generate in PFPX and the CG is within limits, the aircraft will fly just fine.

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I don't even care if there's a slight mismatch, plane works fine anyway. Sometimes it's off by 50.2 to 47.8 or something similar. I just trim it out during T/O if needed. I sometimes don't bother updating Pfpx and Topcat with the correct profile when I fly a new livery. Right plane type (e.g., a B738 vs B737 etc.), right engine type and I'm happy.

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