ahuimanu

747-400F Polar Air Cargo after update... MTOW/GW

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Hi,

Did some values on the 747-400F change after the update to include the 747-8F?  My PFPX values don't work correctly now.

Thanks.

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Hi Paul,

That's a great thread and it was what I used to grab a 747-8F profile for PFPX.  However, what I'm talking about is changes to the 747-400F.  Before the 747-8 release, the numbers seemed to have allowed for greater weights.  Now, however, the numbers are lower.

Thanks.

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Hi, I'm near a computer and able to better illustrate with data.

On the Polar Air Cargo model I prefer to fly, the following engines are modeled: GE CF6-80C2-B1F at 56,500 lbs of thrust x 4.  

I made a table below based on this Boeing document - http://www.boeing.com/resources/boeingdotcom/company/about_bca/startup/pdf/freighters/747-400f.pdf - which shows that a "basic" 747-400F configuration will facilitate, and the values found in the .CFG file for the 747-400F as would be installed as of this writing:

Boeing B747-400F Values                                PMDG B747-400F Values

MTOW - 800,000 lbs (362,870 kgs)                   850,000 lbs (385,554 kgs)  <-- why is this value higher?

MLW - 652,000 lbs (295,740 kgs)                      652,000 lbs (295,740 kgs)

MZFW - 610,000 lbs (276,690 kgs)                   610,000 lbs (276,690 kgs)

So, I wonder why the MTOW numbers are higher?  I noticed this as values for flights that used to work just fine in the 744F (using PFPX and the FMC) have been wrong since the -8F was released (which caused the base product to be updated too).

I would just manually edit the max_gross_weight variable in the aircraft.cfg, but that doesn't seem like a good idea.

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Looking at the Boeing documentation I have, I see five options for maximum take-off weight, 800,000, 833,000, 850,000, 870,000, and 875,000. So it just comes down to what the airline selected. Even on your Boeing documentation, it gives you the option for three maximum take-off weights, with 800,000 pounds being the lowest and 875,000 pounds being the highest.

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Plus there are two cf6-80 engines options available the b1f and the b5f. Of the b5f is not so common.

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If it’s of any help I can confirm with 100% certainty that the real world aircraft in question has the 875,000 (396893kg) MTOW. 

Edited by Jetlinker

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20 minutes ago, Captain Kevin said:

Looking at the Boeing documentation I have, I see five options for maximum take-off weight, 800,000, 833,000, 850,000, 870,000, and 875,000. So it just comes down to what the airline selected. Even on your Boeing documentation, it gives you the option for three maximum take-off weights, with 800,000 pounds being the lowest and 875,000 pounds being the highest.

This is correct, it’s really a matter of the options selected by the carrier. 

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Thanks gents.  What I am wondering is why this changed when the product was upgraded in conjunction with the -8 release.

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Jeff,

During the update the whole W&B system of both the -400 and the -8 was revised to allow for more accurate cg effects/calculations. During this process base data, payload stations locations & numbers etc. were updated and results were verified against various airline companies trim sheets.

I can't recall what was it that led to the specific 747-400F MTOW change. Probably done for consistency in selecting similar MTOW options for the various 747-400 variants.

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Hello Michael,

Thank you for your answer. I'm guessing that this will now curtail the published/expected range with full load?  I ask because some variants are indicated in the livery downloader/manager as containing an aircraft config that was verified as being accurate (likely panel, options, systems).  However, it seems that all 747-400Fs are the same (this odd addition of 50,000 lbs).  I ask because the -400ERF numbers are what Boeing publishes, but these -400F numbers are modified.

With the change, many routes are no longer viable. 

I'll end with a question please:

If I manually change these values in the aircraft.cfg file, what would the negative impact be?  I think I hear you say that the plane is now "tuned" to these values in terms of the .air file.

I appreciate your reply.

Edited by ahuimanu

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6 hours ago, ahuimanu said:

Hi, I'm near a computer and able to better illustrate with data.

On the Polar Air Cargo model I prefer to fly, the following engines are modeled: GE CF6-80C2-B1F at 56,500 lbs of thrust x 4.  

I made a table below based on this Boeing document - http://www.boeing.com/resources/boeingdotcom/company/about_bca/startup/pdf/freighters/747-400f.pdf - which shows that a "basic" 747-400F configuration will facilitate, and the values found in the .CFG file for the 747-400F as would be installed as of this writing:

Boeing B747-400F Values                                PMDG B747-400F Values

MTOW - 800,000 lbs (362,870 kgs)                   850,000 lbs (385,554 kgs)  <-- why is this value higher?

MLW - 652,000 lbs (295,740 kgs)                      652,000 lbs (295,740 kgs)

MZFW - 610,000 lbs (276,690 kgs)                   610,000 lbs (276,690 kgs)

So, I wonder why the MTOW numbers are higher?  I noticed this as values for flights that used to work just fine in the 744F (using PFPX and the FMC) have been wrong since the -8F was released (which caused the base product to be updated too).

I would just manually edit the max_gross_weight variable in the aircraft.cfg, but that doesn't seem like a good idea.

I attached some info for you that might help to understand what's goin on, at the same time all these specs varies from a/c to a/c so there is no standard number.

Each airplane is different in many aspects. That's the reason why we have a/c differences book and normally we check before flight and the last resort is the flight plan release where most relevant data is outlined (especially in terms of weight).

 https://www.dropbox.com/s/pahj29pt0qd09a0/WEIGHTS.pdf?dl=0

 

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1 hour ago, ahuimanu said:

However, it seems that all 747-400Fs are the same (this odd addition of 50,000 lbs).  I ask because the -400ERF numbers are what Boeing publishes, but these -400F numbers are modified.

The Boeing documentation I'm looking at lists 850,000 pounds as one of the five options for maximum take-off weight, so I don't know where you get the idea that these numbers are modified.

1 hour ago, ahuimanu said:

With the change, many routes are no longer viable. 

Not really sure where you're getting at with this. The documentation I'm looking at lists the maximum payload weight, zero fuel weight, and fuel capacity as being all the same from the 800,000-pound variant and the 850,000-pound variant. Your limiting factor is the take-off weight, so it's a trade-off between carrying payload and carrying fuel. If you want to carry more fuel, you reduce the payload weight.

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Thanks Kevin,

 

If you look at Michael's response to me, there were changes from the pre -8F and post -8F versions of the 747-400 base.  The changes are actually a reduction from the previous max weights.  The increased weight meant that I could fly further with a full load.

 

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Yes, I am aware of what he said. I wasn't aware that you were trying to fly this at maximum payload regardless.

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20 hours ago, Jetlinker said:

If it’s of any help I can confirm with 100% certainty that the real world aircraft in question has the 875,000 (396893kg) MTOW. 

5Y? 🙂

 

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14 hours ago, ahuimanu said:

Thanks Kevin,

 

If you look at Michael's response to me, there were changes from the pre -8F and post -8F versions of the 747-400 base.  The changes are actually a reduction from the previous max weights.  The increased weight meant that I could fly further with a full load.

 

Hi Jeff,

I haven't noticed any problems using PFPX, but I only fly routes that I am familiar with.  The longest I fly is ANC-HKG up on R220.  Again like all freighter flights I'm familiar with MZFW and MGLW are almost always the limiting factors for me, especially MGLW. 🙂

Grace and Peace, 

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Thanks.

 

The pre-update 747-400F and PFPX aligned almost perfectly.  Since the update, not so.  I suppose my issue is to develop a better PFPX profile.

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If you pick a profile on PFPX, you'll have to mess with the fuel and drag bias for better results. If you run the simulator, pick an altitude and speed, and there's a window that requires you to enter gross weight, altitude, ground speed, true airspeed, static air temperature, and I think a few other things. Enter that information in, and it'll figure it out on its own. Best to do this with no weather.

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On 11/22/2018 at 2:23 AM, ahuimanu said:

Thanks Kevin,

 

If you look at Michael's response to me, there were changes from the pre -8F and post -8F versions of the 747-400 base.  The changes are actually a reduction from the previous max weights.  The increased weight meant that I could fly further with a full load.

 

The MTOW figure is not always structural and this particular value definitely is not. Airlines often artificially 'write down' the MTOW figures to save on landing and air traffic control charges (which are based on the certified MTOW) - if they only fly short routes that never need the extra weight, the easy solution is to get Boeing to certify the aircraft with a lower MTOW.

Nothing changes structurally - same engines, same airframe, same landing gear etc. It's just a paperwork exercise - and so it is in PMDG's case also. 

If you know that a particular airframe has an MTOW greater than the figure provided in the PMDG information (as Jetlinker says) go ahead and use it. No need to change anything in the aircraft.cfg. Provided you load the aircraft so that the CG is within limits and the actual certified MTOW of the airframe isn't exceeded, the wings won't fall off and the aircraft won't fall out of the sky - it'll behave just like a 747 would at whatever weight you have loaded it to...

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Thank you Simon and Kevin,

I suppose my real issue is that the change broke some harmony between the PFPX profile and my planning routine.  Perhaps the new PMDG product will allow us these variances between aircraft.  I will use the suggestions provided to improve my PFPX utility.

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What I suggested will adjust the numbers to the PFPX profile, so to speak.

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