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ArjenVdv

Payload import

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Thanks to your great WIND DATA REQUEST I got the idea of a similar PAYLOAD REQUEST option in the CDU. The reason being, it is always very hard - and sometimes even impossible - to match your flightplan's payload to the one in the aircraft itself. That is because flightplanners such as PFPX, distinguish between adults, children, infants, cargo, bagage, etc., while the CDU only distinguishes between passengers and cargo. You also can't find out about your payload distribution unless you have TOPCAT with the correct profile (which does not apply for the 777 for example). 

If I try to match the payload from my flightplan in the CDU payload page, I often end up with completely different weights. If I enter the amount of adults from my PFPX flightplan into the CDU, it takes an average percentage of children and infants which lowers to total passenger weight again. Also PFPX doesn't tell me how the passengers are distributed over the different classes throughout the plane. The same thing applies for cargo and bagage.

The only thing I can currently do to get my weights somewhat close to my PFPX flightplan, is by simply entering the ZFW. But of course then, you end up with a completely different balance between passengers and cargo. The payload distribution could as well be way off either. 

This brought me to the idea of PMDG implementing a PAYLOAD REQUEST option into the CDU, so that your payload ends up being the same as the one on your flightplan, and don't end up with a wrong CG, fuel calculation, VSpeeds, etc.

 

 

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This actually simulates a little realism.  You really think everyone back there weighs exactly what the dispatch software assumes they weigh?  Nope.  I don't understand why simmers think everything will match perfectly, and all numbers must be exact.

 

PFPX also isn't meant to be a load planner.  It's a dispatch software (route and fuel).  Balancing loads is for TOPCAT...

 

Know your software!

 

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This actually simulates a little realism.  You really think everyone back there weighs exactly what the dispatch software assumes they weigh?  Nope.  I don't understand why simmers think everything will match perfectly, and all numbers must be exact.

 

PFPX also isn't meant to be a load planner.  It's a dispatch software (route and fuel).  Balancing loads is for TOPCAT...

 

Know your software!

 

Hi Kyle,

 

Thanks for you comment, but you don't seem to be getting my point here.

 

In fact, I perfectly know what PFPX and TOPCAT are for, but as I explained in my original post I am running into trouble. Of course weights will always be slightly off, but you can run into trouble if they are several hundreds of KGs off. The reason the weights are off is because PFPX and TOPCAT ask me to enter adults, children and infants while the CDU asks me to enter passengers only. Let's say I want 120 passengers onboard, I would just enter 120 in the PAYLOAD page. But, I don't know the balance between adults, children and infants. I can of course enter 120 adults into TOPCAT and PFPX, and end up with a total of 10080 KGs of passenger weight, but of course I could also enter 100 adults and 20 children and end up with 9100 KGs of total passenger weight, even though I have 120 passengers in both cases. That's a 980 KG difference! That can seriously influence your calculations. 

 

So my point being, what you enter in terms of passengers and cargo in the CDU, can result in completely different weights compared to PFPX and TOPCAT even though the amounts in both cases match up. 

 

Of course I can spend load of time figuring it all out manually, but wouldn't it be much easier if PFPX and/or TOPCAT could create some sort of payload.xx file that you can import into your airplane while in FSX in the same way you can enter the wind data in the 777? In that case, your passenger amounts will at least match up with the passenger weights.

 

Same thing for cargo, I can ALT+TAB all the time to look up the numbers in TOPCAT to enter and distribute my cargo correctly, while it could be done much easier.

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I do not understand your problem:

 

At operational flight plan there are predicted operational impacts for weight. 

 

Calculate your performance for actual load, not for estimated load. Performance calculator is available in cockpit, you do not need dispatch office for that.

 

You basically should not worry about estimated vs actual load difference, unless you are exceeding maximum mass values (structural or any other).

 

Few months ago, I (and 10 other people) missed our connection flight. Do you really think captain cried because 1000+kg missing in his aircraft?

 

Also, print your operational flight plan and write all actual data on it. That's the purpose of it.

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After I created a whole route with PFPX I go to the "details" tab and look for the calculated ZFW.

Then I go to the CDU of my 777 and change under the "payload" tab the ZFW in the same number as PFPX said.

The same I do with the fuel.

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Let's say I want 120 passengers onboard, I would just enter 120 in the PAYLOAD page.  But, I don't know the balance between adults, children and infants. I can of course enter 120 adults into TOPCAT and PFPX, and end up with a total of 10080 KGs of passenger weight, but of course I could also enter 100 adults and 20 children and end up with 9100 KGs of total passenger weight, even though I have 120 passengers in both cases. That's a 980 KG difference! That can seriously influence your calculations.

 

Use ZFW instead.  Weight is weight.  I understand people get really uppity about the exact CG location and making sure it matches PFPX, but again, there is variation between the reported load and actual load.

 

Ever notice that the child weight is conveniently just about half of the adult weight?  Again, since we're applying a law of averages to living, breathing things, there's going to be variation.

 

As far as your numbers issue goes, you seem to (like most simmers) be operating in black and white.  Children's weights are conveniently about half of an adult's weight.  As such, just count them as half of a person, and you're good.  That amounts to only 140kg difference using your numbers above.

 

 

 


So my point being, what you enter in terms of passengers and cargo in the CDU, can result in completely different weights compared to PFPX and TOPCAT even though the amounts in both cases match up.

 

That's more of a numbers issue that needs to be resolved between the programs.  Perhaps a future update of TOPCAT will help to resolve the discrepancies between the programs.

 

As always, remember that it's the weight that matters - not the passenger count that the sim community seems to be perpetually hung up on.

 

 

 


Of course I can spend load of time figuring it all out manually, but wouldn't it be much easier if PFPX and/or TOPCAT could create some sort of payload.xx file that you can import into your airplane while in FSX in the same way you can enter the wind data in the 777?

 

Then everything will be exact, sure, but that's not reality.  It's only ever going to be exact when airlines start weighing each passenger prior to every flight.  Plus, you can already load the NGX with TOPCAT.  You've been able to do that since the original NG.  Note the "export to flight sim" button at the bottom right of the TOPCAT load page.

 

Plus, you'll note that the real side of the FMC (not the PMDG Options / Setup, FS Actions menus that don't exist on the real one) only asks for weight.  Why?  Because it couldn't care less about passenger counts.  All it cares about is weight.  Why?  Weight is all that matters.

 

Sure, the CG issue remains, but how do you accommodate that in the programs anyway?  PFPX doesn't do zones - only weights.  TOPCAT does zones, but I don't recall the zones matching the zones in the aircraft anyway (the NG zones are from the FS9 NG, not the NGX, and can't be changed in TOPCAT).  In the end, the only thing that you're checking for is that you're within CG limits (and setting the weight through the CDU isn't going to give you an out-of-CG condition, in my experience).  The FMC will calculate the trim for the CG from there (which is the only other reason you'd look at it).

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But do the CGs influence the takeoff performance at all? And what about fuel calculations? If so, then the raw weight is not the only thing to take into account...

 

Sent from my GT-I9300 using Tapatalk

 

 

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Arjen

 

Just make PFPX ZFW or payload agree with what is in the CDU. Most of the time I have a 77LR payload of 110000 lbs in the CDU and 35000 lbs for the NGX. I have the pax and cargo to reach those weights recorded on a spreadsheet. I enter 210 pax for the 77LR and 151 for the NGX in PFPX and use the cargo weight to reach the payload figure I am going to enter into the CDU. The only things I use PFPX for is to generate a route if I need it and the fuel required. As long as ZFW are the same in PFPX and the CDU I am good to go.

 

The only PMDG plane where I pay attention to the CG is with the MD-11F load manager. The CG in TOPCAT does not agree with PMDG figures. I go with PMDG. I figure if something is wrong with the CG in the 77LR or the NGX, the CDU will either put a message on the scratchpad or some figure will turn up in amber as oppossed to white.

 

Michael Cubine

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But do the CGs influence the takeoff performance at all?

 

Performance?  Negligible.

 

Trim?  Yes, as already stated.

 

 

 


And what about fuel calculations?

 

In theory, yes, but I don't think PFPX or similar calculators evaluate CG on performance (thus the lack of a box to ask you the value; or the lack of an input screen to calculate CG for you).  The performance numbers in the books just assume you're in trim.

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That's a 980 KG difference! That can seriously influence your calculations.

Don't get fixated on the numbers too much. In the real world, as Kyle said, the pilots don't really know what is the real payload either.

 

980kg seems a lot for you and me but it's not much for a plane. Let's say we really somehow did know the aircraft's real weight, and let's say it's TOW 161000lb (I work in pounds--sorry!), which is pretty typical for a 738. Now let's say that the dispatch over estimated the payload by 980kg, or 2160lb, giving you TOW 163160lb on the paperwork (or 163.2 in the FMC). Well, that 980kg only made a difference of 163200/161000 = 101.3% !

 

(The other way for under estimating would be 159.8/161 = 98.6%).

 

For simmer, it's actually more realistic to enter a slightly different weight in the payload than what's shown on the paper! (but then use the weight on the paper in the FMC perf).

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I think you have all brought up some good points. Being a load controller on the 77W I can definitely say that the actual aircraft TOW is nearly never the planned TOW. Speaking from experience, we are typically 3,000 LBS to 5,000 LBS under PTOW on a daily basis. This is primarily due to two reasons:

  • no show passengers and
  • reduced children weights. 

Contrarily, when I load planned for 767F aircraft, we were always spot on with the actual take off weight (TOW) reflecting the planned take off weight (PTOW). This is obvious due to our exact knowledge of cargo pallet weights.

 

Rob 

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