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Mephic

737 NGX with Topcat - seriously confused

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Hi! 

 

I just purchased TOPCAT which is apparently a great addition to best addon ever made for FSX (PMDG 737 NGX just in case anyone has doubts) 

 

The software is really easy to use but I got stuck on DOW and ZFW. TOPCAT allows me to upload aircraft.cfg into it and that's what I did - 737-800 WL Ryanair standard PMDG config shows 42 991 kg of ZFW. 

Unfortunately when I go into FSX, fire up 737 NGX, set payload to 0 (both cargo and pax) I receive ZFW of 41.4 which is over a TON lower...

 

Now this is where I am confused - what is a real sim value? Is this the one from config or the one from FMC? I would assume it's the one from config and FMC has just an error here. The reason why I really care about the answer is that I want to know if: 

 

a) I don't understand something about the weights/payload

B) I do understand it well and this discrepancy is well known among the NGX community

 

If it's B) than: 

 

1) what default pax weight should I set to have the numbers matching each other? 

2) is there anything else I should set to make sure there is no issues later on, as ZFW impacts the whole flight and takeoff calculations? 

 

Thanks in advance :) 

 

P.S.: 

 

By my calculations default PAX weight should be set to 79.31 kg [13800 kg which is the kg value shown in FMC with 174 pax/174 and FMC itself is just wrong in showing when I did go over the ZFW/MTW/MLW but I may be wrong here. 

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The answer is way simpler: do not use TOPCAT to load the NGX. The loader part of TOPCAT simply doesn't work with complex addons like PMDG's because these use customized loading processes that makes TOPCAT not compatible.

 

However the takeoff and landing calculations should work fine.

 

To load the NGX with payload and fuel, enter the values in the  CDU options pages (either as pax number or ZFW in tons, and fuel in litres).

Then use the GW value given by the FMC for the TO and landing calculations in TOPCAT.

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Now I am really surprised by what you have said here (even if you are 100% right :) )

 

Why? Because I thought most important thing in FSX is not FMC of some addon but the aircraft.cfg from which the weights and other data are read. If my assumption is right than whatever is written there is "more correct" than what is given in FMC. 

 

Again this rises the question - am I wrong here? If yes, than why? Once again - I have uploaded 737-800 RyanAir livery aircraft.cfg to TOPCAT so I would assume this shows real sim values. 

 

I don't want to be misunderstood here - I am not trying to load any values via Topcat to FSX. 

 

What I'm trying to do is to get default numbers straight to be sure my takeoff and landing performance calculations are in fact true. 

 

What I discovered till now is - FMC and aircraft.cfg within same addon (PMDG 737 NGX) are not matching each other and I do not get why 

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Romain is  correct about  topcat you don't  use the upload to load  any of the pmdg aircraft,  you have  to do it  manually  with the figures  that topcat gives  you

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Well the FMC gets its data from the aicraft cfg file and I could be wrong but I think the point is that TOPCAT cannot update correctly the cfg file so that it is correctly read by the FMC.

 

The point was discussed already somewhere but it needs to be searched for in the forum.

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You fly in the cockpit of the PMDG, you don't fly the PMDG with TOPCAT.

 

From memory you can put into TOPCAT the config file of the 737-600  to 900, and topcat will give you figures of how the aircraft behave.

 

It will give you, take of and landing figures and V speeds, which you take away like a bug card. Flap settings, trim, and power settings based on the conditions.

 

Maybe in the past, other add-ons and old versions of PMDG saves back to config file, but this isn't the case these days. And I think this cofuses people, as to what the purpose of Topcat is. Unless you are questioning the config that PMDG designed? Are you saying it isn't as you'd expect?
.

 

By my calculations default PAX weight should be set to 79.31 kg [13800 kg which is the kg value shown in FMC with 174 pax/174 and FMC itself is just wrong in showing when I did go over the ZFW/MTW/MLW but I may be wrong here

 

 

Maybe TOPCAT interpretation of passenger weight are different, it is a different program after all.  There are different cabin configuations in the PMDG MENU as well.

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If you have PFPX, you can use that to calculate TO performance since it had a handy interface that would autofill TOPCAT. However, PFPX's profile is also a bit off in terms of empty weight for NGX.

 

As for performance calculation themselves, as long as TOW is correct the numbers should be correct as far as weight goes, for all I know.

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Thanks to all for clarification. I was wrong because I thought cfg file defines pmdg sim weights but in fact it's done via fmc which is logical. I will be using fm c first and than input ZFW information to top cat based on fmc calculations not other way around. Thank you all!

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Don't use TOPCAT for loading or weight and balance. This will only work with the legacy addon for FS9.

 

It works nicely for computing the take-off speeds, though.

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Don't use TOPCAT for loading or weight and balance. This will only work with the legacy addon for FS9.

 

It works nicely for computing the take-off speeds, though.

 

The NGX FMC computes the takeoff speeds. What is the purpose of Topcat?

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More accurate data. Keep in mind that the FMC calculations are only a reference (good enough for flightsim, of course). Aside from that, without any further reference you can only guess how much of a de-rate is actually possible and what stopping margin you have. You may also not find that your take-off is not even allowed in a certain configuration because of obstacles, terrain etc. TOPCAT will provide you with these information.

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Thanks but is topcat calcuLation really correct for NGX? Let's say ZFW. NGX fmc tolerates high values there. Add fuel and by the top cat profile I should not be able to takeoff safely. By fmc I can do it and there is still some margin until mtow. So if this data is incorrect in topcoat profile how can it give good values for derate for weight which is over its limits?

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I only use Topcat for calculating payload distribution and takeoff-performance. If you create a flightplan in PFPX, then you can export this to Topcat and the values (ZFW) should match. What you need to do then is simply entering fuel and payload into the FMC. I see no point in using Topcat alone, or well, as I said, you may calculate takeoff performance.

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Thanks but is topcat calcuLation really correct for NGX?

 

Certainly so. Just don't expect the TOPCAT values to differ much from the FMS reference – that's their purpose after all: if you have large discrepancies between them, this is probably because there are wrong entries on whichever end, and you should start investigating. If you only use either TOPCAT or the FMS reference you are more prone to errors, as there is no independent double check. The real advantage of TOPCAT is that it tells you which flap setting is optimal (if not required) and what de-rate options you have (if any).

A real-world example on the B777:

 

https://youtu.be/ly4ajn5lvY0?t=2m40s

 

You can see the following reference speeds: V1: 151, Vr: 154, V2: 158. The EFB calculations however have provided the following numbers. V1: 153, Vr: 158, V2: 161. Not a major difference but the more accurate, the better.

 

By the way: 777 posts. :smile:

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