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Mephic

Issue with 777 and Topcat (N1 discrepancy)

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My issue on screenshot below - any ideas why the discrepancy? Temperatures matches each other so why such big delta? Due to that issue all values I get from TOPCAT are always different than what I get in triple 7 FMC (regardless if it's TO/DTO or temp way of reducing thrust. 

 

1z8jql.jpg

 

is it clearly a TOPCAT issue considering default % value in TOPCAT for full thrust is 96.0?

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The next question is on the Init Ref page is it the exact same engine Referenced between the two. I ask because there are many variations available and it's actually simpler to overlook.

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Engine in FMC GE90-110B1L2

Engine in TOPCAT: BOEING 777-200LR GE90-110B1L

 

Is this different? I mean I use PMDG 777 and I thought TOPCAT is compatible... is it possible to choose different engine for PMDG?? 

 

One more interesting thing is DTO, DTO1 and DTO2 are OK. Temp derates are wrong. 

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I would say check and see if there is a different Topcat profile. I'd have to check and see what's available anymore. Do you mean TO, TO 1, TO 2 are correct and the assumed temp variant (D) are incorrect?

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Yes Sir. If I set TO, TO1, TO2 it matches (there is 0.4 delta - higher in 777 when not running packs, I guess it's due to lack of air conditioning load same as in NGX) . But always delta is same and after engines are started and packs on there is a match. 

 

Temperatures are wrong. 

 

When you say different topcat profile - I'm using default from 2.74 not sure what else and where could be available but I thought this is the one which will be spot on 

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Which profile did you get? Might be a better one out by now. I really piped in because I saw the discrepancy between Topcat calling for TO2 and the selected TO in the CDU. I'm sure there is multiple profiles. Who knows maybe the Topcat profile you have wasn't updated after a SP published by PMDG that addressed some performance issues.

My suggestion would be to find the most current profile in use though with the highest download rate.

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What version of Topcat do you have installed?  Seems they updated it in 2.74.  If its the latest and greatest I'd let them know the goofed in their numbers.  You might even be able to open the profile yourself and adjust some variables and find the "sweet spot."

 

http://www.topcatsim.com/forum/

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Temperatures matches each other so why such big delta?

 

Because, as mentioned, the TOPCAT N1 is for TO2, not full TO as you have selected.

 

There are many variables, not least the fact that as also mentioned above the TOPCAT profile is not for the same engines as those used in the PMDG.

 

Plus, there are many, many variables at play. For a start, the FS atmosphere and engine model are far from exact. I don't know how accurately PMDG have been able to model the engines but I would hazard a guess there is an excellent chance that even if you used the real Boeing OPT software you would struggle to get a precise match in all conditions.

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Well, again , as mentioned in next post even if I choose it difference is huge. 

 

In case of NGX it is correct in all conditions so IMO it's just a bug. 

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Because, as mentioned, the TOPCAT N1 is for TO2, not full TO as you have selected.

 

There are many variables, not least the fact that as also mentioned above the TOPCAT profile is not for the same engines as those used in the PMDG.

 

Plus, there are many, many variables at play. For a start, the FS atmosphere and engine model are far from exact. I don't know how accurately PMDG have been able to model the engines but I would hazard a guess there is an excellent chance that even if you used the real Boeing OPT software you would struggle to get a precise match in all conditions.

 

All our products have the exact performance tables from Boeing inside the FMC - there is no guarantee this is going to match whatever other performance calculator is being used unless they also use exactly the same data. We've run into this a bunch in the 747 development - testers saying it doesn't match PFPX/TOPCAT etc - you can't argue with the real data from Boeing, which ours matches.

 

We keep talking internally about making a performance calculator/OPT type thing specifically for our products. At some point maybe we'll do it.

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A discrepancy with the TOPCAT profile maybe. Not with the PMDG model. Topcat is supposed to derive its numbers from the aircraft they are modeling not the other way around. As I said might be best to see if you have the latest progile from them first.

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We keep talking internally about making a performance calculator/OPT type thing specifically for our products. At some point maybe we'll do it.

 

money2vu42.jpg

 

You got one customer!

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I'm afraid TOPCAT ain't up to much for performance with the T7. 

 

The real Boeing OPT says for your takeoff:

 

V1 175

VR 180

V2 180

 

SEL TEMP 54C

 

%N1 91.8 for TO, I don't have the numbers for TO2.

 

TOPCAT gives:

 

163/169/173

 

46C

 

97.7%

 

Miles out! 

 

PMDG's 92.1 N1 setting is pretty much on the money, however.

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Thanks Ben. 

I'm sure I would be unhappy if I bought it specifically for triple 7, fortunately works for NGX like a charm. 

I am going to look into TOPER calculator as I plan to get 300 expansion anyway and TOPCAT didn't cover it. Hope they did it better. 

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You guys should really make a performance calculator... And the mobile/iOS/Android version tooo...

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I use TOPCAT to get in the ballpark as far as assumed temperature, derates, flaps and margin are concerned. If there is enough margin left I will enter the temperature, derates, and flaps into the FMC. If the V speeds are close, I am satisfied. I use the V speeds calculated by the FMC. I don't even look at N1.

 

The current version of TOPCAT is 2.74. Development on the product has stopped and I don't believe it will ever be resumed. There are no "newer" profiles for TOPCAT. What comes with the Program is the end of the road.

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Thanks Ben. 

 

I'm sure I would be unhappy if I bought it specifically for triple 7, fortunately works for NGX like a charm. 

 

I am going to look into TOPER calculator as I plan to get 300 expansion anyway and TOPCAT didn't cover it. Hope they did it better.

 

In fairness to TOPCAT they did only ever say the 777 profile was beta. TOPER is not exactly on the money either, from the testing I've done.

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Yeah it's too bad, such potential with that program.  I guess there is no profile out there for the -300ER is there?

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Haven't flown the 737 in a while but I recall there's a slight discrepancy in the N1% as well.

 

What is the best solution to get around this? I now try to match the N1%, but may use a different ATM (e.g. +40°C in TOPCAT and +45°C in the FMS to get the same value), as I think that is what counts.

 

If you ask me, what is really missing from PMDG addons is some sort of comprehensive peformance calculator.

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If you ask me, what is really missing from PMDG addons is some sort of comprehensive peformance calculator.

 

I agree, and I've read comments from one of the developers musing how he would like to do that but they are been very busy with new products.

 

As for matching N1...., just take what TOPCAT offers with a grain of salt.  It is not a professional product whereas the NGX was developed based on Boeing licensed data.

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