Hi guys,

 

Have you guys noticed a huge discrepancy between the FMC's and TOPCAT's calculated N1 values when entering a assumed temperature? I have tried this on multiple locations and with different Wx and liveries loaded. Every time I use Topcat to calculate my takeoff thrust with an asumed temperature and I load the temp to the FMC, the FMC's calculated N1 value is usually at least 5% below what Topcat calculates. This puts me in a tough spot, needless to say.

 

 

 

I suspect it is a problem within TOPCAT itself and it's probably being worked on since 777 calculations are still in Beta, but I'd just like to confirm this finding with my trusted fellow PMDG forum members. 

 

Now, I know I could forget about the assumed temperature and just gun it and climb like a space shuttle to thrust reduction (it's the 777 after all); but I like to do things as close to realism as possible and I want to keep my GEs bright and shiny for longer if possible. 

 

Short of having the 777 FPPM is there a workaround to get reasonable takeoff thrusts that won't have me lifting off like a F-18 off a cat launch?

 

Thanks for the replies!

Aurasim, now owned by Airline2sim says their LR data is almost complete

Thx for the reply Bryan. I would be willing to buy a registration for the 777 once its out, considering the friendly price. I just hope they did a better job than Topcat´s Beta. 

 

Well I seem to have discovered a viable workaround. I don´t know how accurate it is, but I would rather roll down the runway with excess thrust than 7 or 8% below the ideal N1 setting for a given weight, especially in those cases where the margins are close. 

 

I decided to take the N1 value calculated by Topcat and achieve it in the FMC by simple trial and error with lower assumed temperatures. For example yesterday I was taking off from SBGR at 200,000 kg and with the current Wx conditions Topcat calculated an optimum takeoff as: Flaps 5, TO-2, and 58ºC of assumed temperature with yelded a topcat figure of 88.7% N1. When I input those parameters in the CDU, it spit out only 81% of thrust. So I decided to switch to TO-1 and after some fidgeting with the temp selection I was able to get an N1 of 88.9% with 40ºC. I know this is very far form ideal, but untill Topcat gets its act together concerning the T7 I think this is the best solution. I´m sure they´ll smooth it out eventually. Their calculations for the NGX are spot on. If only they´d allow for SFP calculations with TO-B...

I use PFPX in addition to Topcat and OpusFSX as my weather app. Since PFPX and OpusFSX share the same data source I know the data weather should be identical. For the logest time I was oblivious to the fact that OpusFSX wasn't injecting weather into FSX has it supposed to (user error). I found out about the synchronicity issue when my N1Topcat calc didn't jive with the N1 FMC calc at full thrust. Now that I have OpusFSX working as it should, my N1 Topcat calculation is exactly in line with the FMC once the in game weather stabilizes.

The weather is important. I'm using ASN when flying in FSX, so I have ASN as my weather source for both PFPX and TOPCAT.  It's critical to select the proper weather files in both respective programs.

 

I also make sure I start ASN before anything else and let it download updated weather so I'm feeding both programs valid data.

 

Doesn't make much sense to have a program like PFPX and Topcat and not have some sort of weather engine otherwise it's garbage = in garbage out

I use PFPX in addition to Topcat and OpusFSX as my weather app. Since PFPX and OpusFSX share the same data source I know the data weather should be identical. For the logest time I was oblivious to the fact that OpusFSX wasn't injecting weather into FSX has it supposed to (user error). I found out about the synchronicity issue when my N1Topcat calc didn't jive with the N1 FMC calc at full thrust. Now that I have OpusFSX working as it should, my N1 Topcat calculation is exactly in line with the FMC once the in game weather stabilizes.

 

Well that´s worth looking into Xaver, thanks. But like Steve, I use ASN and I use exactly the same procedure described by him. I load it up and let it download live Wx before I open anything else. Next, I plan my flight with PFPX and export the weights to Topcat. I never fail to to upload Topcat with current ASN Wx, and I always confirm the Wx I see on FSX matches the METARs on the main ASN. And still my FMC calculations are very different from what I get on Topcat. This does not happen to the NGX, leading me to believe that something is amiss on my T7 or, more likely, TOPCAT itself. 

 

The weather is important. I'm using ASN when flying in FSX, so I have ASN as my weather source for both PFPX and TOPCAT.  It's critical to select the proper weather files in both respective programs.

 

I also make sure I start ASN before anything else and let it download updated weather so I'm feeding both programs valid data.

 

Doesn't make much sense to have a program like PFPX and Topcat and not have some sort of weather engine otherwise it's garbage = in garbage out

 

Steve, would you mind comparing results with me when laoding the 777 at same weights in the same place with identical Wx so I can verify the issue?

Sure we can do that. Also did you notice the weights /pax/cargo don't match between TOPCAT, PFPX and the 777? I tried to glean as much info as I could form the aircraft config file and then change the values in PFPX and TOPCAT to match. Can I ask how you did it and what numbers we are using to make sure the result is the same?

The TOPCAT calculations are terrible for the 777F/LR, they take 5 months to release this and when they do its junk data.

Now that I'm focusing on this I noted a discrepancy between PFPX and TOPCAT - PFPX seems to be changing between KG and pounds by itself in the configuration part of the program under Weights -  which can result in several thousands of pounds difference in PAX and baggage.

 

Even though I had set my Planning /Units to Pounds/Feet the passenger and baggage weights in the Weights section still showed KG...Twice I click back to planning / units just to verify it was in pounds. I checked the math on a calculator and the program was taking the smaller numbers shown as KG's and using them as LB's. so my 24lb /each bags were being read as 11 LB

 

Clicking back and forth between the Planning  / Unit  and Weight and hitting OK corrected it.

 

The exact same flightplan with identical numbers gave 2 different results. and the weights were quite a bit different

It seems the problem really lies in these programs from your findings Steve. Perhaps we should report it to the devs. I still haven´t witnessed this weight problem because all of my calculations are in kgs. And I always make sure that the Takeoff weight in topcat matches the actual weight I hav loaded into FSX, Even so, I continue to get all kinds of ridiculous calculations. What is funny is that sometimes Topcat N1 values and the FMC values match perfectly. But most times the assumed temperature Topcat calculates results in underthrust by at least 5% of N1. 

 

I´ll try taking off from EGLL rwy 27L with ASN set to historical mode from 29 aug 1200Z. I´ll set my weight TOW at 300,000kg (661,400 lbs). I´ll let Topcat calculate for optimum flaps and derate with antice auto packs on. I´ll post results here and if you want you can try to repeat the experiment.

Using TOPCAT beta, and I'm getting a ctd everytime I try to generate a take off and landing report (f5) for any 777-200 flight. Anyone else having this issue?

Not my case Ethan.

 

 

Have you guys noticed a huge discrepancy between the FMC's and TOPCAT's calculated N1 values when entering a assumed temperature?

 

 

my primary goal isn't "optimal" flaps/thrust config but rather a margin of 800-1000m.

 

So i manually set thrust/flaps/assumed temp. to minimum required setup which gives me that margin.

 

trim calc and speeds are done by fmc. Work fine on every flight because it covers any possible inaccuracies.