Hello ladies and gent'safter a long time using the Topcat with the NGX with inaccurate results, i decided to put that subject up.when i am planning a flight with the topcat on the payload section, there's baggage's and pax,1. how do i simulate it on the NGX i mean is that part of the ZFW? if i put it in ZFW the passenger's are not accurate.2. how can i simulate children, infant's and adult's separately?in other subject, the stb. trim always showing less then what the FMC gives me, let's say topcat says +5.5, the FMC tells +6.3.what should i do to make it right? and the final problem is when i calculate the assume temperature, it always needs a lot warmer temperature. for instance topcat calculate that i will need 15c TO2 i always need to put 30c or so. BTW should i take FMC calculations of IAS speeds for takeoff or topcat calculation?thanks very much for the helpers!

The 737 FMC is always right. You only need topcat for the info that the FMC can't provide you.On the ZFW weight issue. What I do is that I enter the correct amount of payload and pax in the 737 FMC and find out it's ZFW. I then enter the corresponding weight in topcat by simply dragging the sliders until I get the same ZFW in topcat. Also I transfer the fuel weight.Finally on the assumed temperature problem, how do you know that the assumed temperature is wrong?Manfred

The 737 FMC is always right. You only need topcat for the info that the FMC can't provide you.On the ZFW weight issue. What I do is that I enter the correct amount of payload and pax in the 737 FMC and find out it's ZFW. I then enter the corresponding weight in topcat by simply dragging the sliders until I get the same ZFW in topcat. Also I transfer the fuel weight.Finally on the assumed temperature problem, how do you know that the assumed temperature is wrong?Manfred

Hey Manfred,first thanks for the help, I didn't really understand what you're doing with the ZFW so i will just answer your question, so i know the assume temperature is wrong because it's give me a number that when i put it in the assume temperature the thrust is by far not what topcat calculated. thanks again

Finally on the assumed temperature problem, how do you know that the assumed temperature is wrong?Manfred

I don't think he is saying the assumed temperature is wrong - there are just not enough of them to use up the whole runway for takeoff roll plus stopping distance. If you use a long runway like 28 at KORD and derate the takeoff to 2, TOPCAT will compute the temperature and the highest temperature might be 43 with a margin of 4285 ft. So in that case you could easily use 60 as an assumed temperature and still have margin left for even a higher temperature.Michael

I don't think he is saying the assumed temperature is wrong - there are just not enough of them to use up the whole runway for takeoff roll plus stopping distance. If you use a long runway like 28 at KORD and derate the takeoff to 2, TOPCAT will compute the temperature and the highest temperature might be 43 with a margin of 4285 ft. So in that case you could easily use 60 as an assumed temperature and still have margin left for even a higher temperature.Michael

I can get that, but shouldn't it be accurate? thanks again.

I can get that, but shouldn't it be accurate? thanks again.

DanielYou would think it should be accurate but I don't think it has been updated in over a year. You know that the 800 in TOPCAT is not the NGX but the FS9 version. And some values cannot be edited so that they are correct. I don't use it any more for the NGX - just the MD-11 and 747. And I am not all that happy with the flex and assumed temperature calculations for those aircraft.Michael

I noticed some differences between the default values in Topcat for weight limits and the PMDG values. However just search Youtube (NGX topcat) and you will find a tutorial where the guy explains which valuest to use to match the PMDG.Everything in mine now agrees except the stab trim which never does.I have another related question though.In the PMDG FMC V1 and VR are always essentially the same value. I assumed that this was due to the FMC not accounting for runway length. I assumed that Topcat would do this. Although Topcat does appear to be accounting for runway length in the V speed calculation it still gives a V1 and VR about the same. I imagined that for a short runway that in order to stop safely after RTO that a much lower V1 speed than VR would be required.Hopefully someone can clarify this.

great question, i have noticed it to, so basically what you're saying is to add to the temperature so it will match the thrust that topcat calculated? thanks(:

GraemeI don't believe V1 and VR would change for a short runway. The thrust would be increased by TOPCAT lowering the assumed temperature to be entered into the FMC. The increased thrust would give you a shorter roll to V1 and VR thereby leaving more of the runway to stop on.Michael

FSX and FS9 versions don't matter at all. TOPCAT is using performance tables for the real aircraft. The only reason the version of FS matters is if you're trying to tell it what the default weight numbers are. Those can be configured in the individual aircraft's page. Basically, you just need to make sure the weights are the same between the sim and TOPCAT. You should also be sure that the engine types are the same. Furthermore, make sure your data is the same (if TOPCAT is using real weather and your sim isn't, that's a problem).Basic moral of the story:[Trash] in [trash] out.Give the planner trash data and it'll give you trash back.Learn how to properly use both TOPCAT and the FMS (hint, manuals do this for you), and you're golden.

Michael Hello, can you confirm, that if let's say topcat gave me an assume temperature of 35-85.7% thrust and after putting that in the FMC it gave me 89% thrust, i should rise the temperature? till i get 85.7%? thanks, cheers my friend.

GraemeI don't believe V1 and VR would change for a short runway. The thrust would be increased by TOPCAT lowering the assumed temperature to be entered into the FMC. The increased thrust would give you a shorter roll to V1 and VR thereby leaving more of the runway to stop on.Michael

I agree that for a shorter runway a higher thrust is required. But my understanding of V1 is the speed at which a safe RTO can still be made based on remaining runway length. VR on the other hand is of course the safe takeoff speed and rotation point. If those definitions are right I don't see why both these quite different conditions are always met at exactly the same time and hence V1 and VR are always the same. Put simply why bother with a V1 speed if it is always the same as VR?

V speeds has plenty things to consider. Braking, surface wet or dry, weight, and a few others. It will most likely not be the same for 2 737's leaving the same airport at the same time. FRED

I too would like to now how to get accurate calculations with topcat. Even though i am certain the weights in topcat match the ngx, I vant seem to get the right N1 calculations from topcat :)

Michael Hello, can you confirm, that if let's say topcat gave me an assume temperature of 35-85.7% thrust and after putting that in the FMC it gave me 89% thrust, i should rise the temperature? till i get 85.7%? thanks, cheers my friend.

I have noticed the very same inconsistency between the two.I did some simple tests under certain conditions and it looks to me that we should aim for N1, not assumed temperature. That is, if for example Topcat tells me assumed temperature of 40C should result in N1 of 89% i will go and find assumed temperature in the FMC that gives me N1 of 89%. There is usually 6C difference between Topcat and FMC for the same N1.Uh, i hope i'm clear ;)