ZFW/ZFWCG Calculation

[michael1508]

Hi all,

I notice, there is a diference between the calculation of CG value between Topcat initial loadsheet creation and after fuel data uplink of Topcat data into the Sim.

I.E. for a quick test flight today
- the loadsheet within Topcat shows a ZFWCG of 59.7 / 33.8
- after exporting to the Sim and using the fuel data uplink in the INIT B page a ZFWCG of 59.7 / 36.3 is shown

Can anyone explain, where the difference is coming from?
Does JL has it's own calculation of the exportet weight data?

Thanks,
Michael

[balu69]

Hi Michael
Unfortunately I don't have a solution either, but I can confirm the situation.
This used to be the case, at some point (possibly V58?) the values were identical and for a long time they no longer correspond.

Hallo Michael
leider habe ich auch keine Lösung, kann aber den Sachverhalt bestätigen.
Ganz früher war dies auch so, irgendwann waren (evtl. V58?) die Werte identisch und seit länger Zeit stimmen diese wieder nicht mehr überein.

[jeehell]

my software is able to compute fuel effect on CG, the distribution is not a single point so when fuel is burnt the CG moves. I believe topcat cannot do that...

[dkreiskott]

I've noticed the same thing. However, I don't understand JL's answer.
The problem occurs even though the engines are not yet running. So no fuel is used yet.

[jeehell]

It's not a matter of used fuel, it's a matter ly soft computes exact CG position based on all weights. And if topcat does not set the proper stations, or even puts 0 in the ADJ stations then you get weird behaviour.

[michael1508]

Thanks for your quick reply JL.

So which CG value are we supposed to enter? We only have the one from Topcat. Would it make a big difference, to enter this one, if we prefer to enter the value manually instead of data uplink? Or is data uplink recommended for an improved flight stability?

[dkreiskott]

I think it's due to the Aircraft.ini that was made for TopCat in 2017.
If I remember correctly, it was Christoph who created the file back then, but I'm no sure.
Jean Luc has changed a lot in the meantime, so the INI values will no longer be correct.
I looked at it yesterday, but I'm not sure what needs to be changed there.
Maybe Jean Luc can help us with this?

[bbruechmann]

i allways put the ZFW/CG data from the TopCat load sheet manually into the MCDU and have no issues so far. As long we have no FlySmart-like EFB i have to live with TopCat and it´s limitations which are marginal. I like to put all data into the MCDU manually, even the fuel etc., because this is what you have to do in the real aircraft too and it keeps you aware which data have been set. The upload functions have no benefit or me, as they are not show the procedure like in reality, but nevertheless they are comfortable for unexperienced users.

[michael1508]

Hi Bernd, that's also my preferred method.
Good to hear that this should not impact the safety of our passengers