centre of gravity in cdu

Hi

You need to put in the CofG position into the CDU and it will give you the take-off trim. Typical values are around 25% but it depends on the way the a/c is loaded. The CDU does not read the MSFS CofG position. Typical take-off trims for a normal weight 737 are between 3.5 and 4degrees of up trim. Again, testing has to be done re your flight model.

The trim scale indication on the GC has to be set as per the txt info in the type.txt for these a/c types for it to match. Note that the trim setting in MSFS is totally different to real a/c due to the fact that it goes into negative values. Where as on a real a/c (just an example for 737) the scale goes from 0 to +15. So, some careful work has to be done to get all these things to match-up if you want to also use the EICAS GC trim indication.

Regards
Jonathan Richardson

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Originally Posted by JonathanRichardson

Hi

You need to put in the CofG position into the CDU and it will give you the take-off trim. (...) So, some careful work has to be done to get all these things to match-up if you want to also use the EICAS GC trim indication.

Regards
Jonathan Richardson

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And how all this has to be done will be revealed in the new documents that will be released in the near future, I guess. I'll wait and see.

Thanks,

JWS

Hi

Not really, I only discuss weight and balance that needs to be observed. You put in the CofG in terms of a percentage in the CDU take-off page... you can do this without new docs, the doc part is only to draw attention to this, because I visisted a few sims where people were complaining about bad FD and AP control and it turned out they were flying around without paying any attention to weight and balance at all - things were very badly balanced and they were pointing blame in the wrong place. This goes for pro level sims as well as hobby level sims. So, I just added a section. You have been able to add the CofG percentage in the CDU for a long time, arriving at the percentage though is another matter, for normal a/c it is 25% but swept wing a/c it is different. If the load is more or less correct, you should have a take-off trim of 3.5 to 4.5. You can get an idea of whether this correct by simply performing a few tests, after rotation, if the a/c climbs with a good pitch to FD indication (i.e. you are not having to make large [or perhaps any] initial trim changes with a specific take-off power setting in TOGA, then you know the a/c was basically in balance and you had a good take-off trim setting for this payload and fuel weight. The idea is to make notes with constant factors, and then keep the payloads and fuel the same - if you want to fly with different payloads and fuel, then you have to make your own tables based on your tests re the trim settings etc. For the sim here, we have one set of weights that we fly with most of the time.

Right now, the CDU does not automatically read the CofG position and so you need to enter it if you want the trim indication *but* it is really best to arrives at your own actual values through testing because the CDU system is only a simulation and not really knowing the actual CofG, we might add it automatically reading the payload for the future which has already been discussed, perhaps the next step will be to try and read the CofG and to see if it does provide accurate information.

Regards
Jonathan Richardson

Quote:

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Originally Posted by JonathanRichardson

Hi

You have been able to add the CofG percentage in the CDU for a long time, arriving at the percentage though is another matter, for normal a/c it is 25% but swept wing a/c it is different. If the load is more or less correct, you should have a take-off trim of 3.5 to 4.5. Regards
Jonathan Richardson

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Jonathan,

:o Didn't know that this was possible. Always thought it was something for future developments. A 3.5 to 4.5 % that is (?). OK, thx. See what can do about it.

JWS

Hi Jonathan,
Thanks a lot for all the info regarding de CoG. I really didn't knew this was implimented already in the PM cdu to that level. Will check this out and compare in the next days.
Certainly in the B744 with his huge weight differences trim settings are extremly important.
B. rgds
Michel

Hi

Just to confirm, it has been in the CDU software for over 1.5yrs now I think, but if you read my posts, it is a simulation, you need to accurately test your trim settings with reference to your weight and balance because the CDU does not read the actual MSFS CoG (yet).

Regards
Jonathan Richardson

Okidoki, thanks for further clarification.
B Rgds
Michel

Quote:

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Originally Posted by michelmvd

Hi Jonathan,
Will check this out and compare in the next days.
Michel

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Michel,

can you keep us posted about the results, please?

Grtz,

JWS

Sure I will, but looks not so easy as it is als airfile/ model related.
B Rgds
Michel

Here are my results:
PMDG 737-800 Winglets 27% is ok on my SIM