centre of gravity in cdu

[telly53]

How does one get a figure to enter in the cdu page for centre of gravity?

[dodiano]

That depends on the plane actually! But for example on the A-320 25.0 is like a mean for the C.G.... But actually that is determined when they load the plane!

Regards,

Roberto

[telly53]

yeah i was wondering if the figure is diplayed in fs, or does one need an aftermarket payload/fuel loader program to show it.

i just often wonder how much it affects the performance of the aircraft in flight. i also wonder if the top of climb temp and toc wind speed/direction should be worried about either.

anything to help the pm cdu from going bannanas !!

sean.

[David Rogers]

It's a good point, I too am a little uncomfortable about never touching this setting...

Certainly not something you could ignore on Concorde, or even Mike's 727

.......but in the scheme of issues with the Boeing PM CDU, it's not too high on the list!

[dodiano]

Ok on the real plane at least on the Airbus and I must think it is the same on the Boeing all performance calculations made by the plane which affect fuel consumption, estimates, Optimum Levels and all that, are taken from the Loading and performance Data you insert into the FMGS so it will deffinatelly affect the performance on the plane... But again in real life is a bit more crittic as well as the data is made by a dispatch center... I would advise to get a dispatch proggram that helps you with that stuff!!

Regards,

Roberto

[JonathanRichardson]

Hi

Actually, the CofG and weight and balance is a very important factor for all accurate simulated flight. Whilst it is not important for the PM CDU itself, loading the a/c correctly, entering the Empty Weight and payload weight into the CDU type.txt file is very important for correct perfromance data. But aside from that, if the CofG is wrong or too far out of limits it makes the life of the MCP far more difficult to keep accurate control of the a/c especially with regard to the vertical modes with the AP engaged and without the FD indications - it will try and compensate for errors - but usually this results in much greater trim changes than should normally be used giving an impression of instability. If it is really bad, it can result in overshoots and undershoots of target altitudes. Also, for accurate T/O if the W&B is done correctly and you have correct elevator trim for your a/c model type (usually you have to run tests) but once you have determined a correct W&B / CofG with given payload and fuel, it makes Take-offs much more accurate and the FD will give you very accurate information to fly without having to make big trim changes or corrections with the elevator directly after T/O. It is an area often not paid enough attention. It is however all flight model based - it will only effect PM if you are out of limits - or degrade performance the further you stray from those limits.... I added a section about this to our docs which will be released in the next version.

Regards
Jonathan Richardson

[Michael Carter]

In the 727 it's all in the weight and balance tables. There is a summer table and a winter table. Weight is figured for each and every passenger in every seat and row.

After the weight is figured and the CG determined as a % of MAC, it in turn is used for the trim setting.

Unfortunately, not many people have a 727 POH available to them (not that they'd spend upwards of an hour to use them if they did), so Dreamfleet included a small MAC guage on the engineer's lower panel.

This can be used directly to figure a trim setting based on flap setting.

Performance for FS aircraft, or at least the DF727 can and does change with a shift of CG and/or weight. After installing the DF727 on the new system, I had forgotten that the default pax load was set to full with a full forward and aft cargo load. I couldn't figure out why my canned flight plan settings were giving me problems on approach even with the correctly calculated fuel load.

The aircraft felt 'dumpy' and my flying technique for the previous load and CG wasn't cutting it. Stabilizing an ILS approach was an exercise in futility. after resetting the previous pax and cargo load, the aircrat once again handles as it did before.

No matter how much fuel is loaded aboad the 727, the CG change is negligable, but those pax and cargo have a huge impact.

[JWS]

Hi

Also, for accurate T/O if the W&B is done correctly and you have correct elevator trim for your a/c model type (usually you have to run tests) but once you have determined a correct W&B / CofG with given payload and fuel, it makes Take-offs much more accurate and the FD will give you very accurate information to fly without having to make big trim changes or corrections with the elevator directly after T/O. It is an area often not paid enough attention. It is however all flight model based - it will only effect PM if you are out of limits - or degrade performance the further you stray from those limits.... I added a section about this to our docs which will be released in the next version.

Jonathan, that's good to hear. Hope you fill us in on how to enter correctly the right data. I usually press the line select key and hope it presents the weight & fuel numbers that are in FS itself, but I'm not sure about this.
Does the weight changes automatically when I select in FS another payload?

Grtz,

JWS

[JonathanRichardson]

>Does the weight changes automatically when I select in FS another payload?

Hi

No, the CDU needs to know two bits of information that must be added to the type.txt manually by the user. These are the Netweight (emptywieght) of the a/c model you are using and the payload. The CDU will read the fuel load as in the real a/c automatically. It is very important to get this info from the FS airfile and add it to the CDU type.txt. If you change a/c models, then you must update your type.txt file weights otherwise all your perfromance data is not going to be correct. Note that this data must be entered in LBS in the type.txt.

Regards
Jonathan Richardson

[JWS]

Thank you, Jonathan.

BTW, I read another thread about trimsettings and the difference between the CDU and the GC trim scale. Maybe I've overlooked something but where do I find in the (737) CDU the trimsetting?

JWS