747-400 fuel system

I'm in the process of redoing the system logic for the 747 and have a question.

What offset would you use to read the flap value?

As you know, the 747 uses the center fuel tank initially, assuming that it has greater than 16,000 pounds of fuel, for takeoff and initial climb. However, system logic turns off the crossfeed valves 2 & 3 when flaps are extended for takeoff (flaps 10 or 20) to feed engines 2 & 3 from Main 2 & 3.

I've tried to use offset OBDC, which according to Pete Dowson's documentation should be read/write but can't get it to initiate the change.

Any thoughts from the experts out there?

Cheers,

Jon

A follow up to the earlier post...

I've been able to model the 747 fuel system in FSX, but not it FS9. When you look at the offsets as they read in PM it appears that 2 & 3, when written to 2054 et al, show in pminst as "left" and "right" which works fine for the 737, but translates to left tip and right tip in the 747. Reading 19 and 20 respectively gives you the left and right main tanks for FSX, but defaults again to left tip and right tip in PM.

So, I've accurately modeled the fuel system for the 747 in FSX but am at a loss as to how to tackle this beast for FS9. I've tested all of the results in PM from 0 to 20 using FS9 and several work (left/right aux, centre, centre2, centre3, crossfeed l/r, crossfeed r/l, left/right tip.... just not left main or right main.

Has anyone out there cracked the code?

Cheers,

Jon

I didt this in pmsystem but not with the offset mentioned before, because they dont work in 747400 FS9. The trick was to read all fuel tanks, and calculating the burned fuel for each tank (this is the 'real' logic part;), depending on pumps, valves, the fuelflow per engine, the APU....) and wrote them back to the FS offsets for the tank. This works fine, but I have to initiate the system (means tell pmsystem to copy the FS tank values to local pmsys variables). I use one Hardware switch for this. After theis pm calculates the Tankslevels in this pmsys variables and writes back the result to FS and in this way to the EICAS.

Best Regards from Austria
Peter

Hi Peter,

Thanks for sharing your approach to this issue. Actually, I had had no problem getting the tank selector and fuel flows to work fine in both FSX and FS9, except for the upper two values (19 & 20) of the tank selector in FS9

. The offsets themselves are working fine. You can write to 2054, and read the result in 2058. The issue appears to be that several of the values end up reading as tip tanks, not left/right. While 19 and 20 read correctly, they don't appear to be recognized in FS9, rather they appear to default to tips, then aux, then mains.

The logic works fine for FS9 when selecting and drawing from the centre, centre 2 and reserve tanks. The issue is limited to the left/right main tanks. The problem is further complicated in that Enrico has the left tip/right tip transposed with the left/right aux in his fuel synoptic display. Oh well.....

At least everything works well in FSX.

I wondering if Thomas (if he visits the forum) can give any comments too.
Big efforts has been made recent weeks by customers to bring the B744 PMSystems into a much realistic level. Some help from PM would be greatly appreciated.
Until so far all our emails to support for help or suggestions on this subject are just UNANSWERED !!!!
I must say I become rather UPSET of that kind of behavior.
Michel

Quote:

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Originally Posted by michelmvd

I wondering if Thomas (if he visits the forum) can give any comments too.
Big efforts has been made recent weeks by customers to bring the B744 PMSystems into a much realistic level. Some help from PM would be greatly appreciated.
Until so far all our emails to support for help or suggestions on this subject are just UNANSWERED !!!!
I must say I become rather UPSET of that kind of behavior.
Michel

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Well Michel Thomas does drop by here from time to time. Lets keep out fingers crossed for ya!!

Hi Bob,
I'm fully aware he is dropping in from time to time, just as Jonathan is doing btw.
Just hope he will be able to adress the problem and give us accurate info how to program PMsystem in that matter, as it looks we can't count on the official support from PM anymore. All emails just remains unanswered, not even a received adknowledge message ...
B. Rgds
Michel