aircraft center of gravity

[AeroHawk]

To the aircraft designers,  In FS9 under the Create A Flight window, the Fuel and Payload button produces the image of an aircraft with the center of gravity displayed.  On several aircraft, the CG is out on the nose of the aircraft.  In the real aircraft, the CG is somewhere near the middle of the aircaft.  If the CG  of a real aircraft were out there, the aircraft would fly like a shuttlecock.  Wherever the nose was pointed, there the aircraft would go with the rest of the aircraft fluttering behind.  Which is exactly how those particular aircraft in FS9 fly.  One is contantly trimming and putting in control inputs to stop the fluttering aircraft.  My question is why are the computer models made with the CG way out front?  Doesn't that require a huge pitch MOI to get the aircraft any where close to stable flight?  Is the reference for the empty CG being  confused for the reference datum point for building the aircraft?   Thanks. Ron   Retired Pilot    

[Milton]

Hi Ron, and welcome.

[microlight]

Hi Ron, welcome.

There is an adjustment that you can make in the aircraft.cfg file that will put the CofG back into the central envelope. It doesn't appear to have much effect on the rest of the FDE design, fortunately. It doesn't fix any other FDE shortcomings, but at least it should help to cure the trimming and balance issues. Look for the following line under [airplane_geometry]:

wing_pos_apex_lon= 1.000

Increasing the positive number will move the CofG backwards - use trial and error until you get the CofG where you want it.

Hope this helps.

[Brett_Henderson]

The problems start when an aircraft.cfg and .air file are "adopted" from a similar model... and then forced to fit..

[microlight]

Brett, I don't disagree. If you have the time, knowledge and enthusiasm to build your own FDE from scratch then for sure, you end up with something that needs little adjustment. However if you're trying to 'fix' somebody else's FD so that it flies better, sometimes a quick fix is a better option than either staying with the original (potentially unflyable) version, or spending ages trying to de-construct it, fix what's wrong and then building it all up again. That can be frustrating!

Also, it seems to me that the FS flight engine isn't really sensitive enough to accurately mimic specific aircraft types just by putting the numbers in, and that a lot of the final tweaking is to do with 'feel' - I can't define it any better than that. I'm a regular traveller in all kinds of Boeings and Airbuses and as a passenger, I can't really tell what the differences are between a 737 and an A320 in flight, although obviously the pilots can in terms of control and again, 'feel'.

Getting an errant A320's CofG back to where it should be at least means you can use the controls as designed, rather than having to compensate for a heavy nose all the time.