Centre of Gravity

[Pat Pattle]

Is it the c.o.g parameters in the cfg file that determine whether an aircraft flies straight and level or not?
The DH89 is nearing upload state again but I want to improve the fm as it requires constant trimming to bring the nose up. I did fiddle with this entry but didn't see much difference.

I must admit my eyes glaze over when I open these files! :icon_lol:

Thanks,

Clive

[Milton Shupe]

Hi Pat,

I am sure there are some similarities among the flight engines for CFS3, FS9, and FSX.

Assuming that is the case, there are many variables to consider.
However, without getting into those "eye-glazing" things, I suspect that this issue is with air file table 404 and wing incidence.

Two basic things you can experiment with in the aircraft.cfg are the cruise_lift_scalar in the Flight Tuning parameters and wing_pos_apex_lon in the Geometry section.

You should have MAC around 25% of wing cord and center of lift at or slightly rearward. You can adjust CoL in the air file at tables 1204 and 1534 (not sure what CFS3 uses.)

It helps to ensure that all your big weight items (fuel tanks) are positioned near 25% MAC and that the engine thrustline is very close to 0,0,0.

If you have a tool to look at these things (like Herve Sors' AFSD or Jerry Beckwith's test panel at www.mudpond.org (http://www.mudpond.org)), then its a lot easier to get it right.

[Pat Pattle]

Hi Milton :)

Thanks for the pointers,will have a try.

With your Beech 18, I just plonked the FS9 files straight into CFS3 and they worked. It's odd that with the Beech I didn't have to do anything but with the DH89 it's not quite right. There must be a few parameters that don't port over, the same DH89 FM files fly great in FS9.

[Milton Shupe]

Pat,

Is there an FS9 version I can look at? Maybe I can spot something or tweak the critical parts if need be.

[lewis11777]

Clive I used to adjust the empty_weight_CG_position when the aircraft seemed to fly out of balance. That sometimes helps but also causes some aircraft to fly irradically. I now use the steps below to reduce nose pitch up that some planes have as airspeed increases. It nuetralizes pitch tendencies induced by airspeed. You should be able to reverse the numbers if the planes pitches down too much.



1. To reduce that tendancy open the .air file
2. Scroll to 1525: Elevator Trim Deflection
3. Change the factor number listed below the IAS that causes the nose to pitch up
4. The number should be positive, 3 is a good base number to start with
5. Adjust the factor 1 whole number at a time and check aircraft pitch attitude after each adjustment
6. If this does not have enough effect you may need to open the .cfg file and scroll down to "flight tuning", increase the "elevator_trim_effectiveness" a couple points higher and repeat as necessary.

[NachtPiloten]

If you want send it my way and I'll take a look. Need all the files including the mesh. I'll make it right....

[swpierce]

"it requires constant trimming to bring the nose up"

This is probably completely unrelated but just in case: I had a problem like that once and it turned out that I had autotrim turned on in the sim.

[Pat Pattle]

Well I've spent a few hours on this but to no avail. :(

Ted, once again you are my knight in shining armour..you have mail. :)

Thanks for the help Milton and Lewis! :icon29:

Milton - the fs9 version I based it on is the Dave Garwood model. I wish my effort was half as good as his model!