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+--- Thread: CG Problem (/showthread.php?tid=4868)
CG Problem - MadBirdCZ - 28-07-2005
I'm doing a payload model for DC-9. In the payload editor I get an OK for the CG. When I load the FS and put in passengers, fuel and cargo I get the
CG meter on the center. However when I press the OK - load flight button in the datasheet manifest the CG is stated as something like -80%?!
Is this normal?
Should the stations in payload editor be positioned so the CG in payload editor is as close to 0 as possible? Because if I do it this way the CG in
the manifest is iven "less" (like -90%)
I'm really confused here....
Is this problem documented somewhere?
Re: CG Problem - MadBirdCZ - 28-07-2005
Loading aircraft like this:
![[Image: dc9load.jpg]](http://www.junction.cz/files/dc9load.jpg)
Results in load manifest like this:
![[Image: dc9manifest.jpg]](http://www.junction.cz/files/dc9manifest.jpg)
Or is it normal?
Re: CG Problem - Steve Mc Lean - 29-07-2005
Hi,
Would you be so kind as check or post the actual CofG of the plane from the cfg file, I suspect that the Cof G is off to start with. The model
pay load tool is not a perfect but works well and better if the plane has a simple C of G. So, I suggest one way around all this if your a/c
cofg is off to start with.
But, by the look of it on the picture from your post, all the weight is forward of the C of G (25% of the wing cord) so unless you put zeros as
fore and aft values you will never get it right for the reason stated below. All the weight must be moved back and far back.
Here's how to put zeros.
Make a back up copy of the cfg file and change the actual values in the CoG paragraph to: z=0 to keep the weight centered from fore and
aft, Y (up or down) values do not matter as they only help in making the model more stable or more unstable and normally the x (left and
right) nulls themselves out. The most important values to have a good c of g are the fore and aft.
If you want to go on with it, and feel that the C of G of the model cfg is accurate,
You should not have any problems with your payload aircraft model if you are carefully placing the stations fore and
aft together with the cargo compartments. To do that you calculate the total moment for each compartement. There are many ways to
calculate all this but here's how I do it. Distance from the datum (C of G) to the center of the compartment, (+ aft or - fore), multiplied by
the weight of the compartment, divided by the total weight of the a/c. It gives smaller values to work with. In the end the sum of your
moments should be equal to zero. If not, then, you are bound for flying problems as you are now having.
As you probaly know already, do not forget when you place your weights that: 10 pounds, 10 feet away carries the same moment that
100 pounds, 1 foot away. ex ( 10 X -10 = -100 moment a) + (1 X +100 = +100 moment b) = 0 total moment , thus balanced.
Why put zeros in the cfg when you have multiple stations along the a/c with real distance and weights, you might wonder? well, as one
will find out, some models cannot be realisticaly balanced if the datum line was not set on the actual and real C of G during the model
creation. One way to see if a plane was designed with the right location for its real c of g, look at it revolve in FS when you choose the
plane. If it spins around the nose or the tail or in the middle of the cabin, it will be impossible to input the real moments in order to get a
balanced model. Old planes designed for older versions of FS are notorious for that particularity, this is why sometimes you must fudge
the actual moments to make an old model flyable in FS9 by using the zeros fore and aft.
Now see that example from my planes, my dc-9-32 version 2001. see for yourself, I still fly it in 2004 only because I zeroed it, even with
that the C og G is on the forward limit of the flyable enveloppe in FS and, If I was to buy it for an FSP use I would work the load model with
zeros for and aft in order to make it look real and still flyable.
[WEIGHT_AND_BALANCE]
reference_datum_position=0.000000,0.000000,0.000000
empty_weight_CG_position=0.000000,0.000000,0.000000
max_number_of_stations=50
station_load.0=0.000000,0.000000,0.000000,0.000000
empty_weight=79301.000000
empty_weight_roll_MOI=1176326.000000
empty_weight_pitch_MOI=1578989.000000
empty_weight_yaw_MOI=1974986.000000
empty_weight_coupled_MOI=1300.000000
max_gross_weight=118951.500000
I hope I did not confuse you more than I helped you.
Cheers!
Steve
Re: CG Problem - MadBirdCZ - 29-07-2005
Thanks for the reply
Problem is (well it prolly is not a problem) that in aircraft.cfg the empty CoG and reference datum are zeroed:
Quote:[WEIGHT_AND_BALANCE]my question was more aimed like whether should I make the payload model so the "guessed" CoG in the payload editor is equal to 0 as much as possible
max_gross_weight = 114000
empty_weight = 56850
reference_datum_position = 0.0, 0.0, 0.0
empty_weight_CG_position = 0.0, 0.0, 0.0
and how should I understand the -90% CoG value in the load manifest when while loading the CoG scale is centered?
Re: CG Problem - Mako - 21-11-2011
Hello Steve,
Don't know if you're still here, but I wanted to say thank you for your post. It's taught me a great deal about W&B handling in FS9.
Although your advice didn't directly work for the Project OpenSky 747-400s that I have, your post put me on the right track. I learned how to
experiment and have now got four of them that fly right and are earning me money in FSPassengers. I really appreciate it after days of being
frustrated by tail-heavy aircraft that slam themselves into the runway as soon as they're loaded.
Warmest regards,
Chris.
Re: CG Problem - timtomairways - 22-11-2011
um
Mako since your new. ill tell you before a mod does. Necro posting is a big no no
this thread is over 5 years old. im actualy wondering how you found it.
just please dont revive old threads. if you must thank steve, just PM him. and considering his post status is "new Recruit" and this is a 5 year old
thread. i dbout hes still around
Re: CG Problem - Mako - 22-11-2011
I'm sorry - I had no idea. I only ever visit these forums when I have a problem and wasn't aware of the culture, nor did I notice the dates on the OP.
Your advice is opposite to most other forums I belong to, who don't like new threads being created for an old topic. But it is duly noted and I'll
think twice before ever posting here in future - thanks for the heads-up.
As for how I found it, I did a root-level search for "CoG position".
Re: CG Problem - timtomairways - 23-11-2011
your free to post here. we just ask you dont revive old threads from the netherrelm.
im not a member of meany fourms, but the ones i am on, Necro-posting is frowned upon. but its okay. no harm done