Weight & Balance

[David Vega 348]

Fellow aviators,Given an airplane that shows its center of gravity indicator outside of its weight and balance envelope, is there a way to adjust either the .air file or the configuration file to make the center of gravity be within the W&B envelope?The airplane is the POSKY CRJ7. Great looking airplane, but its center of gravity indicator is on the nose, outside of the W&B envelope. Yes, I've posted in the POSKY forum, and they promptly replied that that the indicator "is messed up. If you have full passengers and a decent amount of cargo, your actual cog is fine, even though graphically it shows it off."Since I don't necessarily want to have full aircraft all the time, I would like to learn how to adjust this. This isn't a criticism against POSKY, they gave us a very good looking bird, for free. Any clues?Best regards,David Vega

[n4gix 4,947]

The CG point is defined by the offset from the model's origin point (0,0,0). If the model's center point isn't set correctly, then you have to make adjustments to the empty_weight_CG_position entry in the aircraft.cfg file.As you can see from the following, when I built the CJ1+ I carefully positioned the model's center point to precisely the correct location:aircraft's water line (a line fore/aft that bisects the nose coneaircraft's lateral center pointaircraft's 1/4th Mean Aerodynamic Chord (MAC)Because of this, both of the following entries use 0,0,0 (no offset required!)

reference_datum_position = 0, 0, 0empty_weight_CG_position = 0, 0, 0

Every other required coordinate entry in the aircraft.cfg file is offset from the reference_datum_position coordinates. Since the CJ1+ use the same coordinates for both reference_datum_position and empty_weight_CG_position, it makes life a lot simpler... :( The first step will be to determine the correct empty_weight_CG_position. You must have ZERO fuel and ZERO passengers/crew during this step.The easiest way to accomplish this task would be using Aircraft Container Manager, which is unfortunately no longer available.

[David Vega 348]

Thank you. Your precision approach to the CJ1 construction reminds me of quality initiatives at BMW. Since ACM isn't available, as you stated, is there another method to perform the task that, though harder, doesn't require too much time to explain? Clearly I'm not an aircraft modeler but would like to repair this particular aircraft. Regards,David Vega

[n4gix 4,947]

http://www.mudpond.org/contact_points.pdf - Jerry BeckwithI highly recomment Milton Schupe's tutorial:http://www.aerodynamika.com/cgi-bin/yabb/Y...?num=1139371963-and-http://www.sim-outhouse.com/sohforums/showthread.php?t=944

[David Vega 348]

Bill,Reviving an old post, but with renewed emphasis. The references point to a solution for a compression ratio issue while I'm trying to determine "the correct empty_weight_CG_position." Not having Aircraft Container Manager, any way this could be done?Regards,David Vega

[n4gix 4,947]

empty weight cg position is normally defined as a point on the waterline that is just forward of the main gear (approximately the forward edge of the tire). This gives you a good starting point...