Aircraft Design Forum
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Date: Tue Mar 13 05:02:36 2001     Number: 14749 of 14758
From: pvarn  (Paul R. Varn)
Subj: Re: Location of CofG of Aircraft 
Status: Public, Read

COG: While constructing the 3D model, design software has you set a rather arbitrary "COG" location for the center of the design drawing. In reality, this is a "Center of View" reference that FS will use as the view center while looking at your plane from an external view. The complication arises from the air file referencing this "COG" as a point from where locations of dynamic parts of the aircraft are located for effect. Fuel tanks for instance are located (in FS98 air files) so many inches from the "COG" etc. As far as actual WEIGHT and BALANCE effects, there are a few settings that are very important in that area. One of those mentioned below is the WING OFFSET mentioned below as positioned 10% in front of the intended Center of Lift, or 10% of the MAC. This rule of thumb is a good starting place. A MORE IMPORTANT setting is referred to in AirEd as "Center of Lift" and seems to have a very powerfull influence on flight balance. Together with fuel tanks placement, a proper "COL" largely determines the trim of the plane in normal cruise level flight. I have found once the "COL" and fuel tanks are set properly, horizontal trim becomes easily controllable and the so-called "wing position offset" mentioned above becomes nearly irrelevant. During the 3D design process, it helps a lot in the air file editing if the "COG" is placed carefully in respect to a "reasonable" wing location and to provide a good external view. A good example all of us can use as a BAD example of 3D COG placement is the default MS Concorde. Switch your view to external, set the zoom up-down perameter to zero in the options dialog and zoom into a tight close view where you only see a few feet of the plane. This "spot" you're looking at is the COG set by the 3D artist. In the Concorde this is set near the front of the plane. An obnoxious spot for subsequent air file editing and in the external view, prevents the plane from being centered in the view. -Pv-

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