The Long Island Flying Eagles

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Finding the Center of Gravity

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Here's the skinny on finding the CG. Finding the Center of Gravity or CG of a wing section si a fairly simple process. Simple straight wings with no sweep only require you to go back about 1/4 of the way back from the leading edge to find the CG. For more complicated wing sections, you will need to find the Mean Aerodynamic chord or MAC. The MAC is a line that runs parallel to the center of the wing (and fuse) that defined the average chord of the wing section.

 

The drawing below shows a swept wing section. One way to find the MAC is to add the tip chord dimensions (y) to the leading and trailing edges of the root. Then add the root chord dimension (x) to the leading and trailing edges of the wing tip. Finally, connect the end points with diagonal lines as shown below. Draw a line parallel to the center of the wing along the chord where the two lines intersect. This is the MAC line. The CG for normal aircraft will be located about 25% or 1/4 of the way back from the leading edge along this line.

 

Note that the 50% chord line also intersects at the same point.

 

 

MAC Calculation

 

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