For CG, you might want to calculate the MAC (mean aerodynamic chord). According to Dave Patrick, for monoplanes, most “conventional” designs fly best when balanced 30% - 33% of MAC. (Biplanes are about 25% - 30% of MAC). Here’s how he says to do it:

- Measure the chord of the wing at the root, e.g., let’s say it’s 8 inches.
- Measure the chord of the wing at the tip, e.g., let’s say it’s 6 inches.
- Determine what percentage of MAC you want to find, e.g., let’s say it’s 33%. We would find that:
- 33% of an 8-inch root chord = 2.64 inches. (8” x .33 = 2.64”)
- 33% of a 6-inch tip chord = 1.98 inches. (6” x .33 = 1.98”)
- Next, measure back from the leading edge at the root chord 2.64 inches and back from the leading edge at the tip 1.98 inches. A line between the two reference points is the “average 33% line.”
- Cut the “average 33% line” in half; at the dividing point, you will have an approximation of the 33% MAC balancing point. Check balance at the dividing point.

According to Patrick: this system works well on most straight leading- and training-edge wings; ignore a faired or shaped tip, it’s insignificant; ignore any wing fairing at the fuselage.

You said that your balance is currently right about 3.75”. To be in the 30% - 33% range, if measuring just at the wingtip, you need to have a tip chord measurement of 12.5” (3.75”=.3(x); 3.75”/.3=12.5”) to be at 30% of MAC. To be at 33%, you need a tip chord measurement of 11.36” (3.75”=.33(x); 3.75”/.33=11.36”).

Dan