rcairflr,

You are correct, a change to the cg can be calculated if you have a known cg. In this case let's say 18.0 inches aft of the datum line. Let's say the datum is the end of the prop shaft. If you add .5 lbs at 28.0 inches the following would be the result. I converted to ounces for the example.

Weight x arm = moment

Moment Arm WT
7200 18.0" 400 OZ. (current CG)
+224 28.0 + 8 oz.
__________________________________________________ __

7424 18.19" 408 oz.

Adding 8 oz. at 28.0" aft of the datum moves the cg .19 inches aft. The important thing is to have a fixed datum to do you calculations from.

Jim