#### Zero1Niner

##### Well-Known Member

I am working in the Gleim Flight/Ground Instructor book, and they suggest a formula that they say is 'a single, universal, uncomlicated formula' that can be used to answer all weight shift or change questions, and that they provide this formula instead of the FAA formula found in the PHAK. The explanation as it appears in the 2008 version of the Gleim book (page 130) is as follows:

The formula is: NEW CG = Original Moment +- New Moment / Original Weight +- New Weight

In the Gleim, they give this example problem and break it down in detail, but I am just not following.

EXAMPLE QUESTION:

What is the maximum weight that could be added at Station 130 without exceeding the aft CG limit?

Total Weight 2,900lbs

CG Location Station 115.0

Aft CG Limit Station 116.0

I follow the formula for this portion:

116.0 = 2,900(115.0) + 130.0 (X) / 2,900 + X

I get lost on this next line

2,900 (116.0) + 116.0(X) = 2,900(115.0) + 130.0(X)

Where does the 2,900(116.0) on the left side come from all of the sudden?

Then, the next line down in the explanation it shows:

336,400 + 116X = 335,500 + 130X

336,400 – 333,500 = 130X – 116X

Then here, the 335,500 switches from the left side to the right side, and the 116X switches from the left side to the right side.

2,900 = 14X

207.1 = X

Please help. Remember...I am a dope. Please explain in detail.