Zero1Niner
Well-Known Member
OK. Having the toughest time with one particular type of weight shift problem, and I just cant wrap my mind around this for the life of me. Its been a while since I've practiced up on my algebra skills, so I am hoping someone can dumb this down for me somehow.
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.
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.