Hi there
By looking at the LE and TE you can see that MAC is 200 long. 10% of 200 is 20, therefore the old CG position was 20 aft of the LE and 820 aft of the datum. Now the CG needs to be repositioned at 25% which is one quarter of 200, thus being 50 aft of the LE and 850 aft of the datum.
To summarise, the CG was at 820 and needs to be moved to 850
With me so far?
If the question is how much mass needs to be transferred from 400 to 1200 then use the following equation:
Mass to move distance between cargo holds = aircraft mass x distance to move the CG
M x D = M x cc
M x (400-1200) = 70000 x (850 – 820)
M x 800 = 70000 x 30
M x 800 = 2100000
M = 2100000 / 800
M = 2625 kg
If the question is asking how much needs to be loaded into a hold positioned at 1200 then use the following equation:
Mass to move x distance between cargo hold and new CG position = aircraft mass x distance to move the CG
M x GD = M x cc
M x 350 = 70000 x 30
M x 350 = 2100000
M = 2100000 / 350
M = 6000 kg
The correct answer all depends on the way the question is worded.
Did a mass and balance brush up Cranfield Aviation Training School. It was worth every penny an more.
Hope this helps