Hi everyone got my PPL Exam in a week and I'm still struggling with the loading systems especially when they ask you how much weight can be added or removed once you have calculated the ZFW and Take-off weight.

Can anyone shed any light on the easiest way?

An example I'm having trouble with is in the Bob Tait PPL Casa example Q 65.

I try by adding a weight then calculating say (150kg) work out the weight and moment however not sure if u plot it against the ZFW or the take off weight. From there I always struggle when the line passes out of the graph where to take the difference in weight from. I hope this has made sense if not I'm happy to clarify.
Looking for some help ASAP.
Thank you !!!!!!!!!!!!!!!!! ✈️✈️✈️✈️✈️✈️✈️✈️✈️✈️✈️✈️✈️

The solution requires you to plot two points on the envelope. One representing the situation before weight is added, and one representing the situation after weight is added. Here is an example illustrating the procedure [this is an example only and it does not represent any particular question or any particular aircraft]. Image that, before the weight is added you were 2100 pounds and 190 moment index. Imagine that the questions asks how much more weight can now be added to some compartment.



Plot the point before any weight is added, then add any amount of weight [in this example, 100 pounds] to the appropriate compartment and calculate a new weight and moment after the weight is added.
Plot this point and join the two points with a straight line. Locate the point where this straight line cuts the edge of the envelope. Take a line from there across to the weight scale. The difference on the weight scale between the original weight and the weight corresponding to the point where the straight line cut the edge of the envelope indicates the weight to add.