This question is in relation to Question 2 On page 5.39 from excercise 5.9

How do we know where we are supposed to add the weight?
First go I subtracted weight from the rear and added it to the wing locker

I found the compartment arm which is 3550

I noticed that I got an answer in the negatives since the compartment arm is more than the required CoG. What does this mean?
If from doing questions like this from now on should I assume that compartment arm must be less than the required CoG to obtain a correct answer?

Thanks.

If you subtracted weight from the rear and then added it to the wing lockers you effectively shifted weight. You are out of the aft limit, so the question is not asking you to shift weight, it is asking you to subtract weight from the rear to move the centre of gravity further forward onto the aft limit.

Present weight is 2630 kg and present moment is 708 index units. So present CofG is 2692. You need to move the CofG 12 mm forward to achieve the aft limit of 2680 mm. You are asked to do that by subtracting weight from the rear. The fully worked answer on Page 5.74 shows that you will need to subtract 14 kg from the rear compartment to achieve this.

No worries thanks for clearing that up Bob. After moving further forward in the book I'm now doing excercise 5.11. Just have a question in relation to Question No. 7. After adding 5kg of weight to the nose compartment the arm was 2688mm (still out).
Instead of using fuel as ballast I added more weight to Row 1 assuming the seats were taken out and a total of 164kg can be added, meaning I could add another 10kg of hard ballast. This put the arm at 2686mm (still out), however it reduced the amount of fuel ballast required down to 17.4kg instead of 23kg. Just wondering if I did something wrong?

This leads me to my next question:

It says that "Passenger seats may be removed to increase the volumetric capacity of the cabin. Each passenger seat weighs 5kg and the maximum weight of cargo that can be placed on the area otherwise occupied by a seat is 82kg". That being said you can have a total of 82kg + 82kg = 164kg?

And if that's the case why do some of the questions in excercise 5.11 have weights above that value? Such as question 6: Row 1 has 165kg and Row 2 has 170kg.

Pretty sure I'm misunderstanding something but just wanted to run it by you


Thanks for the help so far Bob

It is sometimes possible to place a spreader on the floor of the aircraft to spread the weight more evenly. That means you are not placing weight in a area otherwise occupied by a seat. In that case, you could put more weight in row 2 or row 3.

It's good to see that you are thinking about those limits, but if you are presented with a question that says there is more than 164 kg in row 2, then just accept that and go ahead with the calculation. It was never intended that the question was setting out to trick you.

Good luck with the exam, I'm sure you will do well.

Bob

Without looking at the book, I would assume then that the Row 1 165kg and Row 2 170kg aren't cargo, but pax