Good afternoon!

I'm almost ready to sit my performance exam but I still finding myself struggling to figure out when I should be using the flow charts (which I love) or the graph.
The CPL Final exam Question 11, in the book, has got me very confused, I used the flow chart to figure out how much fuel could be added but the answers have used the graph, why can I not use the flow chart?

Kind regards,
Esha

There is only one time when you cannot use the flow chart. That is when you are ADDING OR SUBTRACTING weight to reach the FORWARD LIMIT.

Since the forward limit itself varies with changing weight, you don't know how much weight to add until you know the forward limit and you don't know what the forward limit will be until you know how much weight you are going to add.

Catch 22. You must use the graph to solve these problems.

However, if you are SHIFTING WEIGHT, you can ALWAYS use the flow chart for either aft or forward limit problems. You can also always use the flow chart for ALL problems involving the aft limit.

It is only when you are changing weight to hit the forward limit when you must use the centre of gravity graph.

ohhhh okay, great!
Thank you so much! I thought that is what I had read in the book but then I wasn't 100% sure because I used the flow chart and my answer wasn't far off the answer in the book!
This is my lucky last exam and Im the most nervous for it! But I whole heartedly trust your books! They have served my very well for the previous six!

Kind Regards,
Esha

I have gone back and had a look at the question (Question 11 'final test' in the text book) which confused me, now I am just stuck on how you know when its a forward limit problem. Do I use the Centre of Gravity equation and check if it is beyond 2400mm ie 2442mm? and if it is, then I know the problem involves the forward limit?

Thank you!
Regards,
Esha

Hi guys, I'm having the same trouble working out when to use the graph or flow chart. Bob said to use the graph to see if it's a forward limit problem or an aft problem. Would it be correct in saying anything after 2680mm is an aft problem and anything before 2680mm is a forward limit problem.

Any help is much appreciated as it's my final exam and would love a pass on the first attempt

OK, of course the first thing you need to know is whether the problem is going to be at the forward or aft limit. The best way to do that is to look at the starting combination of weight an moment - that has to be given in the question. Then if you do a rough check on the envelope (even if it just with your finger tip) you will see where you are to start with. You may not be going to use the envelope to solve the problem, you are just getting a rough idea of where you are to start with.

If you're just inside the forward limit and you are going to add fuel to the main tanks or cargo to the nose locker you are going to have a forward limit problem. If you are just outside the forward limit and are asked to find the max cargo or ballast to add, once again you will be working to the forward limit. In that case, you can only use the flow chart if you are shifting weight.

Also, if you look at the arms of the compartments, you will see that there are only three places that are ahead of the forward limit - the nose locker (500mm), row one (2290mm) and the main fuel tanks (1780 mm). Since the most forward position of the forward limit is 2400mm, you don't need any mathematics to see that those compartments will always be ahead of the forward limit. Adding weight to those positions will always move the centre of gravity forward and subtracting weight from those positions will always move it aft.

Every other position where you can put weight is behind the aft limit. row 2 (3300mm), row 3 (4300mm), rear compartment (5000mm) and the auxiliary fuel tanks (3550mm) are all well behind the aft limit of 2680mm. Adding weight to those positions will always move the centre of gravity aft and subtracting weight from those positions will always move it forward.

You can breathe a sigh of relief if the problem turns out to be an aft limit problem, because in that case, you can always use the flow chart.

Hi Bob, thanks so much for the reply, I have just noticed that question 10 on page 236 the moment index is 2620mm and the weight is 650. Now the question ask how much more fuel we can add to the aux tanks, being behind the aft limit I thought we could use the flow chart rather than the graph but it seems that my understanding is wrong yet again. Excuse my ignorance but when you plot 2620mm and 650kg on the graph how do I know it's a forward or aft limit. Am i correct in saying if it's before the envelope line it's a forward limit and if its behind the envelope line it's an aft limit problem. After reading your previous comment I'm still a little confused how to tell on the graph if it's a forward or aft limit problem.

Thanks so much for taking the time out to to always provide us with help. We all appreciate it

Could you maybe draw an example on the envelope.

Thanks bob

Thank you so much for your help, that graph has made things so much more clear,

thank you so much!