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##### PPL Video Lectures (10 Jul 2020)

PPL Video Lectures covering Aerodynamics, General Knowledge, Performance, Meteorology And Navigation are now available through our website see front page for details.

× Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

## Practice exam question

• Posts: 105

### MissSoph created the topic: Practice exam question

Ok... I’m wondering what I’m doing.... so basically...
gross weight 2655kg and 666 index units... main tanks full... aux empty... max fuel that now can be added in the aux tanks.....
So it’s similar to question 3 of ex 5.13?.., but I’m not getting the sums to work.....!

• Posts: 2184

### bobtait replied the topic: Practice exam question

Can you give me the question number and page number please.

• Posts: 105

### MissSoph replied the topic: Practice exam question

Hey Bob... it was question 25 of the practice exam 1...
I’m just confused as in the book, says adding fuel to the aux tanks will move the c of g back.. so why now... when adding fuel to the aux tanks... am I going to the forward limit by adding to the aux tanks?

• Posts: 2184

### bobtait replied the topic: Practice exam question

I agree. there's something wrong there. Looks like it should have said 'how much fuel can now be burnt from the aux tanks. We'll check it out.

• Posts: 2184

### bobtait replied the topic: Practice exam question

OK. I've checked it out. There's nothing wrong with the question, but it is a tricky one.

While it is true that adding fuel to the aux tanks will move the centre of gravity back, the FORWARD LIMIT also goes back as weight increases. It turns out the the forward limit goes back faster than the centre of gravity does.

So adding weight to the aux tanks will eventually put you outside the forward limit even though the centre of gravity is moving back.

The only way to solve the problem is with the 'two point' method because you are adding weight to hit the forward limit.