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## Only given IU

• Posts: 162

### MissSoph created the topic: Only given IU

Hey again ... just curious if anyone has had a question pop up that was simular to this...
So I’m referring to the load echo data in the workbook...
In given GW/ total moment index at taxi is 2700 kg/ 740
So I’m asked to find the min amount of fuel to be carried as ballast in the main tanks to bring the aircraft c of g to 730 IU....
So instead of saying that they want this brought back to the aft c of g... I just work out the required c of g using the IU given to me.?

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 702

### John.Heddles replied the topic: Only given IU

given GW/ total moment index at taxi is 2700 kg/ 740

That's fine.

find the min amount of fuel to be carried as ballast in the main tanks to bring the aircraft c of g to 730 IU

Perhaps you might check both IU numbers, again ?

(I note that IU is not a CG so it is very careless to say bring the aircraft c of g to 730 IU even if we know what is meant by the words).

Engineering specialist in aircraft performance and weight control.

• Posts: 162

### MissSoph replied the topic: Only given IU

Thanks John... I double checked the question... and it definitely asks me to work out min fuel to be carried as ballast in main tanks to bring the aircraft centre of gravity to 730 IU....
I used the flow chart in Bob’s book ... weight to add... but I have a very different outcome to the answer given..... perhaps if I e mail you the working I did... and the answer working you could nut it out for me... I mean... what else is there to do on a Tuesday....

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 702

### John.Heddles replied the topic: Only given IU

Sophie,

I'm not surprised that you experienced some confusion - the question is unsound. However, let's have a look at the working and we can identify the problems. Probably it will need Bob's/Stuart's revamping the question to make the problem go away.

Actually what does surprise me is that they have such a low rate of errors - they really do do a fine job of what they do.

Engineering specialist in aircraft performance and weight control.

• Stuart Tait

### Stuart Tait replied the topic: Only given IU

That is not our question John

• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 702

### John.Heddles replied the topic: Only given IU

That is not our question John

My confusion. Apologies for the comment.

However, when Sophie posts some more detail, there will be some learning benefits for the wider student cohort.

Engineering specialist in aircraft performance and weight control.