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## Index units in relation to aft limit?

• Steve M
• Topic Author

### Steve M created the topic: Index units in relation to aft limit?

Just a point of confusion re a cyber exam question

An Echo is loaded so that its total moment index is 14.1 index units inside the aft limit.

The maximum amount of cargo that may now be shifted from the wings to the rear compartment is closest to -

97 kg (correct)
110 kg
155 kg
80 kg

After going through the book and other enquiries, I can't get a start on this as I can't start a flow chart without aircraft weight etc.

I could try a few things with the C of G being 14 mm inside the rear limit (ie 2666) but with an index unit, I can't work it out. I keep thinking that I need a weight and/or a start point.

Any ideas?

• Posts: 1914

### bobtait replied the topic: Re: Index units in relation to aft limit?

Steve

When you multiply present weight by CofG shift required you are actually finding the moment change required. So if the examiner gives you the moment change required, he has done that multiplication for you. All you need to do is divide by the difference in compartment arms. An alternative formula to find weight to shift [when you don't know the weight], is:

Weight to shift = Change of moment [in kg/mm] / difference in arms.

To work the example you have given.

Weight to shift = 141000 / 1450 = 97 kg.

See the working for Question 5 on page 5.83 of the Performance book.