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practice exam question

Rich C

Topic Author

Rich C created the topic: practice exam question

Hi Bob,
I came across a question in my last performance practice exam that I need a little clarification of please. The question went something like this:
'An echo is loaded so that its moment index is 15 index units outside the aft limit. The minimum weight which must be shifted from the rear comp to the nose is...'

Does this mean aft limit 2680mm + (15 x 10,000kgmm), and if so, how do I calculate this?

I normally dont have too many probs with shift/add/fuel ballast type questions !

bobtait replied the topic: Re: practice exam question

2680mm is a distance from the datum and 15 index units x 10000 is a moment. You cannot add them because they are two different quatities. There is an alternative formula for weight to shift when you don't know the present weight.

Change of moment divided by the difference in compartment arms.

So take 15 x 10000 and divide it by the difference in the arms between the compartment you are shifting from and the compartment you are shifting to. That will give you the weight that must be shifted.

When you use the flow chart for weight to shift, you calculate the product of the present weight [whatever it may be] and the required shift in the centre of gravity. When you do that, you are actually calculating the moment change required - in this case, 15 index units.

The above formula is useful when you know the moment change required but not the gross weight of the aircraft.