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Forward and Aft Limit Calculations

Aviatordan

Topic Author

Aviatordan created the topic: Forward and Aft Limit Calculations

Hey Bob,

Just wondering if its fair to say that when you're dealing with a calculation involving the aft limit (i.e. shifting, adding or subracting weight) you will always use the aft C of G position as the 'required C of G' and you will always use the present zero fuel weight as the 'present weight'.

And;

When you're dealing with question involving the forward limit you work out the required C of G using the formula and the weight you always use is the take-off weight?

wadner1 replied the topic: Re: Forward and Aft Limit Calculations

Sir,
I have this question in my practise test :

An Echo aeroplane is loaded at zero fuel weight as follows:

Gross weight ............. 2625 kg
Total moment index ....... 712 index units

This centre of gravity position is -

1 on the aft limit for this weight
2 8.5 index units beyond the aft limit for this weight
3 6.5 index units forward of the aft limit for this weight
4 12 index units beyond the aft limit for this weight

Submitted Answer was Answer 3 (Incorrect).
Please sir whats the calculation?

Richard replied the topic: Re: Forward and Aft Limit Calculations

Hi Wadner,

The current aircraft weight is 2625kg and the total moment index is 712 index units. First off where is the current CofG position?

(712 x 10 000) / 2625 = 2712 mm aft of the datum.

We know the aft limit for the Echo is at 2680mm so we are 32mm beyond the aft limit. Options (1) and (3) can already be ignored.

To work out how far beyond the aft limit we are in index units, let's see what the total moment index would be if the aircraft was actually loaded right on to the aft limit i.e. with a CofG position of 2680mm:

2625kg x 2680mm / 10 000 = 703.5 index units

So, if the aircraft was on the aft limit we would have a total moment index of 703.5 index units. However, we are told we have 712 index units. This is a difference of 8.5 index units.

The answer is therefore option (2) 8.5 index units beyond the aft limit.