Hi All,

This is really weird. When I check the BT Supplement P17 it says re the Echo Forward Limit: (I have scanned this AND the CASA workbook)

The forward limit for the centre of gravity:
2400mm aft of the datum for gross weights OF 2360 KG OR LESS

In the CASA workbook - page 18 it says:
Centre of Gravity RANGE is as follows:
2400mm to 2680mm at 2360kg or less

For example in the final mock exam (which I didnt do so well in not to mention I dont have a copy of ERC 7 laying about at the moment) we get a question on at forward c of g at 2300kg.

Now using the BT way you would say well 2300kg - forward c of g easy its just 2400mm - easy!

But using our wonderful CASA diagram, it says to use linear variation, and says its 2400mm to 2680 mm at 2360 kg OR LESS, or 2560 to 2680mm at 2950KG with linear variation BETWEEN THE POINTS GIVEN.

So based on that using the CASA way you would say (2300-2360) x 0.27 PLUS 2400mm which equals -60 x 0.27 (-16.2) PLUS 2400mm = 2383.8mm.

Both different answers, and different formulas, and I have the exam tomorrow!

I can't see what the problem is Brook. The CASA booklet says the centre of gravity range is from 2400 to 2680 when the aircraft weight is 2360kg or less. So the forward limit is constant at 2400mm for all weights of 2360kg or less. That's the same as what I have given in the Performance Supplement.

Bob

Maybe its my reading of it Bob - can you see anywhere in the CASA supplement that defines the forward limit of 2400mm? I can only find this in your supplement, but not CASA's.

What I do see also is that in your supplement you mention a LIMIT whereas CASA only mention a RANGE, so I guess I can just take the lower limit of the range and that will suffice.

Its just a bit ambiguous for example you might be inclined to use the formula (total weight - 2360) x 0.27 + 2400 Kg on a weight that is less than 2360 which would work out incorrectly.

It could just be my reading and interpretation of it.

The phrase 'centre of gravity range' means the distance from the forward limit to the aft limit. So when CASA say the centre of gravity range is from 2400 to 2680, they are telling you that the forward limit is 2400mm and the aft limit is 2680mm. It's just another way of saying the same thing.

Bob

Thanks Bob, I think its pre exam nerves getting the better of me You are right, the outside figures on a range ARE a limit in themselves, it just doesn't stand out like your sheet does. Thanks!